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Deep insight into the crystallization mechanism of amorphous silicon is of theoretical and technological significance for the preparation of high-quality microcrystalline/polycrystalline silicon. In this work, we intensively compare the present two plasma-involved routes, i.e., the direct deposition and recrystallization of precursor amorphous silicon (a-Si) films, to fabricate microcrystalline silicon. Both the directly deposited and recrystallized samples show multi-layered structures as revealed by electronic microscopy. High-density hydrogen plasma involved recrystallization process, which is mediated by the hydrogen diffusion into the deep region of the precursor a-Si film, displays significantly different nucleation configuration, interface properties, and crystallite shape. The underlying mechanisms are analyzed in combination with the interplay of high-density plasma and growing or treated surface.

Being a key issue in the research and fabrication of silicon heterojunction (SHJ) solar cells, crystalline silicon (c-Si) surface passivation is theoretically and technologically intricate due to its complicate dependence on plasma characteristics, material properties, and plasma-material interactions. Here amorphous silicon (a-Si:H) grown by a planar inductively coupled plasma (ICP) reactor working under different antenna-substrate distances of d was used for the surface passivation of low-resistivity p-type c-Si. It is found that the microstructures (i.e., the crystallinity, Si-H bonding configuration etc.) and passivation function on c-Si of the deposited a-Si:H were profoundly influenced by the parameter of d, which primarily determines the types of growing precursors of SiHn/H contributing to the film growth and the interaction between the plasma and growing surface. c-Si surface passivation is analyzed in terms of the d-dependent a-Si:H properties and plasma characteristics. The controlling of radical types and ion bombardment on the growing surface through adjusting parameter d is emphasized.

The surface properties of photocatalysts strongly affect interfacial catalytic reaction and determine photocatalytic activity. In this work, surface-modified graphitic carbon nitride (g-C3N4) nanosheets were prepared via plasma treatment in H2, H2-CH4, and Ar atmosphere. Hydrogenated g-C3N4 nanosheets with hydrophilic group C-N-H, defect state, and exfoliated morphology were obtained via treating g-C3N4 nanosheets with H2 plasma at room temperature. The hydrogenated g-C3N4 nanosheets possessed the improved photocatalytic activity for hydrogen evolution, and the rate of hydrogen evolution exceeded that of pristine g-C3N4 by a factor of 4.8. Photocatalytic activity improvement is due to the introduction of hydrophilic group C-N-H, defect states, and exfoliated nanosheet morphology. Hydrophilic functional group of C-N-H can effectively capture water molecules. Defect states generated via plasma treatment acted as a capture center to suppress carrier recombination and transfer the trapped electrons to the adsorbed water molecules. Exfoliated nanosheet morphology provided a large number of active sites for catalytic reaction. Optical emission spectroscopy supported the introduction of hydrogen species during H2 plasma treatment of g-C3N4. First-principle density functional theory calculations confirmed the enhanced adsorption capacity of hydrogenated g-C3N4 for water molecules. The mechanism of enhanced photocatalytic H2-production activity was further proposed.