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# 1.1: Introduction to Nanoscience

Difficulty Level: At Grade Created by: CK-12

## Unit Overview

Contents

• (Optional) Size Matters: Pretest
• (Optional) Size Matters: Posttest

Name_______________

Date_______________

Period_______________

### Size Matters: Pretest

1. How big is a nanometer compared to a meter? List one object that is nanosized, one that is smaller, and one that is larger but still not visible to the naked eye.

2. Name two properties that can differ for nanosized objects and much larger objects of the same substance. For each property, give a specific example.

3. Describe two reasons why properties of nanosized objects are sometimes different than those of the same substance at the bulk scale.

4. What do we mean when we talk about "seeing" at the nanoscale?

5. Choose one technology for seeing at the nanoscale and briefly explain how it works.

6. Describe one application (or potential application) of nanoscience and its possible effects on society.

Name_______________

Date_______________

Period_______________

### Size Matters: Posttest

1. How big is a nanometer compared to a meter? List one object that is nanosized, one that is smaller, and one that is larger but still not visible to the naked eye.

2. Name two properties that can differ for nanosized objects and much larger objects of the same substance. For each property, give a specific example.

3. Describe two reasons why properties of nanosized objects are sometimes different than those of the same substance at the bulk scale.

4. What do we mean when we talk about "seeing" at the nanoscale?

5. Choose one technology for seeing at the nanoscale and briefly explain how it works.

6. Describe one application (or potential application) of nanoscience and its possible effects on society.

## Introduction to Nanoscience

Contents

• Introduction to Nanoscience: Student Reading
• Introduction to Nanoscience: Student Worksheet
• Scale Diagram: Dominant Objects, Tools, Models, and Forces at Various Different Scales
• The Personal Touch: Student Reading
• The Personal Touch: Student Worksheet

What is Nanoscience?

Way back in 1959, a physicist named Richard Feynman shared his vision of what very small things would look like and how they would behave. In a speech at the California Institute of Technology titled "There’s Plenty of Room at the Bottom," Feynman gave the first hint about what we now know as "nanoscience"[1]:

"The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom."

More generally, nanoscience is the study of the behavior of objects at a very small scale, roughly 1\begin{align*}1\end{align*} to 100nanometers\begin{align*}100\;\mathrm{nanometers}\end{align*} (nm)\begin{align*}(\;\mathrm{nm})\end{align*}. One nanometer is one billionth of a meter, or the length of 10\begin{align*}10\end{align*} hydrogen atoms lined up. Nanosized structures include the smallest of human-made devices and the largest molecules of living systems.

What is the Big Deal About Nanoscience?

You might ask, "What is the big deal with nanoscience? Isn’t it just a bunch of really small things?" It is, in fact, a bunch of small things. But it is a whole lot more. What makes the science at the nanoscales special is that at such a small scale, while all physical laws affect the behavior of matter, different laws dominate over those that we experience in our everyday lives. For example, the element gold (Au) as we are used to seeing it has a nice yellowish-brown color to it—the color we know as "gold." However, if you had only 100\begin{align*}100\end{align*} gold atoms arranged in a cube, this block of gold would look very different—its color would be much more red. Color is just one property (optical) that is different at the nanoscale. Other properties, such a flexibility/strength (mechanical) and conductivity (electrical) are often very different at the nanoscale as well.

Surface Area is Big!

The smaller something is, the larger its surface area is compared to its volume. This high surface-to-volume ratio is a very important characteristic of nanoparticles.

For example, imagine that you have a big block of ice with one-meter sides (see Figure 1). This block has a surface area of 6square meters\begin{align*}6\;\mathrm{square\ meters}\end{align*} (1square meter\begin{align*}1\;\mathrm{square\ meter}\end{align*} on a side ×6\begin{align*}\times 6\end{align*} sides) and a volume of 1cubic meter\begin{align*}1\;\mathrm{cubic\ meter}\end{align*}. In this case, the surface area to volume ratio for the ice block is 6/1\begin{align*}6/1\end{align*} or 6\begin{align*}6\end{align*}.

Suppose that cut the ice into 8\begin{align*}8 \end{align*} pieces that are one-half of a meter per side. The surface area of each piece of ice would be 1.5square meters\begin{align*}1.5\;\mathrm{square\ meters}\end{align*} (0.5m×0.5m×6\begin{align*}0.5 \;\mathrm{m} \times 0.5 \;\mathrm{m} \times 6\end{align*} sides). So the total surface area of all the pieces would be 12square meters\begin{align*}12\;\mathrm{square\ meters}\end{align*}. However, the total volume of ice would stay the same: we haven’t added or removed any ice. So in this case, the surface area to volume ratio is 12/1\begin{align*}12/1\end{align*}, or 12\begin{align*}12\end{align*}––twice the surface area to volume ratio of the block before it was cut. If you cut the ice into 27\begin{align*}27\end{align*} pieces, the surface area increases to 18square meters\begin{align*}18\;\mathrm{square\ meters}\end{align*}, and the surface area to volume ratio is 18/1\begin{align*}18/1\end{align*} or three times that of the uncut block. If you keep going, and cut the ice into 1000\begin{align*}1000\end{align*} small pieces, the surface area to volume ratio is 60/1\begin{align*}60/1\end{align*} or ten times that of the uncut block!

Imagine how big the surface area to volume ratio would be for something as small as a bunch of nanoscale particles.

Total surface area increases as you cut the block into smaller pieces, but the total volume stays constant [2].

The vastly increased ratio of surface area to volume makes interactions between the surfaces of particles very important. If something has more surface area, there are more places for other chemicals to bind or react with it. For example, fine powders offer greater reaction speed because of the increased surface area. Think about how much faster you can cool a glass of water if you put crushed ice in it rather than ice cubes.

Nanoscale particles maximize surface area, and therefore maximize possible reactivity!

Why is Large Surface Area Important?

The large surface area to volume ratio of nanoparticles opens many possibilities for creating new materials and facilitating chemical processes. In conventional materials, most of the atoms are not at a surface; they form the bulk of the material. In nanomaterials, this bulk does not exist. Indeed, nanotechnology is often concerned with single layers of atoms on surfaces. Materials with this property are unique. For example, they can serve as very potent catalysts or be applied in thin films to serve as thermal barriers or to improve wear resistance of materials.

Can We Make Small Devices?

Yes indeed. Over the past few decades, there have been many attempts to create devices at a small scale. If you look at the evolution of technology all around us, you’ll notice that it’s continually getting smaller.

Back in 1965, Gordon E. Moore (co-founder of Intel) observed that the number of transistors squeezed onto a computer chip roughly doubles every 18\begin{align*}18\end{align*} months. This "rule" is known as "Moore’s Law." The more transistors on a chip, the smaller their size and closer their spacing (see Figure 2). And as size decreases, speed and performance rise rapidly. This is why computers the size of a room in the 1950s now fit on your lap.

Indeed, many modern-day electronics already contain nanoscale-size components. For the semiconductor industry (Figure 2), nanotechnology has been the result of a continuous series of improvements in processing and materials over decades. Moore's Law won't last forever, though. At some point, the laws of physics will make it impossible to keep downsizing microelectronics at this exponential rate. Why? Because eventually, you get down to manipulating individual molecules, and at that level, a few atoms out of place could ruin an entire computer chip. The packed-in transistors also generate a lot of heat, which could melt the chip. Engineers are looking to nanoscience for tools and materials to enable computer chip manufacturing on an atomic scale. [4]

The decreasing minimum feature size of transistor components [3]. Note that size is graphed on a logarithmic scale, so the change is exponential.

Another group of devices that are considered small, but not quite at the nanoscale, are MEMS (micro-electromechanical systems) devices. Imagine machines built to the scale of microns, with gears, motors, levers, and so on, which are capable of moving things. One useful application of MEMS devices is in tiny acceleration sensors that quickly deploy the airbags in your car during an accident.

MEMS accelerometer [5].

What Kind of Nanostructures Can We Make?

Two interesting structures that have been constructed and fall into the nanoscale range are carbon nanotubes and buckyballs. You’ll find these structures mentioned in almost any book or article on nanotechnology. Like diamond, carbon nanotubes and buckyballs are constructed solely out of carbon atoms. (Because carbon bonds so strongly to itself, it is a natural for use in nanotechnology.) What is most interesting about these two structures is that they possess some very unusual chemical and physical properties.

What is a Carbon Nanotube?

Carbon nanotubes are cylindrical carbon molecules with interesting properties. For example, they can be made to be excellent electrical conductors or semiconductors just by controlling how they are formed ("rolled"). With traditional materials, you have to add chemicals or elements to them to make them behave as conductors. With nanotubes, you just twist them! Another unique property of nanotubes is that they are very resilient and flexible, as well as extremely strong. We also know that nanotubes are very "hydrophobic"—they don’t like water—and that they bind easily to proteins. Because of this last property, they can serve as chemical and biological sensors by being sensitive to certain molecules but not others by coating them in different ways. Nanotubes can also be made from elements other than carbon, such as gold and silver. Although they are not as strong as carbon nanotubes, they also have unique electrical and optical properties.

How Could Nanotubes be Used?

Carbon nanotubes have been used in a wide variety of products. For example, Toyota uses a carbon-nanotube-based composite in the bumpers and door panels of some of its cars, not only to make them stronger and lighter but also to make painting them easier since carbon nanotubes make the plastic electrically conductive so that the same electrically bonding paints that are used on metal parts can be applied.

Computer-generated models of carbon nanotubes [6, 7]

Model of a buckyball with single bonds (red) and double bonds (yellow) highlighted [8].

What is a Buckyball?

Buckyballs also have a unique set of properties that are based on their structure. Notice how the molecular model of the buckyball looks like a soccer ball. The usual structure for this molecule is made of 60\begin{align*}60\end{align*} carbon atoms arranged in a soccer ball-like shape that is less than one nanometer in diameter. Because of the "hollow-ball" shape of this structure, scientists are currently testing to see how effective buckyballs are as drug carriers in the body. The hollow structure can fit a molecule of a particular drug inside, while the outside of the buckyball is resistant to interaction with other molecules in the body. Even though much more research is needed in this area, buckyballs appear to be relatively safe functional drug "containers" that can enter cells, without reacting with them.

What Nanostructures Exist in Nature?

There are many natural nanoscale devices that exist in our biological world. Some examples are ion pumps, "molecular motors," and photosynthetic processes. Inside all cells, molecules and particles of various sizes have to move around. Some molecules can move by diffusion, but ions and other charged particles, such as neurotransmitters, have to be specifically transported around cells and across membranes. The classic example of an active ion pump is in the enzyme ATP synthase. In this enzyme, the a central protein structure rotates as ATP is synthesized and ions are moved across a cellular membrane.

Another example is kinesin. Kinesin is a molecular motor that transports larger particles around cells on microtubules. The kinesin molecule acts like a train car on a microtubule nanosized track to carry proteins and larger particles to specific sites in cells. The photosynthetic machinery in plants (chloroplast) and bacteria is also a complex nanomachine. It includes a light-harvesting component, a reaction center, and an ion pump, all arranged in a specific layout within the cell membrane that allows for the conversion of light into energy that the plant can use.

So How Do We "See" These Small Things?

As the field of nanoscience has grown, new tools have made it easier for scientists to see, image, and manipulate atoms and molecules. One type of microscope that works at the nanoscale is the scanning tunneling microscope (STM) which was developed in 1981. The very end of the tip of this microscope is one atom in size. The "tunneling" of electrons (quantum tunneling) between the tip and the substance being viewed creates a current (flow of electrons). The strength of the current and how it changes over time can be used to create an image of the surface of the substance. Today’s scanning microscopes can do much more than just see. Among other things, they can be used to move atoms around and arrange them in a preferred order.

A different type of microscope, the atomic force microscope (AFM), uses a tiny tip that moves in response to the electromagnetic forces between the atoms of the surface and the tip. As the tip moves up and down, the motion is recorded and an electronic image of the atomic surface is formed.

Schematic of a scanning tunneling microscope [9].

Tip of an atomic force microscope [10].

How Do You Build Things That Are So Small?

Building nanoscale devices isn’t quite as straightforward as simply making your tools smaller and using powerful microscopes. When you are dealing with objects at this scale, things literally start to become very "sticky." Nanoparticles are attracted to each other via electrostatic forces, and this effect makes it very hard to handle and move things that are very, very small.

However, this difficulty hasn’t stopped advances in how scientists and engineers build or fabricate nanomaterials. Here are the main nanofabrication techniques that are used to build small things:

1. Atom-by-Atom Assembly

Assembly atom-by-atom is similar to bricklaying in that atoms are moved into place one at a time using tools like the STM and AFM. Using this technique, scientists have, for example, positioned xenon atoms on nickel and buckyballs on copper to create nanoscale structures like the IBM logo and nanoscale abacus shown below. As you might guess, building structures one atom at a time is very time consuming. Examples of this type of assembly have typically been "proof of concept" to show that it can be done but don’t necessarily have practical application because the process is expensive and slow.

IBM logo assembled from individual xenon atoms arranged on a nickel surface [11].

Nanoscale abacus buckyball "beads" placed on a copper surface [12].

2. Chisel Away Atoms

Imagine taking a block of wood or stone and carving it away to create an object that you want. The smallest features you can create depend on the tools you use.

Photolithography, a process of chiseling away material to make integrated circuits [13].

Like sculptors, scientists can also chisel out material from a surface until the desired structure emerges. The computer industry uses this approach when they create integrated circuits. They use a process called photolithography, in which patterned areas of material are etched away through physical or chemical processes.

3. Self-Assembly

Self-assembly means setting up an environment such that atoms assemble or grow automatically on prepared surfaces. In this approach, an environment is created in which structures assemble automatically. Examples include chemical vapor deposition and the patterned growth of nanotubes. Nature, of course, uses self-assembly mechanisms, such as the self-assembly of cell membranes. Our ability to create nanostructures improves as we gain understanding of biological self-assembly, develop new molecular structures, and construct new tools.

Polystyrene spheres self-assembling [14].

Summary

Although substances have existed for a long time that are composed of nanosized particles, it has been only after the invention of the new AFM and STM category of microscopes that we have been able to observe, gather data on, and even manipulate molecules and atoms. We are discovering that when molecules and atoms assemble into particles between 1\begin{align*}1\end{align*} and 100nanometers\begin{align*}100\;\mathrm{nanometers}\end{align*} in size, different laws dominate at that scale than in our everyday experience of objects. Unique properties begin to emerge for substances at the nanoscale, including unique optical, mechanical, electrical, and thermal properties.

Nanoscale science is an exciting area of current research. Applications in information technology, medicine, composite materials, and other fields, are now open for further exploration. Nanoscience is emerging as a way to describe the behavior of substances in biology, chemistry, physics, earth science, metrology, medicine, and engineering. It is a truly interdisciplinary field that can be the basis for the development of new, even revolutionary technologies of all kinds. These little particles and devices may soon have a huge impact on our daily lives.

References

(Accessed August 2006.)

