The growth and characterization of GaN grown on an Al2O3 coated (001)Si substrate by metalorganic vapor phase epitaxy

Single crystal GaN films have been grown on to an Al2O3 coated (001)Si substrate in a horizontal-type low-pressure MOVPE system. A thin Al2O3 layer is an intermediate layer for the growth of single crystal GaN on to Si although it is only an oriented polycrystal him as shown by reflection high electron diffraction. Moreover, the oxide was not yet converted to a fully single crystal film, even at the stage of high temperature for the GaN overlayer as studied by transmission electron microscopy. Double crystal X-ray diffraction showed that the linewidth of (0002) peak of the X-ray rocking curve of the 1.3 mu m sample was 54 arcmin and the films had heavy mosaic structures. A near band edge peaking at 3.4 eV at room temperature was observed by photoluminescence spectroscopy. (C) 1998 Elsevier Science B.V. All rights reserved.

Characterization of GaSb substrate wafers for MOCVD III-V antimonides

The qualities of GaSb substrates commonly used for the preparation of III-V antimonide epilayers were studied before and after growing GaInAsSb multi-layers by MOCVD using PL, FTIR and DCXD together with the electrical properties and EPD value. The correlation between the substrate qualities and epilayer properties was briefly discussed. The good property epilayers of GaInAsSb and, then, the high preformance of 2.3 um photodetectors were achieved only using the good quality GaSb wafers as the substrates.

The influence of substrate nucleation on HVPE-grown GaN thick films - art. no. 684105

Thick GaN films were grown on sapphire in a home-made vertical HVPE reactor. Effect of nucleation treatments on the properties of GaN films was investigated, including the nitridation of sapphire, low temperature GaN buffer and MOCVD-template. Various material characterization techniques, including AFM, SEM, XRD, CL and PL have been used to assess these GaN epitaxial films. It was found that the surface of sapphire after high temperature nitridation was flat and showed high density nucleation centers. In addition, smooth Ga-polarity surface of epitaxial layer can be obtained on the nitridation sapphire placed in air for several days due to polarity inversion. This may be caused by the atoms re-arrangement because of oxidation. The roughness of N-polarity film was caused by the huge inverted taper domains, which can penetrate up to the surface. The low temperature GaN buffer gown at 650 degrees C is favorable for subsequent epitaxial film, which had narrow FWHM of 307 arcsec. The epitaxial growth on MOCVD-template directly came into quasi-2D growth mode due to enough nucleation centers, and high quality GaN films were acquired with the values of the FWHM of 141 arcsec for (002) reflections. After etching in boiled KOH, that the total etch-pit density was only 5 x 106 cm(-2) illustrated high quality of the thick film on template. The photoluminescence spectrum of GaN film on the MOCVD-template showed the narrowest line-width of the band edge emission in comparison with other two growth modes.

High-brightness GaN-based blue LEDs grown on a wet-patterned sapphire substrate - art. no. 68410T

Patterning sapphire substrate can relax the stress in the nitride epilayer, reduce the threading dislocation density, and significantly improve device performance. In this article, a wet-etching method for sapphire substrate is developed. The effect of substrate surface topographies on the quality of the GaN epilayers and corresponding device performance are investigated. The GaN epilayers grown on the wet-patterned sapphire substrates by MOCVD are characterized by means of scanning electrical microscopy (SEM), atomic force microscopy (AFM), high-resolution x-ray diffraction (HRXRD), and photoluminescence (PL) techniques. In comparison with the planar sapphire substrate, about a 22% increase in device performance with light output power of 13.31 mW@20mA is measured for the InGaN/GaN blue LEDs grown on the wet-patterned sapphire substrate.

Heteroepitaxial Growth of 3C-SiC on Si (111) Substrate using AlN as a Buffer Layer

Using AlN as a buffer layer, 3C-SiC film has been grown on Si substrate by low pressure chemical vapor deposition (LPCVD). Firstly growth of AlN thin films on Si substrates under varied V/III ratios at 1100 degrees was investigated and the (002) preferred orientational growth with good crystallinity was obtained at the V/III ratio of 10000. Annealing at 1300 degrees C indicated the surface morphology and crystallinity stability of AlN film. Secondly the 3C-SiC film was grown on Si substrate with AlN buffer layer. Compared to that without AlN buffer layer, the crystal quality of the 3C-SiC film was improved on the AlN/Si substrate, characterized by X-ray diffraction (XRD) and Raman measurements.

