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Dislocation-related conduction paths in n-type GaN grown by molecular-beam epitaxy and a mechanism for local suppression of current flow along these paths are analyzed using conductive atomic force microscopy, scanning Auger spectroscopy, and macroscopic current-voltage measurements. Application of an electric field at the GaN surface in an ambient atmospheric environment is shown to lead to local formation of gallium oxide in the immediate vicinity of the conduction paths, resulting in the strong suppression of subsequent current flow. Current-voltage measurements for Schottky diodes in which local conduction paths have been suppressed in this manner exhibit reverse-bias leakage currents reduced by two to four orders of magnitude compared to those in Schottky diodes not subjected to any surface modification process. These results demonstrate that the dislocation-related current leakage paths are the dominant source of leakage current in Schottky contacts to n-type GaN grown by molecular-beam epitaxy, and elucidate the nature of a microscopic process for their suppression. (C) 2003 American Institute of Physics.

This work demonstrates the growth of three-dimensional (3D) ZnO-framed La0.7Sr0.3MnO3 (LSMO)-ZnO heteroepitaxial thin films in a vertically aligned nanocomposite (VAN) form on SrTiO3 (STO) substrates. Such 3D framed structures are formed by interlayering pure ZnO layers in LSMO-ZnO VAN thin films to thus achieve a ZnO-framed nanocomposite structure. Tailoring the thickness of the ZnO interlayer enables fine-tuning of the overall strain state of the two phases and thus leads to the tuning of the physical properties, such as the metal-insulator transition temperature, and magnetotransport properties. The optimum thickness of the ZnO interlayer is determined to be ∼2 nm to obtain a maximum magnetoresistance of 31% by a combined strain tuning and magnetoresistance tunneling effect. This work demonstrates effective strain tuning using the 3D framed design and provides a comprehensive perspective on the strain- and property-tuning using 3D nanocomposite frameworks. [ABSTRACT FROM AUTHOR]

The electromagnetism and microwave absorption properties were investigated in the frequency range of 2–18 GHz for the nanocomposites NiCo-SWCNTs/CoFe2O4consisting of Ni-Co attached single-walled carbon nanotubes (NiCo-SWCNTs) and CoFe2O4 nanocrystals with different ingredient weight ratios. NiCo-SWCNTs were mass-produced by a direct current arc discharge in helium and CoFe2O4 was synthesized by a sol-gel method. Premium microwave absorption properties (mainly in Ku-band, i.e., 12–18 GHz) were obtained due to the appropriate combination of the complex permeability and permittivity resulting from the magnetic nanocrystals and high-crystalline NiCo-SWCNTs. The NiCo-SWCNTs/CoFe2O4nanocomposites with 15 wt.% NiCo-SWCNTs exhibited the best microwave absorption property, whose reflection loss (RL) value reached -47.9 dB at 14.7 GHz and the absorption bandwidth (RL < -10 dB) was up to 7.1 GHz (from 10.5 to 17.6 GHz) with a matching thickness of only 1.8 mm. Our results indicate that the studied nanocomposite could be used as a promising candidate for lightweight microwave absorption materials. [ABSTRACT FROM AUTHOR]

Various studies are conducted for examining the mechanisms involved in the GaSb molecular beam epitaxial growth on p-InP(001). The article also presents an analysis of the properties exhibited by the in situ deposited [Al.sub.2][O.sub.3] gate oxide.

