Coating Gd2O3 : Eu phosphors with silica by solid-state reaction at room temperature

Silica coating on Gd2O3:Eu particles was obtained by a simple method, e.g. solid-state reaction at room temperature. The urea homogeneous precipitation method was used to synthesize the Gd2O3:Eu cores. Transmission electron microscopy (TEM) shows that the core particles are spherical with submicrometer size which is the soft agglomerates with nanometer crystallites. The TEM morphology of coated particles shows that a thin film is coated on the surface of Gd2O3:Eu cores. Scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analysis indicate that the coating of silica can be used to avoid agglomeration of Gd2O3:Eu particles to obtain smaller particles. X-ray photoelectron spectra (XPS) show that silica is coated on the surface of core particles by forming the chemical bond. Photoluminescence (PL) spectra conform that Gd2O3:Eu phosphors remain well-luminescent properties by the silica coating.

Coating nano-hemalite on (Y,Gd)BO3 : Eu3+ phosphors by a facile method

(Y, Gd) BO3:Eu3+ particles coated with nano-hematite were prepared by a facile method I for example (humid) solid phase reaction at room temperature. The resulted hematite-coated (Y, Gd)BO3:Eu3+ particles were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and photoluminescence spectra (PL). The SEM and EDS analyses indicate that the particles are coated with a very thin layer of iron oxide. XPS results further confirmed that the coating was hematite, and the coating thickness was in nanometer range. XRD patterns showed that either the hematite coating was too thin or the content of hematite was too small, so that the XRD cannot detect it. The emission spectra illustrate that the peak near 580 nm disappears due to the coating of iron oxide, and when the coating is very thin, the ratio of D-5(0)-> F-7(2) to D-5(2)-> F-7(1) of coated particles is higher than that of uncoated ones, which indicates that the color purity of the phosphor is increased by coating nano-hematite.

Properties of high k gate dielectric gadolinium oxide deposited on Si(100) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.

Properties of high k gate dielectric gadolinium oxide deposited on Si(100) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.

The fabrication of self-aligned InAs nanostructures on GaAs(331)A substrates

Self-aligned InAs quantum wires (QWRs) or three-dimensional (3D) islands are fabricated on GaAs(331)A substrates by molecular beam epitaxy (MBE). InAs QWRs are selectively grown on the step edges formed by GaAs layers. The surface morphology of InAs nanostructures is carefully investigated by atomic force microscopy (AFM) measurements. Different growth conditions, such as substrate temperature, growth approaches, and InAs coverage, exert a great effect on the morphology of InAs islands. Low substrate temperatures favour the formation of wirelike nanostructures, while high substrate temperatures favour 3D islands. The shape transition is attributed to the trade-off between surface energy and strain energy. A qualitative agreement of our experimental data with the theoretical results derived from the model proposed by Tersoff and Tromp is achieved.

Effects of rapid thermal annealing on the emission properties of highly uniform self-assembled InAs/GaAs quantum dots emitting at 1.3 mu m

The authors report the effects of rapid thermal annealing (RTA) on the emission properties of highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3 mu m grown on GaAs substrate by metal organic chemical vapor deposition. Postgrowth RTA experiments were performed under N-2 flow at temperatures ranging from 600 to 900 degrees C for 30 s using GaAs proximity capping. Surprisingly, in spite of the capping, large blueshifts in the emission peak (up to about 380 meV at 850 degrees C) were observed (even at low annealing temperatures) along with enhanced integrated photoluminescence (PL) intensities. Moreover, pronounced peak broadenings occurred at low annealing temperatures (< 700 degrees C), indicating that RTA does not always cause peak narrowing, as is typically observed with traditional QDs with large inhomogeneous PL linewidths. The mechanism behind the large peak blueshift was studied and found to be attributed to the as-grown QDs with large size, which cause a larger dot-barrier interface and greater strain in and near the QD regions, thereby greatly promoting Ga-In intermixing across the interface during RTA. The results reported here demonstrate that it is possible to significantly shift the emission peak of the QDs by RTA without any additional procedures, even at lower annealing temperatures. (c) 2007 American Institute of Physics.

