Search

Microstructure evolution of three Al-Ag alloys with different Ag contents (1 wt. % Ag, 5 wt. % Ag, and 15wt. % Ag) was studied by positron annihilation spectroscopy during the aging process. In situ measurements of the positron lifetime and Doppler broadening of annihilation radiation indicate the fast formation of Ag-rich clusters during natural aging of the alloys. The formation of Ag-rich clusters was further confirmed by coincidence Doppler broadening measurements. The Ag signal reflected by the Coincidence Doppler broadening spectrum increases with increasing Ag content and is further enhanced after subsequent artificial aging at 140 °C. This might be due to the increase in the size of Ag clusters. The temperature dependence of the Doppler broadening spectra between 10K and 290K was measured for the Al-Ag alloys after natural and artificial aging. Detrapping of positrons from Ag clusters with increasing temperature was observed for all the three Al-Ag alloys after natural aging and for the Al-1wt. % Ag after artificial aging. This indicates that Ag clusters act as shallow positron trapping centers. The thermal detrapping of positrons becomes ambiguous with increasing Ag content in the alloy and is nearly invisible in the artificially aged Al-5wt. % Ag and Al-15wt. % Ag. The positron binding energy of the Ag cluster is roughly estimated to be about 18.8 meV and 50 meV in the Al-1 wt. % Ag sample after natural aging and artificial aging at 140 °C, respectively, which suggests that the confinement of positrons in the quantum-dot like state depends on the size or chemical composition of clusters. Theoretical calculations confirm positron trapping by Ag nanoclusters, and the confinement of positrons is enhanced with increasing Ag cluster size. [ABSTRACT FROM AUTHOR]

Co2Y hexaferrites have attracted intensive interests due to its potential high temperature magnetoelectricity as the single phase multiferroics. Numerous efforts have been paid to enhance their magnetoelectric properties at high temperatures through increasing the magnetic transition temperature and decreasing the conductivity. In this work, we investigated the conductivity and magnetic properties of the polycrystalline Ba0.5Sr1.5Co2(Fe1-xAlx)12O22 (0≤x≤0.12) hexaferrites and found that Al-doping has important effects on both the conductivity and magnetic properties. The underlying physical mechanisms were also systematically analyzed. Most importantly, a very much enhanced resistivity (over 10MΩ cm), and a high magnetic transition temperature (~346 K) have been obtained at a doping amount of x=0.04. These improvements are very promising for achieving significant magnetoelectric effect at room temperature. The current research can provide the basic understanding of the Y-type ferrites for future applications in magnetoelectric and other fields. [ABSTRACT FROM AUTHOR]

Ion source development over the last 20 years at the IMP is reviewed. For versatile purposes, several types of ion sources have been involved in the research and development work at the IMP, i.e., the highly charged ECR (Electron Cyclotron Resonance) ion source, intense microwave ion source or the 2.45 GHz intense beam ECR ion source, and laser ion source (LIS). In the development of ECR ion sources, SECRAL (Superconducting ECR ion source with Advanced design in Lanzhou), Lanzhou ECR ion source, and Lanzhou all permanent magnet ECR ion source series have been made, which can cover the operation microwave frequency range of 10–28 GHz. The LIS with an Nd:YAG laser with a maximum output energy of 8 J in 8 ns pulse duration has been developed for very intense short pulse ion beams from solid materials such as C, Ti, Ni, Ag, and so on. Microwave ion sources have been built to produce intense pulsed or direct current beams from several mA to 100 mA for either high intensity accelerators or applications. This paper will give an overview of the high intensity ion source development at the IMP, especially on the recent progress and new results, such as the status of the fourth generation ECR ion source (first fourth generation ECR ion source), the production of recorded highly charged ion beams with SECRAL sources, key technology research studies, and so on. [ABSTRACT FROM AUTHOR]

The role of the Nd-rich phase in developing microstructure and properties of isotropic and anisotropic NdFeB magnets has been investigated. Melt spun Nd-rich Nd13.5Fe73.5Co6.7Ga0.5B5.6 and Fe-rich Nd7.7Pr2.6Fe84.1B5.5 alloy powders were mechanically mixed with different ratios. The mixed powders were consolidated into isotropic magnets and anisotropic magnets by spark plasma sintering (SPS) and SPS followed by hot deformation, respectively. The composition and microstructure of diffusion area between Nd-rich and Fe-rich compositions for isotropic and anisotropic magnets were investigated. The gradient distribution of Nd content from Nd-rich to Fe-rich area due to the diffusion of liquid Nd-rich phase in the SPS and hot deformation was observed, which leads to gradually changes in grain structure. The remanent polarization of 1.29 T, coercivity of 995 kA/m, and maximum energy product of 293 kJ/m3 are obtained for an anisotropic magnet. The role of the Nd-rich phase has to be carefully considered in order to achieve deformation anisotropy and fine grains in the NdFeB magnets. [ABSTRACT FROM AUTHOR]

