Evolution of the surface relief of annealed copper and palladium samples under load

Abstract

The evolution of submicrodefects on loaded Cu and Pd surfaces annealed after polishing is investigated by tunneling profilometry. The shallowest defects formed in a sample under tension appear in the form of prismatic indentations with a vertex angle ≈70°. On Cu surfaces they have a depth of 15±3 nm and dimensions in the plane of the surface 50×50 nm. On Pd surfaces the defects have a depth of ≈5 nm and dimensions in the plane of the surface 10×20 nm. The defects grow with time, attaining depths ≈1 µm and areal dimensions of a few micrometers before fracture. This process evolves in a stop-go pattern: The defect depth remains approximately constant for a certain time, then changes suddenly, stabilizes again, changes once more, and so on. Defects of depth <100 nm are distributed uniformly over the surface of the sample, while defects of depth ⩾200 nm are clustered at the boundaries of blocks.