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Abstract ZnO nanowire nucleation mechanism and initial stages of nanowire growth using the carbothermal reduction technique are studied confirming the involvement of the catalyst at the tip in the growth process. Role of the Au catalyst is further confirmed when the tapering observed in the nanowires can be explained by the change in the shape of the catalyst causing a variation of the contact area at the liquid–solid interface of the nanowires. The rate of decrease in nanowire diameter with length on the average is found to be 0.36 nm/s and this rate is larger near the base. Variation in the ZnO nanowire diameter with length is further explained on the basis of the rate at which Zn atoms are supplied as well as the droplet stability at the high flow rates and temperature. Further, saw-tooth faceting is noticed in tapered nanowires, and the formation is analyzed crystallographically.

ZnO nanowire nucleation mechanism and initial stages of nanowire growth using the carbothermal reduction technique are studied confirming the involvement of the catalyst at the tip in the growth process. Role of the Au catalyst is further confirmed when the tapering observed in the nanowires can be explained by the change in the shape of the catalyst causing a variation of the contact area at the liquid-solid interface of the nanowires. The rate of decrease in nanowire diameter with length on the average is found to be 0.36 nm/s and this rate is larger near the base. Variation in the ZnO nanowire diameter with length is further explained on the basis of the rate at which Zn atoms are supplied as well as the droplet stability at the high flow rates and temperature. Further, saw-tooth faceting is noticed in tapered nanowires, and the formation is analyzed crystallographically. [ABSTRACT FROM AUTHOR]

Aluminum Zinc Oxide (AZO) thin films are grown on glass substrates by RF Magnetron Sputtering using a single target of zinc oxide (99 wt%) and aluminum oxide (1 wt%) with argon as the plasma. Photolithographic process is then performed on the films in order to obtain a Transmission Line Model structure (TLM) of the metal contact system, namely aluminum and gold. The specific contact resistivity, ρ[sub c], of these two metal-semiconductor systems, which will undergo different rapid thermal annealing (RTA) environment, are determined. X-Ray diffraction patterns for these samples are obtained to investigate phase formations or micro-structural changes so as to justify for the differences in specific contact resistivity obtained for these contact systems. The different RTA environment are simulated by purging either nitrogen or argon gas, with a pressure of 40 psi at a temperature of 400 °C for 60 s; and annealing in vacuum (10[sup -6] Torr) also at the same temperature and duration. One-dimensional TLM (1D-TLM) measurements are performed on the TLM structures to obtain the specific contact resistivity, ρ[sub c]. Results show that aluminum contacts on AZO without RTA give the lowest pc as compared to those in other environment, while gold contacts on AZO annealed in vacuum yield the lowest ρ[sub c]. Adhesion of aluminum contacts on AZO is good even when subjected to ultrasonic bath test but not true for the case of gold contact, which adheres poorly on AZO films. [ABSTRACT FROM AUTHOR]

• Many Rh catalysts were tested for N 2 O decomposition under diesel conditions. • Rh/CeO 2 is the only catalyst with good activity in a wet feed after aging. • Aging does not deactivate Rh/CeO 2 but significantly increases its activity. • Removal O 2 from the catalyst has been demonstrated to be the rate limiting step. Numerous Rh catalysts were evaluated for N 2 O decomposition for automotive applications. Some Rh-containing spinel materials exhibit excellent fresh activities in the absence of H 2 O but become inactive after hydrothermal aging or when tested in a wet feed. Rh catalysts supported on zeolites can be very active in a dry feed even after aging but are extremely sensitive to H 2 O. Rh/CeO 2 is an exceptional catalyst for this reaction in the presence of both H 2 O and O 2. Hydrothermal aging (750 °C/20 h) significantly increases its activity. A similar activity enhancement was found by calcining the support before Rh impregnation. XPS results show a surface enrichment of Rh species on the aged Rh/CeO 2 catalyst relative to the fresh catalyst. Aberration corrected STEM images reveal that Rh is buried in the bulk on the fresh catalyst and pulled out onto the surface of the support after thermal treatments. All catalysts are inhibited by H 2 O with the zeolite-based Rh catalysts being the worst. The aged Rh/CeO 2 catalyst is less sensitive to H 2 O relative to others. DRIFTS data show that H 2 O sensitivity is related to catalyst hydrophilicity; a high coverage of OH groups on a catalyst reduces its N 2 O decomposition activity. H 2 -TPR results show that a Rh/CeO 2 catalyst can be readily reduced at < 100 °C. On a reduced Rh/CeO 2 catalyst, near complete N 2 O conversion can be obtained with a lean feed at 250 °C for a duration equivalent to its oxygen storage capacity. The N 2 O-DRIFTS experiments over a pre-reduced Rh/CeO 2 catalyst show that Ce3+ sites are quickly oxidized to Ce4+ upon contacting N 2 O at room temperature, resulting N 2 and adsorbed O, with the latter being an efficient oxidizer. Based on these results, a N 2 O decomposition mechanism is proposed for the Rh/CeO 2 catalyst. [ABSTRACT FROM AUTHOR]