Photoluminescence spectroscopy and positron annihilation spectroscopy probe of alloying and annealing effects in nonpolar m-plane ZnMgO thin films

Temperature-dependent photoluminescence characteristics of non-polar m-plane ZnO and ZnMgO alloy films grown by metal organic chemical vapor deposition have been studied. The enhancement in emission intensity caused by localized excitons in m-plane ZnMgO alloy films was directly observed and it can be further improved after annealing in nitrogen. The concentration of Zn vacancies in the films was increased by alloying with Mg, which was detected by positron annihilation spectroscopy. This result is very important to directly explain why undoped Zn1-xMgxO thin films can show p-type conduction by controlling Mg content, as discussed by Li [Appl. Phys. Lett. 91, 232115 (2007)].

Numerical simulations of interrupted and conventional microchannel heat sinks

We provide three-dimensional numerical simulations of conjugate heat transfer in conventional and the newly proposed interrupted microchannel heat sinks. The new microchannel heat sink consists of a set of separated zones adjoining shortened parallel microchannels and transverse microchambers. Multi-channel effect, physical property variations, and axial thermal conduction are considered. It is found that flow rate variations in different channels can be neglected, while heat received by different channels accounts for 2% deviations from the averaged value when the heat flux at the back surface of the silicon chip reaches 100 W/cm(2). The computed hydraulic and thermal boundary layers are redeveloping in each separated zone due to shortened flow length for the interrupted microchannel heat sink. The periodic thermal developing flow is responsible for the significant heat transfer enhancement. Two effects influence pressure drops across the newly proposed microchannel heat sink. The first one is the pressure recovery effect in the microchamber, while the second one is the head loss when liquid leaves the microchamber and enters the next zone. The first effect compensates or suppresses the second one, leading to similar or decreased pressure drop than that for the conventional microchannel heat sink, with the fluid Prandtl number larger than unity.

RELATION BETWEEN THE METASTABILITY OF EL2 AND THE PHOTOSENSITIVITY OF LOCAL VIBRATIONAL-MODES IN SEMIINSULATING GAAS

Recent infrared spectroscpic observations of local vibrational mode absorptions have revealed a number of photosensitive centers in semi-insulating GaAs. They include (OVAs) center which has three modes at 730 cm(-1) (A), 715 cm(-1) (B), and 714 cm(-1) (C), respectively, a suggested NH center related to a line at 983 cm(-1) (X(1)), and centers related to hydrogen, such as (H-O) or (H-N) bonds, corresponding to a group of peaks in the region of 2900-3500 cm(-1). The photosensitivity of various local vibration centers was observed to have similar time dependence under near-infrared illumination and was suggested to be due to their charge-state interconversion. Mainly described in this work is the effect of the 1.25-eV illumination. It is confirmed that this photoinduced kinetic process results from both electron capture and hole capture, which are closely related to the photoionization behavior and metastability of the EL2 center.

Linear spatio-temporal instability analysis of ice growth under a falling water film

A linear spatio-temporal stability analysis is conducted for the ice growth under a falling water film along an inclined ice plane. The full system of linear stability equations is solved by using the Chebyshev collocation method. By plotting the boundary curve between the linear absolute and convective instabilities (AI/CI) of the ice mode in the parameter plane of the Reynolds number and incline angle, it is found that the linear absolute instability exists and occurs above a minimum Reynolds number and below a maximum inclined angle. Furthermore, by plotting the critical Reynolds number curves with respect to the inclined angle for the downstream and upstream branches, the convectively unstable region is determined and divided into three parts, one of which has both downstream and upstream convectively unstable wavepackets and the other two have only downstream or upstream convectively unstable wavepacket. Finally, the effect of the Stefan number and the thickness of the ice layer on the AI/CI boundary curve is investigated.

X-ray spectra produced by interaction of Ar16+ and Ar17+ with Zr

The 10-20 qkeV Ar16+ and Ar17+ ions produced by SECRAL enter on metallic surface of Zr. In this interaction, the multi-electron excitation possibly occurred in the neutralization of the highly charged Ar16+ ions, which produced vacancy in the K shell. Electron of the high n state de-excited to K vacancy gives off X-ray. The experimental results show that X-ray intensities for the Ar hollow atom decrease with increase of incidence energy, and L beta X-ray intensities of target atom Zr increase with increasing incidence energy. K alpha X-ray yield per ion for Ar17+ was five orders of magnitude greater than that for Ar16+

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs

In the present work, the cross-over rates of methanol and ethanol, respectively, through Nafion(R)-115 membranes at different temperatures and different concentrations have been measured and compared. The changes of Nafion(R)-115 membrane porosity in the presence of methanol or ethanol aqueous solutions were also determined by weighing vacuum-dried and alcohol solution-equilibrated membranes. The techniques of anode polarization and adsorption stripping voltarnmetry were applied to compare the electrochemical activity and adsorption ability, respectively. To investigate the consequences of methanol and ethanol permeation from the anode to the cathode on the performance of direct alcohol fuel cells (DAFCs), single DAFC tests, with methanol or ethanol as the fuel, have been carried out and the corresponding anode and cathode polarizations versus dynamic hydrogen electrode (DHE) were also performed. The effect of alcohol concentration on the performance of PtRu/C anode-based DAFCs was investigated.

Characterization of saccharides and phenolic acids in the Chinese herb Tanshen by ESI-FT-ICR-MS and HPLC

This study sought to determine the main components (saccharides and phenolic acids) in crude extract of the Chinese herb Tanshen by electrospray ionization Fourier transform ion cyclotron resonant mass spectrometry (ESI-FT-ICR-MS) in negative-ion mode. Eleven compounds were identified as phenolic acids by exact mass measurement and further confirmed by sustained off-resonance irradiation (SORI) CID data. In addition, monosaccharicles and oligosaccharides (n = 2 similar to 5) and a serial of corresponding anionic adducts of saccharide were observed without adding any anions additionally to the extract solution, and the anionic components were unambiguously identified as H2O, HCl, HCOOH, HNO3, C3H6O2, H2SO4 and C5H7NO3 according to the exact mass measurement results.

Selective synthesis of hexagonal and monoclinic LaPO4:Eu3+ nanorods by a hydrothermal method

The hexagonal and monoclinic LaPO4:Eu3+ nanorods can be selectively synthesized through a simple hydrothermal method by only adjusting the reaction temperature. Hexagonal and monoclinic LaPO4:Eu3+ nanorods can be prepared at 120 and 180 degrees C, respectively. The phase conversion of LaPO4:Eu3+ under different temperatures is investigated in detail. Moreover, the influence of the temperature on the intensity and the shift of the peaks of the excitation and emission spectra is discussed, and the decay lifetime of the Eu3+ ions of the sample obtained at different temperature also have been investigated in this paper.

Mechanism on flame retardancy of polystyrene/clay composites-The effect of surfactants and aggregate state of organoclay

Effects of organically modified montmorillonites (OMMTs) with different type and amount of modifiers on flame retardancy of polystyrene (PS) have been studied. The results from morphology analysis, gas chromatography-mass spectrometry and cone calorimeter have showed different mechanisms for the flame retardancy of PS/OMMTs composites, depending on surface property of OMNTrs. One is the catalysis of acid sites formed on the surface of octadecylammonium modified MMT (c-MMT) via Hoffman decomposition on the carbonization of degradation products, which promotes the formation of clay-enriched char barrier.