Polarity determination for GaN thin films by electron energy-loss spectroscopy

The intensity of the N K edge in electron energy-loss spectra from a GaN thin film shows a pronounced difference when the orientation of the film approaches the (0002) and (000-2) Bragg reflections, along the polar direction. This experimental result can be interpreted by the effect associated with interference between the Bloch waves of the incident electron in the GaN crystal. The theoretical calculations indicate that, at the Bragg condition of g=0002 along the Ga-N bond direction, the thickness-averaged electron current density on the N atom plane is much higher than that at g=000 (2) over bar, with a maximum as the specimen thickness is about 0.4xi(0002) (the two-beam extinction distance). The delocalization effect on the experimental spectra is also discussed. (C) 2002 American Institute of Physics.

Improvement of the photoluminescence from gallium nitride layers grown by MBE with an additional incident indium flux

The effect of using an indium flux during the MBE growth of GaN layers was investigated. The properties of these layers were studied using electron probe microanalysis, secondary ion mass spectroscopy, photoluminescence and cathodoluminescence. The optical properties of the GaN layers are shown to improve as compared with undoped GaN layers grown under nominally the same conditions but without an additional indium flux.

QUANTITATIVE-ANALYSIS OF INXGA1-XAS BY AUGER-ELECTRON SPECTROSCOPY

Quantitative Auger electron spectroscopy analysis for the ternary system InGa1-xAs grown by molecular-beam epitaxy has been studied. The relative sensitivity factors are determined by with an internal reference element. The matrix correction factor for In relative to Ga was shown to be 1.08. No preferential sputtering of As for the ternary compounds was found, and the sputter correction factor, K(s)InGa is 0.75. The results are compared with that measured by the x-ray double-crystal diffraction analysis, electron probe microanalysis, and Auger analysis without matrix and sputter corrections.

LIQUID-PHASE EPITAXY GROWTH AND PROPERTIES OF GAINASSB/ALGAASSB/GASB HETEROSTRUCTURES

The GaInAsSb/AlGaAsSb/GaSb heterostructures were grown by the liquid phase epitaxy (LPE) technique. The materials were characterized by means of optical microscopy, electroprobe microanalysis (EPMA), double-crystal X-ray diffraction, capacitance-voltage (C-V) and Van der Pauw measurments, infrared absorption spectra, photoluminescence and laser Raman scattering. The results show that the materials have fine surface morphology, low lattice mismatch and good homogeneity. Room-temperature light-emitting diodes with an emission wavelength of 2.2-mu-m were obtained by using the GaInAsSb/AlGaAsSb DH structures.

Wear mechanism map of uncoated HSS tools during drilling die-cast magnesium alloy

A wear mechanism map of uncoated high-speed steel (HSS) tools was constructed under the conditions of dry-drilling die-cast magnesium alloys. Three wear mechanisms appear in the map based on the microanalysis of drilled HSS tools by SEM, including adhesive wear, abrasive wear and diffusion wear. In the map, there exists a minor wear region which is called "safety zone". This wear mechanism map will be a good reference for choosing suitable drilling parameters when drilling die-cast magnesium alloys.

ELECTROCHEMICAL FORMATION OF NI-Y INTERMETALLIC COMPOUND LAYER IN MOLTEN CHLORIDE

The reduction of Y(III) ions in molten chloride is known to be a one-step three electron reaction [1, 2, 3], but a voltammogram of YCl3 in molten LiCl-KCl-NaCl at a nickel electrode shows at least two reduction peaks of Y(III) ions, indicating the possibility of formation of Ni-Y intermetallic compounds. Using a galvanostatic electrolysis method, samples were prepared at several current densities at 450, 500, 600 and 700-degrees-C, respectively, and were identified with X-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods. The results show that Ni2Y, Ni2Y3 and NiY can be produced by electrolysis and Ni2Y is found to be the predominant Ni-Y intermetallic compound under the experimental conditions. Nickel appears to diffuse in Ni2Y faster than yttrium, and the diffusion process is the rate determining step during Ni2Y formation.

Effect of sulfate-reducing bacteria on corrosion behavior of mild steel in sea mud

Microbiologically influenced corrosion (MIC) is very severe corrosion for constructions buried under sea mud environment. Therefore it is of great importance to carry out the investigation of the corrosion behavior of marine steel in sea mud. In this paper, the effect of sulfate-reducing bacteria (SRB) on corrosion behavior of mild steel in sea mud was studied by weight loss, dual-compartment cell, electronic probe microanalysis (EPMA), transmission electron microscopy (TEM).combined with energy dispersive X-ray analysis (EDX) and electrochemical impedance spectroscopy (EIS). The results showed that corrosion rate and galvanic current were influenced by the metabolic activity of SRB. In the environment of sea mud containing SRB, the original corrosion products, ferric (oxyhydr) oxide, transformed to iron sulfide. With the excess of the dissolved H2S, the composition of the protective layer formed of FeS transformed to FeS2 or other non-stoichiometric polysulphide, which changed the state of the former layer and accelerated the corrosion process.