Scanning tunneling microscopy using CO-terminated probes with tilted and straight geometries

Scanning tunneling microscopy using a CO-functionalized tip is combined with simulations to explore the impact of the CO tilt angle on topographies of a single Cu atom and CO molecule adsorbed on Cu(111). Images of the Cu atom acquired with varying tip tilt angles and sample voltages are reproduced by the calculations. The agreement between measured and simulated data allows us to unveil the tip-orbital composition of the tunneling current, which highlights the role of the different $p$ orbitals of the CO tip. Microscope data of adsorbed CO and their dependence on voltage and probe-surface distance are captured for the nontilted junction geometry and in the limit of weak tip-surface interaction assuming sufficiently large tip-sample separations.