Glossary

atom
The smallest particle of an element that retains the chemical identity of the element; made up of negatively charged electrons, positively charged protons, and uncharged neutrons.
atomic force microscope (AFM)
A high-powered instrument able to image surfaces to molecular accuracy by mechanically probing their surface contours.
catalyst
A material that speeds up a chemical reaction without being used itself.
chemical property
A characteristic of a substance that cannot be observed without altering the identity of the substance, only can be observed when substances interact with one another.
chemical bond
A mutual attraction between different atoms that bonds the atoms together.
conductor
A material that contains movable charges of electricity. When an electric potential difference is impressed across separate points on a conductor, the mobile charges within the conductor are forced to move, and an electric current between those points appears in accordance with Ohm’s law.
electrical conductivity
The current (movement of charged particles) through a material in response to electrical forces. The underlying mechanism for this movement depends on the type of material.
electrical conductor
A material that contains charges that can move freely throughout the material. When these charges are forced to move in a regular pattern from one point towards another (due to an electrical force), this movement is called a current.
electrical insulator
A material that does not allow electricity to flow through it.
electromagnetic forces
Particles with charge (or areas of charge) exert attractive or repulsive forces on each other due to this charge. Particles with magnetic properties exert attractive or repulsive forces on each other due to these magnetic properties. Since magnetism is caused by charged particles accelerating (for example by the electron "spin" in materials such as iron), these forces are considered to be two aspects of the same phenomenon and are collectively called electromagnetic forces.
electrostatic force
The attractive or repulsive force between two particles as a result of their charges. Like charges repel, unlike or different charges attract. The size of the force increases as the amount of charge on the particle increases, and the force rapidly decreases as the distance between the two particles increase.
element
A substance that cannot be separated into simpler substances by a chemical change; simplest type of pure substance.
enzyme
A protein that catalyzes a chemical reaction.
hydrophobic
Water repelling.
ion pump
A mechanism of active transport that moves potassium ions into and sodium ions out of a cell.
MEMS (micro-electro-mechanical systems)
A technology that combines computers with tiny mechanical devices such as sensors, valves, gears, mirrors, and actuators embedded in semiconductor chips.
molecule
The smallest particle of a substance that retains all of the properties of the substance and is composed of two or more atoms bonded by the sharing of electrons.
nanomaterial
A material with an average grain size less than 100nanometers\begin{align*}100\;\mathrm{nanometers}\end{align*}.
nanometer
One-billionth of a meter (109m)\begin{align*}(10-9\;\mathrm{m})\end{align*}. The prefix ‘nano’ is derived from the Greek word for dwarf because a nanometer is very small. Ten hydrogen atoms lined up side-by-side are about 1nanometer\begin{align*}1\;\mathrm{nanometer}\end{align*} long.
nanoparticle
A microscopic particle whose size is measured in nanometers.
nanoscale
Refers to objects with sizes in the range of 1\begin{align*}1\end{align*} to 100nanometers\begin{align*}100\;\mathrm{nanometers}\end{align*} in at least one dimension.
nanoscience
The study of phenomena at the nanoscale (e.g. atoms, molecules and macromolecular structures), where properties differ significantly from those at a larger scale.
nanotechnology
The design, characterization, production and application of structures, devices and systems that take advantage of the special properties at the nanoscale by manipulating shape and size.
neurotransmitter
A chemical substance responsible for communication among nerve cells. Typically reside in sacs at the end of an axon that carries nerve impulses across a synapse.
physical property
Properties that can be measured without changing the composition of a substance, such as color and freezing point.
photosynthesis
A biochemical process in which cells in plants, algae, and some bacteria use light energy to convert inorganic molecules into ATP, a source of energy for cellular reactions.
protein
A compound whose structure is dictated by DNA. Proteins perform a wide variety of functions in the cell including serving as enzymes, structural components, or signaling molecules.
quantum tunneling
A phenomenon in which a very small particle passes through an energy state that is "classically-forbidden" (meaning that it is not possible based on Newton’s laws of physics). Another way of saying this is that the particles can pass through barriers that should be impenetrable and be found in places that Newton’s laws would predict to be impossible. The classical analogy is for a car on a roller coaster to make it up and over a hill that it does not have enough kinetic energy (energy of motion) to surmount.
reactivity
A substance’s susceptibility to undergoing a chemical reaction or change that may result in side effects, such as an explosion, burning, and corrosion or toxic emissions.
scanning tunneling microscope (STM)
A machine capable of revealing the atomic structure of particles. The microscope uses a needle-like probe to extend a single atom near the object under observation. When the probe is close enough, an electromagnetic current can be detected. The probe then sends a tiny voltage charge. This charge creates an effect known as tunneling current. The tunneling current is measured by scanning the surface of the object and mapping the distance at various points, generating a 3D image. Scanning tunneling microscopes have also been used to produce changes in the molecular composition of substances.
semiconductor
A solid material whose electrical conductivity is greater than an electrical insulator but less than that of a good electrical conductor. The conductivity of semiconductors can also be manipulated by "doping" - adding certain impurities that change the ways electrons can travel through the material. This makes semiconductors a useful material for computer chips and other electronic devices
sensor
A device, such as a photoelectric cell, that receives and responds to a signal or stimulus.
transistor
A tiny device that turns the flow of electrons on and off to regulate electricity in a circuit. This on/off ability is used to represent binary digits, the digital data used for storing and transmitting information in a computer.

Name_______________

Date_______________

Period_______________

### Student Worksheet

Below is a set of questions to answer during and/or following the introduction to nanoscience slide presentation.

1. What is the range of the "nanoscale"?

2. What is the smallest size (in meters) that the human eye can see?

3. How much more "power" can a light microscope add to the unaided eye? In other words, what is the smallest resolution that a light microscope can show?

4. Briefly describe how light microscopes and electron microscopes work.

5. Name one of the new microscopes that scientists have used to view objects at the nanoscale and explain how that microscope allows you to view objects.

6. Give a short explanation of why the nanoscale is "special."

7. Name one example of a nanoscale structure and describe its interesting properties.

### The Personal Touch (Prom Day, 2045 A.D.): Student Reading

"So, Aladdin, how’m I doin’?" Sandra asked the household artificial intelligence (AI) as she walked into the bathroom.

Recognizing her unique voiceprint, the system answered, "Sandra, if you place your hand on the wall panel, I’ll do a quick checkup."[1]

[1] Although a voiceprint is a highly accurate identifier, the touch panel that reads both fingerprints and DNA in the skin is an extra insurance of privacy.

"OK," Sandra slapped her hand against the panel, "and you can start the shower for me."

"Sandra," the bathroom said, "you should take a "C" tablet after you finish your shower. You are starting to show signs of a cold. Otherwise all your physical functions appear to be fine. There is one exception; your pulse rate is slightly elevated." [2]

[2] Two approaches could be used for sensing Sandra’s physical conditions: Chronic embedded nanosensors that emit signals to be picked up by nearby analytic equipment, or nanosensors that read the presence of substances in the body by contact with the skin or sampling breath.

"OK!" she replied, stepping into the stream of water. "Guess the pulse rate is just because I’m looking forward to the prom tonight." Sandra knew that the diagnostic intelligence built into the house AI didn’t care if she answered or not, but somehow it seemed to have a personality.

As she adjusted the hot water, enjoying the play of the hot shower on her skin, the communication implant below her ear signaled for attention. [3]

[3] Communication devices will be built of components assembled at a molecular level and will be able to receive and transmit to local "WiFi" devices in the environment (e.g., house or car). Implants placed on bone tissue near the ear could generate sound that would be heard through bone conduction. The scale of memory devices will permit application specific computers to operate with minimal power, such as that generated from room lights or body heat.

"It’s Victoria calling, do you wish to answer?" the implant said through bone conduction.

"Yes, put her on... Hi, Vicky! What’s up?"

"Hi, Sandy. So, hey, did you end up renting that Lauren Sigali gown we were talking about?"

"Yeah, and it’s awesome. I was playing with it today. It can even generate dynamic patterns," Sandy replied. [4]

[4] Quantum dots embedded in the fabric of clothing may be controlled to switch colors and create patterns based on electrical impulses from a device sold with the clothing.

"That is so cool. Mine isn’t as good as that, but it has great shading and pretty good luminosity. So what color are you going to hue it? I think you should wear blue...it will go with your eyes."

"Yeah. A pale blue...I like that. And I could play a pattern when we start dancing. How about you, Vic?"

"I think I’ll hue mine a bright red...make me stand out from the crowd. Maybe I’ll flip to green when we dance."

"Sounds great, Vic. So did you hear that Munira got an ad gown? It was free."

"Ugh. I just hope it doesn’t play one of those tacky logo collages."

"So, what kind of pattern could I make that’s personal for this evening?"

They talked for another fifteen minutes before Sandra finally said, "Phone disconnect."

After toweling off and taking the "C’ tablet, she turned her attention to makeup. [5] The oil in the cosmetics was broken down so finely that it felt like a second skin. In addition, it acted as a sunblock, which was important here in Nanocity, Arizona. [6]

[5] The "C" tablet contains nanobiological machines that attract and attach to viruses, preventing them from infiltrating cells.

[6] Nanobots are used to break the oil down into smaller molecular clusters than can be done with refining methods alone.

For the thousandth time Sandra wondered why Nanocity had to be built so far away from any other place. She understood that when the geostationary orbiting space platform had been tethered to the ground, more than half the country thought it would be dangerous. [7] Now, years later, with the "splatform" still up there, and being the key to space exploration and research, nobody worried.

[7] The tether, made of carbon nanotubes weaved into a huge cable, reaches from the ground station to the splatform about 36,000kilometers\begin{align*}36,000\;\mathrm{kilometers}\end{align*} above the earth. Fibers of the cable are electrically conductive, permitting transmission of power to elevator motors, which lift items into space much mor e economically than rockets could.

Her dad—who managed the ground station, the tether, and the elevator up to the spatform––had mentioned that there were other political problems to deal with now. In fact, her boyfriend, Lenny had told her that his mother was up at the splatform doing some controversial experiments.

As Sandra took her leisurely time preparing for the evening, Len was finishing his last few laps at the high school track. Light filtered through the translucent concrete dome that covered the stadium, protecting it from the ravages of the sun and, right now, shielding the field from the thunderstorm encircling the valley. [8]

[8] The dome is made of sheets of concrete layered internally with carbon nanotubes and light conductive fiber so that it appears translucent.

Len felt good as he finished his laps. The leg he had broken in his clumsy attempt at pole vaulting had healed quickly after the doctor injected the nanofiber diamond-coated prosthesis to support the bone until it healed. [9]

[9] Diamondoid structures are a derivative of the carbon-based nanotubes, but are anatomically neutral, and thus cannot harbor infection.

Now it was straight to the gym for a shower and then home to get dressed for the prom.

Out of habit, he placed his hand on the wall panel signaling Mother to perform a physical check. The school’s AI, nicknamed "Mother" by the kids, recognized him. A few moments after he stepped into the shower, it chirped, "Leonard Gonzales, all systems are go. You have not ingested any prohibited substances." The same message was recorded in the coach’s log files. Any time the coach wanted to, he could get a view of the condition of every player from readings of their chronic sensor implants.

Len grinned,... "all systems are go," he laughed. Mother was an old AI system still using outdated phrases.

He dressed quickly, went out to his car in the parking lot, and pressed his thumb against the keyspot on the door to unlock it. [10] Len was proud of his first car. Like his dad’s, it had a lightweight nanotube reinforced fiber body that was the same color all the way through, so even deep scratches didn’t show. The main difference was that his car was electric and his Dad’s car, built for longer distance driving, was hydrogen powered. The hydrogen, of course, was refilled at the solar fuel station on the highway. [11] Len’s car captured some electricity from solar conversion and braking, and he fully recharged it by plugging into the grid, usually at home.

[10] The keyspot is similar to the wall panel identifier in note 2.

[11] Electricity from the national (or international) power grid is used locally at the filling station to power the nanomachine chemical conversion of water to hydrogen and oxygen. Burning the hydrogen in the car’s engine results in a nonpolluting exhaust (the only exhaust product is water).

As he put his hands on the steering wheel, there was a slight pause as the car checked his breath (to make sure that he hadn’t had anything that would impair his driving) and his prints, again, to make sure that he was the registered owner or a designated alternate driver. In less than a second, the green light came on and he shifted into "drive."

Before he pulled out of the school lot, his communication implant signaled a call from his mother, who was taking the elevator home from work. Len’s mom had been up at the spaltform’s isolation lab supervising the start of a new series of experimental nanocapsules for prescription drug delivery via the blood to specific cell types in the body. [12]

[12] Nano encapsulation technologies (using, for example, nanotubes and fullerines) can be treated to bond with cells of specific organs of the body and deliver their load of medication directly rather than spreading it throughout the body. (Kidney medication to kidney cells, etc.)

"I can’t seem to reach your father, Len, and I wanted him to know that the storm may slow us down a bit. You know... the risk of electrical interference."

"Mom, I don’t understand why the isolation lab has to be on the splatform. I think you have the longest commute of anyone I know." [13]

[13] The splatform is far above Earth’s atmosphere, where there are few air particles to provide friction. With less friction, the electrically powered elevator running on the tether can achieve speeds that would not be possible within Earth’s atmosphere, making such a commute possible on a daily basis.

"Maybe you’re right about the commute, Len. But tell your father that I’ll be delayed a bit. He should go ahead with dinner without me."

"OK, but really, Mom, you don’t need a weightless environment for the lab work. Everyone knows that nano particles are influenced more by inertia, friction, and Brownian motion than by gravity."

"That’s true, Len. The reason for the isolation lab being on the splatform is political, not scientific. You know, for example, that nanotubes and buckyballs can be toxic if you’re overexposed. Well, a lot of people are worried about the possible toxic effects of other nanoscale particles. Enough of them fear some strange new ‘world plague’ that they have passed laws prohibiting some research from being done on Earth, so we do it in space. If something goes wrong, we abandon the lab, thrust it, and have it burn up before it hits the Pacific."

"But why do you have to be there?" Len asked. "I thought the lab was automated."

"Well, Len, one thing that our best AI can’t do is adapt to unforeseen circumstances...there’s always a need for the personal touch."

"Yeah, I guess...but it’s still a long commute." Len grumbled.

"Sorry, kiddo. Have a good time tonight and I’ll see you in the morning."

Len signed off and signaled his implant to stream music from his favorite narrowband.

After driving home, he pulled into the garage and the charger moved out to plug into the car. The car was covered with solar converter paint that recharged the battery from sunlight, but this wasn’t always enough to keep the car fully charged [14]. Electricity generated by solar converters placed in large areas throughout the world, such as these Arizona deserts, was fed into the national grid.

[14] The "paint’ is composed of a medium in which molecular solar energy conversion cells are implanted. In the future, nano solar cells that could be rolled out, ink-jet printed, or painted onto surfaces.