The conventional carrier-blocking design of the exciton formation zone used in nearly all organic light emitting diodes is shown to be problematic, due to exciton quenching from accumulated radical cations. To reduce exciton quenching, a single layer of 4,4′-N,N′-dicarbazole-biphenyl (CBP) is used as hole transport layer, resulting in a dramatically improved device efficiency even at high luminance (e.g., 20.5 cd/A at 100 000 cd/m2 for fluorescent green). Various high work function transition metal oxides (WO3, V2O5, and MoO3) coated on indium tin oxide anodes have been shown to enable direct hole injection into the deep highest occupied molecular orbital of CBP (6.1 eV). [ABSTRACT FROM AUTHOR]

Nanogranular CoAlO thin films were fabricated by rf magnetron sputtering using Co target partially covered by Al2O3 chips in argon atmosphere. The films consist of Co nanograins with a mean diameter of 5–30 nm surrounded by an amorphous Al–O phase. It was found that Co grains of face-centered-cubic and hexagonal-close-packed structures coexist in the films with relatively low (Al,O) content, whereas Co grains of face-centered-cubic structure are preferentially formed in the films with higher (Al,O) content. Due to the microstructure changes with increasing (Al,O) content in the films, coercivity and magnetization decrease but the anisotropy field increases. The high frequency properties of the CoAlO films were experimentally characterized, and the effects of magnetization, anisotropy field, and damping factor on the permeability spectrum are also analyzed using the Landau-Lifshitz-Gilbert equation. The ferromagnetic resonance frequency was found to increase from 2.1 to 2.8 GHz with the microstructure change in the films. [ABSTRACT FROM AUTHOR]

Rare-earth iron-boron (RE-Fe–B) thin films with a c-axis texture were prepared on a Ta (110) buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The microstructure, magnetic structure, and magnetic properties of these films were studied as a function of the deposition temperature. The results show that c-axis texture can be obtained over a wide range of deposition temperatures and that the degree of c-axis orientation improves with deposition temperature. It was established that deposition of a RE-Fe–B thin film to obtain grains with a strong c-axis RE2Fe14B texture, coexisting with an amorphous phase, followed by annealing at higher temperature, is an effective route for obtaining excellent hard magnetic properties. Initial results show that a film, which was deposited at 470 °C and annealed at 590 °C, had a high perpendicular coercivity of 1.8 T, in combination with a large maximum energy product of 238 kJ/m3. [ABSTRACT FROM AUTHOR]

Hollow glass microspheres coated with thin Ni films of various thicknesses (about 50–250 nm) were obtained by electroless plating technique. The resultant magnetic microspheres had very low densities (∼0.39–1.28 g cm-3) and low coercivities (<40 Oe). As-plated films comprised of nanocrystallites embedded in amorphous matrix and postannealing treatment led to a submicrocrystalline structure and an increased saturation magnetization. The high frequency properties of the composites consisting of Ni-plated microspheres and polymer were investigated. The permittivity and permeability increased with increasing microsphere content in the composite and increasing Ni film thickness. These composites had ferromagnetic resonance peak in the range of 5–12 GHz. Postannealing also had an effect on the microwave properties. The reflection loss of the composite was found dependent on the absorber material thickness, polymer:microsphere ratios, the Ni film thickness, as well as the heat treatment of the microspheres. [ABSTRACT FROM AUTHOR]

FeCoN soft magnetic thin films with various nitrogen contents were fabricated by varying the gas flow rates of the argon and nitrogen gas mixture used during reactive rf magnetron sputtering. It was found that the resistivity of FeCoN film increased up to 211 μΩ cm with increasing nitrogen content. The film produced at the gas flow rate of 7 sccm exhibited the best soft magnetic properties with small coercivity and relatively large saturation magnetization. The microstructure of the films was examined by high-resolution transmission electron microscopy and α″-FeCo phase with very high saturation magnetization was observed in the films. The high-frequency properties of the FeCoN thin films were experimentally characterized and theoretically examined. The Hoffmann’s ripple theory was used to explain the permeability spectra for the films with strong magnetization dispersion. We found that the ripple effect is responsible for the large damping in the films, and those films with larger coercivities have stronger magnetization dispersion. With the gas flow rate of the argon and nitrogen gas mixture increasing from 0 to 15 sccm, the low-frequency permeability decreased from 680 to 245 and the ferromagnetic resonance frequency increased from 2.09 to 2.99 GHz. [ABSTRACT FROM AUTHOR]

