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VISUALIZING AND MANIPULATING ATOMS:

    HOW TO SEE/FEEL THE INVISIBLE
  1. VISUALIZATION
  2. MANIPULATION

 

HOW TO SEE/FEEL THE INVISIBLE

         Atoms are incredibly small - so small that they cannot physically be seen in the traditional sense. Even the most powerful optical microscope could never resolve an atom since it is not possible to "see" anything smaller than the wavelength of the light used to visualize it. The wavelength of light in the visible spectrum ranges from ~380 nm to 750 nm. A typical atom might be 1/10th of a nanometer (nm) or one Ã¥ngström (10−10 meters) in diameter, and is therefore several thousand times too small to be seen using light from the visible part of the electromagnetic spectrum.

 

VISUALIZATION IBM scientists discovered how to move and position individual atoms on a metal surface using a scanning tunneling microscope. The technique was demonstrated in April 1990 at IBM's Almaden Research Center in San Jose, California, where scientists created the world's first structure assembled one atom at a time, spelling out the letters

         There are ways to visualize individual atoms, however. One such method is called Scanning Tunnelling Microscopy (STM) is a powerful technique that allows the shape of an individual atom, which is really the shape of its electron cloud surrounding the inner nucleus, to be determined. Using an STM, an atoms' electron cloud can be mapped by a metallic tip that interacts with the electrons in the cloud around the atom. As the tip moves over a sample of atoms, a 'tunnelling' current passes from the atoms (electrons) to the metallic tip. The current varies based on how close/far the tip is from the atoms as it moves over them, constructing a map of the shape and size of the individual atoms, as well as the topography of the entire sample. A computer is used to construct a 3D relief map of the surface from the data. Atoms look like extremely tiny spheres, or cones when sitting on a surface of other atoms. Another imaging technique called Atomic Force Microscopy (AFM) works in a similar way by moving a metallic tip over a sample, but in this case vibrating at a certain frequency. As the tip nears an atom, mechanical forces cause its frequency to shift. Using a computer to record these frequency changes at different positions, a map of the shape, size and position of atoms in a sample can be made.

 

MANIPULATION

        Interestingly, the same tools that are used to "see" atoms can also be used to move them. To image the topography of a surface on an atomic scale with a STM, you apply a current to the microscopic needle tip (instead of measuring the current in order to image the atoms) Individual atoms may be picked up, dragged and positioned to construct artificial atomic-scale structures by bringing the tip of an STM close to a surface atom.

         A similar effect has been observed using the AFM in reverse by putting pressure on an atom with the tip, an individual atom can be broken free from its electrical bond to its neighboring atoms.

 

Microscopy Scale

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