Silver islands formed after air annealing of amorphous Ag–Cu–Mn–O sputtered films

Ag–Cu–Mn–O films were deposited on glass substrates by co-sputtering of manganese and Ag60Cu40 targets in an Ar–O2 reactive mixture. The currents applied to the targets were fixed to obtain a (Ag+Cu)/Mn atomic ratio close to 3. As-deposited films were X-ray amorphous. Air annealing at 350 °C did not modify the film aspect. On the other hand, higher annealing temperatures (450 and 550 °C) led to the formation of crystals that were eye-visible. X-ray diffraction analysis of such films revealed the formation of crystalline silver phase. This result was confirmed by X-ray energy dispersive spectroscopy (EDS) analyses and UV–visible reflectance measurements. Observations by scanning electron microscopy showed that annealed films are composed of silver islands of approx. 100 μm in diameter dispersed on oxide surface. Furthermore, silver islands exhibited a highly facetted morphology. The effect of the film thickness on the shape of silver islands was studied. Chemical etching in hydrochloric acid was performed to dissolve the silver islands and to analyse by EDS and observe by scanning electron microscopy the surface of the remaining oxide. Finally, the effect of copper on the stability of Ag–Cu–Mn–O films was discussed.