A cool-down step deposition process (multistep deposition with cool-down interval) was used to grow nanocomposite FeAlO thin films of various thicknesses up to 440 nm by magnetron sputtering at a substrate temperature of 15 °C. The effect of the number of cool-down steps on the soft magnetic properties and high frequency characteristics of the nanocomposite FeAlO films were investigated. The deposition process was proved very effective in improving the soft magnetic properties and high frequency characteristics of the films. The eight-layered samples, fabricated by eight cool-down step deposition process, of thicknesses of 220 and 440 nm had obvious in-plane uniaxial anisotropies while the single-layered films were nearly isotropic. The resulting real permeability value of the eight-layered films was larger than 300 for the 220 nm film and between 200 and 300 for the 440 nm film. [ABSTRACT FROM AUTHOR]

The FeTaN thin films were deposited on the flexible plastic substrates by rf magnetron sputtering. Good soft magnetic properties with coercivity <10 Oe have been obtained in the films with thickness <250 nm. Relatively high values of the complex permeability and ferromagnetic resonance frequency were obtained and they can be adjusted by changing the film thickness. However, compared to the films on the rigid substrate, a decrease of the permeability level and a shift of the resonance peak in the permeability spectra have been noticed for the films on the flexible substrate. The electric properties, including sheet resistance, resistivity, and magnetoresistance for the films with various thicknesses, have also been investigated. [ABSTRACT FROM AUTHOR]

Brain-inspired neuromorphic computing has attracted much attention for its advanced computing concept. However, the massive hardware cost in fully-connected architectures makes it challenging to build a large-scale neuromorphic system. In this work, we report a compact, programmable, versatile, and scalable neuromorphic architecture. To demonstrate the concept of the neuromorphic architecture, a neuromorphic system consisting of four cores is implemented on an FPGA platform. On the one hand, the neuromorphic system is extremely compact and hardware-saving. The computing block based on a simple digital leaky Integrate-and-Fire (LIF) model only costs 69 logic elements (LEs); only one physical neuron is implemented in each core, and it can be reused as hundreds of virtual neurons by time-division-multiplexing; only four 9-bit synaptic weights are assigned to each neuron, which effectively alleviates the hardware explosion in fully-connected architecture. On the other hand, the neuromorphic system is programmable and versatile, and can perform different neural network computing. The neuromorphic system mapped with a three-layer feedforward network successfully recognizes the MNIST handwritten digits with an accuracy of 96.26%, and it also effectively realizes different convolution operations which are basic computing operations in convolutional neural networks. Last but not least, each neuromorphic core has its own router module, making it convenient to scale up. [ABSTRACT FROM AUTHOR]

FeZrN thin films with in-plane anisotropy were deposited on both rigid substrate (Si) and flexible substrate (Kapton) by magnetron sputtering. The as-prepared films had the microstructure of nanocrystallites with a small amount of intergranular amorphous phase. The thickness dependent coercivity showed different behaviors for flexible and rigid films. The dynamic magnetic properties of the films have been characterized. Although the high frequency characteristics are closely related to the thickness, composition, and anisotropy, the flexible films have relatively smaller values of real permeability μ' but larger values of ferromagnetic resonance frequency fr than the rigid films. Due to the flexibility, the properties of the flexible films varied with each other. Nevertheless, both rigid and flexible films can find important applications in microwave absorber due to their excellent high frequency properties up to 5 GHz. [ABSTRACT FROM AUTHOR]

The exchange interactions for rapidly solidified (Nd/Pr)(Fe/Co)B hard magnetic alloys with remanence enhancement were studied by analyzing characteristic magnetic curves and Henkel plots. The exchange coupling can be improved by increasing soft phase content within hard matrix. With increasing temperature, the exchange interaction is enhanced due to the increased exchange length. An increased recoil susceptibility was found for the alloys with improved exchange coupling. Analysis of the microstructure parameters indicated that Co substituting Fe and introducing soft α-(Fe,Co) phase not only reduce the stray field effects but also enhance the exchange interaction. [ABSTRACT FROM AUTHOR]

