MEASUREMENT OF SITE SPECIFIC BINDING ENERGY OF SURFACE ATOMS

Abstract
The binding energies of kink site surface atoms have been determined from a measurement of ion energy distribution in low temperature field evaporation. With improvements in both the electronic and vacuum systems, and elaborate calibrations, the high-resolution pulsed-laser time-of-flight atom-probe has achieved an energy resolution of one part over 50000, just adequate for this study. The binding energy of pure metals such as Rh or W can be measured at well defined crystal planes and sitesat low temperatures. We find that the cohesive energy of metals measured with thermodynamic method is equal to the binding energy of kink site atoms. For instance, the binding energy of kink site atoms at Rh(100) surface, or at W(110) surface, is the same as the cohesive energy of Rh, or W listed in standard tables. For compound materials, such as PtRh alloy or GaAs, surface atoms of different kinds have different binding energies which are different from those of the pure elements. We measure the binding energy of Pt and Rh from the surface of PtRh, and of Ga from the surface of GaAs.