Orientational ordering and melting of molecular H2 in an a-Si matrix: NMR studies

Molecular hydrogen in hydrogenated amorphous silicon has been observed directly in the NMR spectrum, occurring as a powder-averaged Pake doublet in the orientationally ordered state. The molecular H2 content is found to be approximately 0.25 at.% and to increase on annealing to about 1 at.%. In both cases, the H2 orientationally orders and solidifies at temperatures considerably higher than in pure, normal H2, because of the additional forces exterted on the H2 by the a-Si container.