Single-crystal electrolytes silicon

Silicon has been and will most probably continue to be the dominant material in semiconductor technology. Although the defect-free silicon single crystal is one of the best understood systems in materials science, its electrochemistry to many people is still a matter of alchemy. This view is partly a result of the interdisciplinary aspects of the topic Physics meets chemistry at the silicon-electrolyte interface. 

Porous silicon was discovered over 35 years ago by Uhlir.28 The porous material is created by electrochemical dissolution in HF-based electrolytes. Hydrofluoric acid, on its own, etches single-crystal Si extremely slowly, at a rate of only nanometers per hour. However, passing an electric current between the acid electrolyte and the Si sample speeds up the process considerably, leaving an array of deep narrow pores that generally run perpendicular to the Si surface. Pores measuring only nanometers across, but micrometers deep, have been achieved under specific etching conditions. 

The conditions of low-temperature nano-sized Si02 film synthesis in electrochemical treatment of silicon have been investigated. The influence of physicochemical properties of the electrolyte and single-crystal silicon and of the conditions of rapid thermal annealing has been examined. 

It was shown that "odd" forbidden small-angle reflections in the X-ray pattern appeared even from a fresh fracture of a single crystal at room temperature [1-3]. Therefore, the surface layer of the electrolyte cannot be attributed to contamination of the SOE surface with impurities, primarily silicon (see, for example, [32]). Impurities and, also, segregation of SOE components, e.g., yttrium, on the electrolyte surface undoubtedly influence properties of the SOE surface layer. 

An electrolyte of this type has been used to synthesize alkyl derivatives of tin, zinc, antimony, indium, magnesium [74-77], silicon, and germanium [78] (Table 8). It is interesting to note that an attempt to synthesize organogermanium compounds on a germanium single crystal as anode was unsuccessful [86]. 

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