A comparison between AlN films grown by MOCVD using dimethylethylamine alane and trimethylaluminium as the aluminium precursors

Aluminium nitride (AlN) films grown with dimethylethylamine alane (DMEAA) are compared with the ones grown with trimethylaluminium (TMA). In the high-resolution x-ray diffraction Omega scans, the full width at half maximum (FWHM) of (0002) AlN films grown with DMEAA is about 0.70 deg, while the FWHM of (0002) AlN films grown with TMA is only 0.11 deg. The surface morphologies of the films are different, and the rms roughnesses of the surface are approximately identical. The rms roughness of AlN films grown with DMEAA is 47.4 nm, and grown with TMA is 69.4 nn. Although using DMEAA as the aluminium precursor cannot improve the AlN crystal quality, AlN growth can be reached at low temperature of 673 K. Thus, DMEAA is an alternative aluminium precursor to deposit AlN film at low growth temperatures.

Study on Er3+ emission from the erbium-doped hydrogenated amorphous silicon suboxide film

The erbium-doped hydrogenated amorphous silicon suboxide films containing amorphous silicon clusters were prepared. The samples exhibited photoluminescence peaks at around 750 nm and 1.54 mum, which could be assigned to the electron-hole recombination in amorphous silicon clusters and the intra-4f transition in Er3+, respectively. Correlations between the intensities of these two photoluminescence peaks and oxidation and dehydrogenation of the films during annealing were studied. It was found that the oxidation is triggered by dehydrogenation of the films even at low annealing temperatures, which decisively changes the intensities of the two photoluminescence peaks. On the other hand, the increase of Er content in the erbium-doped hydrogenated amorphous silicon suboxide film will enhance Er3+ emission at 1.54 mum, while quench amorphous silicon cluster emission at 750 nm, such a competitive relationship, was also observed in the erbium-doped silicon nanocrystals embedded in SiO2 matrix. Moreover, we found that Er3+ emission is not sensitive to whether silicon clusters are crystalline or amorphous. The amorphous silicon clusters can be as sensitizer on Er3+ emission as that of silicon nanocrystals. (C) 2003 American Institute of Physics.

Effect of rapid thermal annealing on InGaAs/GaAs quantum wells

We have studied the effect of rapid thermal annealing (RTA) on highly strained InGaAs/GaAs quantum wells by using photoluminescence (PL) and double-crystal X-ray diffraction (DCXRD) measurements. It is found that a distinct additional PL emission peak can be observed for the annealed samples. This PL emission possesses features similar to the PL emission from InGaAs/GaAs quantum dots (QDs) with the same indium content. It is proposed that this emission stems from QDs, which were formed during the annealing process. This formation is attributed to the favorable diffusion due to the inhomogeneous strain distribution in the InGaAs layer intersurface. The DCXRD measurements also confirm that the dominant relaxation is strain enhanced diffusion under the low annealing temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.

Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with beta-Phase Nucleating Agent

The microstructure and mechanical properties of beta-nucleated iPP before and after being annealed at different temperatures (90-160 degrees C) have been analyzed, Annealing induced different degrees of variation in fracture toughness of beta-nucleated iPP samples. namely, slight enhancement at relatively low annealing temperatures (< 110 degrees C) and great improvement at moderate temperatures (120-130 degrees C), whereas dramatic deterioration at relatively high temperatures ( > 140 degrees C) has been observed. The variation of fracture toughness of beta-nucleated iPP is observed to be dependent on the content of beta-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the beta-nucleated iPP after being annealed.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone). V: Estimation of temperature distribution during cure process

A numerical method to estimate temperature distribution during the cure of epoxy-terminated poly(phenylene ether ketone) (E-PEK)-based composite is suggested. The effect of the temperature distribution on the selection of cure cycle is evaluated using a suggested alternation criterion. The effect of varying heating rate and thickness on the temperature distribution, viscosity distribution and distribution of the extent of cure reaction are discussed based on the combination of the here-established temperature distribution model and the previously established curing kinetics model and chemorheological model. It is found that, for a thin composite (<=10mm) and low heating rate (<=2.5K/min), the effect of temperature distribution on cure cycle and on the processing window for pressure application can be neglected. Low heating rate is of benefit to reduce the temperature gradient. The processing window for pressure application becomes narrower with increasing thicknesses of composite sheets. The validity of the temperature distribution model and the modified processing window is evaluated through the characterization of mechanical and physical properties of E-PEK-based composite fabricated according to different temperature distribution conditions.

CHARACTERIZATION OF BLENDS OF POLYPROPYLENE WITH A SEMIRIGID LIQUID-CRYSTAL COPOLYESTER

Blends with a liquid-crystal polymers (LCP) as one component show, in general, very interesting properties. Reduction of shear visocity and improvement of mechanical properties are very remarkable. High melting temperatures and high costs of the LCP limit the use of these blends. A new class of thermotropic LCPs with flexible spaces, with relatively low melting temperatures, can overcome the first problem. In this work, rheological and mechanical properties of blends of polypropylene with low contents of this LCP are presented. Torque during extrusion and viscosity decrease with LCP content. Elastic modulus is remarkably increased when the LCP phase is oriented.

