Surface Hydride Composition of Plasma-Synthesized Si Nanoparticles

We have determined the surface hydride composition of amorphous and crystalline Si nanoparticles (NPs) (3-5 nm) synthesized in a low-temperature SiH(4)/Ar plasma using in situ attenuated total reflection Fourier-transform infrared spectroscopy and H(2) thermal effusion measurements. With increasing power to the plasma source, the particles transition from amorphous to crystalline with a corresponding increase in the fraction of SiH species on the surface. The surface hydride composition indicates that Si NPs synthesized at higher plasma powers crystallin in the gas-phase due to a greater degree of plasma-induced heating, which enhances the desorption rates for SiH(2) and SiH(3). Furthermore, these Si NPs do not contain any detectable H in the bulk

The relation between the bandgap and the anisotropic nature of hydrogenated amorphous silicon

The bandgap of hydrogenated amorphous silicon (a-Si:H) is studied using a unique set of a-Si:H films deposited by means of three different processing techniques. Using this large collection of a-Si:H films with a wide variety of nanostructures, it is demonstrated that the bandgap has a clear scaling with the density of both hydrogenated divacancies (DVs) and nanosized voids (NVs). The presence of DVs in a dense a-Si:H network results in an anisotropy in the silicon bond-length distribution of the disordered silicon matrix. This anisotropy induces zones of volumetric compressed disordered silicon (larger fraction of shorter than longer bonds in reference to the crystalline lattice) with typical sizes of ~0.8 up to ~2 nm. The extent of the volumetric compression in these anisotropic disordered silicon zones determines the bandgap of the a-Si:H network. As a consequence, the bandgap is determined by the density of DVs and NVs in the a-Si:H network