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Poly-silicon passivating contacts, consisting of a stack of tunnel-oxide and doped poly-silicon layers, can simultaneously provide excellent surface passivation and low contact resistivity for silicon solar cells. Nevertheless, the microscopic interfacial characteristics of such contacts are not yet fully understood. In this work, by investigating the surface passivation evolution of poly-silicon passivating contacts under increasing annealing temperatures, we unveil these characteristics. Before annealing, we find that the Si and O atoms within the tunneloxide layer are mostly unsaturated, whereas the O atoms introduce acceptor-like defects. These defects cause Fermi-level pinning and high carrier recombination. During annealing, we identify two distinct chemical passivation regimes driven by surface hydrogenation and oxidation. We attribute the excellent chemical passivation activated by high-temperature annealing (850°C) mainly to the tunnel oxide reconstruction, which effectively reduces the acceptor-like state density. During the oxide reconstruction, we also find that sub-nanometer pits (rather than pinholes) are formed in the oxide. A combination of experimental and theoretical investigations demonstrates these sub-nanometer pits provide excellent surface passivation and efficient tunneling for majority carriers.

Microcalorimetric techniques have been employed to investigate the adsorption of water on chemically modified, high surface area carbons. A matrix of treatments and carbons were selected to test some hypotheses. Heats of adsorption of water indicate that adsorption is a strong function of surface chemistry. Three mechanisms of water adsorption are delineated according to measured differential heats of adsorption (H ads ): (i) chemical adsorption with H ads > 12 kcal/mol, (ii) condensation with H ads approximately 10 kcal/mol, and (iii) physical adsorption with H ads < 10 kcal/mol. The absolute and relative amounts of water adsorption arising from each mechanism are a function of surface chemistry. Adsorption of water on carbons dried at 175 °C in N 2 generates typical Type V adsorption isotherms. Heat of adsorption data for water adsorbed on dried carbon indicates that condensation accounts for the sharp rise in adsorption at a relative humidity of approximately 0.5. Treating carbons with N 2 at 950 °C generates surfaces that initially adsorb water through a mechanism of chemical adsorption, followed by condensation, and finally physical adsorption. On high-temperature N 2 -treated carbons heats of adsorption exceed 100 kcal/mol, suggesting chemisorption of water at unsaturated carbon surface sites produced during the high-temperature reduction of oxygen species. Carbons reduced with H 2 at 950 °C are hydrophobic, and microcalorimetric data reveals that the small amount of adsorption observed arises from either chemical or physical adsorption rather than condensation. Hydrophobic carbon surfaces subsequently oxygenated at 150 °C showed significant increases in the amount of water adsorbed through physical adsorption. These results demonstrate that microcalorimetric techniques complement standard isotherm measurements in describing the nature of water adsorption on carbon surfaces.

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Highly selective oxidation of aliphatic alcohols to aldehydes over bismuth oxyhalide photocatalysts is achieved for the first time.

A series of alumina supported ruthenium catalysts, which prepared by hydrogen treatment or hydrazine reduction, were characterized by N 2 adsorption, X-ray diffraction (XRD), X-ray fluorescence (XRF), CO chemisorption, and Temperature-programmed desorption of hydrogen (H 2 -TPD). In contrast to the samples with conventional hydrogen reduction, there was almost no residual chlorine in the samples using RuCl 3 as precursor with hydrazine treatment. Furthermore, the dissolved aluminum could be removed much more easily in basic solution, which led to the higher BET surface and pore volume of hydrazine-reduction catalysts. Therefore, the active phase (Ru metal) would not be contaminated. Three main peaks, which occurred at about 150, 375, and 650°C, respectively, were observed in the H 2 -TPD profiles of Ru/Al 2 O 3 catalysts with a high amount of residual chlorine. A new peak of desorption hydrogen centering at 240°C, which was completely suppressed by the high amount of residual chlorine, might appear in the profiles of the samples with the washing procedure following hydrogen reduction or hydrazine treatment. The peaks with the desorption temperature lower than 500°C were relative with dissociatively adsorbed hydrogen and spillover hydrogen simultaneity, and the peak at above 500°C was caused by spillover hydrogen and would be stabilized by hydroxyl groups on alumina surface.