西秦岭新生代火山岩中的地幔捕虏体和捕虏晶研究

Western Qinling, a conjunction region of the North China Craton, the Yangtze Craton and the Tibetan Plateau, has very complicated history of geologic and tectonic evolution. Previous studies mainly focus on tectonics and petrology of volcanic rocks in the western Qinling. Therefore, little is known about the Cenozoic lithospheric mantle beneath the western Qinling. Mafic, ultramafic and/or alkaline volcanic rocks and their entrained mantle peridotitic xenoliths and xenocrysts are known as samples directly from the lithospheric mantle. Their petrological and geochemical characteristics can reflect the nature and deep processes of the lithospheric mantle. Cenozoic volcanic rocks in the western Qinling contain abundant mantle xenoliths and xenocrysts, which provide us an opportunity to probe the lithospheric mantle beneath this region and a new dimension to insight into geologic evolution. Cenozoic volcanic rocks (7-23 Ma) from the western Qinling are sparsely distributed in the Lixian-Dangchang-Xihe Counties, Gansu Province, China. Volcanic rocks contain plenty of mantle-derived xenoliths, including spinel lherzolites with subordinate wehrlite, dunite, olivine websterite, clinopyroxenite and garnet lherzolite, and few olivine, clinopyroxene and spinel xenocrysts. These peridotitic xenoliths show clear deformed textures and their major minerals show excellent orientation. Thus, these peridotites are typical deformed peridotites. Olivine xenocrysts have clearly-zoned textures. The peridotitic xenoliths can be divided into two groups based on their compositions, namely, the H-type and L-type. The H-type peridotites are characterized by high Fo (>90) in olivines in which fine-grained ones have higher Fo than the coarse grains, low CaO (<20 %) in clinopyroxenes, high Cr# (>40) in spinels and high equilibration temperatures. They may represent the refractory lithospheric mantle. In contrast, the L-type peridotites contain low Fo (<90) olivines (with lower Fo in fine-grained olivines), high CaO (>20 %) clinopyroxenes, low Cr# (<20) spinels and low equilibration temperatures. They experienced low degree of partial melting. The Cenozoic lithospheric mantle beneath the western Qinling was refractory in major element compositions based on the mineral compositions of xenoliths and xenocrysts and experienced complicated deep processes. The lithospheric mantle was modified by shear deformation due to the diapirism of asthenosphere and strong tectonic movements including the collision between North China Craton and Yangze Craton and the uplift of Tibetan Plateau, and then underwent metasomatism with a hydrous, Na, Ti and Cr enriched melt.