The geometric and spin-resolved electronic structure of a graphene-adsorbed Ni(111) surface has been investigated by density functional theory (DFT) calculations without and with a semiempirical long-range dispersion correction (DFT-D). DFT calculations with generalized gradient approximation (GGA) functional cannot predict well about the adsorption properties of graphene to the Ni(111) surface. While DFT-D calculations with the same GGA functional give reasonable values of the adsorption energy and layer distance from graphene to the substrate. The geometry of top_fcc is the most energetically favorable in all geometries. Strong hybridization of graphene with the ferromagnetic Ni substrate induces significant shift partially in graphene π states towards the Fermi level yielding spin polarization. The spin polarization is positive at the shallow levels of modified π states and slightly negative at the deeper levels of fundamental π states, which is indicated by the calculated spin density distributions and plane-averaged density of states at the vacuum side. The opposite spin polarization is consistent with our experimental result of spin asymmetry obtained by spin-polarized metastable-atom de-excitation spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The adsorptions of Xe atoms on the Pd(111) and Cu(111) surfaces are investigated by first-principles calculations. The van der Waals interactions are considered in the optimization of the geometric structure. The equilibrium distance from the Xe atom to the topmost surface layer and the rumpling of the substrate are closer to the experimental data than by conventional calculations without including van der Waals interactions. The existence of the induced states, which are partially filled by electron back donation, is predicted by the calculated local density of states. The mechanism of the sublevel splitting of the 5p3/2 states is discussed. The differential electron densities are used to analyze the electron redistribution by the adsorption of Xe atoms. [ABSTRACT FROM AUTHOR]

We investigate the photoluminescence (PL) behavior of the porous silicon nanowire (PSiNW) arrays synthesized via metal-assisted electroless etching method on the n-Si (100) substrate. Two PL bands with different origins dependent on the post-chemical treatments were detected. The red emission band, the peak position of which is insensitive to temperature and excitation source, is considered to originate from the excitons localized at the interface between the Si nanostructure and the oxide layer. An anomalous blue shift of the near-infrared PL band was observed when the temperature increased from 80 to 290 K. The maximum intensity appears around 160 K and the emission energy is strongly dependent on the excitation energy and power. The triplet-singlet state transition is introduced to explain the PL behavior for this emission band. The absorption spectra are also induced to confirm the PL origins. [ABSTRACT FROM AUTHOR]

This paper deals with the influence of relative humidity on nano-scaled domain switching caused by the electric field of atomic force microscopy (AFM) in a LiNbO3 single crystal. Experimental results show that the switched domain size under AFM tip does not increase monotonously with relative humidity. The domain radius increases slightly in lower relative humidity conditions (< 40%), and decreases dramatically in higher relative humidity conditions (40-99%). The domain is not created under a relative humidity of 99%. Experiments on the AFM force-distance curve prove that there is a water bridge between the tip and the sample surface, whose size increases with the rise of humidity. The influence of water bridges on the effective electric field acting on the domain switching in the sample is discussed. [ABSTRACT FROM AUTHOR]

Bi3+-Ln3+ (Ln = Dy, Er, Ho, Eu, and Sm) co-doped YVO4 phosphors are proposed as UV-absorbing luminescent converter candidate to enhance the power conversion efficiency and photochemical stability of dye-sensitized solar cells (DSSCs). The phosphors can efficiently convert UV photons in a broad range from 250 to 400 nm into visible emissions, which can be absorbed by DSSCs. Efficient broadband down-conversion UV light into near-infrared emission around 1000 nm was achieved in the YVO4:Bi3+,Yb3+ phosphors. The energy transfer from V5+-Bi3+ charge-transfer state to Yb3+ was shown to be a cooperative down-conversion type by the luminescence spectra, energy transfer efficiency, and luminescence decay curves. The YVO4:Bi3+,Yb3+ phosphors are promising for boosting the efficiency of crystalline silicon solar cells by down-converting the UV part of the solar spectrum to near-infrared photons with a twofold increase in the photon number. This research may open up promising new perspectives for designing novel luminescent materials for photovoltaic cells with high efficiency. [ABSTRACT FROM AUTHOR]

Intriguing electronic and magnetic properties of boron nitride (BN) layer with noble metal (Pd, Pt, Ag and Au) doping are obtained by first-principles calculations. Adsorbed Pd (or Pt) reduces the bandgap of BN sheet owing to the induction of impurity states. The unpaired electrons in the Ag (or Au)-adsorbed and the Pd (or Pt)-substituted BN layers are polarized, and thus, exhibit a magnetic moment of 1.0 μB, leading to these BN configurations to be magnetic semiconductors. The half-metallic feature of the Ag-substituted BN layer, along with the delocalization of spin states, renders this configuration an excellent spin filter material. Thus, these findings offer a unique opportunity for developing BN-based nanoscale devices. [ABSTRACT FROM AUTHOR]

