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 differen t substrates are considered, one a normal metal (Cu) and another a semi-met al (graphite). Our study involves the molecular dynamics simulations for th e atomic structure during the growth of the contact, and selfconsistent fie ld electronic structure calculations of deformed bodies. We develop a theor y 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 differen t from contacts on normal metals, (C) 1999 Elsevier Science B.V. All rights reserved.