Molecular hydrogen in a-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 H(2) is trapped in a number of samples in microbubbles (~10angstroms) under high pressure (~2kbar) at room temperature, solidifies around 25K and undergoes an orientational phase transition around 15K. The data are reviewed here and the effects that such H(2) microbubbles may have on the properties of a-Si:H are discussed.