Cu/In deposited at room temperature: morphology, phases and reactions

Bilayers of a slightly copper-rich composition of copper and indium deposited (in that order) at room temperature by vacuum evaporation, electroplating, and r.f. sputtering, were analyzed by MeV ⁴He backscattering spectrometry, scanning electron microscopy and X-ray diffraction before and after thermal annealing at 400 °C in vacuum. The surface morphology of as-deposited samples is roughest for evaporated samples and smoothest for samples deposited by sputtering with low r.f. power. All as-deposited samples contain copper and indium phases and the metastable CuIn compound. After 1 h at 400 °C, this metastable phase and that of copper disappear and are replaced by some copper-rich compound (Cu₉In₄, Cu₇In₄) in all cases. Simultaneously, the surface morphology smooths out considerably for the initially rough samples. Bilayers of various Cu/In compositions were also prepared. The results are consistent with the absence of stable compounds outside the 26–38 at.% indium range, as indicated by published phase diagrams.