Beam Damage of Self-Assembled Monolayers

The interfacial properties of CaF₂ on Si(lll) under two different deposition conditions are studied using x-ray photoelectron spectroscopy (XPS). The CaF₂/Si sample grown at a fixed temperature of 600 °C exhibits B-type epitaxy. For the second sample, the Si substrate was ramped from 100 to 600 °C in 5 min and then held at 600 °C until the end of the deposition. Under these conditions, the film exhibits A-type epitaxy, with very different electrical properties. The XPS analysis shows that for both samples, Si is bonded with both Ca and F at the interface. Significant differences are observed, however, for the chemical environment of Ca in the interfacial region for the two samples. In the first sample, Ca-Si bonding is relatively more pronounced, while in the second sample Ca-O bonding is observed to be predominant. In addition, for the sample grown under ramped temperature conditions, the fluorine dissociation is observed to be less and more F-Si bonds form at the interface. The results of this study help to explain the widely different electrical properties of the two films.