State-of-the-art green emission efficiency has been achieved with light-emitting diodes incorporating CdMgZnSe color-converting quantum well heterostructures, although dark line defects (DLDs) limit the device reliability. We have determined that misfit strain plays an important role in the formation of extended stacking faults (SFs) and DLDs in II-VI green converters. Even small strain causes SFs to extend to accommodate misfit strain and extended SFs further give rise to DLDs when they intersect active regions. Detailed strain relaxation mechanisms for both tensile and compressive strain have been investigated, which may apply for other semiconductor heterostructures with an fcc lattice. Careful control of the layer strain via close lattice matching prevents the extension of SFs and leads to DLD-free converters. [ABSTRACT FROM AUTHOR]

The current-voltage (I-V) properties along the c axis of stripe-ordered La1.6-xNd0.4SrxCuO4 (LNSCO, x=0.10, 0.12, 0.15, and 0.18) bulk single crystals are studied. For all the samples, the I-V curves exhibit Josephson junctionlike characteristics, the voltage jumps at some critical currents and clear hysteresis without multiple branches appears below the superconducting transition temperatures. With increasing Sr doping level, the characteristics of intrinsic Josephson junctions in LNSCO change from a superconductor-insulator-superconductor type to a superconductor-normal metal-superconductor one. The field dependence of critical current Ic exhibits a periodical perturbation with a large scale of magnetic field. A fourfold symmetry of the angular dependent Ic for the rotation of the CuO2 plane in magnetic fields confirms the vortex pinning effect of the static stripes. The abrupt jump of voltage at a rather large Ic in LNSCO may be used as a high-power current restrictor or switch. [ABSTRACT FROM AUTHOR]

Using terahertz time-domain spectroscopy, we measured the frequency dependent complex dielectric response and conductivity of n-type single-crystal ZnO epilayers with different carrier concentrations over the frequency range from 0.1 to 3.0 THz. The measured complex dielectric response and conductivity are analyzed using Drude model. [ABSTRACT FROM AUTHOR]

This paper studies the nonlinear vibration of a single-walled carbon nanotube (CNT) embedded in a polymer matrix aroused by van der Waals (vdW) forces using elastic beam models. The interfacial vdW forces are described by a nonlinear function in terms of the deflection of the CNT. According to different beam end conditions, the relation between deflection amplitudes and resonant frequencies of free vibrations of the CNT is derived through harmonic balance method. This relation is found to be sensitive to end conditions, diameters, and lengths of the embedded CNT. The axial load effect upon the vibrational behavior of the CNT and postbuckling of the embedded CNT are also discussed. Due to the influence of the surrounding polymer, the prediction on the critical buckling loads and resonant frequencies for embedded CNTs is quite different from that for free-standing CNTs. In addition, the applicability and accuracy of both Euler–Bernoulli and Timoshenko beam models are investigated. It is found that the Euler–Bernoulli beam model may provide comparable results as the Timoshenko beam model even for CNTs with smaller length-to-diameter ratios due to the constraint from the surrounding medium. [ABSTRACT FROM AUTHOR]

We investigate the photoconductivity properties of ZnO thin films prepared by pulsed laser deposition with and without metals (Au or Pt) on the surface. The covering of nanostructured metals can largely enhance the photocurrent. Meanwhile, the dark currents have been increased significantly due to the increase in carrier concentration and mobility near the surface of ZnO thin film. Although plasmonic effect was observed by the photoluminescence enhancement, the main mechanism of the increase in the dark current and photoresponsivity for ZnO photoconductors has been interpreted by surface states, interface states, and persistent photoconductivity. [ABSTRACT FROM AUTHOR]