塔里木盆地塔北、塔中地区早古生代白云岩形成机理

In Tarim Basin, extensive carbonates of Lower Paleozoic occur, in which thick Cambrian and Lower Ordovician dolostones are widespread and show a potential perspective in hydrocarbon exploration. So they are viewed as an important target for exploration. Tarim Basin is a poly phase composite basin, which underwent multiphase tectonic modification and volcanic activities; these exerted significant influences on the basin-fills and basin fluid evolution, thereby the diagenetic history, particularly on the deep-buried Lower Paleozoic dolostones. Referring to the classification of dolomite texture proposed by Gregg & Sibley (1984) and Sibley & Gregg (1987). In view of crystal size, crystal shape, crystal surface and contact relation, eight genetic textures of dolomite crystals are identified, based on careful petrographic examinatoins. These textures include: 1) micritic dolomite; 2) relict mimetic dolomite; 3)finely crystalline, planar-e(s), floating dolomite; 4)finely crystalline, planar-e(s) dolomite; 5) finely-coarse crystalline, nonplanar-a dolomite; 6)coarse crystalline, nonplanar saddle dolomite; 7) finely-medium crystalline, planar-e(s) dolomite cement; 8) coarse crystalline, nonplanar saddle dolomite cement, in which the former six textures occurs as in matrix, the latter two in the cements. Detailed geochemistry analysis is carried out on the basis of genetic textures of dolomite and related minerals such as quartz and calcite. The result showed that the calcite has the highest average content in Sr, which can be sorted into two groups; micritic dolomite has the highest average content in Sr among all kinds of dolomites; the REE patterns of all kinds of dolomites is similar to those of marine limestone samples. Saddle dolomite cement has δ13C values from -2.44‰ to 1.27‰ PDB, and δ18O values from -13.01‰ to -5.12‰ PDB, which partially overlap with those of matrix dolomite (δ13C values from -2.83‰ to 2.01‰ PDB, δ18O values from -10.63‰ to -0.85‰ PDB). Saddle dolomite cement has 87Sr/86Sr ratios from 0.7086 to 0.7104, which totally overlap with those of matrix dolomite (0.7084 ~ 0.7116). Compared with saddle dolomite derived from other basins all over the world, the saddle dolomites of Tarim Basin have similar δ13C, δ18O and 87Sr/86Sr ratios values with those of matrix dolomite. This scenario reflects the unusual geological setting and special dolomitizing liquid of Tarim Basin. The values of δ18O, δ13C and 87Sr/86Sr ratios of calcite also can be sorted out two groups, which may been resulted from the one stage of extensive uplift of Tarim Basin from Mesozoic to Cenozoic. Fluid inclusion microthermometry data of the diagenetic mineral indicates that matrix dolomite has relatively low homogenization temperatures (Th) of 80～105oC and salinities of 12.3％ (wt% NaCl equivalent); saddle dolomite has highest Th values, which concentrate in 120～160oC and salinities of 13.5～23.7％ (wt% NaCl equivalent); quartz has relatively low Th of 135～155oC and salinities of 17.8～22.5％ (wt% NaCl equivalent); calcite has relatively low Th of 121～159.5oC and salinities of 1.4～17.5％ (wt% NaCl equivalent). These data suggest that the saddle dolomites could have formed in thermal brine fluids. Based on comprehensive petrographical study, detailed geochemistry and fluid inclusion microthermometry analysis on Lower Paleozoic dolomite of Tarim Basin, three types of dolomitisation mechanism are proposed: Penecontemporaneous dolomitisation (Sabkha dolomitisation & Reflux dolomitisation); Burial dolomitisation (shallow-intermediate burial dolomitisation & Deep burial dolomitisation ); Hydrothermal cannibalized dolomitisation. In view of host-specified occurrences of hydrothermal dolomite, the low abundance of saddle dolomite and high geochemical similarities between saddle dolomite and host dolomite, as well as highest Th and high salinities , the hydrothermal dolomite in Tarim Basin is thus unique, which could have been precipitated in modified fluid in the host dolomite through intraformational thermal fluid cannibalization of Mg ions from the host. This scenario is different from the cases that large scale dolomitizing fluid migration took place along the fluid pathways where abundant saddle dolomite precipitated. Detailed observations on 180 petrographic and 60 casting thin sections show original pores in Lower Paleozoic dolomite were almost died out by complicated diagenetic process after a long time geologic evolution. On the other hand, deep-buried dolomite reservoirs is formed by tectonic and hydrothermal reforming on initial dolomites. Therefore, the distribution of structure-controlled hydrothermal dolomite reservoirs is predicted in Tabei and Tazhong Area of Tarim Basin based on the geophysical data.

Heating, current drive and confinement regimes with the JET ICRH and lhcd systems

During its 1990 operation, 2 large RF systems were available on JET. The Ion Cyclotron Resonance Heating (ICRH) system was equipped with new beryllium screens and with feedback matching systems. Specific impurities generated by ICRH were reduced to negligible levels even in the most stringent H-mode conditions. A maximum power of 22 MW was coupled to L-mode plasmas. High quality H-modes (tau-E greater-than-or-equal-to 2.5 tau-EG) were achieved using dipole phasing. A new high confinement mode was discovered. It combines the properties of the H-mode regime to the low central diffusivities obtained by pellet injection. A value of n(d) tau-E T(i) = 7.8 x 10(20) m-3 s keV was obtained in this mode with T(e) approximately T(i) approximately 11 keV. In the L-mode regime, a regime, a record (140 kW) D-He-3 fusion power was generated with 10 - 14 MW of ICRH at the He-3 cyclotron frequency. Experiments were performed with the prototype launcher of the Lower Hybrid Current Drive (LHCD) systems with coupled power up to 1.6 MW with current drive efficiencies up to < n(e) > R I(CD)/P = 0.4 x 10(20) m-2 A/W. Fast electrons are driven by LHCD to tail temperatures of 100 keV with a hollow radial profile. Paradoxically, LHCD induces central heating particularly in combination with ICRH. Finally we present the first observations of the synergistic acceleration of fast electrons by Transit Time Magnetic Pumping (TTMP) (from ICRH) and Electron Landau Damping (ELD) (from LHCD). The synergism generates TTMP current drive even without phasing the ICRH antennae.