Theoretical simulation of non-contact atomic force microscopy imaging of the α-alumina(0001) surface

We have studied the interactions responsible for the contrast formation in nc-AFM imaging of the alpha-alumina(0001) surface using the oxide and Si dangling bond tip models. The full image simulation performed using the rigid oxide tip and common cantilever parameters suggests the possibility of atomic and chemical resolution on the plane surface in a narrow range of experimental parameters. The interaction of both the oxide and Si dangling bond tips with the surface is stronger at the centres of triangles formed by three oxygen ions. This makes the image interpretation for the Si dangling bond tip unique-the bright spots should correspond to the centres of O triangles and centres of dark spots are located above the surface Al ions. In the case of the oxide tip, the image pattern depends on the tip polarity and is different, but easily recognizable. However, only Al ions or triangles formed by three oxygen ions could be resolved in the simulated images.