Melting and electromigration in thin chromium films

Chromium films with a thickness of 10–40 nm deposited onto silicon substrates by magnetron sputtering are subjected to the action of electric current induced by the tip of an atomic force microscope (AFM) cantilever in air under regular environmental conditions. The melting process at the nanoscale, electric field-induced migration of material, and the chemical reaction of chromium oxidation that occur in melt craters formed around the region affected by the current are investigated using optical and scanning electron microscopies, AFM, and Raman spectroscopy. The flow of melted material induced by electric current is accompanied by the formation and motion of an array of spherical nanoparticles in the melt crater along its periphery. We propose that the formation of nanodrop array at relatively low current densities can be explained by the chromium oxidation reaction and the surface tension of melted material on the silicon substrate.