Synthesis and characterization of nanoporous copper thin films by magnetron sputtering and subsequent dealloying

Abstract

Nanoporous copper (NPC) films with ligament sizes ranging from 18 to 46 nm were synthesized by dealloying CuxAl100-x (x = 22–37 atomic percent) precursor films with thickness from 0.5 to 1.2 μm in 0.01–1 M NaOH. The precursor alloy films were deposited on silicon (100) via magnetron co-sputtering. Effects of precursor alloy and dealloying conditions on the morphology of NPC films were investigated by the use of scanning electron microscopy and energy-dispersive X-ray spectroscopy, while the cross-sectional areas were characterized using focused ion beam. The yield strengths of NPC films were measured by the nanoindenter. The morphology of NPC films transformed from well-distributed to aggregated clusters with the increase of Cu concentration from 22 to 37 atomic percent. Limited residual Al and oxidation can be detected in NPC films, regardless of dealloying conditions. The ligament size of NPC films shows no significant difference with the change of NaOH concentrations, while cracks observed in NPC films seem to be mitigated with extended dealloying time. The yield strengths of NPC thin films are higher than those predicted by bulk Cu or pure Cu films.