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Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge 1-xCx (x=0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge 0.998C0.002 shows a bandgap reduction supporting these results. Growth of Ge 0.998C0.002 using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III-V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition. [ABSTRACT FROM AUTHOR]

Recent experimental studies report rapid and efficient reduction of N-nitrosodimethylamine (NDMA) and related aquatic micropollutants mediated by palladium (Pd) and nickel (Ni) surfaces, but differing mechanisms have been reported for the surface reactions. Here, NDMA adsorption and fragmentation on Ni and Pd surfaces has been studied using supercell slab density functional theory (DFT) calculations. NDMA adsorbs in two stable configurations on each surface. Upright binding through the NO fragment is slightly preferred energetically and provides entrance to an exothermic NO dissociation pathway with moderately high activation barriers. Flat binding through the NNO plane is somewhat less favorable but leads to a facile and exothermic dissociation across the NN bond. These results suggest that both mechanisms are in competition and may contribute to the observed catalytic reduction of NDMA over these metals in aqueous solution. DFT calculations are used to contrast the contributions of NN and NO bond cleavage to the catalytic reduction of the environmental pollutant N-nitrosodimethylamine (NDMA). [ABSTRACT FROM AUTHOR]