Conductance through atomic contacts created by scanning tunneling microscopy

We investigate conductance through contacts created by pressing a hard tip, as used in scanning tunneling microscopy, against substrates. Two different substrates are considered, one a normal metal (Cu) and another a semi-metal (graphite). Our study involves the molecular dynamics simulations for the atomic structure during the growth of the contact, and selfconsistent field electronic structure calculations of deformed bodies. We develop a theory predicting the conductance variations as the tip approaches the surface. We offer an explanation for a quasiperiodic variation of conductance of the contact on the graphite surface, a behavior which is dramatically different from contacts on normal metals.