Nanoelectronics: the future of Electronics
   As transistor’s size becomes much smaller than micron, Microelectronics becomes 
        Nanoelectronics (www.itrs.net/Common/2003ITRS/ExecSum2003.pdf )
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                    Challenges and Solutions
    •  Challenge: preparation of a new generation of workers 
       with solid skills in Nanoelectronics and Nanotechnology, 
       overall
    •  General approach to solution: acquiring the practical 
       skills in Nanoelectronics through hands-on experience
    •  Our specific solution: Interdisciplinary Nanoelectronics 
       Laboratory for the Engineering/Science Undergraduate 
       Curriculum 
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           Scanning tunneling microscopy
    This  novel  technique  yields  surface  topographies  in  real  space  and  work 
    function profiles on an atomic scale directly in real space. 
    We know that the removal of an electron from the conduction band of a solid, 
    requires a certain amount of energy called the affinity. For a metal or a doped 
    semiconductor,  when  the  conduction  band  is  partially  filled,  the  energy  to 
    remove an electron is lower and it is called the work function. Let us consider 
    two conducting solids separated by a space. In terms of classical physics, a 
    transfer process of an electron from one solid into another can be thought of 
    as an electron transfer over a vacuum barrier. The process requires additional 
    energy and because of this it has a small probability. According to quantum 
    mechanics,  a  particle  can  penetrate  in  classically  forbidden  spatial  region 
    under  a  potential  barrier.  This  phenomenon  was  called  tunnelling.  Thus, 
    electron  transfer  between  two  solids  can  occur  as  a  tunnelling  process 
    through (under) the vacuum barrier. 
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    Different tunneling experiments have been performed, for example, by using 
    two metal films separated by vacuum or a solid-state insulator (a sandwich 
    structure).  Each  of  the  metal  films  can  be  considered  as  an  electrode  and 
    when a voltage bias is applied to these electrodes a so-called tunneling electric 
    current is produced. This current can give information on electronic properties, 
    but obviously the information will be averaged over the area of the metal film 
    surface. By appropriate shaping of one of the electrodes spatial resolution of 
    far  smaller scales than that of sandwich structures can be achieved. Since 
    vacuum  is  conceptually  a  simple  tunnel  barrier,  such  experiments  pertain 
    directly  to  the  properties  of  the  electrodes  and  their  bare  surfaces.  Clearly, 
    vacuum  tunneling  offers  fascinating  and  challenging  possibilities  to  study 
    surface physics and many other related areas. 
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     The tunnel current, J , is a sensitive function of the gap between the tip and the surface, s, 
                          T
     i.e.,
                                                    1/2
                                     J      V  exp(-Aφ  s) 
                                     T     T
     where φ is the average barrier height; the numerical value of A is equal to unity if φ is 
     measured in eV and s in Å.                The control unit, applies a DC voltage, V, to the 
                                                                                         z
                                               piezodrive, P , such that J  remains constant when 
                                                            z           T
                                               piezodevices  P   and  P ,  move  the  tip  over  the 
                                                              x        y
                         P                     surface  of  the  sample.  At  constant  function  φ, 
                          z                    V(x,y) yields the topography of the surface, that is 
                 V                        P     z
                  z                         x  z(x,y), directly, as illustrated at a surface step in the 
                                               figure. B
                                       δ
            Py                      A
               V                                         C
                 Δs
     Control   T                                                     Fig.  1.  The  principles  of 
      Unit           s       IT                                      operation of the Scanning 
                                                                     Tunnelling Microscope.
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