Scanning Microscopy


The vacuum tunneling microscope has been extensively utilized in the study of the surface atomic configuration of conducting materials. Analysis of features in both the tunneling images and in the tunnel junction I-V characteristic yields insight into a wide variety of processes occurring at surfaces. In the last few years, elementary chemical reactions occurring at surfaces have been examined in this manner, principally adsorption of simple gas species such as H2, O2, and NH3 on semiconductors and metals. Adsorption sites have been deduced from changes brought about in surface configuration subsequent to gas exposure. The relationship of these sites with one another and their evolution as a function of exposure has been utilized to constrain mechanisms for the adsorption process.

More recently, work has been performed where the scanning tunneling microscope (STM) takes on an active role. Hydrogen terminated silicon surfaces have been prepared and imaged with the STM. The tunneling images and infrared absorption spectra showed that configurations of both the terraces and steps are radically changed due to hydrogen capping. Moreover, the low-energy high-current density electron source, which is formed by the STM tip, has been used to selectively desorb this species from the surface. This process results in configuration changes which are derived from both the desorption kinetics and the long-range configuration of the initial surface.

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