Electronic Structures Of SnO₂(110)doped Surface And Adsorptions Of Small Molecules: A First-principles Study

Tin dioxide (SnO₂) is an important semiconductor with a wide-band gap (3.6 eV) and has wide applications in many fields, especially; SnO₂ is a potential candidate for designing solid gas sensors. Since the surface properties of SnO₂ are inherently related to its applications, increasing effects have been carried out to investigate the surface electronic structures of SnO₂ both experimentally and theoretically in recent years.In this thesis, three systems, namely, perfect and defect SnO₂(110) surfaces, Ti and Ru-doped surfaces and the adsorptions of small molecules on above perfect surfaces have been studied in details by using the first-principles method with the combination of pseudopotential plane-wave and atomic basis sets. The structural stability, surface states and the surface chemistry of undoped and metal doped SnO₂(110) surfaces have been discussed, which can provide the theoretical rules to improve the surface properties of this special functional material. For the perfect SnO₂(110) surface, similar to rutile TiO₂(110), it exhibits the same characteristic of surface relaxation. Our results indicate that, when the thickness of slab is smaller than 3 nm, the oscillations of surface energy and the displacements of surface atoms as a function of the number of layers are observed. Compared with bulk, several energy bands associated with 2py and 2pz states of bridging oxygen appear in the bulk gap. By examining the vacancy formation energy of three kinds of defect SnO₂(110) surface, the most energetically favorable defect surface is that the surface possesses the coexistence of bridging and in-plane oxygen vacancies, which is different with the traditional defect model by only removing bridging oxygen. According to the results of band structures, the electronic structure characteristic of this defect surface is similar to that of SnO surface. When the Sn atom at the top layer or sublayer is replaced by Ti or Ru, due to the lengths of Ti-O and Ru-O bond is smaller than that of Sn-O bond, the obvious changes of the surface relaxations are observed with respect to the undoped one, especially whenTi or Ru substitutes for the six-fold Sn atom at the top layer. Further investigations show that new surface states are derived by the doping, which may lead to the changes of the surface properties of SnO₂(110). It seems that the type of doping atom has great effects on the positions of doping states. For Ti doped surface, in most cases, the doping states...