In-situ characterization of O-terminated Cu tips for high-resolution atomic force microscopy

Abstract

Functionalizing a metal tip with a single CO molecule (CO tip) leads to an unprecedented spatial resolution of small organic molecules by frequency-modulation atomic force microscopy (FM-AFM) at low temperatures. O-terminated Cu tips (CuOx tips) show comparable imaging capabilities as CO tips but exhibit a much stiffer apex. So far, to verify tip functionalization with oxygen (i.e., CuOx tips), scanning tunneling microscopy and AFM images, together with force spectroscopy curves of copper oxide domains, have been compared with calculated data for different tip models. Here, we apply the carbon-monoxide front atom identification (COFI) method and additional force spectroscopy to characterize CuOx tips in-situ on a Cu(110) surface. In COFI, a single CO molecule adsorbed on a Cu surface is imaged to atomically resolve the tip apex. Based on our findings, we suggest accompanying tip fingerprinting with COFI and force spectroscopy to identify the atomic and chemical compositions of the apex of CuOx tips for high-resolution AFM experiments.