Exciton dissociation process at indium tin oxide (ITO)/copper phthalocyanine (CuPc) interface of ITO/CuPc(370 nm)/Al is studied by transient photovoltage method. A negative-to-positive change in the polarity of photovoltage upon pulsed laser irradiation is observed in CuPc thin film. The polarity change is regarded as a summation of the effect of exciton dissociation at ITO/CuPc interface (fast process) and that of free carrier separation by built-in field (slow process). Further experiments confirm the existence of exciton dissociation at ITO/CuPc interface, and the direction of which is electron injected into ITO, with holes left in CuPc film. This is opposite to that of the interfacial dissociation at donor/acceptor (D/A) interface in single heterojunction cells (ITO/D/A/buffer/Al). 3-nm-thick LiF insulating layer is inserted between ITO and CuPc to inhibit the exciton dissociation at ITO/CuPc interface. Thereby, the open-circuit voltage and power conversion efficiency of the single layer cell have been increased by several times. [ABSTRACT FROM AUTHOR]

ZnO nanotubes were fabricated by vapor-phase transport using the mixture of ZnO and graphite powders in air. A self-catalyzed growth mechanism was proposed based on microstructure analysis by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Raman scattering, integrated photoluminescence, and time-resolved photoluminescence were employed to explore the optical properties and the dynamic process. Combing with crystal structure and the spectral characteristics of the ZnO nanotubes, the charge carrier transport process was discussed. [ABSTRACT FROM AUTHOR]

Surface defect passivation for ZnO nanocombs (NCBs), random nanowires (RNWs), and aligned nanowires (ANWs) was performed through a metal plasma immersion ion implantation with low bias voltages ranging from 0 to 10 kV, where Ni was used as the modification ion. The depth of surface-originated green band (GB) emission is thus probed, revealing the surface origin of the GB. It is also found that the GB is closely related to oxygen gas content during growth of the nanostructures. The GB origin of NCBs and RNWs grown with higher oxygen content is shallower (∼0.5 nm), which can be completely quenched with no bias applied. However, the GB origin of ANWs grown at lower oxygen content is much deeper (∼7 nm) with a complete quenching bias of 10 kV. Quenching of the GB can be attributed to passivation of the surface hole or electron trapping sites (oxygen vacancies) by Ni ions. [ABSTRACT FROM AUTHOR]

Combustion-aided suspension plasma spraying (SPS) was developed for the synthesis of Y2O3 nanoparticles. Numerical models for Ar, Ar/O2, and combustion-aided plasma fields were built using FLUENT V6.3.2© to compare their different plasma thermophysical properties. Modeling and experimental results both indicate that the plasma field was substantially altered by combustion-aided SPS. The plasma exhibited an elevated volume average temperature and reduced velocity as well as a broadened plasma plume, which resulted in an enhanced vapor supersaturation degree and a faster quenching rate in the radial direction. These can be attributed to the dual effects of oxygen dissociation/recombination and acetone solvent combustion. Consequently, productivity of the obtained nanoparticles increased remarkably and the particles’ morphology was improved, with a smaller mean particle size and a narrower size distribution in comparison with those of powder feeding spraying. Furthermore, plasma-induced cubic→monoclinic phase transformation in the as-sprayed Y2O3 particles was restrained by combustion-aided SPS to some extent. [ABSTRACT FROM AUTHOR]

Indium-tin-oxide (ITO) anode treated by different gas plasma or UV ozone has been used for photovoltaic (PV) cells with structure of ITO/copper phthalocyanine (CuPc)/C60/bathocuproine/Al. Both surface energy and work function of the ITO substrates were affected by these treatments. However, the main performance parameters of PV cells, including short circuit current, open circuit voltage, power conversion efficiency, and fill factor, were almost unaffected. On the other hand, series and shunt resistances of the PV cells derived from numerical fitting of I-V curves were not significantly changed with different treatments. Therefore, no significant impact of substrate treatment on hole collection was concluded, although hole injection under forward bias showed strong dependence on treatment methods. It indicates that hole transfer from CuPc layer to ITO is not the bottleneck in the CuPc/C60 based organic solar cells. [ABSTRACT FROM AUTHOR]