He left a message for his father and started to prepare for the prom. As he laid out his clothes on the bed, his stomach growled, so he went to the kitchen for a snack. It might be late by the time the food was served at the prom, and a small sandwich couldn’t hurt. Afterwards, he took a mouthful of Nanodent. The nanomachines in the mouthwash recognized particles of food, plaque, and tartar and lifted them from the teeth and gums to be rinsed away. [15]

[15] Being suspended in liquid and able to swim about, nanobots could reach surfaces beyond reach of toothbrush bristles or the fibers of floss. After a few minutes in the body, they would fall apart into harmless fiber. With such easy daily dental care from an early age, tooth decay and gum disease may never arise.

Within an hour, he was dressed and on his way across town to pick up Sandra.

At Sandra’s house, Ms. Houston met him at the door. "Sandra will be ready in a few minutes. You know that girls going to a prom can’t be ready on time. It would violate some rule of the universe," she laughed. "Have a seat, Lenny. Want something to drink while you wait?"

"That would be macro, thanks. Maybe some juice?" Len sat in the living room feeling a little awkward with his formal clothes and corsage box in hand.

Ms. Houston brought in some grape juice and handed it to Len. A bit nervous about these relatively rare meetings with Sandra’s mother, he spilled some of the juice on his white shirt.

"Oh, sh…!" He stopped what he was about to say.

Ms. Houston laughed reassuringly. "No worries. Here, let me get a damp cloth, Lenny. These rented formal clothes reject anything that is non-fabric. It’ll just wipe off." [16] She led Len to the kitchen and wiped off the stain.

[16] Nanofibers in cloth will not allow dirt or other objects to adhere. These "nanowhiskers" act like peach fuzz and create a cushion of air around the fabric so that liquids bead up and roll off.

"Thanks, Ms. Houston." Len grinned. "I guess I’d better just sit down and wait."

Finally, after a seemingly interminable dozen minutes, Sandra walked into the room in glimmering pale blue gown and asked breezily, "Have I kept you waiting, Len?"

Len grimaced and Sandra laughed.

He handed her the corsage box and she beamed when she opened it.

"Goodnight, Mom," Sandra called out.

"Goodnight, Ms. Houston," Len echoed.

"Don’t forget to send me a few pictures of the prom." Ms. Houston waved as they walked away.

"I’ll be too busy, Mom," Sandra replied. But they’ll be taking class pics at the entrance. They’ll go right onto the class net."

As they walked out to the car, Sandra looked at Len and touched his shoulder, turning him around to face her. With a smile, she grabbed his hand and placed it on her shoulder. He leaned in for a kiss.

"Hold on, sport, I’m just recording your hand’s temperature gradient. I already recorded mine. My gown will use them to create a pattern of color gradients. You’ll see when we dance." Sandy worked the gown’s controller. [17]

[17] See note 4. Quantum dots can be tuned to emit different wavelengths of light. These small nanoscale crystalline structures will also be used as fluorescent labels in biological imaging and drug discovery research.

"Well I’m glad I’m good for something," he said.

"There’s always a need for the personal touch," she quipped.

"Seems I’ve heard that somewhere else today," Len mumbled to himself.

(Accessed August 2005.)

• Top 10 future applications of nanotechnology.
• Nanotechnology predictions.
• Space elevator made with carbon nanotubes.
• Dreaming about nano health care.
• Nanodentistry.
• Quantum dot pigments and infrared paints.
• Meeting energy needs with nanotechnology.
• Nanotechnology in construction.
• Nanotechnology in clothing.

Name_______________

Date_______________

Period_______________

### The Personal Touch: Student Worksheet

You will read a story that describes how nanotechnology might impact daily life in 2045. The story is fictional, but is based on current or proposed research, and in some cases, already existing technology.

1. BEFORE you read the story, predict, and write below, TWO ways that you think that nanoscience or nanotechnology might affect your life in the future.

Prediction 1:

Prediction 2:

2. READ THE STORY SILENTLY TO YOURSELF.

3. Summarize, and write below, FOUR applications of nanotechnology mentioned in the story.

Application 1:

Application 2:

Application 3:

Application 4:

4. What application mentioned in the story do you think is MOST believable, and why?

5. What application mentioned in the story do you think is LEAST believable, and why?

Question 1:

Question 2:

## Scale of Objects

Contents

• Visualizing the Nanoscale: Student Reading
• Scale Diagram: Dominant Objects, Tools, Models, and Forces at Various Different Scales
• Number Line/Card Sort Activity: Student Instructions & Worksheet
• Cards for Number Line/Card Sort Activity: Objects & Units
• Cutting it Down Activity: Student Instructions & Worksheet
• Scale of Objects Activity: Student Instructions & Worksheet
• Scale of Small Objects: Student Quiz

### Visualizing the Nanoscale: Student Reading

How Small is a Nanometer?

The meter (m)\begin{align*}(m)\end{align*} is the basic unit of length in the metric system, and a nanometer is one billionth of a meter. It's easy for us to visualize a meter; that’s about 3feet\begin{align*}3\;\mathrm{feet}\end{align*}. But a billionth of that? It’s a scale so different from what we're used to that it's difficult to imagine.

What Are Common Size Units, and Where is the Nanoscale Relative to Them?

Table 1 below shows some common size units and their various notations (exponential, number, English) and examples of objects that illustrate about how big each unit is.

Common size units and examples
Unit Magnitude as an exponent (m)\begin{align*}(m)\end{align*} Magnitude as a number (m)\begin{align*}(m)\end{align*} English Expression About how big?
Meter 100\begin{align*}10^0\end{align*} 1\begin{align*}1\end{align*} One A bit bigger than a yardstick
Centimeter 102\begin{align*}10^{-2}\end{align*} 0.01\begin{align*}0.01\end{align*} One Hundredth Width of a fingernail
Millimeter 103\begin{align*}10^{-3}\end{align*} 0.001\begin{align*}0.001\end{align*} One Thousandth Thickness of a dime
Micrometer 106\begin{align*}10^{-6}\end{align*} 0.000001\begin{align*}0.000001\end{align*} One Millionth A single cell
Nanometer 109\begin{align*}10^{-9}\end{align*} 0.000000001\begin{align*}0.000000001\end{align*} One Billionth 10\begin{align*}10\end{align*} hydrogen atoms lined up
Angstrom 1010\begin{align*}10^{-10}\end{align*} 0.0000000001\begin{align*}0.0000000001\end{align*}   A large atom

Nanoscience is the study and development of materials and structures in the range of 1nm(109m)\begin{align*}1\;\mathrm{nm} (10^{-9} \;\mathrm{m})\end{align*} to \begin{align*}100\;\mathrm{nanometers}\end{align*} \begin{align*}(100 \times 10^{-9} = 10^{-7} \;\mathrm{m})\end{align*} and the unique properties that arise at that scale. That is small! At the nanoscale, we are manipulating objects that are more than one-millionth the size of the period at the end of this sentence.

What if We Measured the Size of Various Objects in Terms of Nanometers?

A typical atom is anywhere from \begin{align*}0.1\end{align*} to \begin{align*}0.5\;\mathrm{nanometers}\end{align*} in diameter. DNA molecules are about \begin{align*}2.5\;\mathrm{nanometers}\end{align*} wide. Most proteins are about \begin{align*}10\;\mathrm{nanometers}\end{align*} wide, and a typical virus is about \begin{align*}100\;\mathrm{nanometers}\end{align*} wide. A bacterium is about \begin{align*}1000\;\mathrm{nanometers}\end{align*}. Human cells, such as red blood cells, are about \begin{align*}10,000\;\mathrm{nanometers}\end{align*} across. At \begin{align*}100,000\;\mathrm{nanometers}\end{align*}, the width of a human hair seems gigantic. The head of a pin is about a million nanometers wide. An adult man who is \begin{align*}2\;\mathrm{meters}\end{align*} tall \begin{align*}(6\;\mathrm{feet}\ 5\;\mathrm{inches})\end{align*} is about \begin{align*}2\;\mathrm{billion\ nanometers}\end{align*} tall!

So is That What Nanoscience is All About––Smallness?

No, smallness alone doesn’t account for all the interest in the nanoscale. Nanoscale structures push the envelope of physics, moving into the strange world of quantum mechanics. For nanoparticles, gravity hardly matters due to their small mass. However, the Brownian motion of these particles now becomes important. Nanosized particles of any given substance exhibit different properties and behaviors than larger particles of the same substance.

For now, though, we’ll focus just on the smallness of nanoscale, and ways to visualize how extremely tiny the nanoscale is.

How Can We Imagine the Nanoscale?

Another way to imagine the nanoscale is to think in terms of relative sizes. Consider yourself with respect to the size of an ant \begin{align*}(3-5\;\mathrm{millimeters})\end{align*}. An ant is roughly \begin{align*}1000 \;\mathrm{times}\end{align*} smaller than you are. Now think of an ant with respect to the size of an amoeba (about \begin{align*}1\;\mathrm{micron}\end{align*}). An amoeba is about \begin{align*}1000\;\mathrm{times}\end{align*} smaller than an ant. Now,consider that a nanometer is roughly \begin{align*}1000\;\mathrm{time}\end{align*} smaller than an amoeba! You would have to shrink yourself down by a factor of \begin{align*}1000\end{align*} three times in a row in order to get down to the level of the nanoscale.

Imagine Zooming In on Your Hand

Let’s try to conceptualize the nanoscale yet another way. Look at your hand. Let’s zoom into your hand by a factor of ten, several times in a row (see Figure 1, below).

In frame \begin{align*}1\end{align*}, at the \begin{align*}10\;\mathrm{centimeter}\end{align*} scale \begin{align*}(10^{-1} \;\mathrm{m})\end{align*}, we can see fingers and skin clearly. As we zoom in by a factor of ten to the \begin{align*}1\;\mathrm{centimeter}\end{align*} scale \begin{align*}(10^{-2} \;\mathrm{m})\end{align*}, we can begin to see the structure of skin (frame \begin{align*}2\end{align*}). If we move in another factor of ten to the \begin{align*}1\;\mathrm{millimeter}\end{align*} scale \begin{align*}(10^{-3} \;\mathrm{m})\end{align*}, we can see cracks in the skin clearly (frame \begin{align*}3\end{align*}). Moving in again by another factor of ten to the \begin{align*}100\;\mathrm{micron}\end{align*} level \begin{align*}(10^{-4} \;\mathrm{m})\end{align*}, the cracks look like deep crevices (frame \begin{align*}4\end{align*}). Zooming in again, to \begin{align*}10\;\mathrm{microns}\end{align*} \begin{align*}(10^{-5} \;\mathrm{m})\end{align*}, we can see an individual cell (frame \begin{align*}5\end{align*}). At the next level, \begin{align*}1\;\mathrm{micron}\end{align*} \begin{align*}(10^{-6} \;\mathrm{m})\end{align*} we can see the membrane of the cell and some of the features that exist on it (frame \begin{align*}6\end{align*}). Moving in another factor of ten to the \begin{align*}100 \;\mathrm{nm}\end{align*} scale \begin{align*}(10^{-7} \;\mathrm{m})\end{align*}, we begin to see the individual DNA strands that exist within nucleus of the cell. This is the scale at which computer technology is currently being fabricated (frame \begin{align*}7\end{align*}). Zooming in again to the \begin{align*}10 \;\mathrm{nm}\end{align*} length scale \begin{align*}(10^{-8} \;\mathrm{m})\end{align*}, we see the double helix that make up DNA. Finally, zooming in one last time to the \begin{align*}1\;\mathrm{nanometer}\end{align*} scale \begin{align*}(10^{-9} \;\mathrm{m})\end{align*}, we can see the see individual atoms that make up DNA strands!

Zooming in on your hand by powers of 10 [1].

What is This Powers of 10 Stuff?

In the above example, each picture is an image of something that is \begin{align*}10\;\mathrm{times}\end{align*} bigger or smaller than the one preceding or following it. The number below each image is the scale of the object in the picture. In the text above, the scale is also written in powers of ten, or exponential notation (e.g., \begin{align*}10^{-2}\end{align*}) where the scale is mentioned. Since the ranges of magnitudes in our universe are immense, exponential notation is a convenient way to write such very large or very small numbers.

The Molecular Expressions Web site offers a nice interactive visualization of magnitudes in our universe; see http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ The interactive Java applet on this site moves through space in successive orders of magnitude from the Milky Way galaxy \begin{align*}(10^{21} \;\mathrm{m})\end{align*}. our solar system \begin{align*}(10^{13} \;\mathrm{m})\end{align*}. towards the Earth \begin{align*}(10^{18} \;\mathrm{m})\end{align*}, to a city \begin{align*}(10^4 \;\mathrm{m})\end{align*}, a tree \begin{align*}(10^1 \;\mathrm{m})\end{align*}, a leaf \begin{align*}(10^{-1} \;\mathrm{m})\end{align*}, cells \begin{align*}(10^{-5} \;\mathrm{m})\end{align*}, strands if DNA \begin{align*}(10^{-7} \;\mathrm{m})\end{align*}, an atom \begin{align*}(10^{-10} \;\mathrm{m})\end{align*}, and eventually quarks \begin{align*}(10^{-16} \;\mathrm{m})\end{align*}. Check it out!

Another Shrinking Exercise

Recall that we said that you’d have to shrink yourself down by a factor of \begin{align*}1000\end{align*} three times in a row to get to the nanoscale. Let’s try that! [2]

Imagine you are sitting at your desk with the following items: A box, a baseball, a marble, and a grain of salt, as show below. These items represent a length spread of \begin{align*}3\end{align*} orders of magnitude. Each item is \begin{align*}10\;\mathrm{times}\end{align*} longer than the item to its left. The box is \begin{align*}1000\;\mathrm{times}\end{align*} longer than the grain of salt. These objects are in the realm of what is often referred to as the macroscale.

The macroscale.

What if we zoomed in \begin{align*}1000\;\mathrm{times}\end{align*}, so that the grain of salt was as big as the box?

• We could stand next to the grain of salt, and use it as a bed or a desk.
• Dust mites would look like hand-sized turtles, and your hair would look like giant ropes.
• Blood cells would be little red and white marbles.
• Bacteria on your skin would look like little grains of sand.

These objects, measured in microns, are in the realm of what is referred to as the microscale.

The microscale.

What if we zoomed in \begin{align*}1000\;\mathrm{times}\end{align*} again, so that the bacteria were as big as the box?

• We could sit on the bacteria like easy chairs.
• We could use viruses for batting practice.
• We could play marbles with proteins and large molecules.
• Atoms and small molecules would look like little grains of sand.

These objects, measured in nanometers, are in the realm of what is referred to as the nanoscale.

The nanoscale.

Summary

Although many sizes in the universe—including the nanoscale—are hard for us to comprehend because they are far removed from our experience, we can represent such sizes in mathematical notation and through relationships and analogies. Hopefully the examples and analogies used here help you better comprehend the size and scale of the nanoworld.

References

(Accessed August 2005.)