RE–Fe–B films were prepared on a Ta buffer layer on thermally oxidized Si substrates by dc magnetron sputtering. The structure, magnetic structure, and magnetic properties of RE–Fe–B films were studied. The results show the preparation procedure of deposition at 470 °C to obtain a strong c-axis RE2Fe14B texture coexisting with an amorphous phase and following annealing at 590 °C can effectively fabricate RE–Fe–B thin films with highly texture. The result shows that the film, which was deposited at 470 °C and following annealing at 590 °C, has a high perpendicular coercivity μ0 iHc=1.8 T and large magnetic energy product (BH)max=238 kJ/m3. [ABSTRACT FROM AUTHOR]

MnBi magnets with a high content of low temperature phase (LTP) and excellent magnetic properties were prepared by spark plasma sintering (SPS) using ball milling powders as precursors without magnetic purification. A complicated intergranular phase, which contains Mn phase, Bi phase, MnO phase, and even amorphous phase in MnBi magnets, was characterized and reported systematically. It was found that the formation of intergranular phase which was contributed by ball milling precursors and sintering mechanism, jointly, had important influence on the magnetic properties. The appropriate content of intergranular phase was beneficial in improving the coercivity due to the strong magnetic isolation effects. The optimum magnetic properties with Mr=26.0 emu/g, Hci= 7.11 kOe and (BH)max=1.53 MGOe at room temperature, and a maximum value Hci= 25.37 kOe at 550 K can be obtained. Strongly favorable magnetic properties make SPSed MnBi magnets an attractive candidate material for small permanent magnets used in high-temperature applications. [ABSTRACT FROM AUTHOR]

The microstructure and magnetocaloric effect of the La0.8Ce0.2(Fe0.95Co0.05)11.8Si1.2 strip-cast flakes annealed between 1273K and 1423K for different time have been investigated. For the flakes annealed for 2h from 1273K to 1423K, the shape and distribution of α-Fe, La-rich and NaZn13-type 1:13 phases are quite sensitive to the annealing temperature. Especially, at a high annealing temperature of 1423K, the 1:13 phase began to decompose into macroscopic α-Fe conglomerations and La-rich dendrites. With the increase of annealing time from 0 to 12h at 1323K, the amount of 1:13 phase increased significantly and reached ∼93.50 wt.% at 12h. However, an overlong annealing time also led to 1:13 phase decomposition and influenced the magnetic performance. For the flakes annealed at 1323K for 12h, large magnetic entropy change value of 18.12Jkg-1K-1 at 5T has been obtained. The present results indicate that strip casting method can potentially be used in mass production of high performance magnetocaloric materials. [ABSTRACT FROM AUTHOR]

Mn-Zn ferrites doped with different Sm2O3, Gd2O3, Ce2O3 or Y2O3 were prepared by traditional ceramic technology using industrial pre-sintered powders. A small amount of Sm2O3, Gd2O3, Ce2O3 or Y2O3 can significantly improve the microstructure and magnetic properties. The single spinel phase structure can be maintained with the doping amount up to 0.07 wt.%. A refined grain structure and uniform grain size distribution can be obtained by doping. For all rare earth oxides, a small amount of doping can significantly increase the permeability and reduce the coercivity and magnetic core loss. The optimized doping amount for Sm2O3 or Gd2O3 is 0.01 wt.%, while for Ce2O3 or Y2O3 is 0.03 wt.%. A further increase of the doping content will lead to reduced soft magnetic properties. The ferrite sample with 0.01 wt.% Sm2O3 exhibits the good magnetic properties with permeability, loss, and coercivity of 2586, 316 W/kg, and 24A/m, respectively, at 200 mT and 100 kHz. The present results indicate that rare earth doping can be suggested to be one of the effective ways to improve the performance of soft ferrites. [ABSTRACT FROM AUTHOR]

The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm. [ABSTRACT FROM AUTHOR]

Examines electron cyclotron resonance (ECR) ion sources in China. Emphasis on high charge state ECR ion sources which have been mainly developed by Institute of Modern Physics; Compact proton ion source with permanent magnets.

