Imaging molecules on bulk insulators using metallic tips

Abstract

We describe how one can produce, control, and characterize sharp metal coated tips and how these tips can achieve atomic resolution on insulating surfaces at large tip-surface separations. Our experimental results combined with DFT calculations confirm that the Cr tips possess permanent electric dipoles with the positive ends oriented towards the sample surface. By imaging the surface ions with atomic resolution, we determine the effective tip dipole moment using the image corrugation. Chemical resolution of surface ions and images of small adsorbed molecules can then be determined by using a point dipole model for representing the tip.Moreover, we demonstrate that these tips may be able to probe the dipole moment of polar molecules at the surface. Thus using metallic tips greatly reduces the complexity of interpreting experimental data while allowing for an unambiguous identification of ionic species on polar surfaces.