Experimental studies of O2-SnO2 surface interaction using powder, thick films and monocrystalline thin films

Surface properties of solids and the interactions between molecules and solid surfaces are important for many technical applications. They also involve a range of physical and chemical phenomena of fundamental scientific interest. The importance of oxygen chemistry at SnO₂ surfaces follows from the fact that SnO₂ is used as an active material in gas sensor applications. The operation principle of these sensors is usually based on measurable conductance response of the material, which is understood in terms of reactions of gas molecules with different oxygen species adsorbed onto the surface. The role of the lattice oxygen, but in particular, the bridging oxygen atoms on SnO₂ surfaces, is also active. Detailed understanding of the reaction mechanisms of various oxygen species at SnO₂ surfaces is important, as it offers a way to improve the sensitivity and selectivity of the sensors.Oxygen adsorption-desorption kinetics at the SnO₂ surface is studied experimentally using O₂-temperature-programmed desorption (TPD) method together with conductance measurements in the case of SnO₂ powder and polycrystalline thick films made from the powder. In addition, CO-TPD is studied and the transient behaviour of various oxygen species is considered. Molecular beam epitaxy (MBE) was also used to fabricate polycrystalline and monocrystalline thin films with the SnO₂(101) face on single crystal sapphire substrate. Simultaneous surface potential and conductance measurements during heating and cooling in different ambient atmospheres were used to characterize the monocrystalline SnO₂(101) surface after various surface treatments.