Tungsten disulfide (WS2) films were grown on c-plane sapphire in a cold-wall gas-source chemical vapor deposition system to ascertain the effect of the chalcogen precursor on the film growth and properties. Tungsten hexacarbonyl (W­(CO)6) was used as the tungsten source, and hydrogen sulfide (H2S) and diethyl sulfide (DES-(C2H5)2S) were the chalcogen sources. The film deposition was studied at different temperatures and chalcogen-to-metal ratios to understand the effect of each chalcogen precursor on the film growth rate, thickness, coverage, photoluminescence, and stoichiometry. Larger lateral growth was observed in films grown with H2S than DES. The reduced lateral growth with DES can be attributed to carbon contamination, which also quenches the photoluminescence. Thermodynamic calculations agreed well with the experimental observations, suggesting formation of WS2 with both sulfur precursors and additional formation of carbon when deposition is done using DES.

Flow distribution and mass transfer characteristics during CO 2 -water flow through a parallel microchannel contactor integrated with two constructal distributors have been investigated numerically and experimentally. Each distributor comprises a dichotomic tree structure that feeds 16 microchannels with hydraulic diameters of 667 lm. It was found that constructal distributors could ensure a nearly uniform gas-liquid distribution at high gas flow rates where the ideal flow pattern was slug-annular flow. Nevertheless, at small gas flow rates where the ideal flow pattern was slug flow, a significant flow maldistribution occurred primarily due to the lack of large pressure barrier inside each distributor, indicating that dynamic pressure fluctuation in parallel microchannels greatly disturbed an otherwise good flow distribution therein. It was further shown that the present parallel microchannel contactor could realize the desired mass transfer performance previously achieved in one single microchannel under relatively wide operational ranges due to the integration of constructal distributors. V

International audienceA complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films is dependent strongly on the nature of the interfacial bonds