Gd5Si2.05-xGe1.95-xNi2x (2x = 0.08, 0.1) alloys were prepared by arc melting followed by annealing at 1273 K for 96 h. Mixed monoclinic Gd5Si2Ge2-type phase, orthorhombic Gd5Si4-type phase, and a small amount of Gd5Si3-type phase were obtained in these alloys. Gd5Si2.01Ge1.91Ni0.08 alloy undergoes a second-order transition (TC) around 300 K, whereas Gd5Si2Ge1.9Ni0.1 alloy exhibits two transitions including a first-order transition (TCІІ) at ∼295 K and second-order transition (TCІ) at ∼301 K. Ni substitution can effectively reduce the thermal hysteresis and magnetic hysteresis while maintaining large magnetic entropy change. The maximum magnetic entropy changes (|ΔSMmax|) of Gd5Si2.05-xGe1.95-xNi2x alloys with 2x = 0.08 and 0.1 are 4.4 and 5.0 J kg-1 K-1, respectively, for 0-2 T, and are 8.0 and 9.1 J kg-1 K-1, respectively, for 0-5 T. Low hysteresis performance and relatively large magnetic entropy change make these alloys favorable for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of polycrystalline GdCo9Si2 compound have been investigated. It has a BaCd11 structure and undergoes two magnetic phase transitions: an antiferromagnetic to ferrimagnetic transition occurring at ∼93 K, and a ferrimagnetic to paramagnetic transition at 420 K, which results in a positive and a negative magnetic entropy change, respectively. The two peak values of magnetic entropy change are -0.6 and 1.1 J·kg-1·K-1 for ΔH = 5 T. Furthermore, there exists a metal-semiconductor transition temperature (TP), below which the resistance increases with increasing temperature, while the semiconductor characteristic is observed above TP. The magnetic domain structures are characterized by stripe and grid structures 1 μm wide. Although the MCE is small for applications, its study is useful to clearly understand the nature of multiple magnetic phase transitions in the GdCo9Si2 compound. [ABSTRACT FROM AUTHOR]

Density functional calculations are performed to study the electronic structure of recently proposed graphene/graphane based core/shell quantum dots, which have a type I band alignment and exhibit quantized carrier energy levels. Strong confinement is robust with shell thickness. The bandgap, band offset, and the number of confined carrier orbitals with different size and geometry are determined. Our findings indicate that these core/shell dots are potentially well suited for the design of advanced diode lasers and room-temperature single electron devices. The proposed method to determine the number of confined orbitals is applicable for other quantum dot systems. [ABSTRACT FROM AUTHOR]

A simplified trilayer green phosphorescent organic light emitting diode with high efficiency and an ultralow efficiency roll-off has been demonstrated. In particular, the external quantum efficiency drops <1% from 100 to 5,000 cd/m2 and remains as high as ∼21.9% at 10,000 cd/m2. The power efficiency is also significantly improved, reaching 78.0 lm/W at 100 cd/m2, 50.5 lm/W at 5,000 cd/m2, and 42.8 lm/W at 10,000 cd/m2. The working mechanism of this simple device structure with an unprecedented high efficiency is also discussed. [ABSTRACT FROM AUTHOR]

It is found that the device performance of organic light emitting diodes (OLEDs) can be significantly improved by separating the carrier accumulation zone from the exciton formation interface. The improvement is explained by suppression of exciton quenching caused by accumulated carriers at the exciton formation interface. It is also found that the position of the exciton formation interface in OLEDs correlates well with the interfacial dipole measured using ultraviolet photoelectron spectroscopy at the interface between a hole transport layer and an electron transport layer. The findings of this work provide useful material selection guidelines in designing high performance OLEDs. [ABSTRACT FROM AUTHOR]

A large gap was acquired between electrodes (up to 5.5 mm) of Ar atmospheric pressure glow discharge in radio frequency dielectric barrier discharge (rf-DBD). The discharge of Ar plasma was characterized by I-V curve and Lissajous plot, and the effective power of the discharge was calculated based on the measured Lissajous plot and found to be higher than 90% of the input power. To gain a thorough understanding of the mechanism, the rf-DBD with a single dielectric barrier layer operating in γ mode glow discharge of N2 plasma was diagnosed in spatial resolution through optical emission spectroscopy. It was concluded that secondary electron emission might be responsible for the sustainable glow discharge in the large gap rf-DBD plasma. [ABSTRACT FROM AUTHOR]

The interface between ultraviolet (UV) ozone treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and N,N′-diphenyl-N,N′-bis-(1-naphthyl)-1-1′-biphenyl-4,4′-diamine (α-NPD) was investigated using single carrier hole-only devices and in situ ultraviolet and x-ray photoelectron spectroscopy to elucidate the implications for device applications. It is found that although the work function of PEDOT:PSS is increased by UV ozone treatment, the injection barrier to α-NPD is in fact increased, resulting in lower current density in devices. The apparent increase in work function is attributed to a metastable surface dipole as a result of UV ozone treatment, which does not significantly influence the energy-level alignment. [ABSTRACT FROM AUTHOR]