Glossary

amoeba
A single-celled organism with a nucleus, found in fresh or salt water environments.
bacterium
A structurally simple single cell with no nucleus. Bacteria occur naturally almost everywhere on Earth including soil, skin, on plants and many foods.
Brownian motion
The random motion of microscopic particles suspended in a liquid or gas, caused by collision with surrounding molecules.
DNA
The genetic material of almost every organism. It is a long, double-stranded, helical molecule that contains genetic instructions for growth, development, and replication.
protein
An organic compound whose structure is dictated by DNA. Proteins perform a wide variety of functions in the cell including serving as enzymes, structural components, or signaling molecules.
quantum mechanics
A scientific model useful for describing the behavior of very small particles (such as atoms and small molecules). Motion is described by probabilistic wave functions and energy can only exist in discrete (quantized) amounts.
quark
The basic building block of matter. Quarks combine with gluons to make the protons and neutrons that make up every atom in the universe.
virus
A structure containing proteins and nucleic acid. Viruses can infect cells and reproduce only by using their cellular machinery.
wave function
A mathematical equation used in quantum mechanics to describe the wave characteristics of a particle. The value of the wave function of a particle at a given point of space and time is related to the likelihood of the particle's being there at the time.

Name_______________

Date_______________

Period_______________

### Number Line/Card Sort Activity: Student Instructions & Worksheet

In this activity, you will explore your perception of the size of different items. Your task is to create a "powers of \begin{align*}10\end{align*}" number line and place items appropriately on the number line.

Materials

• Cards for the objects
• Cards for the units, in powers of \begin{align*}10 \;\mathrm{meters}\end{align*}

Instructions

On a surface like a lab table, order the cards for powers of \begin{align*}10\end{align*} in a vertical column, with the largest at the top and the smallest at the bottom. Space the cards equidistant from each other, leaving a gap between the cards for \begin{align*}10^{-10}\end{align*} and \begin{align*}10^{-15}\end{align*}. This is your number line.

Next, place each object next to the closest power of \begin{align*}10\end{align*} in the number line that represents the size of that object in meters. Some objects may lie between two powers of \begin{align*}10\end{align*}.

When you are done placing all of the cards, record your results in the table on the next page and answer the questions that follow.

Size (meters) Objects
\begin{align*}10^0\end{align*}
\begin{align*}10^{-1}\end{align*}
\begin{align*}10^{-2}\end{align*}
\begin{align*}10^{-3}\end{align*}
\begin{align*}10^{-4}\end{align*}
\begin{align*}10^{-5}\end{align*}
\begin{align*}10^{-6}\end{align*}
\begin{align*}10^{-7}\end{align*}
\begin{align*}10^{-8}\end{align*}
\begin{align*}10^{-9}\end{align*}
\begin{align*}10^{-10}\end{align*}
(large gap)
\begin{align*}10^{-15}\end{align*}

1. Which objects were the hardest for you to estimate size for? Why?

2. Why are we using powers of \begin{align*}10\end{align*} for the number line instead of a regular linear scale (like a meter stick)?

### Cards for Number Line Activity: Objects

(Printing on card stock paper is recommended; then cut to separate.)

 1. thickness of a penny 2. nucleus of an oxygen atom 3. diameter of a red blood cell 4. height of a typical 5-year-old child 5. width of a proteinase enzyme 6. length of a dust mite 7. width of a typical wedding ring 8. length of an amoeba 9. width of an electrical outlet cover 10. diameter of a ribosome 11. thickness of sewing thread 12. width of a water molecule 13. width of a bacterium 14. length of an apple seed 15. diameter of a virus 16. length of a business envelope 17. diameter of a quarter 18. length of a human muscle cell 19. diameter of a carbon nanotube 20. length of a phone book 21. height of a typical NBA basketball player 22. diameter of a nitrogen atom 23. thickness of a staple 24. wavelength of visible light Visible Light Spectrum
(Uses a base
Cards for Number Line Activity: Units

\begin{align*}(1\;\mathrm{femtometer})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-15\end{align*}

\begin{align*}(1\;\mathrm{angstrom})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-10\end{align*}

\begin{align*}(1\;\mathrm{nanometer})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-9\end{align*}

\begin{align*}(10\;\mathrm{nanometers})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-8\end{align*}

\begin{align*}(100\;\mathrm{nanometers})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-7\end{align*}

\begin{align*}(1\;\mathrm{micron})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-6\end{align*}

\begin{align*}(10\;\mathrm{microns})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-5\end{align*}

\begin{align*}(100\;\mathrm{microns})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-4\end{align*}

\begin{align*}(1\;\mathrm{millimeter})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-3\end{align*}

\begin{align*}(10\;\mathrm{millimeters})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-2\end{align*}

\begin{align*}(100\;\mathrm{millimeters})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}-1\end{align*}

\begin{align*}(1\;\mathrm{meter})\end{align*}

On \begin{align*}\;\mathrm{log}_{10}\end{align*} scale: \begin{align*}0\end{align*}

Image Sources for Object Cards

2. Nucleus of an oxygen atom: http://scienzapertutti.lnf.infn.it/P2/nucle.jpg
3. Diameter of a red blood cell: http://www.biopal.com/images/Red_Bl1.jpg
4. Height of a typical 5-year-old child: http://www.lowerallen.pa.us/Parks/ParksImages/soccer%20kid%20cartoon.gif
5. Width of a proteinase enzyme: http://aiims.aiims.ac.in/ragu/aiims/departments/biophy/enzyme5.jpg
6. Length of a dust mite: http://www.owlnet.rice.edu/~psyc351/Images/DustMite.jpg
7. Width of a typical wedding ring: http://www.goldringsplus.com/GRP_img/half/RS.jpg
8. Length of an amoeba: http://gladstone.uoregon.edu/~awickert/ceramics/amoeba.jpg
9. Width of an electrical outlet cover: http://www.punchstock.com/image/comstock/4550022/large/ks2793.jpg
10. Diameter of a ribosome: http://histo.ipfw.edu/images/ribosome.gif
11. Thickness of sewing thread: http://www.techsewing.com/image/left/company-needle.gif
12. Water molecule: http://www.lenntech.com/images/Water%20molecule.jpg
13. Width of a bacterium: http://www.scientific-art.com/GIF%20files/Zoological/microbea.gif
14. Length of an apple seed: http://www.thebestlinks.com/images/thumb/5/5c/250px-Old-appleseed-d402.jpg
15. Diameter of a virus: http://www.xtec.es/~imarias/virus.gif
17. Diameter of a quarter: http://www.pipebombnews.com/readerimages/quarter.gif
18. Length of a human muscle cell: http://dept.kent.edu/projects/cell/tm1.jpg
19. Diameter of a carbon nanotube: http://www.csiro.au/images/activities/carbon_nanotube.jpg
20. Length of a phone book: http://www.rickleephoto.com/phone97.jpg
22. Diameter of an atom: http://web.buddyproject.org/web017/web017/ae.html
23. Thickness of a staple: http://www.unisa.edu.au/printing/images/binding/staple%20icon.jpg
24. Wavelength of visible light: http://esp.cr.usgs.gov/info/sw/climmet/anatomy/index_nojava.html

Name_______________

Date_______________

Period_______________

### Cutting it Down Activity: Student Instructions and Worksheet

How many times do you think you would need to cut a strip of paper in half in order to make it between zero and \begin{align*}10\;\mathrm{nanometers}\end{align*} long? In this activity, you’ll cut a strip of paper in half as many times as you can, and think about the process.

BEFORE you begin cutting the strip of paper, answer the following questions (take a guess):

1. How many times do you need to cut the paper in half to obtain a \begin{align*}10\;\mathrm{nanometer}\end{align*} long piece?

2. How many times do you think you can cut the paper before it becomes impossible to cut?

Now cut the strip of paper in half as many times as you can. Remember to keep track of how many cuts you make.

AFTER completing the activity, answer the following questions.

3. Were your predictions to the above two questions accurate?

4. How many times were you able to cut the paper?

5. How close was your smallest piece to the nanoscale?

6. Why did you have to stop cutting?

7. Can macroscale objects, like scissors, be used at the nanoscale?

8. Can you think of a way to cut the paper any smaller?

Name_______________

Date_______________

Period_______________

### Activity: Student Instructions and Worksheet

In this activity, you will explore your perceptions of different sizes. For each of the following items, indicate its size by placing an "\begin{align*}X\end{align*}" in the box that is closest to your guess.

Key:

A. Less than \begin{align*}1\;\mathrm{nanometer}\end{align*} \begin{align*}(1 \;\mathrm{nm})\end{align*} [Less than \begin{align*}10^{-9}\;\mathrm{meter}\end{align*}]

B. Between \begin{align*}1\;\mathrm{nanometer}\end{align*} \begin{align*}\;\mathrm{(nm)}\end{align*} and \begin{align*}100\;\mathrm{nanometers}\end{align*} \begin{align*}(100 \;\mathrm{nm})\end{align*} [Between \begin{align*}10^{-9}\end{align*} and \begin{align*}10^{-7}\;\mathrm{meters}\end{align*}]

C. Between \begin{align*}100\;\mathrm{nanometers}\end{align*} \begin{align*}(100 \;\mathrm{nm})\end{align*} and \begin{align*}1\;\mathrm{micrometer}\end{align*} \begin{align*}(1 \mu m)\end{align*} [Between \begin{align*}10^{-7}\end{align*} and \begin{align*}10^{-6}\;\mathrm{meters}\end{align*}]

D. Between \begin{align*}1\;\mathrm{micrometer}\end{align*} \begin{align*}(1 \mu m)\end{align*} and \begin{align*}1\;\mathrm{millimeter}\end{align*} \begin{align*}(1 \;\mathrm{mm})\end{align*} [Between \begin{align*}10^{-6}\end{align*} and \begin{align*}10^{-3}\;\mathrm{meters}\end{align*}]

E. Between \begin{align*}1\;\mathrm{millimeter}\end{align*} \begin{align*}(1\;\mathrm{mm})\end{align*} and \begin{align*}1\;\mathrm{centimeter}\end{align*} \begin{align*}(1 \;\mathrm{cm})\end{align*} [Between \begin{align*}10^{-3}\end{align*} and \begin{align*}10^{-2}\;\mathrm{meters}\end{align*}]

F. Between \begin{align*}1\;\mathrm{centimeter}\end{align*} \begin{align*}(1 \;\mathrm{cm})\end{align*} and \begin{align*}1\;\mathrm{meter}\end{align*} \begin{align*}(\;\mathrm{m})\end{align*} [Between \begin{align*}10^{-2}\end{align*} and \begin{align*}10^0\;\mathrm{meters}\end{align*}]

G. Between \begin{align*}1\;\mathrm{meter}\end{align*} and \begin{align*}10\;\mathrm{meters}\end{align*} [Between \begin{align*}10^0\end{align*} and \begin{align*}10^1\;\mathrm{meters}\end{align*}]

H. More than \begin{align*}10\;\mathrm{meters}\end{align*} [More than \begin{align*}10^1\;\mathrm{meters}\end{align*}]

Less than \begin{align*}1 \;\mathrm{nm}\end{align*} \begin{align*}1 \;\mathrm{nm}\end{align*} to \begin{align*}100 \;\mathrm{nm}\end{align*} \begin{align*}100 \;\mathrm{nm}\end{align*} to \begin{align*}1 \;\mathrm{\mu m}\end{align*} \begin{align*}1 \;\mathrm{\mu m}\end{align*} to \begin{align*}1 \;\mathrm{mm}\end{align*} \begin{align*}1 \;\mathrm{mm}\end{align*} to \begin{align*}1 \;\mathrm{cm}\end{align*} \begin{align*}1 \;\mathrm{cm}\end{align*} to \begin{align*}1 \;\mathrm{m}\end{align*} \begin{align*}1 \;\mathrm{m}\end{align*} to \begin{align*}10 \;\mathrm{m}\end{align*} More than \begin{align*}10 \;\mathrm{m}\end{align*}
Object A B C D E F G H
1. Width of a human hair
2. Length of a football field
3. Diameter of a virus
4. Diameter of a hollow ball made of \begin{align*}60\end{align*} carbon atoms (a "buckyball")
5. Diameter of a molecule of hemoglobin
6. Diameter of a hydrogen atom
7. Length of a molecule of sucrose
8. Diameter of a human blood cell
9. Length of an ant
10. Height of an elephant
11. Diameter of a ribosome
12. Wavelength of visible light
13. Height of a typical adult person
14. Length of a new pencil
15. Length of a school bus
16. Diameter of the nucleus of a carbon atom
17. Length of a grain of white rice
18. Length of a postage stamp
19. Length of a typical science textbook
20. Length of an adult’s little finger

Adapted from Tretter, T. R., Jones, M. G., Andre, T., Negishi, A., & Minogue, J. (2005). Conceptual Boundaries and Distances: Students’ and Experts’ Concepts of the Scale of Scientific Phenomena. Journal of Research in Science Teaching.

Name_______________

Date_______________

Period_______________

### Scale of Small Objects: Student Quiz

1. Indicate the size of each item below by placing an "\begin{align*}X\end{align*}" the appropriate box.

Key:

A. Less than \begin{align*}1\;\mathrm{nanometer}\ (1\;\mathrm{nm})\end{align*} [Less than \begin{align*}10^{-9}\;\mathrm{meter}\end{align*}]

B. Between \begin{align*}1\;\mathrm{nanometer}\ (\;\mathrm{nm})\end{align*} and \begin{align*}100\;\mathrm{nanometers}\ 100 \;\mathrm{nm})\end{align*} [Between \begin{align*}10^{-9}\end{align*} and \begin{align*}10^{-7}\;\mathrm{meters}\end{align*}]

C. Between \begin{align*}100\;\mathrm{nanometers}\ (100 \;\mathrm{nm})\end{align*} and \begin{align*}1 \;\mathrm{micrometer}\ (1 \mu m)\end{align*} [Between \begin{align*}10^{-7}\end{align*} and \begin{align*}10^{-6}\;\mathrm{meters}\end{align*}]

D. Between \begin{align*}1 \;\mathrm{micrometer}\ (1 \mu m)\end{align*} and \begin{align*}1\;\mathrm{millimeter}\ (1 \;\mathrm{mm})\end{align*} [Between \begin{align*}10^{-6}\end{align*} and \begin{align*}10^{-3}\;\mathrm{meters}\end{align*}]

E. Between \begin{align*}1\;\mathrm{millimeter}\ (1 \;\mathrm{mm})\end{align*} and \begin{align*}1\;\mathrm{centimeter}\ (1 \;\mathrm{cm})\end{align*} [Between \begin{align*}10^{-3}\end{align*} and \begin{align*}10^{-2}\;\mathrm{meters}\end{align*}]

Less than \begin{align*}1 \;\mathrm{nm}\end{align*} \begin{align*}1 \;\mathrm{nm}\end{align*} to \begin{align*}100 \;\mathrm{nm}\end{align*} \begin{align*}100 \;\mathrm{nm}\end{align*} to \begin{align*}1 \;\mathrm{\mu m}\end{align*} \begin{align*}1 \;\mathrm{\mu m}\end{align*} to \begin{align*}1 \;\mathrm{mm}\end{align*} \begin{align*}1 \;\mathrm{mm}\end{align*} to \begin{align*}1 \;\mathrm{cm}\end{align*}
Object A B C D E
1. Width of a human hair
2. Diameter of a hollow ball made of \begin{align*}60\end{align*} carbon atoms (a "buckyball")
3. Diameter of a hydrogen atom
4. Diameter of a human blood cell
5. Wavelength of visible light

2. Order the following items in order of their size, from smallest to largest.

a. Width of a water molecule

b. Diameter of a gold atom

c. Thickness of a staple

d. Diameter of a virus

e. Length of an amoeba

f. Diameter of a carbon nanotube

Smallest:

________
________
________
________
________

Largest:

________

## Unique Properties at the Nanoscale

Contents

• Unique Properties Lab Activities: Student Instructions
• Unique Properties Lab Activities: Student Worksheet
• Unique Properties at the Nanoscale: Student Quiz

Overview

What is so special about nanotechnology that suddenly we have focused so much attention on this area? The new generation of scientific tools that operate on the nanoscale allow us to collect data and to manipulate atoms and molecules on a much smaller scale than we have ever been able to in the past. With these tools we are finding out that many familiar materials act differently and have different characteristics and properties when we have very small (nanoscale) quantities of them. As we study these materials in nanoscale quantities and generate theories to explain why they behave the way they do, we are learning new things about the nature of matter and developing the ability to manipulate these properties to create all sorts of new products and technologies, like the stain-repellant pants and solar power paint that we hear about in the media.

