Structural Changes and Hydrogen Motion in A-SI:H Observed by Proton Nmr

Abstract

AbstractProton nuclear magnetic resonance (NMR) is applied to investigate hydrogen dynamics and microstructures in a-Si:H. In addition to the generic broad and narrow lines observed in all aSi:H, an additional narrow line (about 1 kHz wide) is observed as the temperature is raised above RT. This narrow line is shifted to the up-field by about 4 ppm with respect to the generic narrow line of a few kHz in width. Below 150°C, the change of the proton spectrum with temperature is reversible; the hydrogen associated with this additional narrow line is shown to originate from hydrogen originally associated with the broad line. The spin-lattice relaxation time T1 of this up-field shifted narrow line is about 0.4 s. This short T1, along with its small linewidth, suggests that this line is associated with molecular hydrogen, possibly trapped in sites of atomic dimensions.