Surface bond-terminating

The surface condition of a silicon crystal depends on the way the surface was prepared. Only a silicon crystal that is cleaved in ultra high vacuum (UHV) exhibits a surface free of other elements. However, on an atomistic scale this surface does not look like the surface of a diamond lattice as we might expect from macroscopic models. If such simple surfaces existed, each surface silicon atom would carry one or two free bonds. This high density of free bonds corresponds to a high surface energy and the surface relaxes to a thermodynamically more favorable state. Therefore, the surface of a real silicon crystal is either free of other elements but reconstructed, or a perfect crystal plane but passivated with other elements. The first case can be studied for silicon crystals cleaved in UHV [Sc4], while unreconstructed silicon (100) [Pi2, Ar5, Th9] or (111) [Hi9, Ha2, Bi5] surfaces have so far only been reported for a termination of surface bonds by hydrogen. 

The photoelectrochemistry at atomically well-defined semiconductor surfaces is one of the current topics related to the nanostructuring of the semiconductor surfaces. Most studies have been made on silicon (Si) surfaces, and it is now well established that hydrogen fluoride (HF)-etched Si surfaces are terminated mainly with Si-hydrogen bonds (SiH , n = 1, 2, or 3)14-171 and that, for Si (111), successive etching with 40% ammonium fluoride (NH4F) produces atomically flat Si(l 11) surfaces, terminated mainly with monohydride (= Si-H).18-221 Alkali etching under negatively applied biases also produces similar atomically flat Si (111) surfaces.231... 

In HF Si-F polarizes ibe underneath Si-Si bond which is then broken by HF or HjO the resulting surface is terminated by Si-H, et al j... 

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