Field-induced tip-sample oxygen transfer in scanning tunneling microscopy on TiO2(1 1 0) (1 × 1)

A study on the field-induced tip-surface oxygen transfer at room temperature and its influence on the tunneling conditions for stable STM imaging of the TiO2(1 1 0) (1 × 1) surface is reported. A simple model of field-induced transfer is applied to tungsten and platinum-iridium tips. The oxygen transition rates from the sample to the tip or from the tip to the sample depend on the oxygen desorption barriers formed at tunneling distance. For stable imaging the applied bias voltage has to balance the oxygen transfer probabilities in both directions. In the case of Pt/Ir tips, the tunneling conditions for images with clear evidence of bridging oxygen point defects have been established.