A Computational Study on SnO 2 Au-Doped Grains: CO Adsorption
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0915-R06-02
A Computational Study on SnO2 Au-Doped Grains: CO Adsorption Anna Mazzone IMM,Sezione di Bologna, CNR, Via Gobetti 101, Bologna, Italy, 40129, Italy ABSTRACT In this study the adsorption properties of nanocrystalline SnO2 containing a metallic dopant are analysed. The analysis is based on semi-empirical Hartree-Fock and scattering theories and the structures considered are SnO2 grains with a rutile lattice and a size comparable with the experimental ones. The grains contain rows of gold atoms located on the grain surface or in an endohedral position, in the grain interior, and the adsorbed system is generated by depositing a CO molecule on the grain surface. The calculations illustrate the dependence of the binding energies and of the conductance on the grain size, on the location of the metallic additives in both the clean and in the CO-adsorbed grains. New mechanisms of adsorption and of current transport are proposed. INTRODUCTION Among the oxides in the rutile family, SnO2 is of considerable technological interest owing to its applications in heat-reflecting filters, as transparent electrode in Si solar cells, and as a sensor of inflammable or poisonous gases. For these applications the nanocrystalline material is of increasing interest as it offers a better selectivity and sensitivity and these performances are improved by the use of metallic additives. In addition, this material is the subject of many fundamental researches whose purpose is the understanding of the physical mechanisms and of the performance improvements [1]. This last strategy is also the one adopted in the present study whose purpose is the assessment of the adsorbing properties of SnO2 with quantum mechanical detail. The study is based on semi-empirical Hartree-Fock and scattering theories and the calculations are applied to a system formed by a CO molecule deposited onto a SnO2 grain. Furthermore, to model a composite system containing metal particles, the grain contains gold atoms on its surface or in an endohedral position, in the grain interior. The calculations illustrate the effects of the metallic additives and of the adsorbed molecule on the grain binding strength and on its conductance. THE COMPUTATIONAL METHODS The grain structures and the simulation method are the ones already used in [2] and therefore only a brief account is presented here. Experimental observations show that nanocrystalline SnO2, grown by a variety of different techniques, contains grains with a linear dimension in the range 10-40 Å formed by clear lattice strings and the plain projection of these grains has an approximately spherical form. However current technologies focus on tin, elongated structures with a ribbon-like geometry [3, 4], and the following calculations are based on a nanowire model. Accordingly, the grains have a columnar structure and are obtained by cutting a cubic box of the crystalline material with a rutile lattice parallel to the (100) crystallographic axes. The grains section is squared and their height can be elongated along
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