Molecular hydrogen ina-Si: H

The past few years have seen a number of studies involving the presence of molecular hydrogen trapped in a-Si: H. The main techniques used have been nuclear magnetic resonance, calorimetry, and infrared absorption. The results suggest that H₂ is trapped in a number of samples in microbubbles ({≈} 10 {}) under high pressure ({≈} 2 kbar) at room temperature, solidifies around 25 K, and undergoes an orientational phase transition around 15 K. The data are reviewed here, and the effects that such H₂ microbubbles may have on the properties of a-Si: H are discussed.