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Bohr Model of the Atom

Also known as the planetary model, electrons are organized into energy levels with the nucleus at the center.

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Scanning Tunneling Microscopy

Scanning Tunneling Microscopy

Credit: Taner Yildirim (The National Institute of Standards and Technology - NIST)
Source: http://en.wikipedia.org/wiki/File:Chiraltube.gif
License: CC BY-NC 3.0

A scanning tunneling microscope (STM) is used to view surfaces at the atomic level. Currently, scanning tunneling microscopy is being used to investigate the properties of carbon nanotubes, such as the one pictured above.

Amazing But True

  • One of the methods currently available to scientists to image individual atoms employs the use of a scanning tunneling microscope. An STM works by the principle of quantum tunneling. To understand quantum tunneling, you must first understand how electrons classically behave in metals. Classically, the loosest electrons in metals are held in the metal unless given enough energy to leave the metal atom. 
  • However, when looked at through the principles of quantum mechanics, the most loosely bound electrons in a metal can "tunnel" through the energy barrier. This requires less energy than would be necessary for the electrons to get over the energy barrier and actually leave the metal atom. 
  • By using a very small electrically charged probe, the electrical current on the surface of a metal can be monitored. From this data, the location of atoms on the surface of a metal can be plotted. This is the basis of how a scanning tunneling microscope can image individual atoms.  
  • Credit: O. Usher (UCL MAPS)
    Source: http://www.flickr.com/photos/uclmaps/11796325765/
    License: CC BY-NC 3.0

    Scanning Tunneling Microscopes attain images of metal surfaces at the atomic level [Figure2]



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Using the information provided above, answer the following questions.

  1. Why don't we see objects tunnel through walls in our everyday life?
  2. Why can't someone use a regular microscope to view atoms?

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Image Attributions

  1. [1]^ Credit: Taner Yildirim (The National Institute of Standards and Technology - NIST); Source: http://en.wikipedia.org/wiki/File:Chiraltube.gif; License: CC BY-NC 3.0
  2. [2]^ Credit: O. Usher (UCL MAPS); Source: http://www.flickr.com/photos/uclmaps/11796325765/; License: CC BY-NC 3.0

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