GROWTH OF HIGH-QUALITY GALLIUM-ARSENIDE ON HF-ETCHED SILICON (001) BY CHEMICAL BEAM EPITAXY

HF etching followed by relatively low temperature (almost-equal-to 600-degrees-C) pretreatment is shown to provide a suitable substrate for the heteroepitaxial growth of GaAs on Si(100) by CBE using TEGa and AsH3 as sources. Rutherford backscattering (RBS), photoluminescence (PL), transmission electron microscopy (TEM), and Raman measurements show the low-defect nature of the GaAs epilayer.

Dielectric properties of Bi2Ti2O7 films grown on Si(100) substrate by APMOCVD

The growth of Bi2Ti2O7 films with (111) orientation on Si(100) substrate by atmospheric pressure metal-organic chemical vapor deposition(APMOCVD) technique at 480similar to550 degreesC is presented. The films were characterized by X-ray diffraction analysis, atomic force microscopy and electron diffraction. The results show high quality Bi2Ti2O7 films with smooth shinning surface. The dielectric properties and C-V characterization of the films were studied. The dielectric constant (epsilon) and loss tangent (tgdelta) were found to be 180 and 0.01 respectively. The charge storage density was 31.9fC/mum(2). The resistivity is higher than 1x10(12) Omega. .cm under the applied voltage of 5V. The Bi2Ti2O7 films are suitable to be used as a new insulating gate material in dynamic random access memory (DRAM).

High-quality metamorphic HEMT grown on GaAs substrates by MBE

Metamorphic high electron mobility transistor (M-HEMT) structures have been grown on GaAs substrates by molecular beam epitaxy (MBE). Linearly graded and the step-graded InGaAs and InAlAs buffet layers hal e been compared, and TEM, PL and low-temperature Hall have been used to analyze the properties of the buffer layers and the M-HEMT structure. For a single-delta-doped M-HEMT structure with an In0.53Ga0.47As channel layer and a 0.8 mum step-graded InAlAs buffer layer, room-temperature mobility of 9000 cm(2)/V s and a sheet electron density as high as 3.6 x 10(12)/cm(2) are obtained. These results are nearly equivalent to those obtained for the same structure grown on an InP substrate. A basic M-HEMT device with 1 mum gate was fabricated, and g(m) is larger than 400 mS/mm. (C) 2001 Elsevier Science B.V. All rights reserved.

Characterization of GaSb substrate wafers for MOCVD III-V antimonides

The qualities of GaSb substrates commonly used for the preparation of III-V antimonide epilayers were studied before and after growing GaInAsSb multi-layers by MOCVD using PL, FTIR and DCXD together with the electrical properties and EPD value. The correlation between the substrate qualities and epilayer properties was briefly discussed. The good property epilayers of GaInAsSb and, then, the high preformance of 2.3 um photodetectors were achieved only using the good quality GaSb wafers as the substrates.

Effect of substrate and annealing on the structural and optical properties of ZnO:Al films

ZnO:Al thin films with c-axis preferred orientation were deposited on glass and Si substrates using RF magnetron sputtering technique. The effect of substrate on the structural and optical properties of ZnO:Al films were investigated. The results showed a strong blue peak from glass-substrate ZnO:Al film whose intensity became weak when deposited on Si substrate. However, the full width at half maxima (FWHM) of the Si-substrate ZnO:Al (0 0 2) peaks decreased evidently and the grain size increased. Finally, we discussed the influence of annealing temperature on the structural and optical properties of Si-substrate ZnO:Al films. After annealing, the crystal quality of Si-substrate ZnO:Al thin films was markedly improved and the intensity of blue peak (similar to 445 nm) increased noticeably. This observation may indicate that the visible emission properties of the ZnO:Al films are dependent more on the film crystallinity than on the film stoichiometry. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

Fabrication of core-shell Au-Pt nanoparticle film and its potential application as catalysis and SERS substrate

In this paper we report the rational design and fabrication of high-quality core-shell Au-Pt nanoparticle film. Such film shows highly efficient catalytic properties and excellent surface-enhanced Raman scattering (SERS) ability.

Quality control autophagy: a joint effort of ubiquitin, protein deacetylase and actin cytoskeleton.

Autophagy has been predominantly studied as a nonselective self-digestion process that recycles macromolecules and produces energy in response to starvation. However, autophagy independent of nutrient status has long been known to exist. Recent evidence suggests that this form of autophagy enforces intracellular quality control by selectively disposing of aberrant protein aggregates and damaged organelles--common denominators in various forms of neurodegenerative diseases. By definition, this form of autophagy, termed quality-control (QC) autophagy, must be different from nutrient-regulated autophagy in substrate selectivity, regulation and function. We have recently identified the ubiquitin-binding deacetylase, HDAC6, as a key component that establishes QC. HDAC6 is not required for autophagy activation per se; rather, it is recruited to ubiquitinated autophagic substrates where it stimulates autophagosome-lysosome fusion by promoting F-actin remodeling in a cortactin-dependent manner. Remarkably, HDAC6 and cortactin are dispensable for starvation-induced autophagy. These findings reveal that autophagosomes associated with QC are molecularly and biochemically distinct from those associated with starvation autophagy, thereby providing a new molecular framework to understand the emerging complexity of autophagy and therapeutic potential of this unique machinery.