Barrier shapes and its detailed microstructures in the double barrier magnetic tunnel junctions were intensively investigated by both high resolution transmission electron microscopy and electron holography. Two broad (>2 nm) potential wells (i.e., shapes of AlOx layers) with slanted interfaces were observed in the electron hologram of the as-deposited samples. However, in the hologram of the annealed samples, two narrowed (down to 1.18 nm) and almost equal (height) potential wells with sharp and steep interfaces were acquired. This indicates that the value of tunnel magnetoresistance can be increased from 12.8% to 29.4% at room temperature by annealing treatment where the sharpness and height of the barriers played a critical role. [ABSTRACT FROM AUTHOR]

Postgrowth annealing was carried out on ZnO thin films grown by metal-organic chemical-vapor deposition. It was found from the scanning electron microscopy and atomic force microscopy measurements that the morphology of the thin films changed drastically after annealing. The as-grown thin films consist of fine nanoscale-sized sheets with random orientation. Upon annealing at 800 °C, the ZnO nanosheets changed to three-dimensional nanoneedles. The different types of the mass transport mechanisms are discussed and correlated with the experimental results. A coarsening kinetics developed by Lifshitz and Slyozov [J. Phys. Chem. Solids 19, 35 (1961)] and Wagner [Z. Elektrochem. 65, 581 (1961)] was used to estimate the activation energy of the coarsening process. The activation energy of the Ostwald ripening in ZnO films was estimated in the first attempt, and the value is at around 1.33 eV. Hall effect and photoluminescence measurements were carried out to investigate the effect of coarsening on electrical and optical properties of the ZnO thin films. [ABSTRACT FROM AUTHOR]

The band structures of wurtzite ZnO are calculated by the empirical pseudopotential method (EPM). The eight parameters of the Zn and O atomic pseudopotential form factors are obtained with the formula of Schluter et al.[Phys. Rev. B 12, 4200 (1975)]. The band parameters are extracted by using a k·p Hamiltonian to fit the EPM results. The calculated band-edge energies (Eg, EA, EB, and EC) at the Γ point are in good agreement with the experimental results. Based on the band parameters obtained, valence subbands of wurtzite ZnO/MgxZn1-xO tensile-strained quantum wells with different well widths and Mg compositions are calculated by the six-band k·p method. [ABSTRACT FROM AUTHOR]

Based on vapor-phase transport method, manganese-doped zinc oxide (ZnO:Mn) tetropod whiskers were fabricated. The pods of the ZnO:Mn whiskers show hexagonal hollow shape with multitips at the front. X-ray diffraction and high-resolution transmission electron microscopy demonstrate that the tube pods and the tips are composed of wurtzite ZnO growing along [0001] direction. The generation of the luminescent center in ZnO whiskers and electron transport between the ground state and the excitation states of Mn2+ are analyzed by Raman-scattering, photoluminescence, and photoluminescent excitation measurements. [ABSTRACT FROM AUTHOR]

The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied. The optical band gap of as-grown ZnO blueshifted from 3.13 to 4.06 eV as the growth temperature decreased from 500 to 200 °C. After annealing, the optical band gap shifted back to the single-crystal value. All the ZnO thin films studied show strong band-edge photoluminescence. X-ray diffraction measurements showed that samples deposited at low temperatures (<450 °C) consisted of amorphous and crystalline phases. The redshift of the optical band gap back to the original position after annealing was strong evidence that the blueshift was due to an amorphous phase. The unshifted photoluminescence spectra indicated that the luminescence was due to the crystalline phase of ZnO, which was in the form of nanocrystals embedded in the amorphous phase. [ABSTRACT FROM AUTHOR]

Nanoheteroepitaxial growth of GaN by metal-organic chemical-vapor deposition on dense arrays of (111) Si nanopillars has been investigated. Scanning electron microscopy, cross-sectional transmission electron microscopy, and electron-diffraction analysis of 0.15-μm-thick GaN layers indicate single-crystal films. Most of the mismatch defects were in-plane stacking faults and the threading dislocation concentration was <108 cm-2 at the interface and decreased away from the interface. High-resolution transmission electron microscopy indicated that grain-boundary defects could heal and were followed by high quality, single-crystal GaN. Facetted voids were also present at the GaN/Si interface and are believed to be an additional strain-energy reduction mechanism. The unusual defect behavior in these samples appears to be related to the high compliance of the nanopillar silicon substrate. [ABSTRACT FROM AUTHOR]