What Does it Mean to Talk About the Characteristics and Properties of a Substance?

Characteristics and properties are ways of describing different qualities of a substance and how it acts under normal conditions. Over centuries, scientists have accumulated a great deal of information about the properties of different substances (such as gold). For example we have information about gold’s optical properties (such as color and transparency), electrical properties (such as conductivity), physical properties (such as density and boiling point) and chemical properties (such as reactivities and reaction rates). We can use this information to predict what gold will do under different conditions and to make decisions about whether or not it is good material to use when we are building or synthesizing new materials.

How Do We Know the Characteristics and Properties of Substances?

We have come to understand the characteristics and properties of atoms and molecules by studying a pure sample of the substance in quantities big enough to measure under normal laboratory conditions. Because atoms and molecules are so extremely small, we need a huge amount in order to see them, measure their mass on a typical laboratory scale and mix specific amounts together (remember just \begin{align*}18\;\mathrm{grams}\end{align*} of water \begin{align*}(1\;\mathrm{mole})\end{align*} contains \begin{align*}6.022 \times 10^{23}\;\mathrm{molecules}\end{align*}). So when scientists make measurements of the different properties of gold, they are actually measuring the average properties based on the behavior of billions and billions of particles and not looking at the behavior of individual atoms or molecules. We have always assumed that these properties are constant for a given substance (gold always acts the same no matter how much of it you have) and in our macro-scale world experiences they have been. This means that even though we measure these properties for large numbers of particles, we assume that the results should be true for any size group of particles.

What’s Different at the Nanoscale?

Using new tools that allow us to see and manipulate small groups of molecules whose size in the nanoscale, scientists have now discovered that these tiny amounts of a given substance often exhibit different properties and behaviors than larger particles of the same substance! We’ve seen that when the number of atoms or molecules bonded together is so small that they only occupy between \begin{align*}1\end{align*} and \begin{align*}100\;\mathrm{nanometers}\end{align*} of space, the properties are no longer predictably the same properties that are listed in tables of "physical properties" of a substance. Consider an analogy with sand on a beach. When looking at a sandy beach from afar, the sand appears to have a uniform color and texture. As you zoom in and examine fewer grains of sand at a time, you discover that the sand is actually made up of a variety of individual colors and textures of particles. As we develop better and better tools that allow us to look at and move these grains of sand (atoms and molecules), our understanding of the nature of matter changes.

How Do These Properties Change?

The color of gold is a classic example of how properties can change based on the size of the particles. When we have an aggregation of gold atoms bonded together in a solid with a diameter of about \begin{align*}12\;\mathrm{nanometers}\end{align*}, we can observe the color of the nanoparticles by looking at a bunch of them suspended in water. If the atoms are in the right bonding arrangement, we see that the gold nanoparticles appear red, not gold-colored. If we add a bunch more atoms in the right arrangement, we see the particles look purple. Why? Each of the different sized arrangement of gold atoms absorbs and reflects light differently based on its energy levels, which are determined by size and bonding arrangement. This is true for many materials when the particles have a size that is less than \begin{align*}100\;\mathrm{nanometers}\end{align*} in at least one dimension.

Reaction time is another phenomenon that changes at this scale. The greater the surface to-volume ratio that reacting substances have, the faster the reaction time. Nanosized groups of particles are so small that they have a very high surface area to volume ratio, and thus react so quickly that precise measurements of time are difficult.

For nanosized objects, some familiar properties also become meaningless. Some physical properties of substances, for example, don’t necessarily make sense at the nanoscale. How would you define, much less measure, boiling temperature for a substance that has only \begin{align*}50\;\mathrm{atoms}\end{align*}? Boiling temperature is based on the average kinetic energy of the molecules needed for the vapor pressure to equal the atmospheric pressure. Some molecules in a pot of water on the stove will be moving fast and some will be moving more slowly. The vapor pressure results from the average force per unit area exerted by the fast moving particles in the vapor bubbles in the water. When you only have \begin{align*}50\;\mathrm{molecules}\end{align*} of water, it is highly unlikely that a bubble would form so it doesn’t make sense to talk about vapor pressure.

Why Do These Properties Change at the Nanoscale?

When we look at nanosized particles of substances, there are four main things that change from macroscale objects. First, due to the small mass of the particles, gravitational forces are negligible. Instead electromagnetic forces are dominant in determining the behavior of atoms and molecules. Second, at nanoscale sizes, we need to use quantum mechanical descriptions of particle motion and energy transfer instead of the classical mechanical descriptions. Third, nanosized particles have a very large surface area to volume ratio. Fourth, at this size, the influences of random molecular motion play a much greater role than they do at the macroscale.

How Does the Dominance of Electromagnetic Forces Make a Difference?

As shown in Table 1, below, there are four basic forces known in nature: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. The gravitational force is the force of attraction between the masses of two objects. This force is directly proportional to the masses of the two objects and inversely proportional to the square of the distance between the objects. Because the mass of nanoscale objects is so small, the force of gravity has very little effect on the attraction between objects of this size. Electromagnetic forces are forces of attraction and repulsion between objects based on their charge and magnetic properties. These forces also increase with the charge or the magnetism of each object and decrease as the distance between the objects become greater, but they are not affected by the masses of objects. Since electromagnetic forces are not affected by mass, they can be very strong even with nanosized particles. The magnetic and electrostatic forces are very important forces that determine the behavior of substances chemically and physically at the particle level. The other two forces, the strong nuclear force and the weak nuclear force, are interactions between the particles that compose the nucleus. These forces are only significant at extremely short distances and therefore become negligible in the nanoscale range. Since electromagnetic, and not gravitational, forces are most influential at the nanoscale, nanoparticles do not behave like macrosized objects. For example, a nanosubmarine (if we could build such a thing) would behave very differently than its macroscopic counterpart. With weak gravitational, but strong electromagnetic forces, the nanosubmarine might just stick to the first surface it encountered or be repelled so that it couldn’t get near another surface at all!

The four basic forces in nature, and the scales at which these forces are influential. Note that all forces exist at all scales, but their size may be so small as to be negligible (also see the Scale Diagram).
Gravitational Force Electromagnetic Forces Weak Nuclear Force Strong Nuclear Force
Cosmic Scale \begin{align*}10^7 \;\mathrm{m}\end{align*} and bigger \begin{align*}X\end{align*} \begin{align*}X*\end{align*}
Macroscale \begin{align*}10^{-2} \;\mathrm{m}\end{align*} to \begin{align*}10^6 \;\mathrm{m}\end{align*} \begin{align*}X\end{align*} \begin{align*}X**\end{align*}
Microscale \begin{align*}10^{-3} \;\mathrm{m}\end{align*} to \begin{align*}10^{-7} \;\mathrm{m}\end{align*} \begin{align*}X\end{align*} \begin{align*}X\end{align*}
Nanoscale \begin{align*}10^{-8} \;\mathrm{m}\end{align*} to \begin{align*}10^{-9} \;\mathrm{m}\end{align*}   \begin{align*}X\end{align*}
Sub-Atomic Scale \begin{align*}10^{-10}\;\mathrm{m}\end{align*} and smaller     \begin{align*}X\end{align*} \begin{align*}X\end{align*}

\begin{align*}^*\end{align*} In places like the sun, where matter is ionized and in rapid motion, electromagnetic forces are dominant.

\begin{align*}^{**}\end{align*} On a human scale, where matter is neither ionized nor moving rapidly, electromagnetism, though important, is not dominant.

How Does a Quantum Mechanical Model Make a Difference?

Classical mechanical models explain phenomena well at the macroscale level, but they break down when dealing with the very small (atomic size, where quantum mechanics is used) or the very fast (near the speed of light, where relativity takes over). For everyday objects, which are much larger than atoms and much slower than the speed of light, classical models do an excellent job. However, at the nanoscale there are many phenomena that cannot be explained by classical mechanics. The following are among the most important things that quantum mechanical models can describe (but classical models cannot):

• Discreteness of energy
• The wave-particle duality of light and matter
• Quantum tunneling
• Uncertainty of measurement

Discreteness of Energy

If you look at the spectrum of light emitted by energetic atoms (such as the orange-yellow light from sodium vapor street lights, or the blue-white light from mercury vapor lamps), you will notice that it is composed of individual lines of different colors. These lines echo the discrete energy levels of the electrons in those excited atoms. When an electron in a high-energy state falls down to a lower one, the atom emits a photon of light that corresponds to the exact energy difference of those two levels (because of the conservation of energy). The bigger the energy difference, the more energetic the photon will be, and the closer its color will be to the violet end of the spectrum. If electrons were not restricted to discrete energy levels, the spectrum from an excited atom would be a continuous spread of colors from red to violet with no individual lines.

It is the fact that electrons can only exist at discrete energy levels that prevents them from spiraling into the nucleus, as classical models predict. This quantization of energy, along with some other atomic properties that are quantized, give quantum mechanics its name.

The Wave-Particle Duality of Light and Matter

In 1690, Christiaan Huygens theorized that light was composed of waves, while in 1704, Isaac Newton theorized that light was made of tiny particles. Experiments supported each of their theories. However, neither a completely-particle theory nor a completely-wave theory could explain all of the phenomena associated with light!

For most light phenomena—such as reflection, interference, and polarization—the wave model of light explains things quite well. However, there are several cases in which the wave model cannot explain the phenomena that are observed, but a particle model can! One such phenomenon is called the "photoelectric effect," discovered by Albert Einstein. The photoelectric effect happens when you shine light on the surface of a metal and some of the electrons in the metal are knocked loose (similar to shooting pellets at sandpaper). With the photoelectric effect,scientists were unable to explain how this happens using the wave model of light. But when they thought of light as small particles, they could explain this effect. So scientists began to think of light as both a particle and a wave, and depending on what experiment you do, you will see light behave in one of these two ways. It is also important to note that the wave-particle duality extends to matter as well—it is not just limited to light—and the wave nature has been observed in experiments. It may be hard to imagine something like a "matter wave," but when you are talking about small particles such as electrons, it is possible to observe wave-like behavior.

Quantum Tunneling

Quantum tunneling is one of the most interesting phenomena to be explained by quantum mechanics. As stated above, in quantum mechanics we talk about the probability of where a particle will be. The probably of finding a particle is explained by a probability wave. When that probability wave encounters an energy barrier, most of the wave will be reflected back, but a small portion of it will "leak" into the barrier. If the barrier is small enough, the wave that leaks through will continue on the other side of it. Even though the particle doesn't have enough energy to get over the barrier, there is still a small probability that it can "tunnel" through it! It would be like trying to drive over a river after part of the bridge has washed out. You couldn’t. But imagine that the gap in the bridge is really small—much smaller than the size of the tire on your car—and the situation changes. In a car, you can imagine jumping the small gap if you are going fast enough. Similarly, electrons can jump across small gaps.

Let's say you are throwing a rubber ball against a wall. You know you don't have enough energy to throw it through the wall, so you always expect it to bounce back. Quantum mechanics, however, says that there is a small probability that the ball could go right through the wall (without damaging the wall) and continue its flight on the other side! With something as large as a rubber ball, though, that probability is so small that you could throw the ball for billions of years and never see it go through the wall. But with something as tiny as an electron, tunneling is an everyday occurrence.

Uncertainty of Measurement

People are familiar with measuring things in the macroscopic world around them. Someone pulls out a tape measure and determines the length of a table. At the atomic scale of quantum mechanics, however, measurement becomes a very delicate process. Let's say you want to find out where an electron is and where it is going. How would you do it? Get a super high-powered magnifier and look for it? The very act of looking depends upon light, which is made of photons, and these photons could have enough momentum that once they hit the electron, they would change the electron’s course! So by looking at (trying to measure) the electron, you change where it is. Werner Heisenberg was the first to realize that certain pairs of measurements have an intrinsic uncertainty associated with them. In other words, there is a limit to how exact a measurement can be. This is usually not an issue at the macroscale, but it can be very important when dealing with small distances and high velocities at the nanoscale and smaller. For example, to know an electron’s position, you need to "freeze" it in a small space. In doing so, however, you get poor velocity data (since you had to make the velocity zero). If you are interested in knowing the exact velocity, you must let it move, but this gives you poor position data.

Why Do the Greater Surface Area to Volume Ratios Make a Difference?

Many of the observed properties of a substance are based on intermolecular forces. When we observe a large number of particles of that substance, the majority of the particles are in the interior of the material and subject to similar forces. But this is not true of the surface particles that experience forces not only from the substance but from the surrounding material as well.

For instance, suppose we have a liter of water at room temperature. Water molecules have a great deal of polarity, and as such, are attracted to each other via hydrogen bonds. These intermolecular hydrogen bonds cause water to be a liquid at room temperature. They also cause water to have a relatively high surface tension, resulting in the typical drop shape of water. What about at the water molecules at the edges of the container? Does the glass beaker have the same amount and type of attraction to the water as the water molecules have to each other? No, it is slightly different. The behavior of the water at the interface between the glass and water is different than within the interior of the water, where the water molecules are only surrounded by other water molecules. What about where the water molecules come into contact with the air? Does the air, composed of mostly nitrogen, have the same attraction to the water molecules as the water molecules have to each other? Again, no. In fact, the water molecules are not generally attracted to the molecules in the air very much at all. These examples highlight the fact that if you have a small (nano) amount of a substance, a greater proportion of the substance will have interactions with surrounding materials (e.g. container, air) than if you have a great (bulk) amount of the substance. This idea of greater surface area to volume ratio for small aggregations of substances can lead to different properties being displayed than for larger aggregations that have lower surface area to volume ratios.

The importance of surfaces is demonstrated by looking at a drop of water that is resting on a waxy surface such as wax paper (see Figure 1, below). We can see that the force of attraction of the water molecules to each other (cohesive forces) is far greater than the force of attraction of the water molecules to the surface of the wax paper (adhesive forces). This results in the drop shape of the collection of water molecules, which is evidence of a high surface tension. When the surface upon which the molecules rest is changed to one in which the molecules of water are more attracted such as plastic wrap, then the shape of water collapses, because the adhesive forces between the water and the plastic wrap are strong enough to overcome the cohesive forces (which we see as surface tension) between the water molecules. You can try this at home with drops of water on wax paper and plastic wrap. This example illustrates the impact of surface features on the behavior of a substance. Nanoscale objects have a far greater amount of surface area than volume, so surface effects are far more significant in general.

