Grain boundary doping of Cu thin films with Bi: A route to create smooth and stable nanocrystalline surfaces

The thermodynamic and kinetic properties of grain boundaries fundamentally influence the smoothness and stability of nanostructured interfaces. Using nanocrystalline Cu thin films as a model system, we address these issues by alloying small amounts of Bi, ranging from 0.1 to 1.0 at.%, during co-deposition from vapor, followed by subsequent annealing treatments. Stabilization of Bi-rich nanocrystalline layers in surface and substrate regions is observed at Bi concentrations as low as 0.5%, accompanied by minimum surface roughness, while lower Bi concentrations allow for partial coarsening.