Physica E 37 (2007) 287–291 SnO 2 nanograins Au-doped: A quantum mechanical evaluation of CO adsorption A.M. Mazzone à , V. Morandi C.N.R-IMM, Sezione di Bologna, Via Gobetti 101, Bologna-40129, Italy Available online 29 September 2006 Abstract In this study an analysis is made of the adsorption properties of nanocrystalline SnO 2 containing a metallic dopant. The analysis is based on semi-empirical Hartree–Fock and scattering theories and the structures considered are SnO 2 grains, with a rutile lattice, whose size and shape are comparable with the nanograins and nanowires produced in experiments. The grains contain rows of gold atoms located externally, on the grain surface, or in an endohedral position, in the grain interior, and the adsorbed system is generated by depositing CO molecules on the grain surface. The calculations illustrate the dependence of the binding energies and of the conductance on the grain size and on the location of the metallic additives in both the clean and in the CO-adsorbed grains. These results show that adsorption and current transport are determined by the intrinsic electronic structure of the adsorbing grains. r 2006 Elsevier B.V. All rights reserved. PACS: 31.15.Ct; 03.36.Nk; 77.84.Bw Keywords: Tin oxide nanograins; Au-doping; CO adsorption; Conductance; Semi-empirical calculations 1. Introduction Among the oxides in the rutile family, SnO 2 is of considerable technological interest owing to its application 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, it is the subject of many fundamental researches whose purpose is the understand- ing of the performance improvements and of the physical mechanisms underlying adsorption [1]. This last strategy is adopted also in the present study whose purpose is the assessment, with quantum mechanical detail, of the adsorbing properties of SnO 2 . The study is based on semi-empirical Hartree–Fock and scattering theories and the calculations are applied to a system formed by CO molecules deposited onto a SnO 2 grain. Furthermore, to model a composite system containing metal particles, the grain contains gold atoms either in an external position, on the grain 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. 2. The computational methods The grain structures and the simulation method are the ones already used in Ref. [2] and therefore only a brief account is presented here. Experimental observations show that nanocrystalline SnO 2 , grown by a variety of different techniques, contains grains with a linear dimension in the range 10–100 A ˚ 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 therefore 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 (1 0 0) ARTICLE IN PRESS www.elsevier.com/locate/physe 1386-9477/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2006.08.006 à Corresponding author. E-mail address: mazzone@bo.imm.cnr.it (A.M. Mazzone).