Atom-resolved surface chemistry using the scanning tunneling microscope

Scanning tunneling microscopy (STM) has been proven to be a powerful technique for the study of the electronic topography of surfaces and adsorbed layers. In this article, we demonstrate that STM topographs and atom-resolved tunneling spectra can be used to study the chemical reactivity of surfaces with atomic resolution and relate it to the local electronic structure. In this way, a unique insight into the factors that influence reactivity can be obtained. First, we give an introduction to the technique and the basic concepts on which it is based. We then discuss in some detail three specific examples: (A) the direct imaging of chemical bonds on the Si(100)-(2×1) surface; (B) the site-selective reaction of NH3 with Si(111)-(7×7); and (C) the interaction of boron with Si(111) and its effect on surface electronic structure, surface reconstruction, and doping effects on chemical reactivity. We close by considering issues relating to the role of the electronic structure of the STM tip and possible future directions in chemical applications of the STM. © 1990 American Chemical Society.