Another example of the importance of surfaces is rate of reaction. Since reactions occur at the interface of two substances, when a large percentage of the particles are located on the surface, we get maximum exposed surface area, which means maximum reactivity! So nanosized groups of particles can make great catalysts.

Surface tension and surface attractive forces for a drop of water on a non-wettable surface like glass (left), or a more attractive surface (right) [1].

Why Does Random Molecular Motion Make a Difference?

Random molecular motion is the movement that all molecules in a substance exhibit (assuming the sample is above absolute zero) due to their kinetic energy. This motion increases at higher temperatures (temperature is actually a macroscale measure of the average kinetic energy of all the particles in a substance). This motion can involve molecules moving around in space, rotating around their bonds, and vibrating along their bonds. While random kinetic motion is always present, at the macroscale this motion is very small compared to the sizes of the objects and thus is not very influential in how object behave. At the nanoscale however, these motions can be on the same scale as the size of the particles and thus have an important influence on how particles behave. For example, the imaginary nanosubmarine we talked about earlier would have its internal parts and mechanisms bending and flexing in all directions in constant random motion.

An example of how random kinetic motion can influence things is Brownian Motion [2]. Brownian Motion is the random movement of tiny particles suspended in a gas or a liquid resulting from bombardment by the fast moving particles of the gas or liquid. Think of a regular submarine in the ocean, even though it is constantly bombarded by the random kinetic motion of the water particles, it is so large that this does not significantly affect its motion through the water. Compare this to the imaginary nanosubmarine that would be constantly jostled around because the fluid molecules might be almost as big as it is!

So What Does This All Mean?

The dominance of electromagnetic force, the presence of quantum mechanical phenomena, the large surface area to volume ratio and the importance of random kinetic motion cause nanoscale sized particles to often have very different properties than their macroscale counterparts. The discovery that the properties of a substance can change with size (made possible by the new generation of scanning probe microscopes) has helped us to expand our understanding of the nature of matter and to develop new products that take advantage of the novel properties of materials at the nanoscale. As we continue to develop better tools and learn more about how and why these properties change, we will be better able to manipulate these properties to meet our needs and develop new materials and products that take advantage of these properties.

References

(Accessed August 2005.)

[2] A nice animation of Brownian Motion is available through the Molecular Workbench software at http://mw.concord.org/modeler1.3/mirror/thermodynamics/brown.html

Glossary

absolute zero
\begin{align*}0\;\mathrm{Kelvin}\end{align*} \begin{align*}(-273.15^\circ C)\end{align*} is the coldest temperature theoretically possible at which all atomic motion stops.
aggregation
A group of something (in chemistry usually atoms or molecules).
classical mechanics
Scientific model useful for describing the behavior of macro and micro sized objects based on Newton’s laws of force and motion.
electromagnetic forces
Particles with charge (or areas of charge) exert attractive or repulsive forces on each other due to this charge. Particles with magnetic properties exert attractive or repulsive forces on each other due to these magnetic properties. Since magnetism is caused by charged particles accelerating (for example by the electron "spin" in materials such as iron), these forces are considered to be two aspects of the same phenomenon and are collectively called electromagnetic forces.
kinetic energy
Energy of motion.
negligible
So small that it can be ignored.
polarity
The degree to which a molecule has a charge separation leading to one part of the molecule being partially positively charged and another part being partially negatively charged.
quantized
Something that is said to exist only in specific units and not all values along a continuum.
quantum mechanics
Scientific model useful for describing the behavior of very small particles (such as atoms and small molecules). Motion is described by probabilistic wave functions and energy can only exist in discrete (quantized) amounts.
wave function
A mathematical equation used in quantum mechanics to describe the wave characteristics of a particle. The value of the wave function of a particle at a given point of space and time is related to the likelihood of the particle's being there at the time.

### Lab Activities: Student Directions

Lab Station A:

Serial Dilution

Purpose

The purpose of this lab is to investigate the effects of decreasing the concentration of a solution of the dual properties of color and odor. Nanosized materials, (from \begin{align*}1\end{align*} to \begin{align*}100\;\mathrm{nm}\end{align*}), often appear to have different colors and scents than they do at larger sizes.

Safety Precautions

• Wear goggles while conducting this lab.
• Do not eat or drink any solutions or chemicals.

Materials

• A stock solution "assigned" the value of \begin{align*}1.0\;\mathrm{Molar}\end{align*}
• Five test tubes that can hold \begin{align*}10-\mathrm{mL}\end{align*} each
• One \begin{align*}25-\mathrm{mL}\end{align*} graduated cylinder
• A test tube holder
• Grease marker
• Tap water
• One \begin{align*}1.0-\mathrm{mL}\end{align*} graduated pipette, plastic or glass
• A sheet of white paper for background, to help students judge color

Procedures

Concentration

1. Label each of your test tubes from 1 to 5.
2. Use a pipette to place \begin{align*}10.0 \;\mathrm{mL}\end{align*} of \begin{align*}1.0\end{align*} Molar of colored solution into test tube #1.
3. Remove \begin{align*}1.0 \;\mathrm{mL}\end{align*} from test tube #1 and inject this into test tube #2. Then add \begin{align*}9.0 \;\mathrm{mL}\end{align*} of water into test tube #2.
4. Remove \begin{align*}1.0 \;\mathrm{mL}\end{align*} from test tube #2 and inject this into test tube #3. Then add \begin{align*}9.0 \;\mathrm{mL}\end{align*} of water into test tube #3.
5. Continue in this fashion until you have completed test tube #5.
6. Note that each subsequent test tube has the concentration of the previous test tube divided by \begin{align*}10\end{align*}.
7. On your lab sheet, record the concentration of the solution in each test tube.

Color

1. Hold the white paper behind your test tubes to determine the color change.

2. Use test tube #1 as the strongest color.

3. Continue from test tube #2 to #5 using the gauge below.

4. Record on your lab sheet the strength of each test tube according to the scale above. At what strength are you no longer able to detect color? Explain why this has happened.

Odor

1. Waft, with your hand, the air over the top of the test tube towards your nose. Sniff. Record the strength of odor according to the scale below on you lab worksheet.
2. Use test tube #1 as the strongest odor.
3. Continue with test tube #2 to #5 in the same manner.

4. Record on your lab sheet the concentration at which the odor of your solution is no longer detectable. Record other observations and questions as asked on the lab sheet. Explain why you think this happened.

Lab Station B:

Ferrofluid Display Cell Lab

Purpose

The purpose of this lab is to design a series of activities that investigate and compare the force of magnetism in ferrofluid (small pieces of iron suspended in fluid) and in a solid piece of iron.

Safety Precautions

• Do not shake or open the bottle of ferrofluid!
• Use care when handling glass.

Materials

• One capped bottle of ferrofluid (nanoscopic iron particles suspended in a liquid)
• A \begin{align*}100-\mathrm{mL}\end{align*} graduated cyclinder
• A large empty test tube, clear plastic if possible, and stopper
• A piece of iron rod, nail or washer
• Two circle magnets

Procedures

1. Make observations and record your observations of the ferrofluid and the iron object separately.
2. Predict how the magnet will influence the ferrofluid and the iron object.
3. Use the magnets to observe how the force of magnetism influences the ferrofluid and the iron object.

Lab Station C:

Bubbles Self-Assembly

Purpose

One of the methods proposed to mass manufacture nanosized objects is use nature’s own natural tendency to self-assemble. Fluid or flexible objects will automatically fill the space of the container, taking the most efficient shape. The purpose of this lab is to demonstrate how bubbles self-assemble.

Safety Precautions

• Do not eat or drink anything in lab.
• Use caution when handling glassware.

Materials

• A bubble solution
• Small shallow dish
• Toothpicks
• Paper towels
• Straw

Procedures

1. Stir the solution with the straw to create bubbles, as needed.
2. Pour about \begin{align*}10.0\;\mathrm{mL}\end{align*} of bubble solution into the shallow dish.
3. Caution: Be careful not to spill the solution or to drop the dish!
4. Draw what you see in your worksheet. This is your "before" diagram.
5. Take the toothpick and pop one of the bubbles. Notice how the arrangement of bubbles changed. Draw what has happened. This is your "after" diagram. Repeat this procedure several times (you do not need to illustrate after the first "before" and "after" observations).

Lab Station D:

Surface Area to Volume Effects...

Which Shape Can Dissolve the Fastest?

Purpose

One of the characteristics of nanosized objects is that the surface area to volume ratio is much greater than bulk sized objects. The purpose of this lab investigation is to compare the effects of varying the surface area to volume ratio for two samples of the same substance and mass, but different particle size, on the rate of dissolving in water.

Safety Precautions

• Do not eat or drink anything in lab.
• Use caution when handling glassware.
• Wear safety goggles.

Materials

• Two sugar cubes
• Granulated sugar
• A digital balance or scale, with readout to \begin{align*}0.1\;\mathrm{gram}\end{align*}, or a triple beam balance
• Two \begin{align*}250-\mathrm{mL}\end{align*} Erlenmeyer flasks
• A \begin{align*}100-\mathrm{mL}\end{align*} graduated cylinder
• A grease marker
• Tap water, about \begin{align*}50-\mathrm{mL}\end{align*}
• A clock or watch with a second hand

Procedures

1. Using a grease marker, label one Erlenmeyer flask #1 and the other #2. (These may have already been marked. No need to mark twice.)
2. Set the scale to zero, after placing a square of paper on top of the scale (this is called "taring").
3. Measure and record the mass of two cubes of sugar. Put the sugar cubes into flask #1.
4. Measure and record a mass of granulated sugar equal to the mass of the two sugar cubes.
5. Put the granulated sugar into flask #2.
6. Using your graduated cylinder, add \begin{align*}100.0 \;\mathrm{mL}\end{align*} of tap water to each flask.
7. Gently swirl each flask exactly \begin{align*}60\;\mathrm{seconds}\end{align*}.
8. Record the relative amount of sugar that has dissolved in each flask on your lab sheet.
9. Swirl each flask for another \begin{align*}60\;\mathrm{seconds}\end{align*}.

Lab Station E:

More Surface Effects...Faster Explosion?

Purpose

The purpose of the following activities is to give you more experience with examining the effects of changing surface area to volume ratios. Faster explosion looks at the effect of different surface area to volume ratios on the speed of reaction.

Safety Precautions

• Do not eat or drink anything in the lab.

Materials

• Two empty film canisters and their lids
• One tablet of Alka Seltzer®
• One small mortar and pestle
• One timer or watch with seconds hand

Procedures

1. Break the Alka Seltzer® tablet in half as exactly as you can.
2. Put one of the halves of the Alka Seltzer® tablet into the mortar and crush it with the pestle until it is finely granulated.
3. Place the uncrushed Alka Seltzer® and the crushed Alka Seltzer® each into a different film canister. Each canister should contain Alka Seltzer® before you proceed to the next step.
4. Simultaneously fill each film canister halfway with tap water. Quickly put their lids on.
5. On your lab sheet, record how much time it takes for each canister to blow its lid off.
6. Rinse the film canisters with water when finished.

Lab Station F:

More Surface Effects...Is All Water the Same?

Purpose

The purpose of the following activities is to provide students with more experience at examining the effects of changing surface area to volume ratios. This lab investigates different surface areas for the same volume of water on the speed of boiling.

Safety Precautions

• Wear safety goggles while conducting this investigation.
• Be careful when handling glass.
• Use extra caution when trying to move hot glassware. Either handle with tongs or wait until glassware is fully cooled.
• Be certain to turn off heat source when you have completed this investigation.

Materials

• Three different size beakers or flasks
• Hot plate(s) or \begin{align*}3\end{align*} Bunsen burners
• One \begin{align*}100-\mathrm{mL}\end{align*} graduated cylinder
• A centimeter ruler
• Tongs designed to use with glassware
• Clock or watch

Procedure

1. Fill in the chart on your lab sheet with the size and type of beaker or flask.
2. Fill each of the beakers with \begin{align*}100.0 \;\mathrm{mL}\end{align*} of tap water.
3. Measure the diameter of each of your beakers and record to the nearest mm. For the Erlenmeyer flask, if you are using one, measure the diameter of the water when it is in the flask.
4. Turn on hotplate(s) or Bunsen burners to an equal flame or setting (if using more than one hotplate) at the same time. Record the start time on your lab sheet.
5. Record the time that the water begins to boil in each of the beakers/flasks. Record this time in the appropriate column on your lab sheet in the table provided.
6. Fill out the rest of the lab worksheet for this investigation.

Lab Station G:

Surface Area to Volume Effects...Burn Baby Burn!

Purpose

These activities demonstrate the effects of an increased surface area to volume ratio on the rate of combustion (burning).

Safety Precautions

• Do not pick up any hot items with your fingers or with paper towels. Let cool first.
• Wear safety goggles.
• Tie back any long hair.

Materials

• One solid rod of steel (or a nail)
• Two sets of tongs
• Two Bunsen burners and starters
• A 2" section of steel wool

Procedures

1. Light the two Bunsen burners to the same level of flame.
2. Pick up the steel rod or nail with the tongs and heat in the hottest part of the flame for \begin{align*}2\;\mathrm{minutes}\end{align*}, then remove from flame and let cool. Record your observations on your lab sheet.
3. Pick up the section of steel wool with the tongs and place in the hottest part of the flame for \begin{align*}2\;\mathrm{minutes}\end{align*}, then remove from flame and let cool. Record your observations on your lab sheet.
4. Once the objects are cooled, deposit any waste into the trash.

Lab Station H:

Surface Area to Volume Effects...Bet I Can Beat’cha!

Purpose

The purpose of this lab activity is to demonstrate the effect of varying surface area to volume ratios of the same materials on the rate of reaction.

Safety Precautions

• Wear goggles during this lab investigation.
• Don’t eat or drink anything at your lab station.
• Deposit chemical waste according to the instructions of your teacher. Do not flush solution into the drain.
• Use caution when handling glassware.

Reagent

• \begin{align*}\;\mathrm{CuCl}_2 \bullet 2H_2O\end{align*} crystals

Materials

• One teaspoon
• One glass stirring rod
• Two \begin{align*}100 \;\mathrm{mL}\end{align*} beakers
• Two squares, \begin{align*}2\;\mathrm{inches} \times 2\;\mathrm{inches}\end{align*}, of aluminum foil
• A pair of tongs
• Paper towels and a solid waste disposal
• A clock or watch with a second hand display

Procedures

1. Fill each of the \begin{align*}100 \;\mathrm{mL}\end{align*} beakers about half full with tap water.
2. Add 1 teaspoon of \begin{align*}\;\mathrm{CuCl}_2 \bullet 2H_2O\end{align*} crystals to each of the beakers of tap water and mix well with the stirring rod.
3. Form \begin{align*}1\;\mathrm{piece}\end{align*} of aluminum foil into a loose ball; leave the other piece as is.
4. Put each of the aluminum foil pieces into their own beaker.
5. On your lab sheet, record the time that it takes for each reaction to be complete.
6. Dispose of solution and waste according to your teacher’s instructions.