In situ synthesis of DNA microarray on functionalized cyclic olefin copolymer substrate.

Thermoplastic materials such as cyclic-olefin copolymers (COC) provide a versatile and cost-effective alternative to the traditional glass or silicon substrate for rapid prototyping and industrial scale fabrication of microdevices. To extend the utility of COC as an effective microarray substrate, we developed a new method that enabled for the first time in situ synthesis of DNA oligonucleotide microarrays on the COC substrate. To achieve high-quality DNA synthesis, a SiO(2) thin film array was prepatterned on the inert and hydrophobic COC surface using RF sputtering technique. The subsequent in situ DNA synthesis was confined to the surface of the prepatterned hydrophilic SiO(2) thin film features by precision delivery of the phosphoramidite chemistry using an inkjet DNA synthesizer. The in situ SiO(2)-COC DNA microarray demonstrated superior quality and stability in hybridization assays and thermal cycling reactions. Furthermore, we demonstrate that pools of high-quality mixed-oligos could be cleaved off the SiO(2)-COC microarrays and used directly for construction of DNA origami nanostructures. It is believed that this method will not only enable synthesis of high-quality and low-cost COC DNA microarrays but also provide a basis for further development of integrated microfluidics microarrays for a broad range of bioanalytical and biofabrication applications.

Quality factor assessment of subwavelength resonant cavities at FIR frequencies

Subwavelength resonators at FIR are presented and studied. The structures consist of 1D cavities formed between a metallized (silver) surface and a metamaterial surface comprising a periodic array of silver patches on a silver-backed silicon substrate. The concept derives from recent discoveries of artificial magnetic conductors (AMC). By studying the currents excited on the metamaterial surface by a normally incident plane wave, the nature of the emerging resonant phenomena and the physical mechanism underlying the AMC operation are investigated. Full wave simulations, based on finite element method and time-domain transmission line modelling technique, have been carried out to demonstrate the effective AMC boundary condition and prove the possibilities for subwavelength cavities. The quality factor of the resonant cavities is assessed as a function of the cavity profile. It is demonstrated that the quality factor drops to about 1/8 of the half-wavelength value for lambda/8 resonant cavity.

Controls on the contemporary distribution of lake thecamoebians (testate amoebae) in the Greater Toronto Area and their potential as water quality indicators.

Thecamoebians were examined from 71 surface sediment samples collected from 21 lakes and ponds in the Greater Toronto Area to (1) elucidate the controls on faunal distribution in modern lake environments; and (2) to consider the utility of thecamoebians in quantitative studies of water quality change. This area was chosen because it includes a high density of kettle and other lakes which are threatened by urban development and where water quality has deteriorated locally as a result of contaminant inputs, particularly nutrients. Fifty-eight samples yielded statistically significant thecamoebian populations. The most diverse faunas (highest Shannon Diversity Index values) were recorded in lakes beyond the limits of urban development, although the faunas of all lakes showed signs of sub-optimal conditions. The assemblages were divided into five clusters using Q-mode cluster analysis, supported by Detrended Correspondence Analysis. Canonical Correspondence Analysis (CCA) was used to examine species-environment relationships and to explain the observed clusterings. Twenty-four measured environmental variables were considered, including water property attributes (e.g., pH, conductivity, dissolved oxygen), substrate characteristics, sediment-based phosphorus (Olsen P) and 11 environmentally available metals. The thecamoebian assemblages showed a strong association with phosphorus, reflecting the eutrophic status of many of the lakes, and locally to elevated conductivity measurements, which appear to reflect road salt inputs associated with winter de-icing operations. Substrate characteristics, total organic carbon and metal contaminants (particularly Cu and Mg) also influenced the faunas of some samples. A series of partial CCAs show that of the measured variables, sedimentary phosphorus has the largest influence on assemblage distribution, explaining 6.98% (P < 0.002) of the total variance. A transfer function was developed for sedimentary phosphorus (Olsen P) using 58 samples from 15 of the studied lakes. The best performing model was based on weighted averaging with inverse deshrinking (WA Inv, r jack 2= 0.33, RMSEP = 102.65 ppm). This model was applied to a small modern thecamoebian dataset from a eutrophic lake in northern Ontario to predict phosphorus and performed satisfactorily. This preliminary study confirms that thecamoebians have considerable potential as quantitative water quality indicators in urbanising regions, particularly in areas influenced by nutrient inputs and road salts.