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CPM Seminar
Regina Hoffmann
Physics Department Why do atoms bond together? Most solid state physics courses start with a discussion of this question. The scanning force microscope (SFM) was originally indended as a tool capable of measuring the forces acting between a single pair of atoms. However it has only recently evolved into an instrument capable of producing atomically resolved images of surfaces with characteristic features and defects. This true atomic-scale contrast is generally interpreted as resulting from the short-range chemical interaction between an atomically sharp AFM tip and the nearest atoms on the surface of the sample. Recently, site-specific force-distance experiments in which it was possible to map the chemical bonding potential between the foremost atom on a SFM tip and a specific atom on the sample have been performed for the first time at low temperatures on the Si(111) 7x7 surface [1]. Other materials that have been studied include alkali halide (001), alkaline earth halide (111) surfaces and the antiferromagnet NiO. The short-range forces on KBr have been calculated using atomistic simulations. Comparison of the calculated and measured results allowed identification of the tip polarity and hence the positive and negative sublattices of the surface in the image.
[1] M. A. Lantz et al., Science
Thursday, November 28th 2002, 15:30 |