Morphological Study of Voids in Ultra-Large Models of Amorphous Silicon

The microstructure of voids in pure and hydrogen-rich amorphous silicon (a:Si) network was studied in ultra-large models of amorphous silicon, using classical and quantum- mechanical simulations, on the nanometer length scale. The nanostructure, particularly voids of device grade ultra-large models of a:Si was studied, in which observed three-dimensional realistic voids were extended using geometrical approach within the experimental limit of void-volume fractions. In device-grade simulated models, the effect of void morphology; size, shape, number density, and distribution on simulated scattering intensities in small- angle region were investigated. The evolution of voids on annealing below the crystallization temperature (≤ 800 K) was examined, where the extent of the void reconstruction was reported by using high-quality three-dimensional rendering software and calculating an average size and volume of the voids. Additionally, the role of bonded and non-bonded hydrogens near the vicinity of the void’s wall in a:Si network was observed. Our simulated results suggested that, in extended void structures, X-ray scattering intensities in the small- angle region were sensitive to the number density, size, shape and the distribution of the voids in unequal strength. In both classical and local ab initio molecular dynamics models of a:Si, the reconstruction of the voids were observed but in later models, with and without present hydrogen reconstruction effect was observed greater. The distribution and dynamics of bonded and non-bonded hydrogen in heavily hydrogenated (≥ 14 at.%) ultra-large models of a:Si suggested that, void’s wall were decorated with more silicon dihydride (SiH2) bonds and 9-13% of the total H were realized as molecular hydrogen (H2) respectively from 300 K- 800 K annealing temperature. This work suggested that, a:Si sample with≥14 at.% H and ≤ 0.2% volume-fraction of voids, may be appropriate for interface hydrogenated amorphous silicon/crystalline silicon (a:Si:H/c-Si) material used in heterojunction silicon solar cell to obtain the better-passivated surface due to the presence of mobile non-bonded hydrogens

Proteomic analysis of salivary proteins and metagenomic analyses of oral and intestinal microflora in a rat model of chronic restraint stress

北海道医療大学令和2年

Temperature-induced nanostructural evolution of hydrogen-rich voids in amorphous silicon: A first-principles study

The paper presents an ab initio study of temperature-induced nano-structural evolution of hydrogen-rich voids in amorphous silicon. By using large a-Si models, obtained from classical molecular-dynamics simulations, with a realistic void-volume density of 0.2%, the dynamics of Si and H atoms on the surface of the nanometersize cavities were studied and their e ects on the shape and size of the voids were examined using first-principles density-functional simulations. The results from ab initio calculations were compared with those obtained from using the modified Stillinger-Weber potential. The temperature-induced nanostructural evolution of the voids was examined by analyzing the three-dimensional distribution of Si and H atoms on/near void surfaces using the convex-hull approximation, and computing the radius of gyration of the corresponding convex hulls. A comparison of the results with those from the simulated values of the intensity in small-angle X-ray scattering of a-Si/a-Si:H in the Guinier approximation is also provided, along with a discussion on the dynamics of bonded and non-bonded hydrogen in the vicinity of voids

Small-Angle X-Ray Scattering in Amorphous Silicon: A Computational Study

We present a computational study of small-angle x-ray scattering (SAXS) in amorphous silicon (α-Si) with particular emphasis on the morphology and microstructure of voids. The relationship between the scattering intensity in SAXS and the three-dimensional structure of nanoscale inhomogeneities or voids is addressed by generating large high-quality (α-Si networks with 0.1%–0.3% volume concentration of voids, as observed in experiments using SAXS and positron annihilation spectroscopy. A systematic study of the variation of the scattering intensity in the small-angle scattering region with the size, shape, number density, and the spatial distribution of the voids in the networks is presented. Our results suggest that the scattering intensity in the small-angle region is particularly sensitive to the size and the total volume fraction of the voids, but the effect of the geometry or shape of the voids is less pronounced in the intensity profiles. A comparison of the average size of the voids obtained from the simulated values of the intensity, using the Guinier approximation and Kratky plots, with that of the same from the spatial distribution of the atoms in the vicinity of void surfaces is presented