In phosphorescent organic light-emitting diodes (OLEDs), a hole transporting layer is traditionally thought to be required to facilitate hole injection into the host molecule. It is found that fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] doped into 4,4′-N,N′-dicarbazole-biphenyl can be used to directly inject and transport holes from an indium tin oxide anode, and thus simplify the device structure and selection of materials. The efficiencies of the simplified bilayer OLEDs exceed 41 lm/W and 57 cd/A at a brightness of 100 cd/m2. We attribute the excellent performance to direct hole injection from the anode to Ir(ppy)3 dopant. [ABSTRACT FROM AUTHOR]

FeCoSiN film consisting of ordered arrays of FeCo nanoparticles embedded in a Si-rich matrix was fabricated on silicon substrate by reactive rf magnetron sputtering. These nanoparticles have a face-centered cubic structure and a mean diameter of ∼7 nm. The FeCoSiN film has a very high resistivity of up to 1000 μΩ cm due to the breakup of the metal continuum into isolated metal nanoparticles. The static and dynamic magnetic properties of the film were also investigated. A saturation magnetization of 1.0 T, coercivity of less than 5 Oe in both easy and hard axes, and anisotropy field of 27 Oe were obtained. The microwave permeability measurement showed a permeability of around 400 at low frequency and a ferromagnetic resonance frequency of about 1.1 GHz. [ABSTRACT FROM AUTHOR]

Zn1-xCdxO films (0≤=x≤=0.179) were grown on Si (001) substrates at 750 °C with a radio-frequency reactive magnetron sputtering method. Difference between the photoluminescence (PL) spectra taken at room temperature (RT) and at 12 K is reported and is deduced to be the result of PL emission from the ZnCdO phases with wurtzite and zinc blende structures. It is also found that the RT PL intensity is in inverse proportion to the carrier concentration in the films. Cd incorporation results in the transform of conductivity from p type to n type and a decrease of carrier mobility [ABSTRACT FROM AUTHOR]

Using reactive radio-frequency magnetron sputtering, epitaxial growth of ZnO film was observed on Si (001) substrate at different temperatures ranging from room temperature to 750 °C. The epitaxial relationship was determined to be ZnO(001)∥Si(001) in the direction normal to the surface of the films with a deviated angle less than 3° and ZnO[100]∥Si[110] or ZnO[310]∥Si[110] in the plan view. Based on (2×1) reconstruction of Si (001), a heteroepitaxial model was suggested to discuss the influence of Si (001) substrate on the growth and morphology of ZnO films at different temperatures. [ABSTRACT FROM AUTHOR]

Wurtzite ZnO/MgO superlattices were grown on Si (001) substrates at 750 °C with a radio-frequency reactive magnetron sputtering method. X-ray diffraction analysis revealed the superlattice to be a highly textured ZnO (001) layer and to be of high crystallinity and homogeneity in thickness. The periodic layer thickness was determined to be 1.85–17.72 nm. Room-temperature photoluminescence was detected for all the samples and showed that the blueshift varied with the well width of the ZnO layer, being consistent with the expectation of quantum-size effect. [ABSTRACT FROM AUTHOR]

Gd65Mn35-xGex (x = 0, 5, 10) alloy ribbons were prepared by melt-spinning. A fully amorphous structure was obtained for the alloys with x = 5 and 10, whereas, in melt-spun Gd65Mn35 ribbons, crystalline phases (α-Gd and GdMn2) precipitate in the amorphous matrix. The magnetic phase transition from ferromagnetic to paramagnetic is second order. The critical exponents are deduced from the Kouvel-Fisher method and scaling behavior. The obtained critical exponents are in agreement with the theoretical values of 3D Ising model. The Ising-like behavior suggests the presence of large anisotropy and short-range magnetic-coupling behavior. The maximum magnetic-entropy changes of the melt-spun alloys with x = 0, 5, and 10 for a magnetic field change from 0 to 5 T are 4.2, 4.1, and 4.5 Jkg-1 K-1, respectively. All three alloys have a broad temperature range of the magnetic-entropy peak, resulting in large refrigerant capacities. [ABSTRACT FROM AUTHOR]

Nd-Fe-Co-B-Nb alloys with Nd contents of 9-9.5 at % were prepared by melt spinning and suction casting. It was found from the melt spun ribbon samples that Nb addition enhanced the glass forming ability and Co addition improved the thermal stability. Larger values of Jr and (BH)max were obtained for the ribbon samples than for the bulk ones due to the finer crystalline structure in the former. Nanocrystallite with amorphous structure was found in the suction cast rod samples. The as-cast Nd9Fe71.5B15.5Nb4 rod in a diameter of 2 mm exhibited the best hard magnetic behavior. A remanence of 0.59 T, a coercivity of 1154 kA/m, and a maximum energy product of 54.2 kJ/m3 have been obtained after heat treatment. The distribution of nonmagnetic FeNb phase plays a key role in the improvement of coercivity. Current work suggests that large size Nd2Fe14B/Fe3B nanocomposite magnets with high Nd contents and good magnetic properties can be obtained using a nanocrystalline precursor instead of bulk metallic glass. [ABSTRACT FROM AUTHOR]