Organic electroluminescent (EL) devices with planar microcavity structure, indium-tin-oxide/ Ag/N,N'-diphenyl-N, N'-bis(3-methylphenyl)-1,1'-biphenyl-4, 4'-diamine/tris(8-hydroxyquinoline)- aluminum (AlQ):4-(dicyanomethylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran/ AlQ/LiF/ Al, were fabricated. The Ag and Al layers acted as not only hole-injection layer and cathode, respectively, but reflective mirrors, resulting in strong microcavity effects, such as spectral narrowing and directional emission. The effects of device parameters on the EL performance were studied in detail and were discussed in terms of conventional microcavity theory. On-axis light magnification with a coefficient (EL enhancement ratio between cavity and noncavity devices) of ~5 was observed, which was consistent with the theoretical calculation. At the same time, optimized microcavity device with bright pure red emission showed maximum luminance of 5140 cd/m2, peak at 624 nm, Commission International de I'Eclairage coordinates of x=0.663 and y=0.336, and high EL efficiency of 1.71 cd/A were obtained. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of laminated (Nd,Dy)(Fe,Co,Nb,B)5.5 /Fe nanocomposites are investigated. Normally, the addition of the soft phase to the hard phase enhances the remanence but deteriorates the permanent-magnet performance of the material by reducing the coercivity. In the present system, the coercivity increases to 1608 kA/m (20.2 kOe) in thermally processed Nd-Dy-Fe-Co-Nb-B(15 nm)/Fe(4 nm) multilayered nanocomposites, which is higher than that of the single-layer hard-magnetic film. The abnormally high coercivity is achieved by annealing at relatively high temperature, which breaks the laminated structure of the as-deposited multilayer. A likely physical explanation of the enhanced coercivity is the introduction of the domain-wall pinning sites that counteract the inevitable decrease of the nucleation field. [ABSTRACT FROM AUTHOR]

The electro-optical and response properties of a nematic liquid crystal cell driven by double-side fringe-field switching [ C. Y. Xiang, X. W. Sun, and X. J. Yin, Appl. Phys. Lett. 83, 5154 (2003) ] have been studied. The transmission-voltage curve of the double-side fringe-field cell can be modeled by the change of the maximum twist angle. It is shown that the liquid crystal layer is linearly twisted before the transmission reaches the maximum. The threshold voltage of double-side fringe-field switching is the same as that of single-side fringe-field switching. The turn-on and turn-off response times, showing four time improvement over the single-side fringe-field switching, have been derived. The experimental turn-off times of the double-sides fringe-field switching and single-side fringe-field switching cell match with the theoretical prediction. The experimental turn-on time of the double-side fringe-field switching cell shows four times improvement over the single-side fringe-field one as predicted by the theoretical analysis. [ABSTRACT FROM AUTHOR]

This article describes defect reduction mechanisms that are active during the growth of GaN by nanoheteroepitaxy on (0001) 6H SiC. Nanoheteroepitaxial (NHE) and planar GaN epitaxial films were grown and compared using transmission electron microscopy, photoluminescence, x-ray diffraction, and time resolved photoluminescence. It was found that in addition to the previously reported defect reduction mechanism that results from the high compliance of nanoscale nuclei, other independent defect reduction mechanisms are also active during NHE including: (i) filtering of substrate defects, (ii) improved coalescence at the nanoscale, and (iii) defect termination at local free surfaces. Also, it was found that the biaxial strain in the GaN film could be significantly reduced by using a “grouped” NHE pattern geometry. Time resolved photoluminescence measurements on NHE GaN samples with this geometry showed a more than tenfold increase in carrier lifetime compared to GaN grown on planar SiC. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nanostructural zinc oxide fibers have been fabricated by a simple vapor transport method of heating the mixture of zinc oxide, gallium oxide, and carbon powders in air. The zinc oxide nanofibers showed cauliflower-like, disordered, vertically and horizontally aligned morphologies in different temperature regions. The aligned nanofibers were composed of hexagonal zinc oxide with good crystallinity. Gallium was doped into zinc oxide with a concentration of 0.73 at. %. The growth process and the characteristics can be interpreted by a vapor-liquid-solid mechanism. The field emission of the vertically aligned zinc oxide fiber array showed a low field emission threshold, high current density, rapid surge, and high field enhancement factor. The threshold electric field is about 2.4 V/μm at a current density of 0.1 μA/cm[sup -2]. The field enhancement factor was 2991. The emission current density and the electric field followed the Fowler–Nordheim relationship. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic properties and exchange couplings of nanocomposite (Nd,Y)[SUB2]Fe[SUB14]B/α-Fe magnets prepared by mechanical milling have been investigated at low temperatures. With decreasing temperature, due to Y substitution for Nd, an extension of the exchange coupling length in nanocomposite magnets occurs in a wider temperature range. This can be attributed a decreasing anisotropy of the hard-magnetic phase so that more soft-magnetic grains participate the exchange coupling. Close to 135 K, due to the spin reorientation, the hard magnetic phase is not more uniaxail, which leads to a drastic decrease of the magnetic properties of the Nd[SUB2]Fe[SUB14]B-based nanocomposite magnets. [ABSTRACT FROM AUTHOR]