Name_______________

Date_______________

Period_______________

### Lab Activities: Student Worksheet

Directions: Go to the lab stations assigned by your teacher. Follow the directions for the lab that are taped to each of the lab stations. Conduct the lab activity and record your data on this lab write up sheet. Answer the questions asked on this lab sheet. Be sure to pay special attention to the purpose of each lab.

Lab Station A: Serial Dilution

Record your data in the following chart:
Characteristics of Solution Test tube #1 Initial Test tube #2 Test tube #3 Test tube #4 Test tube #5 Final
Concentration/ Molarity
Color
Smell

Questions

1. At what molarity of your solution was the color undetectable?

2. What pattern did you notice about the color of the solution as it decreased in strength?

3. At what molarity of your solution was the scent of your solution undetectable?

4. What pattern did you notice about the smell of the solution as it decreased in strength?

5. How does this phenomenon relate to the idea of properties of matter at the nanoscale?

Lab Station B:

Ferrofluid Display Cell Lab

Follow the directions posted at your lab station. Experiment with the ferrofluid, solid iron and magnets to discover the differences and the similarities of the two iron objects. Record your procedures (what you did), your observations (what you saw) and your discussion/conclusions (what you think about what you did and saw). Write down any questions that occurred to you regarding the objects.

Observations (ferrofluid and iron object separately):

Predictions:

Observations (interactions between magnets and: 1) ferrofluid and 2) iron object):

Discussion/Conclusions/Questions:

What difference do you think the size of the particles of iron made on their behavior?

Lab Station C:

Bubbles Self-Assembly

Conduct the lab activity according to directions posted at your lab station. Select a few instances to record in writing and sketch "before" and "after" pictures.

Drawings:
Before After
Describe what you saw. Describe what happened.

Questions

1. What do you conclude about bubbles ability to self-assemble?

2. What possible implications could the idea of self-assembly of objects have on the manufacturing of nanosized objects? You may refer back to your notes about self-assembly.

Lab Station D:

Surface Area to Volume Effects...

Which Shape Can Dissolve the Fastest?

Conduct this lab activity according to the directions on the lab station. Record your measurements here:

Mass Record to the nearest \begin{align*}0.1\;\mathrm{gram}\end{align*} Observations of sugar remaining after \begin{align*}1^{st} 60-\mathrm{seconds}\end{align*} of stirring Observation of sugar remaining after \begin{align*}2^{nd} 60-\mathrm{seconds}\end{align*} of stirring
Sugar cube
Granulated sugar

Questions

1. What do you conclude about the relationship between the volume and surface area on the rate of dissolving?

2. Can you think of additional experiments to conduct?

Lab Station E:

More Surface Effects... Faster Explosion?

Record the time it takes to blow the lid off of each film canister:

Time it takes for lid to blow off
Film canister with \begin{align*}1/2\end{align*} Alka Selzer tablet not crushed:
Film canister with \begin{align*}1/2\end{align*} Alka Selzer tablet crushed:

What do you conclude about the surface-to-volume effects on the speed of reaction based on this experiment?

Lab Station F:

More Surface Effects... Is All Water the Same?

Record the size of each beaker and the time it takes for the water in each beaker to boil.

A B C D E F G H
Type of container for the water Diameter of surface of water \begin{align*}(\;\mathrm{cm})\end{align*} Radius of surface of water \begin{align*}(\;\mathrm{cm})\end{align*} Surface area of water \begin{align*}(\;\mathrm{cm}^2)\end{align*} Surface area to volume ratio Initial time heat is applied Time when water boils Total time taken for water to boil

Hints to fill out the chart:

• A is name of the type of container and the capacity, i.e. \begin{align*}100-\mathrm{mL}\end{align*} beaker.
• B is the diameter of the surface of the water in each beaker, in centimeters; measure across the surface of the water in each container.
• C is the radius of the surface of the water in each beaker; divide the diameter (column B) by \begin{align*}2\end{align*}.
• D is the surface area of the water in each beaker \begin{align*}(\mathrm{cm}^2)\end{align*}; calculate using \begin{align*}\pi r^2\end{align*} where \begin{align*}\pi = \mathrm{pi} = 3.14\end{align*} and \begin{align*}r = \mathrm{radius}\end{align*}.
• E is the surface area to volume ratio of water in each beaker, that is, the surface of the water (column D) divided by the volume of the water. Use the smallest whole number ratio; e.g., \begin{align*}2:1\end{align*} means the surface area is twice the volume of the water.
• F, G, and H are times in minutes and seconds. H is column G minus column F.

Question

What do you conclude about the surface-to-volume ratio and the time it takes to boil?

Lab Station G:

Surface Area to Volume Effects… Burn Baby Burn!

Compare and contrast your observations between when the steel sample was heated and when the steel wool was heated.

What do you conclude about surface-to-volume ratios and the speed of combustion (burning)?

Speculate based on evidence: What effect(s) do you think that the increased surface area of nanosized objects make compared to bigger objects? What evidence do you have that supports your thinking?

Lab Station H:

Surface Area to Volume Effects... Bet I Can Beat’cha!

Record the time that it takes for the aluminum foil to come within an estimated \begin{align*}80\%\end{align*} of a completed reaction.

Time for foil to come within \begin{align*}80\%\end{align*} of completed reaction, in seconds
Flat square of aluminum foil
Balled-up piece of aluminum foil

What do you conclude about the effects of surface-to-volume ratio and reaction rates?

Name_______________

Date_______________

Period_______________

### Student Quiz

For questions 1-4, choose which force best matches the statement. (1 point each)

a. gravitational force

b. electromagnetic forces

_____ 1. Describe(s) the attraction of the masses of two particles to each other.

_____ 2. Dominate(s) for nanosized objects.

_____ 3. Do/does not vary with mass.

_____ 4. Stronger for objects with greater mass.

5. Identify a property that doesn’t have meaning when you only have a few nanosized particles, and explain why. (2 points)

6. Compare the surface-to-volume ratios of a large piece of gold with a nanosized piece of gold. (1 point)

7. Explain in your own words why surface-to-volume ratios are important in determining the properties of a substance. You may use a drawing or example to help clarify your explanation. (3 points)

8. Name and explain three properties that are likely to change as when an object is nanosized. You may give examples to help clarify your explanation. (3 points)

9. Explain the concept of electron tunneling and address why this may be a problem for nanosized objects. (2 points)

## Tools of the Nanosciences

Contents

• Black Box Lab Activity: Student Instructions and Worksheet
• Seeing and Building Small Things: Student Reading
• Seeing and Building Small Things: Student Quiz

Name_______________

Date_______________

Period_______________

### Black Box Lab Activity: Student Instructions and Worksheet

Purpose

To use different probes to determine the layout of objects on the bottom surface of a closed box, and to consider the limitations and challenges in using probes to "see."

Materials

• One black box
• One pencil and magnet probe
• One cotton swab probe
• One skewer probe

Instructions

1. Obtain from your teacher a box, pencil and magnet probe, a cotton swab probe, and a barbecue skewer probe.

2. Place the pencil and magnet probe into the center hole, and determine as best you can what the surface of the bottom of the box looks like. Draw your best guess below.

3. Replace the pencil and magnet probe with the cotton swab probe, using the swab end as the probe. Is there any additional information you are able to conclude about the surface of the bottom of the box? Draw your best guess below.

4. Replace the cotton swab probe with the barbecue skewer probe, using the pointed end of the skewer as the probe. Is there any additional information you are able to conclude about the surface of the bottom of the box? Draw your best guess below.

Questions

1. Describe the technique you used to investigate the surface of the bottom of the box.

2. What kinds of information about the bottom surface were you able to deduce?

3. How accurate do you think your drawing is?

4. What could you do to get a better idea of what the bottom surface looks like, besides opening the box?

5. What if a ping-pong ball was attached to the probing end of the skewer? How might this have affected your interpretations?

6. What difficulties did you encounter in using this probing technique to "see" the unknown? Or what challenges could there be in using such a technique?

### Seeing and Building Small Things: Student Reading

How Do You See and Build Things That Are So Small?

Although Richard Feynman launched the idea of nanotechnology way back in his 1958 speech, it wasn’t until decades later that we were actually able to create things at the nanoscale. Why did it take so long? Because we didn’t have the right tools until then. We had lots of tools to make small devices, but these tools didn’t operate at a small enough scale—until now!

Scanning Probe Instruments

In recent years, new tools have been developed that make it easier for scientists to measure and manipulate atoms and molecules. Some of the first tools were scanning probe instruments, developed in the early 1980s. The idea behind these instruments is simple: If you close your eyes and slide the tip of your finger across a surface, you can tell tree bark from satin from peanut butter. The tip of your finger acts like a probe that measures the force that it takes to move across the surface. It’s easier to slide your finger across satin than across peanut butter because the peanut butter exerts a drag force that pulls the finger back. You can even rearrange the peanut butter by dragging it this way.

Scanning probe instruments are like your finger, but reduced to the nanoscale. They have probes that slide across surfaces and measure properties like force—but the very tip of such probes are often only a single atom in size! With this tiny tip, these instruments can "feel" the force of one atom on the surface and from that, be able to tell what kind of atom it is. They can even be used to move atoms around and arrange them in a preferred order, just as you can move peanut butter with your finger.

What Are Some Types of Scanning Probe Instruments?

One type of scanning probe instrument is the atomic force microscope (AFM). The AFM uses a tiny tip that moves in response to the electromagnetic forces between the atoms of the surface and the tip. Tips are usually made of silicon, though sometimes carbon nanotubes are used for the tip. As the tip is scanned across a surface, the AFM measures the tiny upward and downward deflections of the tip necessary to remain in close contact with the surface. Alternately, the tip can be made to vibrate and intermittently "tap" the surface. In this case, the AFM senses when the tip (briefly) contacts the surface and uses this information to generate a topographical images.

Another type of scanning probe instrument is the scanning tunneling microscope (STM). With this instrument, the "tunneling" of electrons between the tip and the atoms of the surface being viewed creates a flow of electrons (a current). Tungsten is often used for STM tips because it is strong, electrically conductive, and easy to electro-chemically etch to a fine point. Carbon nanotubes may also prove to be suitable for use as STM tips, given their remarkable electrical and mechanical properties.

Scanning tunneling microscope (STM) [1].

Tip of a scanning probe instrument [2].

The AFM was invented to overcome the STM’s basic drawback: it can only be used to sense the nature of materials that conduct electricity, since it relies on the creation of a current between the tip and the surface. The AFM relies on actual contact rather than current flow, so it can be used to probe almost any type of material, including polymers, glass and biological samples.

The signals (forces or currents) from these instruments are used to infer an image of the atoms. The tip’s fluctuations are recorded and fed into computer models that generate images based on the data. These images give us a rough picture of the atomic landscape.

You Mean I Can Move Things Too?

But these microscopes can do much more than just "see": their tips can form bonds with the atoms of the material they are scanning, and move the atoms. Manipulation of atoms by an STM is done by applying a tiny pulse of charge through the tip of the instrument. For example, hydrogen can be removed from hydrogen-silicon bonds by scanning a STM tip over the surface while applying rapid pulses, which pulls the bonds apart.

Nano logo [3].

Nano abacus [4].

Once an atom has been lifted, it can be deposited elsewhere. Using this method with xenon atoms, IBM created the tiniest logo ever in 1990. In 1996, the tiniest abacus was also created by arranging buckyballs on a copper surface.

Is This a Good Way to Make Things?

Creating devices and materials atom-by-atom is more than an academic exercise; it paves the way for the next wave of nanotechnology research. But producing a material one atom at a time is not great for satisfying mass demand, because it’s expensive and slow. For example, using the fastest techniques we have today, it would still take over \begin{align*}60 \;\mathrm{million}\end{align*} years to assemble one aspirin table atom-by atom, because there are a lot of aspirin molecules (about \begin{align*}3.5 \times 10^{20}\end{align*} to be precise) in one aspirin tablet that would need to be assembled! So how else can we manipulate atoms?

What is Self Assembly?

Self assembly is the process by which molecular building blocks "assemble" naturally to form useful products. Molecules try to minimize their energy levels by aligning themselves in particular positions. If bonding to an adjacent molecule allows for a lower energy state, then the bonding will occur. We see this happening in many places in nature. For example, the spherical shape of a bubble or the shape of snowflake are a result of molecules minimizing their energy levels. In cells, DNA is self-assembled from the atomic particles available to the cell. Photosynthesis is a process of self assembly. In fact, all the functions of the cell are variations of self assembly.

Is Self Assembly a Good Way to Build Things?

Through self assembly, large structures can be prepared without the individual tailoring that is required in the methods mentioned above. Just toss atoms or molecules onto a surface, and stand back. Of course it’s not quite that simple––they don’t always go in the places that you want them to! But because of the large number of structures one could create quickly with this method, it will probably become the most important nanofabrication technique.

One particular type of self-assembly is crystal growth. This technique is used to "grow" nanotubes and nanowires. In this approach, "seed" crystals are placed on some surface, some other atoms or molecules are introduced, and these particles mimic the pattern of the small seed crystal. For example, one way to make nanotubes is to create an array of iron nanopowder particles on some material like silicon, put this array in a chamber, and add some natural gas with carbon to the chamber. The carbon reacts with the iron and supersaturates it, forming a precipitate of carbon that then grows up and out. In this manner, you can grow nanotubes like trees!

Growing nanotubes like trees [6]

Summary

The size limit of the smallest features you can create depends on the tools that you use. We’ve seen that STM and AFM’s can be used to measure and manipulate atoms, either in a one-by-one fashion, or through nanolithography methods like DPN. In contrast to this "positional" approach, self-assembly is carried out largely by nature, usually through a chemical reaction. We can use self-assembly to create new structures if we set up the conditions just right. Although there are many examples of self-assembly around us in nature (including ourselves!), the rules that govern these assemblies are not fully understood. Our ability to create nanostructures improves as we gain understanding of biological self-assembly, the chemical development of new molecular structures, and the physical development of new tools.

References

(Accessed August 2005.)