The amorphous alloys Gd60Co40-xMnx (x = 0, 5, 10, 15) were prepared by melt spinning. The Curie temperature, Tc, increases monotonously with Mn addition, ranging from 198 K for x = 0 to 205 K for x = 15, while the maximum values of -ΔSM under the applied field change from 0 to 5 T are 7.7, 7.1, 6.2 and 5.4 J·kg-1·K-1 for x = 0, 5, 10, and 15, respectively. All samples undergo a second order ferri-paramagnetic phase transition. The critical behavior around the transition temperature is investigated in detail, using both the standard Kouvel-Fisher procedure as well as the study of the field dependence of the magnetocaloric effect. Results indicate that the obtained critical exponents are reliable, and that the present alloys exhibit local magnetic interaction. [ABSTRACT FROM AUTHOR]

The thermal stability, magnetocaloric effect, and refrigerant capacity (RC) of Gd-Co-Ni metallic glasses were investigated. These alloys possess high glass transition temperature and crystallization temperature as well as a relatively wide supercooled liquid region ΔTx(ΔTx = Tx - Tg) (40-55 K). With increasing the Co/Ni ratio, the Curie temperature TC of the amorphous Gd-Co-Ni increases from 140 K to 192 K. For a magnetic field change of 0-5 T, the maximum magnetic entropy change (-ΔSMmax) and RC values are in the range of 6.04-6.47 J kg-1 K-1 and 450-502 J kg-1, respectively. These values are comparable with that of La(Fe0.88Si0.12)13 and higher than those for the well known magnetic refrigerant Gd5Si2Ge1.9Fe0.1 alloy. The large magnetic entropy change and refrigerant capacity as well as high thermal stability make the alloys attractive candidates as magnetic refrigeration materials for service temperatures of 100-230 K. [ABSTRACT FROM AUTHOR]

NdFeB based permanent magnetic nanocomposites were prepared by depositing soft magnetic Fe, Co, or Fe65Co35 nanoparticles on the melt spun NdFeB powders with near single phase composition by a chemical reduction method. The effects of the reduction process, the composition, and the concentrations of metal ions on the magnetic properties of nanocomposites were investigated. Introducing and increasing soft nanoparticle content improved the remanence and maximum energy product of the nanocomposites at the expense of coercivity. Fe65Co35 coated NdFeB powders had higher remanence and energy product than Co or Fe coated powders. The inter-grain exchange coupling between hard and soft magnetic grains was demonstrated by the smooth demagnetization curve with high remanent polarization. Remanence enhanced bulk magnets were also fabricated by consolidating the nanocomposite powders using spark plasma sintering (SPS) technique. [ABSTRACT FROM AUTHOR]

The electronic structures and magnetic properties of spinel Co1-x Zn (Cd)xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, and 1.0) have been studied systematically by the first-principles calculation. The optimized structures show that with increasing Zn (Cd) content the crystal lattice parameter increases by 1.47% (5.13%) when the Co ions are completely replaced by Zn (Cd) ions. The results also indicate that the magnetic moment of Co/Fe ion increases and the total spin magnetic moment linearly increases with the Zn (Cd) doping from 3.00 μB for x = 0.0 up to 10.00 μB for x = 1.0 per formula unit. The electronic distribution in the Co spin-down subband is highly localized for the crystal field splitting between t2g and eg levels in the Zn (Cd) doped CoFe2O4 compounds and the energy band moves downwards while doped with Zn (Cd). Meanwhile, the bandgap decreases with the increase of Zn (Cd) except where x = 1 and the spinel structure is half-metal at some degree of doping. [ABSTRACT FROM AUTHOR]

Crystal structure and magnetic properties of R5Sn4 alloys with R = Tb, Dy, Ho, and Er have been studied. R5Sn4, R11Sn10, and R5Sn3 phases coexist in the annealed alloys and the content of 11:10 and 5:3 phases varies between 9 and 17 wt.%. The R5Sn4 major phase has Sm5Ge4-type orthorhombic structure with space group Pnma. Tb5Sn4 has a complex magnetic structure, spin re-orientation and ferrimagnetic-paramagnetic phase transitions occur at ∼54 and ∼84 K, respectively. For Dy5Sn4, Ho5Sn4, and Er5Sn4, the antiferromagnetic-paramagnetic phase transitions occur at about 22, 15, and 8 K, respectively. The magnetic entropy changes (-ΔSM) of all alloys are negative at low temperature and changes to positive at higher temperatures, which could be attributed to the change of magnetic states. [ABSTRACT FROM AUTHOR]

