Study of interactions at the atomic scale

A combined ultra-high vacuum scanning tunneling microscope, atomic force microscope, and field ion microscope UHV (STM/AFM/FIM) system was used to study mechanical and electronic interactions at the atomic scale. A surface science system, consisting of an Auger electron spectrometer, UHV evaporators, ion sputter gun and annealing capabilities, was designed and constructed. A new force sensor preparation method was developed suitable for high stability imaging. Using this improved system, we studied W tip- Au(111) sample interactions in the regimes from weak coupling to strong interaction and simultaneously measured current changes from pA to muA. Close correlation between conductance and interaction forces in a STM configuration was observed. In particular, the electrical and mechanical points of contact were determined based on the simultaneously observed mechanical and electrical response. These points of contact as defined by force and current measurements coincide within measurement error. Ab initio calculations of the current and force as a function of distance in the tunneling regime are in quantitative agreement with experimental results. Simultaneous force-distance and current-distance curves are proven to be essential in understanding processes occurring in scanning tunneling and force microscopies. Finally, the observed contact phenomena and energy dissipation are discussed in the context of nanoelectronics and noncontact atomic force microscopy