Determination of rutile transition metal oxide (110) surface terminations by scanning tunneling microscopy contrast reversal

Abstract

The surfaces of rutile transition-metal oxides $({\mathrm{TMO}}_{2})$ are widely investigated for catalysis, photoelectrochemical solar cells, memristors, and supercapacitors, but their structures have remained controversial. Here we employ density functional theory to predict that a universal behavior of metallic ${\mathrm{TMO}}_{2}$ surfaces, i.e., the stoichiometric ${\mathrm{TMO}}_{2}$ surfaces, exhibit a contrast reversal in simulated scanning tunneling microscopy (STM) images at different scanning biases. The predictions are verified by experimental STM imaging of ${\mathrm{RuO}}_{2}(110)$ surfaces and this feature is shown to enable accurate determinations of the ${\mathrm{TMO}}_{2}(110)$ surface structures under various conditions. This work provides different insights into the electronic properties of ${\mathrm{TMO}}_{2}(110)$ surfaces and offers an effective method to directly map the surface structure and point defects using bias-dependent STM.