High Field Effects and Methods Useful for Transferring Atoms in Scanning Tunneling Microscope

Some of our recent work on atom transfer processes between the tip and the sample in scanning tunneling microscope is summarized. A modified field evaporation model is used to explain the atom transfer process in ultra-high-vacuum. We show that this model is valid with the normal imaging tip-sample separation or longer distances, whereas the first principle theories of Lang, Hirose and Tsukada are valid under a near-contact tip-sample separation. Our model indicates that Au and Si favor negative field evaporation whereas Pt favors positive field evaporation. Available UHV data are consistent with these conclusions. We also show that in air and in an insulating liquid, atom transfer due to mechanical contact is an important mechanism, but other mechanisms may also occur. The actual mechanism depends very much on how an atom transfer experiment is carried out.