Tuning the electronic properties of a clean TiO2(1 1 0) surface via repeated sputtering and annealing: A KPFM and LC-AFM study

Abstract

Repeated sputtering and annealing are standard preparation methods for obtaining a stoichiometric TiO2(110) surface for surface science experiments. However, both processes result in a reduction in TiO2 crystal when used separately, leading to the modification of the physical and chemical properties of oxide materials. Our investigation aims to determine how these two processes affect the electronic properties of the surface and subsurface regions at the nanometer scale. To accomplish this goal, we utilized local microscopy (Kelvin probe force microscopy and local-conductivity atomic force microscopy) and spectroscopy methods (X-ray photoelectron spectroscopy and secondary ion mass spectrometry). We found that repeated sputtering and annealing does, in fact, affect both the conductivity and work function of the surface. The work function, as well as conductivity, increase with increasing number of cycles, but then reach a plateau. Furthermore, we show that the way the surface is prepared, using multiple cycles or one cycle of equivalent ion-beam fluence, matters. We attribute the differences in the crystal properties to the dynamics of stoichiometric changes during sputtering and subsequent annealing which we illustrate using secondary ion mass spectroscopy, which shows that after multiple cycles the subsurface layer is modified, even though XPS shows a stoichiometric surface.