Glossary

buckyball
A soccerball-shaped molecule made up of \begin{align*}60\end{align*} carbon atoms. Also known as Buckminsterfullerene.

electromagnetic forces
Particles with charge (or areas of charge) exert attractive or repulsive forces on each other due to this charge. Particles with magnetic properties exert attractive or repulsive forces on each other due to these magnetic properties. Since magnetism is caused by charged particles accelerating (for example by the electron "spin" in materials such as iron), these forces are considered to be two aspects of the same phenomenon and are collectively called electromagnetic forces.
Feynman, Richard (1918-1988)
One of the most influential American physicists of the 20th century, Richard Feynman greatly expanded the theory of quantum physics and received the Nobel Prize for his work in 1965. He also helped in the development of the atomic bomb and was an inspiring lecturer and amateur musician.

nanometer
One-billionth of a meter \begin{align*}(10-9\mathrm{m})\end{align*}. The prefix ‘nano’ is derived from the Greek word for dwarf because a nanometer is very small. Ten hydrogen atoms lined up side-by-side are about \begin{align*}1 \;\mathrm{nanometer}\end{align*} long.
nanopowder
A dry collection of nanoparticles.
nanoscale
Refers to objects with sizes in the range of \begin{align*}1\end{align*} to \begin{align*}100 \;\mathrm{nanometers}\end{align*} in at least one dimension.
nanotechnology
The design, characterization, production and application of structures, devices and systems that take advantage of the special properties at the nanoscale by manipulating shape and size.
nanotubes
Carbon nanotubes are cylindrical molecules made up of carbon bonded in a hexagonal formation. They are unusually strong, efficient conductors of heat and exhibit unique electrical properties. These characteristics make them potentially useful in extremely small scale electronic and mechanical applications.

nanowires
A "nanowire" is a wire of dimensions of the order of a nanometer \begin{align*}(10 - 9 \;\mathrm{meters})\end{align*}. At these scales, quantum mechanical effects are important - hence such wires are also known as "quantum wires".
photosynthesis
A biochemical process in which cells in plants, algae, and some bacteria use light energy to convert inorganic molecules into ATP (a high energy storage molecule) which they can use for energy later.
polymer
A generic term used to describe a substantially long molecule. This long molecule consists of structural units and repeating units strung together through chemical bonds.
supersaturation
Supersaturation (or oversaturation) refers to a solution that due to special conditions contains more of the dissolved material than could be dissolved by the solvent under normal circumstances.

Name_______________

Date_______________

Period_______________

### Seeing and Building Small Things: Student Quiz

1. Name the scanning probe instrument that uses electrical current to infer an image of atoms. Briefly describe how it works.

2. Name the scanning probe instrument that reacts to forces inherent in atoms and molecules to infer an image of atoms. Briefly describe how it works.

3. Scanning probe instruments can also be used to create things atom by atom. Briefly summarize the downside of using such tools to create an aspirin tablet.

4. How does dip pen nanolithography (DPN) work? Using a drawing in your explanation.

5. Name two things in nature that are created by self-assembly processes.

1:
2:

6. Circle true or false for each of the following.

E-beam lithography is a type of self assembly. True False

One type of self-assembly is crystal growth. True False

Nanotubes can be grown like trees from seed crystals. True False

The rules governing self-assembly are fully understood. True False

## Applications of Nanoscience

Contents

• What's New Nanocat? Poster Session: Student Instructions
• What's New Nanocat? Poster Session: Student Topic List
• What's New Nanocat? Poster Session: Peer Feedback Form

### What's New Nanocat? Poster Session: Student Directions

Overview

When scientists want to share their findings and proposals with other scientists, they often do it at a national meeting with scientists who have the same interests. They often share ideas at what is called a poster session. The scientists come to the meeting with a poster that explains in text and graphics what their findings or proposal is all about. The poster is usually either a rolled up paper about \begin{align*}4 \;\mathrm{feet}\end{align*} long and \begin{align*}2.5 \;\mathrm{feet}\end{align*} wide, or a set of \begin{align*}8-12\end{align*} normal (letter size) printed pages that they tack up on a board. They stand near the poster and as others walk by, they discuss their work with the other scientists and answer questions.

You will assume the role of a prominent nanoscientist working on a new nanotechnology application, and explain the proposed usage of the new technology to replace a current technology in a poster session. You will be given a list of nanotechnology applications (based on what we have discussed in class) from which you can choose, or you can prepare a poster on an application that is not on the list if your teacher approves it. The posters will be displayed in class and you will explain the technology by explaining the poster. Your classmates will assess your poster, and you will assess their posters, using the Poster Feedback Sheet.

Your poster must include the following:

1. A written description of the current technology and how it is used, and how it works.
2. At least one picture or diagram that helps illustrate how the current technology works.
3. A written description of the new, related nanotechnology, how it is proposed to be used, and how it works.
4. At least one picture or diagram that helps illustrate how the new nanotechnology works.
5. A written description of the implications of the new nanotechnology: how it will help improve understanding, solve a problem, and possible ethical or societal issues.

At the poster session, be prepared to discuss the applications and answer questions, so that someone visiting the poster will walk away with a good understanding of the science.

1. Your poster must include all of the elements mentioned above.
2. Your written descriptions and diagrams must have a sound scientific basis.
3. Your design should be neat and have an attractive layout.
4. All text and borrowed diagrams must have source citations.
5. Your oral explanation must be clear and understandable, all team members must participate, and you should be able to answer questions about the poster and how you created it.

### What’s New Nanocat? Poster Session: Student Topic List

Stain Resistant Clothes

Manufacturers are embedding fine-spun fibers into fabric to confer stain resistance on khaki pants and other products. These "nanowhiskers" act like peach fuzz and create a cushion of air around the fabric so that liquids bead up and roll off. Each nanowhisker is only ten nanometers long, made of a few atoms of carbon. To attach these whiskers to cotton, the cotton is immersed in a tank of water full of billions of nanowhiskers. Next, as the fabric is heated and water evaporates, the nanowhiskers form a chemical bond with cotton fibers, attaching themselves permanently. The whiskers are so tiny that if a cotton fiber were the size of a tree trunk, the whiskers would look like fuzz on its bark. Nanoresistant fabric created by NanoTex is already available in clothing available at stores like Eddie Bauer, The Gap, and Old Navy. This innovation will impact not only khaki wearers, but also dry cleaners who will find their business declining, and detergent makers who will find less of their project moving off the shelf. Nanoparticles (e.g., of silver) could also be introduced to destroy microbes and create odor-resistant cloths.

Paint That Resists Chipping

On cars, special nanopaints that hold up better to weathering, are more resistant to chipping and have richer and brighter colors than traditional pigments. The paints contain tiny ceramic particles added to a liquid clearcoat. The particles link and create a very dense and smoothly structured network that provides a protective layer.

Paint That Cleans the Air

Chinese scientists have announced that they have even invented nanotech-based coating material that acts as a permanent air purifier. If the coating proves to be effective at air cleaning, it will be gradually used on buildings across Shanghai in order to improve the city's air quality. The core of the material is a titanic-oxide-based compound that comprises particles at nanoscale achieved by advanced nanotechnology. Exposed under sunlight, the substance can automatically decompose the major ingredients that cause air pollution such as formaldehyde and nitride.

Painting On Solar Cells

Enough energy from the sun hits the earth every day to completely meet all energy needs on the planet, if only it could be harnessed. Doing so could wean us off of fossil fuels like oil and provide a clean energy alternative. But currently, solar-power technologies cost as much as \begin{align*}10 \;\mathrm{times}\end{align*} the price of fossil fuel generation. Chemists at U.C. Berkeley are developing nanotechnology to produce a photovoltaic material that can be spread like plastic wrap or paint. These nano solar cells could be integrated with other building materials, and offer the promise of cheap production costs that could finally make solar power a widely used electricity alternative. Current approaches embed nanorods (barshaped semiconducting inorganic crystals) in a thin sheet (\begin{align*}200 \;\mathrm{nanometers}\end{align*} deep) of electrically conductive polymer. Thin layers of an electrode sandwich these nanorodpolymer composite sheets. When sunlight hits the sheets, they absorb photons, exciting electrons in the polymer and the nanorods, which make up \begin{align*}90\end{align*} percent of the composite. The result is a useful current that is carried away by the electrodes. Eventually, nanorod solar cells could be rolled out, ink-jet printed, or even painted onto surfaces, so that even a billboard on a bus could be a solar collector.

High Density Storage Media

New nanomedia could have a storage density that is a million times higher that current CDs and DVDs. Nano storage applications currently in development use a variety of methods, including self-assembly.

Smaller Devices and Chips

A technique called nanolithography enables us to create much smaller devices than current approaches. For example, dip pen nanolithography is a ‘direct write’ technique that uses an AFM to create patterns and to duplicate images. "Ink" is laid down atom by atom on a surface, through a solvent—often water.

Hybrid Neuro-Electronic Networks

Researchers are studying the electrical interfacing of semiconductors with living cells—in particular, neurons—to build hybrid neuro-electronic networks. Cellular processes are coupled to microelectronic devices through the direct contact of cell membranes and semiconductor chips. For example, electrical interfacing of individual nerve cells and semiconductor microstructures allow nerve tissue to directly communicate their impulses to computer chips. This research is directed (1) to reveal the structure and dynamics of the cell-semiconductor interface and (2) to build up hybrid neuro-electronic networks. Other researchers have built a cyborg, a half-living, half-robot creature that connects the brain of an eel-like fish to a computer and is capable of moving towards lights. Such research explores the new world at the interface of the electronics in inorganic solids and the ionics in living cells, providing the basis for future applications in medical prosthetics, biosensorics, brain research and neurocomputation. For example, neuro-electronic networks could lead implants that can restore sight.

Detecting Disease with Quantum Dots

Quantum dots are small devices that contain a tiny droplet of free electrons, and emit photons when submitted to ultraviolet (UV) light. Quantum dots are considered to have greater flexibility than other fluorescent materials, which makes them suited for use in building nano-scale applications where light is used to process information. Quantum dots can, for example, be made from semiconductor crystals of cadmium selenide encased in a zinc sulfide shell as small as \begin{align*}1 \;\mathrm{nanometer}\end{align*} (one-billionth of a meter). In UV light, each dot radiates a brilliant color.

Because exposure to cadmium could be hazardous, quantum dots have not found their way into clinical use. But they have been used as markers to tag particles of interest in the laboratory. Scientists at Georgia Institute of Technology have developed a new design that protects the body from exposure to the cadmium by sealing quantum dots in a polymer capsule. The surface of each capsule can attach to different molecules. In this case, they attached monoclonal antibodies directed against prostate-specific surface antigen, which is found on prostate cancer cells. The researchers injected these quantum dots into live mice that had human prostate cancers. The dots collected in the tumors in numbers large enough to be visible in ultraviolet light under a microscope. Because the dots are so small, they can be used to locate individual molecules, making them extremely sensitive as detectors. Quantum dots could improve tumor imaging sensitivity tenfold with the ability to locate as few as \begin{align*}10\end{align*} to \begin{align*}100\end{align*} cancer cells. Using this technology, we could detect cancer much earlier, which means more successful, easier treatment.

Growing Tissue to Repair Hearts

Cardiac muscle tissue can be grown in the lab, but the fibers grow in random directions. Researchers at the University of Washington are investigating what type of spatial cues they might give heart-muscle cells so that they order themselves into something like the original heart-muscle tissue. Working with one type of heart muscle cell, they have been able build a two-dimensional structure that resembles native tissue. They use nanofibers to "instruct" muscle cells to orient themselves in a certain way. They have even able to build a tissue-like structure in which cells pulse or ‘beat’ similar to a living heart.

Preventing Viruses from Infecting Us

If we could cover the proteins that exist on the influenza virus, we could prevent the virus from recognizing and binding to our body cells. We would never get the flu! A protein recognition system has already been developed. More generally, this work suggests that assembled virus particles can be treated as chemically reactive surfaces that are potentially available to a broad range of organic and inorganic modification.

Nanobots Making Repairs to the Body

Nanobots are decades off, but if they are developed someday, they could be used to maintain and protect the human body against pathogens. For example, they could (1) be used to cure skin diseases (embedded in a cream, they could remove dead skin and excess oils, apply missing oils), (2) be added to mouthwash to destroy bacteria and lift plaque or tartar from the teeth to be rinsed away, (3) augment the immune system by finding and disabling unwanted bacteria and viruses, or (4) nibble away at plaque deposits in blood vessels, widening them to prevent heart attacks.

Drug Delivery Systems

Nanotubes and buckyballs could serve as drug delivery systems. Researchers have attached florescent markers and proteins to nanotubes and mixed them with living cells. They can see (from the florescent marker) that the nanotubes enter the cell, and could "deliver" the protein inside the cell. The nanotubes don't seem toxic to the cell, so far, but lots more research to be done. Similarly, investigators anticipated that buckyball or fullerene-related structures could serve as "cages" for small drug molecules.

Self-Cleaning Surfaces

Self-cleaning surfaces (e.g., windows, mirrors, toilets) could be made with bioactive coatings. Researchers have already developed water-repellent surfaces that could lead to self-cleaning glass. This surface mimics the surface of the water lily, which is waxy and covered with tiny bumps, so water rolls off. There are spray coatings that currently exist that make glass self-cleaning, but these coatings wear off. Nanotechnology would build this new surface into the surface of the window, so it would work for the lifetime of the window.

Food Storage and Manufacturing

Nanocomposites for plastic film coatings used in food packaging could detect or even prevent contamination in food or food packaging. This could enable wider distribution of food products to remote areas in less industrialized countries.

Water Treatment

Nanotechnology could lead to advanced water-filtering membranes that could purify even the worst of wastewater. Only about \begin{align*}1\end{align*} percent of the water in the world is usable (\begin{align*}97\end{align*} percent is saltwater, and two-thirds of the remaining fresh water rest is ice). With the world population expected to double in \begin{align*}40\end{align*} years, over half the world population could face a very serious water shortage in that time. Even now, \begin{align*}10,000\end{align*} to \begin{align*}60,000\end{align*} people die every day because of diseases caused by bad water. Advanced nanomembranes could be used for water purification, desalination, and detoxification, nanosensors could detect contaminants and pathogens, and nanoparticles could degrade water pollutants and make salt water and even sewage water easily converted into usable, drinkable water.

Health Monitoring

Several nano-devices are being developed to keep track of daily changes in patients’ glucose and cholesterol levels, aiding in the monitoring and management of diabetes and high cholesterol for better health. For example, some researchers have created coated nanotubes in a way that will fluoresce in the presence of glucose. Inserted into human tissue, these nanotubes can be excited with a laser pointer and provide real-time monitoring of blood glucose level. No more discomfort from needles, pricking, or drawing blood!

Clean Energy

Cars of the future may use nonpolluting hydrogen fuel cells. Today, hydrogen fuel is expensive to make, but with catalysts made from nanoclusters, it may be possible to generate hydrogen from water by photocatalytic reactions. Novel hydrogen storage systems could be based on carbon nanotubes and other lightweight nanomaterials, nanocatalysts could be used for hydrogen generation, and nanotubes could be used for energy transport.

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### What’s New Nanocat? Poster Session: Peer Feedback Form

1. What is the topic of the poster you are evaluating?

2. What are the names of the students who developed the poster you are evaluating?

3. The poster contained the following items:

A text description of a current technology and how it works. True False

A picture that helps illustrate how the current technology works. True False

A text description of a new, related nanotechnology and how it works. True False

A picture that helps illustrate how the new nanotechnology works. True False

A text description of the implications of the nanotechnology: how it will help improve understanding, solve a problem, and any possible societal issues. True False

4. How strongly do you agree with the following statements?

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The poster is visually appealing. 1 2 3 4 5
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The poster presenters communicated clearly and answered questions effectively. 1 2 3 4 5
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Jun 11, 2014