Grains, growth, and grooving.

We report the in situ investigation of grain growth and grain boundary migration, performed with a variable-temperature scanning tunneling microscope (STM) on a polycrystalline gold film. Atomic step resolution allowed us to identify the individual grains and, thus, also the grain boundaries. Our special, thermal-drift-compensated STM design made it possible to follow the same sample area over large temperature intervals. In this way, we have directly observed grain boundary migration and grain growth. In a first quantitative analysis we correlate the observed, unexpected changes in surface roughness with the evolution of the grain and grain boundary configuration.