Low-temperature (10 K) microcathodoluminescence spectroscopy with a scanning electron microscope has been used to probe shallow and deep levels within the grains of Bi[SUB2]O[SUB3]-doped ZnO powders prepared under different process conditions. These studies reveal strong electronic state variations between the bulk and boundaries of these submicron ZnO grains, including new emissions at ~3.329 eV at grain boundaries attributed to Bi phase segregation and/or the formation of new electrically active defects. The characteristic deep level defect emission at 2.4 eV due to nonstoichiometric point defects varies spatially, appearing much stronger in the grain bulk than at the boundaries. The 3.329 eV emissions become more pronounced with higher doping concentration and annealing temperature, indicating a strong dependence on processing. The strong temperature and composition dependence of these boundary-specific features are consistent with the known influence of process conditions on the varistor properties of ZnO powder. [ABSTRACT FROM AUTHOR]

We calculated electron energy loss and angular distributions for electrons transmitted through masks for electron projection lithography by a Monte Carlo (MC) simulation method. After comparing the improved continuous slowing down approximation model, the direct MC model, and the intensive direct MC model, the last model was used. The energy loss distributions calculated by the latter two models are much better than by the first model and the intensive direct MC model can be applied to more materials than the direct MC model. The effect of mask thickness on energy loss, transmission, and contrast was analyzed. We found that, for a W/Cr/Si[sub 3]N[sub 4] mask, the thicker the scattering layer the wider the angular distribution, the lower the transmission, and the higher the contrast. But the thickness of the membrane Si[sub 3]N[sub 4] layer has less effect on the contrast. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/A1[sub 2]O[sub 3] interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS, and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. These data, along with electrochemical capacitance-voltage profiling and secondary ion mass spectrometry provide a consistent picture of near-interface doping by O out-diffusion from A1[sub 2]O[sub 3] into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level at 3.447 meV near the interface for such samples, characteristic of O impurities spatially localized to the nanoscale interface. CLS emissions indicate the formation of amorphous A1-N-O complexes at 3.8 eV extending into the A1[sub 2]O[sub 3] near the GaN/sapphire interface. CLS and CL images also reveal emissions due to excitons bound to stacking faults and cubic phase GaN. The temperature dependence of the various optical transitions in the 10-300 K range provides additional information to identify the near interface defects and impurity doping. [ABSTRACT FROM AUTHOR]

An approach improving diamond–metal adhesion has been developed based on modeling predictions and experimental verifications on the interfacial stresses modified by catalytic reaction. It is found that N-plasma irradiating onto Ti and tungsten-carbide substrates generates tensile surface stresses while C-plasma irradiation creates strongly compressive stress at the surfaces, both of which deteriorate the diamond–metal adhesion. It is also found that surface oxidation prevents diamond nucleation. Therefore, we applied a graded TiCN interlayer with carefully adjusting the ratio of C and N in the gas mixture to neutralize the interfacial stress and, hence, we have improved the diamond–metal adhesion substantially. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

