The observation of a threshold in the de-alloying of sputter-deposited PtxAl1-x alloy thin films

Platinum-aluminum alloys of various compositions were synthesized by using DC co-sputter deposition and then immersed in 4 M NaOH under open-circuit conditions. The selective dissolution of aluminum was studied with Rutherford backscattering spectroscopy (RBS) and secondary neutral mass spectrometry (SNMS). A threshold at Pt0.4Al0.6 was observed. For platinum contents above 40 at, RBS analysis showed that little aluminum dissolution occurs. There was also evidence for the formation of a thin (less than 5 nm thick) platinum-rich surface film. At platinum contents lower than 40 at profuse aluminum dissolution occurred. RBS and SNMS analyses suggested that dissolution occurs throughout the film. 4 figs., 23 refs.