Simulation of STM Images of Hematite α-Fe2O3(0001) Surfaces: Dependence on Distance and Bias

Abstract

Experimental scanning tunneling microscopy (STM) images of the hematite (0001) surface exhibit long-range superstructures formed by coexisting domains consisting of different terminations (α, β, γ) of the α-Fe2O3(0001) surface. In this work extensive simulations of STM images of different terminations of hematite (0001) surfaces are performed and compared with measured ones in order to identify the nature of the superstructure unit meshes. Based on DFT calculations of α-Fe2O3(0001) surfaces, the STM images are simulated using Chen’s derivative rules approach. Different bias voltages and tip-sample distances as well as the role of the tip type are considered and discussed. For some terminations an extreme dependence of the simulated image on the distance and bias voltage is found. The difference between simulations of metal and insulator/semiconductor surfaces is discussed. The condition of simultaneous agreement between simulation and experiment for all terminations within a narrow STM parameter range leads to the assignment of the α, β and γ terminations to the ferryl, Fe-Fe-O3- or Fe-O3-Fe-, and O3-Fe-Fe- terminations, respectively.