Atomic-Resolution Imaging of Close-Packed Metal Surfaces by Scanning Tunneling Microscopy

The resolution of individual atoms in scanning-tunneling-microscopy (STM) images of Al(111) is demonstrated. From results of gap-width and energy-dependent measurements the corrugation observed in the STM images cannot reflect the electronic structure of the Al surface near $E_F$, as usually assumed for such images, but must be due to tip-surface interactions. On the basis of an investigation of the process of tip preparation, an elastic deformation of the frontmost end of the tip mediated by adhesive tip-surface interactions is proposed as the predominant factor for atomic-resolution STM imaging of such metal surfaces.