STM
     Scanning tunneling microscope
               History
   • The STM was invented 1981 by Gerd Binnig and 
    Heinrich Rohrer.
   • They received the Nobel prize in physics in 1986 
    for the STM
   • The STM was first used in showing its atomic scale 
    resolution in a image of silicon 7x7 restructed 
    (111) surface.
    
              Theory
  • STM works on the principles of tunneling
  • Electrons can not transfer between the tip of the 
    STM and the sample because there is an energy 
    barrier.
  • When a voltage is imposed between the two, the 
    shape of the energy barrier changes and electrons 
    can move from the sample to the tip wich results 
    in a small current if the distance is sufficiently 
    small
        •
                  The probability distribution is given by:
                     The current is proportional to:
  •
  W here z is the distance and к is given by:
  Where U is the potential energy, h is the 
  planck‘s constant and E is the energy of 
  the electron .