Polarity compensation on KTaO3(001) surfaces

Abstract

This master thesis is focused on the structure of the KTaO3 (001) surface. Along this direction the cleaved surface is polar and several polarity compensation mechanisms are found depending on the applied conditions. In vacuum the as-cleaved surface consists of a mixture of bulk terminated KO and TaO2 terminated regions. At room temperature defect formation is observed and annealing results in rearrangement of the terraces, while the (1×1) termination is retained. The rearranged surface shows a labyrinthine structure with lines of 4-5 atoms width. This reconstruction is stable for annealing temperatures of up to 723 K. Exposure to water results in a hydroxylated surface and the formation of an overlayer with a (2×1) periodicity. The hydroxylated surface is stable for annealing temperatures of ~373 K and starts to decompose at annealing temperatures of ~473 K. Cleaved KTaO3 single crystals, which are doped by Ba, Yb and Cu, were investigated by atomic force microscopy (AFM), scanning tunneling microscopy (STM), low energy ion spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) under ultrahigh vacuum conditions. Experimental details with regard to the sample preparation and the influence of the applied surface science techniques are given. Structural models are proposed based on these experimental results and the stability of these structures is discussed.