The structure and magnetocaloric properties of polycrystalline (Gd12-xTbx)Co7 (x=0, 4, and 8) alloys with Ho12Co7-type monoclinic structure have been investigated. A spin reorientation transition occurs at about 123 K for the alloy with x=0. The peak values of magnetic entropy change -ΔSM under a magnetic field change ΔH of 5 T is 8.8 J·kg-1·K-1 at 160.8 K (Tc), 8.2 J·kg-1·K-1 at 140.8 K (Tc), and 7.1 J·kg-1·K-1 at 118.9 K (Tc) for the alloys with x=0, 4 and 8, respectively. The refrigerant capacities reach 478, 327, and 160 J·kg-1 for x=0, 4, and 8, respectively. The relatively large magnetic entropy change and reversible magnetization behavior make these alloys a good choice for magnetic refrigeration applications in the temperature range of 118-160 K. [ABSTRACT FROM AUTHOR]

Quasi-phase-matching optical parametric and cascaded parametric processes in a two-component quasiperiodic superlattice were studied in theory and experiment. This letter demonstrates how to obtain red at 666 nm and blue at 443 nm simultaneously from the superlattice using a 532 nm laser as a pump through these two processes mentioned above. The result confirms that some nonlinear frequency conversion processes occurring in a high-dimension χ[sup (2)] nonlinear photonic crystal may be efficiently achieved in such a one-dimension quasiperiodic optical superlattice. [ABSTRACT FROM AUTHOR]

Generations of efficient blue light at 447 nm and red light at 671 nm were achieved by frequency doubling and tripling of a diode-pumped, Q-switched 1342 nm Nd:YVO[sub 4] laser with a periodically poled LiTaO[sub 3] (PPLT). The blue light at 447 nm was generated by sum-frequency mixing of the fundamental at 1342 nm with the generated second harmonic at 671 nm. The first-order and third-order reciprocals of the PPLT compensated the phase mismatches of second-harmonic and sum-frequency processes, respectively, making them quasiphase matched. The resulting averaged blue light power of 51 mW and red light power of 207 mW under the averaged fundamental power of 500 mW indicate that the PPLT may be used to construct an all-solid-state blue and red dual wavelength laser. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A low energy beam transport (LEBT) system has been built for a compact pulsed hadron source (CPHS) at Tsinghua University in China. The LEBT, consisting of two solenoids and three short-drift sections, transports a pulsed proton beam of 60 mA of energy of 50 keV to the entrance of a radio frequency quadrupole (RFQ). Measurement has shown a normalized RMS beam emittance less than 0.2 π mm mrad at the end of the LEBT. Beam simulations were carried out to compare with the measurement and are in good agreement. Based on the successful CPHS LEBT development, a new LEBT for a China ADS projector has been designed. The features of the new design, including a beam chopper and beam simulations of the LEBT are presented and discussed along with CPHS LEBT development in this article. [ABSTRACT FROM AUTHOR]

A simplified trilayer green phosphorescent organic light emitting diode with high efficiency and an ultralow efficiency roll-off has been demonstrated. In particular, the external quantum efficiency drops <1% from 100 to 5,000 cd/m2 and remains as high as ∼21.9% at 10,000 cd/m2. The power efficiency is also significantly improved, reaching 78.0 lm/W at 100 cd/m2, 50.5 lm/W at 5,000 cd/m2, and 42.8 lm/W at 10,000 cd/m2. The working mechanism of this simple device structure with an unprecedented high efficiency is also discussed. [ABSTRACT FROM AUTHOR]

The structure and preliminary commissioning results of a new 2.45 GHz ECR proton ion source and a dual-lens low energy beam transport (LEBT) system are presented in this paper. The main magnetic field of the ion source is provided by a set of permanent magnets with two small electro-solenoid magnets at the injection and the extraction to fine tune the magnetic field for better microwave coupling. A 50 keV pulsed proton beam extracted by a three-electrode mechanism passes through the LEBT system of length of 1183 mm. This LEBT consists of a diagnosis chamber, two Glaser lenses, two steering magnets, and a final beam defining cone. A set of inner permanent magnetic rings is embedded in each of the two Glaser lenses to produce a flatter axial-field to reduce the lens aberrations.