New features of the nanoscale structure of amorphous (a)-Si produced by ion-implantation-induced amorphization of crystalline (c)-Si have been determined by the technique of small-angle x-ray scattering (SAXS). Si ion energies up to 17 MeV were used to generate a thick amorphous layer (8 μm) on a c-Si wafer to enable the SAXS measurements. As-implanted and thermally annealed (up to 540 °C) a-Si were studied. No nanovoids were detected within a sensitivity of 0.1 vol %, but the atomic-scale structure produced a measurable diffuse scattering signal that decreased with increasing anneal temperatures. These measurements show that the known density deficit of 1.8% in a-Si relative to c-Si cannot be due to voids and that a-Si is homogeneous on nm length scale.
Defect structure of carbon rich a -SiC:H films and the influence of gas and heat treatmentsHydrogen evolution transients were measured for hydrogenated amorphous silicon prepared by Si implantation of crystalline silicon and subsequent hydrogen implantation. The evolution curves are found to be similar for different H concentrations but with entirely different atomic and nanoscale structures, as was evidenced by small-angle x-ray scattering and infrared absorption investigations ͓Phys. Rev. B 53, 4415 ͑1996͔͒. This behavior is explained by a hydrogen-diffusion controlled effusion with a limited density of sites in the amorphous material that can be occupied by hydrogen. The experimental effusion curves are modeled by using diffusion coefficients in the implanted layers that were determined by secondary-ion mass spectrometry. Diffusion through a highly disordered material of low H content is found to have an activation energy of 2.26 eV.
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