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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]

Abstract: ZnO thin films were deposited on heavily phosphorus-doped (n+-Si) substrates by radio frequency magnetron sputtering. The films were changed from n-type to p-type by phosphorus diffusion from the n+-Si substrates to the ZnO films and being activated thermally during deposition. n-Type ZnO (n-ZnO) films were also deposited onto the p-type ZnO (p-ZnO) films to form n-ZnO/p-ZnO/n+-Si multilayer structures. The cross section of the multilayer structure was examined by scanning electron microscopy. Crystal structures of the p-ZnO films were studied by X-ray diffraction and were confirmed to be highly c-axis oriented primarily perpendicular to the substrate. Photoluminescence spectra of the p-ZnO films showed that band-edge UV emission predominated. The hole concentration of the p-ZnO films was between +1.78×1018 cm−3 and +1.34×1019 cm−3, and the hole mobility was 13.1–6.08cm2/Vs measured by Hall effect experiment. The formation of p-ZnO films was confirmed by the rectifying characteristics of the p-ZnO/n+-Si heterojunctions and the n-ZnO/p-ZnO homojunction on the multilayer structure as well as by the experimental results of Hall effect. [Copyright &y& Elsevier]

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]

Abstract: ZnO thin films were initially deposited on a heavily phosphorus-doped Si (n+-Si) substrate by radio frequency magnetron sputtering. The transition from n-type ZnO to p-type one was realized by phosphorus diffusing from Si substrate to ZnO film and being thermally activated during post annealing. Crystal structures of the ZnO films were confirmed to be highly c-axis oriented wurtzite structure by X-ray diffraction experiment. Photoluminescence spectra of the ZnO films showed strong ultraviolet emissions originated from the recombination of the band-edge excitons. The composition of the films was measured by X-ray photoelectron spectroscopy, and a typical concentration of phosphorus was about 0.48% corresponding to the order of atomic density of 1019/cm3. The hole concentration of the film was +1.28×1019/cm3 measured by Hall effect apparatus. Formation of the p-type ZnO films can be further confirmed by the rectifying I–V curves of p-ZnO/n+-Si heterojunctions. [Copyright &y& Elsevier]

This paper deals with the extension of the synthesis field of microporous zeolite-type materials and types of organic structure-directing agents (OSDA) that can be used to promote their crystallization. The highly hydrophilic hexamethylenetetramine (urotropine), with its C/N ratio = 1.5, which is unusual to act as a structure-directing agent in the crystallization of open-framework silica polymorphs, is used to exemplify the novelty of the employed approach. Namely, the protonation of urotropine in an acidic fluorine-containing medium transforms it into a very efficient OSDA that yields dodecasil 3C (MTN-type). This novel synthesis also allows gaining insights into OSDA-framework interactions in the MTN-type structure. The comprehensive 29Si and 19F MAS NMR indicate a small number of point defects of the framework T sites and the multiple bonding of F− ions to Si in a disordered manner. Based on this finding, a unit cell model has been generated using Monte Carlo simulation and validated with Rietveld refinement using experimental powder X-ray diffraction data. In the model, protonated urotropine cations are located in the center of the big hexakaidecahedral [51264] cages at full occupancy with random orientations. The charge balance is provided by the disordered F− ions. [ABSTRACT FROM AUTHOR]

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]

The zeolite community spent 50 years in pursuing the synthesis of high-silica LTA -type zeolites, and ultimately succeeded with the pure-silica polymorph by applying specific structure-directing agents (SDA). The high-silica zeolite A has exhibited unique properties and strong potential to be applied as an adsorbent and catalyst in several novel processes. In the present study, the high-silica polymorphs of Si/Al ratios from 15 to ∞ were synthesized and subjected to thorough characterizations using multiple physicochemical methods. It has been revealed that there exists strong interactions between the organic SDAs and the framework. Therefore, removing the SDAs by calcination in air is difficult, and can only be done above 700 °C with a certain degree of framework dealumination. The retained framework structure shows connectivity defects and a unique combination of Brønsted and Lewis acidity. Using methanol-to-olefins (MTO) as a probe reaction, the catalytic performance of high-silica LTA -type zeolites has been evaluated. Compared to the well-studied CHA and MFI -type catalysts, high-silica zeolite A exhibited a shorter life-time and higher selectivity towards C 4 olefins, while methane selectivity increased with the deactivation. [Display omitted] • The crystallization of high-silica LTA -type zeolites requires specific structure-directing agents (SDAs). • Strong SDA/framework interactions are evidenced by XRD, NMR and TG. • Complete removal of SDA by calcination accompanied by framework dealumination, while the framework structure retained. • High-silica LTA-type material possesses unique acidity that renders different catalytic performances in MTO reactions. [ABSTRACT FROM AUTHOR]

The fluoride medium synthesis of zeolites, especially in the strongly acidic regions, yields products with unique characteristics such as ultra-hydrophobic surfaces and defect-free lattices. However, it is often difficult to incorporate aluminum into the framework of zeolites in this medium, limiting the acquisition and development of catalytic materials. The present paper shows that inter-zeolite transformation is efficient for obtaining ZSM-5 zeolites with lower Si/Al ratios in a strongly acidic fluoride medium. The critical point is that the parent zeolites can retain some locally ordered fragments during their dissolution, including framework Al atoms, and incorporate them into the ZSM-5 product. The acidic properties of the trans -crystallization products obtained in an acidic medium display significant differences from the traditional ZSM-5 with a similar Si/Al ratio in the amounts, strength, and types of the acid sites; thus, they behave differently in typical acid-catalysed reactions, such as dehydration of alcohols. In strongly acidic fluoride medium * BEA , FER and MOR -type zeolites transform readily into nanometer plates of MFI zeolite because they possess common mor CBU, while FAU zeolite transforms slowly to micrometer MFI crystals. These Al-rich ZSM-5 zeolites have unique acidity and perform differently in catalytic dehydration of light alcohols from the conventional ZSM-5. [Display omitted] • Al-rich ZSM-5 of Si/Al ∼ 20 obtained in acidic fluoride medium via inter-zeolite transformation. • In acidic medium * BEA , FER and MOR zeolites transforms readily into nanometersized plates of MFI because of common mor CBU. • FAU zeolite transforms slowly to micrometer MFI crystals. • These Al-rich ZSM-5 zeolites have unique acidity and perform differently in catalytic dehydration of light alcohols. [ABSTRACT FROM AUTHOR]

Abstract: Investigation on very high frequency (VHF) plasma and its glow discharge mechanism during the deposition of microcrystalline silicon (μc-Si:H) film have been investigated. In situ optical emission spectroscopy (OES) measurements were used to study the influence of deposition conditions on VHF plasma. The study reveals that: the OES intensities of Si*, SiH*, Hα* and Hβ* increase significantly with plasma excitation frequency; all the OES intensities increase initially with plasma power and tend to be saturated at working pressure 120 Pa, a maximum can be observed while at 60 Pa; the variation of the intensities with working gas pressure strongly depends on plasma power, and maximum intensity for every peak was observed between 100 and 120 Pa. Based on the analysis of the OES spectra, the glow discharge mechanism and the relationship between the OES spectra and the deposition rates are also discussed. [Copyright &y& Elsevier]