The approach developed for controlling electronic and chemical properties of semiconductor surfaces is based on the modification of chemical properties of anionic adsorbates (such as HS- ions) prior to their adsorption on a surface of semiconductor. This is achieved through the solvation of the ions with different amphiprotic solvents (water, alcohols). Quantum-chemical calculations show that reactivity of solvated HS- ion depends essentially on composition of the solvation shell. In particular, the hydrated ion is slightly electrophilic, whereas ion solvated by alcohol molecules is strongly nucleophilic. So, the mechanism of interaction of such solvated ions with the semiconductor surface will depend on the solvent. In this connection, the model of interaction of HS- ions solvated by different solvents with clean GaAs(100) surface is proposed based on quantum-chemical calculations. According to this model, the nucleophilic and electrophilic ions solvated by alcohol and water molecules, respectively, would interact with different sites at semiconductor surface forming thus chemical bonds with different properties and surfaces with different atomic and electronic structures.
Experimentally this model was verified using GaAs(100) surface as an example. The HS- ions were adsorbed on a surface from different solvents (water and various single-based alcohols) in an oxygen-free ambient. It was found that such an adsorption results in the formation of As-S bonds with solvent-dependent ionicity, as was manifested by different chemical shift of corresponding component in XPS spectra with respect to As-Ga bulk component. Besides, these surfaces possess different ionization energy, which depends on solvent where adsorption was proceeded. After adsorption of sulfide-ions from different solvents, the electronic properties of GaAs and InP surfaces become strongly dependent on solvent, as was demonstrated by Raman scattering spectroscopy and photoluminescence. The experimental results obtained agree well with the predictions of the model.
Thus, modification of adsorbates chemical properties before adsorption can provide formation of numerous structures with wide variety of unique chemical and electronic properties.
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