Nanocomposites and nanomaterials

Features of the surface of SnO2 nanostructures
А.V. Tymchenko, М.V. Tereshkov, S.V. Nahirniak, T.A. Dontsova
National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Prospect Peremogy, 37, Kyiv-03056, Ukraine.
E-mail: dontsova@ua.fm

The surface of metal oxides plays a major role in the phenomena of adsorption, heterogeneous (photo) catalysis, in the detection of gas molecules in the gas environment, etc., since in these cases all molecular and chemical processes occur on the surface of metal oxide crystals. Adsorption properties and reactivity are due to the presence of free electrons on the surface in the conduction band, of surface and volume oxygen vacancies. Consequently, the surface is a transition region from the crystal's volume to the environment that is in contact with the atmosphere, which leads to the formation of oxide layers, including active adsorbed oxygen, to the depositing on the surface or penetrating into it the water vapor, carbon atoms and other molecules. Accordingly, the adsorbed molecules with the SnO2 lattice form a single quantum-mechanical system and must be considered as a whole and the surface – as a special state of matter with its chemistry.
In SnO2 single crystals, low-index faces (110) and (101) are the most developed. The face (110) is most studied by the researchers both theoretically and experimentally [1]. The surface structure and presence of the certain faces depends crucially on the methods of SnO2 synthesis, which in turn affects the concentration of oxygen on the lattice surface. The obtaining of SnO2 crystals in the absence of oxygen leads to the formation of the face (110) depleted on oxygen. The face (101) in a single crystal has been studied very recently [1]. The dual valence of Stanum contributes to the formation of its charges Sn2+ or Sn4+ on face (101). The transition from one charge to another is particularly easy to accomplish on this face due to the peculiarity of atomic stacking in this crystallographic direction. For the face (110) such a light conversion is not observed, therefore on this face Stanum exists only in the form of Sn(IV). Thus, the question arises about the simulation of the interaction of atmospheric environment with these two faces to explain the experimental results [2]. The latter can be realized in GAMESS (US) – a program that is intended for quantum chemical calculations, and which is capable for calculating with the help of quantum chemistry methods.
1.	Batzill M. Surface Science Studies of Gas Sensing Materials: SnO2. Rewier, Sensors 2006, 6, 1345-1366.
2.	Dontsova T.A., Nagirnyak S.V. et al. SnO2 Nanostructures: Effect of Processing Parameters on Their Structural and Functional Properties, Nanoscale Research Letters 2017, 12 : 332.