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A heterogeneous reaction mechanismbased on elementary reactionsteps is proposed for the prediction of pyrolytic carbon depositionin chemical vapor infiltration, involving 72 surface species and 277surface elementary reactions. A “prototype” gas-phasereaction is chosen to match with the corresponding surface reaction,and correction methods for kinetic data are also proposed for threekinds of surface reactions (i.e., surface/gas reactions, unimolecularsurface reactions, surface/surface reactions) in the present work.Simulation results of deposition kinetics and gas-phase compositionsof propane pyrolysis are validated by previously published experimentalresults of Marquaire’s group, with a surface to volume ratiofrom 5 to 175 cm–1and temperature from 1173 to1323 K. The reaction pathways of the heterogeneous surface reactionsand homogeneous gas-phase reactions are studied on the basis of thereaction flow rate analysis. An acceptable agreement indicates thatthe present heterogeneous reaction mechanism is reasonable, and acetylene,ethylene, and benzene are recognized as the main precursors of thepyrolytic carbon deposition at the present processing conditions. [ABSTRACT FROM AUTHOR]

This work presents a study on the controlled growth of WO3 nanowires via chemical vapor deposition without catalyst, and their potential applications in visible photodetectors. The influence of growth conditions on the morphology of WO3 nanowires is studied in order to understand the growth mechanism of WO3 nanowires, and ultra-long (60 , the longest one ever reported) WO3 nanowires with a spindle shape are achieved by optimizing the growth conditions. It was found that the length of WO3 nanowires increases from 15 to 60 with increasing the argon carrier gas flow rate from 30 sccm to 90 sccm, and then saturates with further increasing the argon carrier gas flow rate. However, the length of WO3 nanowires reduces from 60 to 19 with increasing the tube inner pressure from 2.5 Torr to 3.5 Torr. The photoconductor detectors based on WO3 single nanowires present excellent device performance with a responsivity as high as 19 A W−1 at a bias of 0.1 V, a detectivity as high as 1.06 × 1011 Jones, and a response (rising and decay) time as short as 8 ms under the illumination of a 404 nm laser. These results indicate the great potential of WO3 nanowires for applications in fabricating high performance visible photodetectors. [ABSTRACT FROM AUTHOR]

Due to the poor wettability of the AgCuTi alloy on the SiO2f/SiO2 composite, direct brazing of the composite with an Invar alloy could hardly achieve a reliable joint. To overcome that, the SiO2f/SiO2 composite was decorated with few-layer graphene (FLG) by a plasma enhanced chemical vapor deposition (PECVD) method. Sessile drop experiments indicate that the contact angle dropped from 123.8° to 50.7° after FLG was grown on the surface of the SiO2f/SiO2 composite. Afterwards, the effects of brazing temperature and Ti contents on the microstructure evolution and mechanical properties of joints (Invar/SiO2f-SiO2 modified with FLG) were investigated. The typical interface structure of the joint is SiO2f- SiO2/Ti5Si3 + TiO2 + CuxTi6 - xO(x = 2,3)/Ag(s,s) + Cu(s,s) + Cu-Ti blocks/wave-like Fe2Ti + Ni3Ti/Ag(s,s) + Cu(s,s) + Fe2Ti + Ni3Ti blocks/Invar. As the brazing temperature and Ti contents increase, the reaction layer on the SiO2f/SiO2 side becomes thicker and cracks gradually propagate. Meanwhile, a few dispersive Fe2Ti + Ni3Ti phases change into large-area wave-like compounds and more Cu-Ti compounds form with the increase of the Ti content. The microstructure evolution significantly affects the shear strength of the brazed joints. The highest shear strength is 26 MPa brazed at 860 °C for 10 min with 4.5 wt.% Ti content. [ABSTRACT FROM AUTHOR]

We report on the magnetotransportproperties of chemical vapordeposition grown films of interconnected Bi2Te3nanoplates. Similar to many other topological insulator (TI) materials,these granular Bi2Te3films exhibit a linearmagnetoresistance (LMR) effect which has received much recent attention.Studying samples with different degree of granularity, we find a universalcorrelation between the magnitude of the LMR and the average mobility(⟨μ⟩) of the films over nearly 2 orders of magnitudechange of ⟨μ⟩. The granularity controlled LMReffect here is attributed to the mobility fluctuation induced classicalLMR according to the Parish–Littlewood theory. These findingshave implications to both the fundamental understanding and magnetoresistivedevice applications of TI and small bandgap semiconductor materials. [ABSTRACT FROM AUTHOR]