Non-Local Conductance Modulation by Molecules: STM of Substituted   Styrene Heterostructures on H-Terminated Si(100)
  One-dimensional organic heterostructures consisting of contiguous lines of CF3- and OCH3-substituted styrene molecules on silicon are studied by scanning tunneling microscopy and ab initio simulation. Dipole fields of OCH3-styrene molecules are found to enhance conduction through molecules near OCH3-styrene/CF3-styrene heterojunctions. Those of CF3-styrene depress transport through the nearby silicon. Thus choice of substituents and their attachment site on host molecules provide a means of differentially tuning molecule and substrate transport at the molecular scale. 
Paul G. Piva, Robert A. Wolkow, George Kirczenow