ADSORBATES IN AMBIENT OPERATED SCANNING-TUNNELING-MICROSCOPY - THEIR APPEARANCE, MOBILITY DURING SCANNING, AND ROLE IN SURFACE-DIFFUSION MEASUREMENTS

Adsorbed species are commonly observed when operating a scanning tunne ling microscope in an air environment. Often the quality of images is poor, characteristically appearing streaked, as the tip instantaneousl y interacts with the adsorbates during scanning. On other occasions, t he adsorbates are imaged readily and by changing the tunneling paramet ers, may be forced to relocate, or in the extreme, may be evaporated b y the action of the tunnel current. Furthermore, the subtleties of sca nning tunneling microscope imaging allow the possibility of adsorbed s pecies appearing not only as mounds, but as holes as well, depending o n the value of the adsorbate work function relative to that of the und erlying substrate. It is found that when a combination of both ''mound -like'' and ''hole-like'' adsorbate is present, there is a bias-depend ent preference for the tip to interact with a particular type. A thres hold field is also apparent for the passive removal of adsorbates. It is also found that the presence of adsorbates hinders the surface diff usion process.