Aqueous lateral epitaxy overgrowth of ZnO on (0001) GaN at 90 °C: Part I. Increasing the critical thickness

Thick, epitaxial ZnO thin films have been grown on (0001) GaN buffered Al₂O₃ substrates using an aqueous solution at 90 °C. Films with improved structural, optical and electrical characteristics, were grown using a lateral epitaxial overgrowth (LEO) method. Different photoresist masks were used to enable LEO. The masks included linear windows and two different hexagonal arrays of circular windows. Films that exceeded a critical thickness mechanically failed through buckling, consistent with the large compressive stresses expected due to the mismatch of the ZnO lattice with the underlying GaN substrate. It was shown that improved mechanical stability could be achieved using the LEO method. Without LEO, a film thickness no greater than 4 µm could be grown without buckling. The critical thickness could be increased to 10 µm using linear windows, whereas a critical thickness of 50 μm was achieved with one array of circular windows, and 80 µm for a second array. The two different arrays of circular windows differed relative to their orientation on the substrate. It was also shown that the critical thickness increased with increasing distance between the growth windows. Optical transmission, micro-photoluminescence and Hall Effect measurements showed that the LEO method also results in improved optoelectronic properties.     

Fabrication of Ni2In3 alloy nanotubes

Alloy nanotubes were successfully grown by self-organization. They were produced by annealing of carbon-nickel-indium mixture thin films that were prepared by pulsed laser deposition. The morphology was observed and analysed by both scanning and transmission electron microscopes. The diameters were tens of nanometres and the aspect ratios were more than 2500. The growth is suggested to be due to the driving force that originated from supersaturation of alloying liquid indium with solid nickel.     

钱塘江河口淤积下移对上游洪水位的影响分析

钱塘江河口由于下游围涂缩窄，在遭遇连续枯水年时发生淤积，且淤积部位较以往下移。应用一维动床数值模型，验证了尖山围涂前后2次洪水过程，在此基础上，设计了3种典型地形，计算分析了淤积下移对钱塘江河口杭州段洪水位的影响。结果表明，河口淤积下移后，在不利江道条件下，闸口、七堡洪水位分别抬高了0．18m和0．24m。     

Effects of sprayer configuration on efficacy for the control of scab on crabapple using electron beam analysis

Foliar diseases like apple scab result in significant economic losses to growers each year. Assessment in past studies involved only macroscopic disease ratings. More complete knowledge of the fate and behavior of fungicide has been needed to reduce pesticide use with less off‐target contamination. Field studies were conducted in a production nursery for over 4 years. A moderately susceptible cultivar of ornamental crabapple, Malus spp. cv “Candied Apple”, was sprayed with a fungicide using two sprayer/nozzle configurations. The fungicide used in this study was Mankocide, combination of Cu(OH)₂ and mancozeb that permitted electron beam analysis (EBA) identification based on the presence of Cu, MN and Zn in the molecule and formulation. EBA was conducted using a cold field emission scanning electron microscopy and energy dispersive x‐ray microanalyzer. Fresh leaf samples were placed on sticky stubs after each fungicide treatment. The presence or absence of fungal conidia and fungicide residue were measured. EBA permitted direct visualization and identification of the pathogens, morphologically, and chemical characterization of fungicide present. EBA was useful to quantify disease control related to fungicide coverage, sprayer configuration and treatment efficacy. SCANNING 31: 24–27, 2009. Published 2009 by Wiley Periodicals, Inc.     

A nucleation and growth study of gold nanowires and nanotubes in polymeric membranes

Through the use of a technique known as template synthesis, it has become possible to synthesize a variety of different materials in the form of nanowires or nanotubes. Dependent upon which type of template is used, either randomly or regularly dispersed nanowires or nanotubes with a wide variety of nanopore diameters and lengths can be created. In this experiment, gold nanowires and nanotubes have been synthesized with diameters of 30, 100, and 800 nm in polycarbonate membranes. The kinetics and characteristics of growth can be greatly altered, dependent upon what operational parameters are employed during deposition. This study looks at the different growth factors that need to be considered when employing the template synthesis approach. These factors include the final expected geometry, the distribution of nucleation sites, the grain size distribution, and the deposition rate.     

