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Narrowly dispersed ultrafine Cu clusters of sizes smaller than 2.0 nm have been encapsulated in nanosized silicalite-1 zeolite through direct crystallization in the presence of Cu(en)22+ complex ions as the metal precursor. The growing silicalite-1 crystals are rich in vacancy defects and connectivity defects on the grain boundaries, where the terminating silanols promote the decomposition of Cu(en)22+, thus the deposition of ultrafine Cu species. The obtained composite material as a model catalyst is active for CO2 activation and hydrogenation to methanol. The preliminary in situ FTIR study recognizes a series of surface-adsorbed carbonyl, formyl, carbonate, and formate species when the material is exposed to CO2 and H2. Among others, the adsorbed formate decays most rapidly upon cofeeding CO2 and H2, implying that the most probable pathway toward methanol formation over this material is via the formate-mediated mechanism. [ABSTRACT FROM AUTHOR]

GaAs/SiO2 nanogranular thin films have been fabricated by radio frequency magnetron co-sputtering technique and post-annealing. The existence of GaAs nanocrystals in the SiO2 matrix of the films is supported by the analysis of the X-ray diffraction patterns and the characteristic of the room temperature Raman spectra. The average size of the GaAs nanocrystals was estimated to be 1–3 nm using the Scherrer formula. The compositions of GaAs and SiO2 in the films are demonstrated to be stoichiometric by the Rutherford backscattering spectra. Raman red shifts mainly result from the phonon quantum confinement in the GaAs nanocrystals. Room temperature optical absorption spectra exhibit obvious absorption edge blue shifts with respect to the absorption edge of bulk GaAs. The blue shifts calculated by effective mass model are much larger than those of the experiment. This may result from the exponential increase in the effective mass of the exciton in the GaAs nanocrystals with the decrease of the average radius of the nanocrystals. [Copyright &y& Elsevier]

InP/SiO2 composite thin films have been fabricated on heated slices of silica glass or polished silicon by a radio frequency (RF) magnetron co-sputtering and post-annealing. X-ray diffraction (XRD) patterns and Raman spectra of the films confirmed the presence of InP nanocrystals in the composite films. Pure InP/SiO2 nanocomposite films have been obtained by high temperature (520 °C) annealing in over-pressured phosphorus vapor. Peaks in the room temperature photoluminescence (PL) spectra have been identified approximately, though the amplitudes of the peaks are relatively small. Optical absorption edge blue shifts and large enhancement in optical non-linearity of the films at room temperature have been observed and attributed to strong quantum confinement. [Copyright &y& Elsevier]

The dehydrogenation of formaldehyde (CH2O) on the clean CuO(111) surface and O/OH preadsorbed CuO(111) surface is investigated using density functional theory (DFT) method. The adsorption structures and energies of stationary points in this reaction are explored to map the whole reaction network. The calculated results indicate that the primary intermediates CH2O, CH2O2, and CHO2 prefer to adsorb at the Cusub sites and HCO prefers to adsorb at the Osuf sites. CH2O directly dehydrogenates through the pathway of CH2O → HCO → CO on the CuO(111) surface. In the presence of adsorbed oxygen or hydroxyl species, CH2O directly combines with O or OH on CuO(111) surface, leading to another pathway via CH2O → CH2O2 → CHO2 → CO2. And the preadsorbed O and OH could promote the C–H bond activation of CH2O, HCO, CH2O2, and CHO2 species. [ABSTRACT FROM AUTHOR]