Anomalous large internal friction observed for nm-thick Ag film below room temperature

The internal friction of a nm-thick Ag film deposited on a Si substrate was studied. In a sputter deposited (SD-) Ag film on wet-oxidized high-boron CZ-Si (WO-SiBCZ), pre-exposure of air(wet) brings about the 200-250 K twin peaks, and the warming up to 300 K in a vacuum causes disappearance of the twin peaks. The peak height of the 200-250 K twin peaks shows the maximum at the SD-Ag film thickness of about 80 nm. No or very low peaks are observed in all the SD-Ag films on hydrogen terminated (HT-) or thermally-oxidized Si substrates. The interface region between SD-Ag and WO-SiBCZ containing OH molecules is responsible for the 200-250 K twin peaks. The underlying mechanism of the peaks is not known at present.