X-ray absorption fine structures (XAFS) and electron energy loss spectroscopy (EELS) at the Si L[sub 3,2] edge have been used to investigate a series of Si nanowires (as-prepared and HF refreshed). X-ray excited optical luminescence (XEOL) was also used to study the optical properties of these Si nanowires. Although no noticeable edge-jump blueshift (widened band gap) is observed in XAFS, a noticeable change in the edge jump (a less steep rise and the blurring of spectral features) is observed, indicating considerable degradation in the long-range order and size effects. However, EELS with a nanobeam exhibits a threshold blueshift and parabolic behavior for some selected wires indicating that there are grains smaller than the nominal diameter in these nanowires. Thus, XAFS probes the average of a distribution of wires of various sizes of which the majority is too large to exhibit detectable quantum confinement behavior (blueshift) observed and inferred in EELS and XEOL. The results and their implications are discussed. [ABSTRACT FROM AUTHOR]

The chemical reactivity of hydrogen-passivated surface of silicon nanowires (SiNWs) towards the reductive deposition of silver and copper ions from solution is reported. SiNWs synthesized by laser ablation were used in the investigation. The surface properties of SiNWs after the removal of the surface oxide were studied. It is found that the surface silicon of the SiNWs can readily reduce silver (I) and copper (II) ions to metal aggregates of various morphologies on the SiNW surface at room temperature. The reaction products have been characterized with scanning electron microscopy, energy dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy. By varying the concentration of Ag(I) ions in the solution, nanostructures of silver with different shapes and sizes can be obtained. This approach for synthesis of metal nanostructures offers a potential method for the preparation o! f desired metal catalysts. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Deals with a study which described the growth of cubic-indium-gallium-nitrogen (InGaN) layers on GaArsenic(001) substrates by metalorganic chemical-vapor deposition with different In composition. Experimental details; Calculations of the strain; Photoluminescence of the InGaN films.

The chainlike silicon nanowires SiNWs are synthesized by fluctuating the pressure of the carrier gas in the growth process. The X-ray excited optical luminescence and photoluminiscence spectroscopy show that the relatively strong luminescence from the chainlike SiNWs compared to normal SiNWs arises mainly from silicon oxide in the chainlike SiNWs.

The electro-optical and response properties of a nematic liquid crystal cell driven by double-size fringe-field switching are studied. The findings show that turn-on and turn-off response times, showing four time improvement over the single-side fringe-field switching have been derived.

Focuses on a study which focused on the epitaxial growth of gallium nitride thin films deposited on sapphire(0001) substrates with a thin zinc oxide buffer layer by a liquid target pulsed laser deposition technique. Experimental details; Crystal structures; Photoluminescence measurement of the thin film; Conclusions.

A resonant-cavity-enhanced GaAsSb avalanche photodiode with separate absorption, charge and multiplication regions has been demonstrated. The study shows that by using GaAsSb absorber and SACM structure, low noise, low dark current avalanche photodiodes operating at 1.3 mum can be realized.

Part II. Investigates the effectiveness of titanium-silicon-nitrogen films as diffusion barriers for aluminum and copper metallizations on silicon. Reactive sputtering of titanium-silicon-nitrogen ternary films; Maximum temperature of stability of titanium-silicon-nitrogen films; Electrical resistivity of the films.

Part I. Examines the microstructure, atomic density and electrical resistivity of reactively sputtered titanium-silicon-nitrogen ternary films. Synthesis of titanium-silicon-nitride films in an argon-nitrogen gas mixture; Characterization of ternary films in terms of their composition by backscattering spectrometry; Characterization of microstructure by transmission electron microscopy.

Presents information on a study which introduced a theoretical and experimental description of the interaction of a surface plasmon (SP) with a surface acoustic wave which generates dynamic sinusoidal gratings on the interface. Basic conditions for SP to exist on the interface of two media; Formulas for the intensity of diffracted light; Preparation of the device used in the study.

Presents information on a study that examined the magnetization process of ferromagnetic materials using a computer simulation program based on a two sublattice model. Model and calculation details; Results and discussion on the study.