MnS doped mesoporous silica catalysts for the generation of novel carbon nanocages

Novel MnS impregnated mesoporous silica systems have been originated for the generation of carbon nanocages. The procedure involves a simple catalytic vapour deposition (CVD) method. This is the first time that a transition metal sulfide has been used for the synthesis of carbon nanostructures.     

Mass transport studies at rotating cylinder electrode (RCE): Influence of using plates and concentric cylinder as counter electrodes

This study shows the effect of using four-plate, six-plate and concentric cylinder as counter electrodes on the RCE mass transport characterization. The Cu(II)/Cu(0) process in sulfuric acid is employed as the model reaction. Based on the analysis of Sh = aRe^bSc^0.356 correlation, the values of the constant a, associated with shape and cell dimensions, were 0.012, 0.014, and 0.022 for the four-plate, six-plate and concentric cylinder, respectively. This behavior suggests that both, the shape and area of the counter electrode, influence the values of a. The values of b, associated with the hydrodynamic regime, were similar for the six-plate and the concentric counter electrodes, b = 0.91; whereas for the four-plate counter electrode, b = 0.95. The fact that the four-plate device gives greater values of b suggests that this device has a higher turbulence-promoting action than the others. The mass transport at the RCE with four plates has a performance similar to the concentric counter electrode, which is important from the technical and economics standpoints.     

Reduction of charge injection into PECVD SiNxHy by control of deposition chemistry

The high rate of charge trapping in thin-film silicon nitride causes its electrical properties to change with stressing level and time. The rate of shift of the high-frequency CV curves of Al/SiN_xH_y/cSi capacitors was used here to measure nitride charging rate and to compare PECVD nitrides deposited under various conditions of plasma power and gas mixture in the same parallel-plate reactor. By operating the plasma under high power to activate the NH₃ or N₂ and under low SiH₄ flow to ensure that all of the SiH4 reacts with N, it is possible to deposit N-rich nitride that has no detectable Si—H bonding, which bonding others have correlated with charge trapping. Nitride deposited under these conditions using NH₃ and 13 MHz rf power had charging rates for both gate polarities that were 20 times lower than those of nitride that had a “stoichiometric” N/Si ratio of 4/3 and that had its H distributed among Si—H and N—H bonds. MIS capacitors made with the latter nitride also had a high negative initial flat-bond voltage, indicating the presence of grown-in positive charge. This charge was large enough to invert the surface ofp-Si substrates. N-rich nitride free of Si—H that was deposited either using N₂ or using low-frequency rf power (≤400 kHz) had higher charging rates than did that deposited from NH₃ at 13 MHz. Also, the low-frequency material contained grown-in positive charge that is attributed to H⁺ implanted by the high ion bombardment energy of the low-frequency plasma.     

Epitaxial growth of titanium oxide thin films on MgO(100) single-crystal substrates by reactive deposition methods

We synthesized titanium oxide thin films on MgO(100) single-crystal substrates by two reactive deposition methods and compared the structures of the thin films formed by these methods. In one method (pulsed-molecular-beam deposition method), molecular oxygen is supplied to the substrates by using a pulsed-molecular-oxygen beam source and deposition of one unit layer of titanium and subsequent supply of molecular oxygen are repeatedly performed. In the other method (radical beam deposition method), atomic oxygen is irradiated to the substrates by using an atomic oxygen beam generated by the radical beam source and irradiation of the atomic oxygen and deposition of titanium are simultaneously performed. In the case of the pulsed-molecular-beam deposition method, the crystal structure was changed by increasing the number of oxygen pulses supplied from the beam source. We found that the crystal structure of titanium oxide depended on the composition ratio of O:Ti in the film. The maximum ratio of O:Ti attainable by this method was 1.85, and at this ratio, (100)-oriented pseudorutile was formed. In the case of the radical beam deposition method, (100)-oriented anatase was formed below the titanium deposition rate of 0.10 nm/s and pseudorutile (TiO_2−δ) was formed above 0.15 nm/s. The pseudorutile structure synthesized on this experiment was very stable in air. We concluded that the crystal structure of the pseudorutile is a new crystal structure of titanium oxide.