Atom Resolved Surface Chemistry Using Scanning Tunneling Microscopy

Scanning Tunneling Microscopy provides a completely new way of studying surface chemistry. Unlike other techniques which provide an average response from a macroscopic sample, the geometric and electronic structure obtained from topographs and atom-resolved tunneling spectra allow unreacted or reacted surface sites to be probed on an individual basis. When this unique ability is applied to the study of a surface chemical reaction, the spatial distribution of the reaction may be determined with unprecedented clarity. The activity of different types of surface sites may be compared, and moreover, interactions between sites may be examined directly. These capabilities will be illustrated through a discussion of the reaction of Si(111)-(7x7) with NH sub 3. We can readily distinguish between reacted and unreacted sites. Surface atoms may be divided into three types and these may be ranked with respect to reactivity. We are able to observe changes in electronic structure at unreacted sites which result from chemisorption at neighboring sites.