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Research describing the optical properties of gallium nitride is presented. In particular the deep level properties related to persistent photoconductivity and yellow luminescence are investigated.

The properties and structures of DLC films deposited by MEP-CVD using various gases CH4, HE/CH4, Ne/CH4 and Ar/CH4 are examined. The magnitude of effects on the properties for various inert gases was found as NE, Ar and He on the surface roughness was found as Ar, Ne and He.

The optical transmission spectroscopy of the gadolinium trihydrides GdH(sup 3) for the spectral range from 0.05 to 6 eV is investigated. The analysis indicates that GdH(sub 3) is a wide-gap semiconductor with an energy gap of 2.55 eV.

The evolution of roughness in the Cu6Sn5 intermetallic compound during the soldering reaction of PbSn on Cu and its effects on wettability has been studied. Results indicate that the root mean square roughness and the average distance between asperites have a parabolic dependence on the soldering time. However the ratio of the root mean square roughness with the average distance was observed to increase gradually for the range of soldering periods examined.

This paper reports the electronic transport measurements of the single crystal Pr1.2Sr1.8Mn2O7 and Pr1Sr2Mn2O7 under pressure. The measurements in the ab plane for Pr1.2Sr1.8Mn2O7 show that the pressure induces a phase transition from a semiconducting state to a metallic state at 0.5 GPa, and then the transition temperature decreases rapidly with increasing pressure, indicating the pressure favors the paramagnetic semiconducting state and suppresses the ferromagnetic metallic state after the occurring of the transition. Moreover, for Pr1Sr2Mn2O7, the semiconducting-metallic state transition occurs at ambient pressure and the pressure favors the paramagnetic semiconducting state and suppresses the antiferromagnetic metallic state. [ABSTRACT FROM AUTHOR]

The solar-energy absorption material β-In2S3 was characterized using temperature-dependent photoconductivity (PC) measurements in the temperature range between 30 and 340 K in this study, and thermoreflectance (TR) and photoluminescence (PL) measurements were carried out to identify near-band-edge transitions in the β-In2S3 tetragonal crystal. The experimental analyses of PL, PC, and TR confirmed that β-In2S3 is a direct semiconductor with a band gap of 2.073 eV at 30 K and 1.935 eV at 300 K. The PL and PC spectra manifest some defect-related features in the β-In2S3 single crystal. Two defect emissions and two band-edge luminescences were simultaneously detected in the PL spectrum at 30 K, and the temperature-dependent PC spectra of β-In2S3 from 160 to 300 K reveal an additional defectlike or band-to-band feature with an energy located above the conduction band edge (EC). The temperature dependences of the PC transition features in the β-In2S3 defect crystal were analyzed. The origin and mechanism of all defect states and band-edge transitions in the β-In2S3 single crystal are evaluated and discussed. [ABSTRACT FROM AUTHOR]

Selective enhancement and suppression of the photoluminescence arising from Si0.5Ge0.5/Si multiple quantum wells by photonic crystals (PCs) have been demonstrated. The formation of the stop band in PCs is designed to be a filter as well as a reflector. It is found that the self-assembled PCs are able to selectively enhance the luminescence of the type-II transitions at the interface between Si and Si0.5Ge0.5/Si layers and suppress the emission from Si. Our working principle shown here can be extended to many other material systems and should be very useful for creating high power solid-state emitters. [ABSTRACT FROM AUTHOR]

200-nm-thick La- and Sm-doped BaTiO3 thin films with A/B ratio of unity fabricated by magnetron sputtering on the Pt/Ti/SiO2/Si substrate have been characterized. The effects of post-annealing and the amount of dopant on structure and electrical properties were studied. X-ray diffraction studies reveal that the films annealed at 750 °C show tetragonal BaTiO3 crystal structure without any detectable second phase formation. X-ray photoelectron spectroscopy results confirm that La substitutes the A site and Sm is in the B site in lightly doped films. La2O3 or Sm2O3 is present in the BaTiO3 structure when the dopant content is more than 1.4 at. % La or 1.0% Sm. The permittivity increases with increasing annealing temperature up to 750 °C due to the coarse grains and better crystallinity. The leakage current property is found to vary with the type of dopant. [ABSTRACT FROM AUTHOR]

The vibrational, electronic, and crystalline properties of n-type chlorine-doped ZnSe (ZnSe:Cl) layers with a carrier concentration from 8.2×1015 to 1.8×1018 cm-3 are studied by Raman spectroscopy. The spectral line shapes of the longitudinal-optical-phonon and plasmon coupling mode are analyzed using the Raman scattering efficiency and the dielectric function to obtain the electron densities and mobility. The splitting of the transverse-optical (TO) phonon and the redshift of the chlorine-related impurity vibration mode are clearly observed when pressure is applied. The semiconductor-to-metal phase transition pressure of ZnSe:Cl layers declines as the carrier concentration increases, indicating that n-type doping reduces crystal stability. Additionally, the pressure-induced weakening of the longitudinal-optical-phonon-plasmon coupling efficiency suggests that pressure tends to degrade the n-type characteristic of ZnSe:Cl because of the emergence of the new deep donorlike state. [ABSTRACT FROM AUTHOR]

We have studied the effect of the thickness of catalytic Ni film for the growth of vertically aligned carbon nanofibers (VA-CNFs) on glass substrates coated with a conductive underlayer of Cr. Both the pretreatment process through which the catalytic Ni nanoparticles were formed and the growth of well-aligned CNFs were carried out in an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. The VA-CNFs were characterized by scanning electron microscopy, Raman spectroscopy, as well as field emission measurements. The results of VA-CNF growth shows that as the Ni film thicknesses decrease, not only the length but also the density of the CNFs drop, although the density of catalytic Ni nanoparticles increases. The variation of CNF density with Ni film thicknesses is believed to be a result of the detachment of the CNFs from the substrate, caused by the electrostatic force produced by the plasma sheath electric field, as well as an ion-enhanced chemical etching effect due to atomic/ionic hydrogen, during the ICP-CVD growth. A field emission measurement apparatus based on a metallic probe of spherical anode structure was also constructed in this study. An electrostatic image model was employed to determine the electric field distribution on the cathode surface. Along with the standard F-N field emission model, the dependence of field emission current density on the cathode surface electric field, as well as an effective field enhancement factor, were extracted from the current-voltage measurement results. The threshold electric field (Ethreshold, for a current density of 1 mA/cm2) increases from 9.2 V/μm to 13.1 V/μm, and then drops to 11.5 V/μm for the CNFs with Ni film thicknesses of 20 nm, 30 nm, and 40 nm, respectively. The electrostatic model results also indicate that the 20 nm case has the greatest space-charge effect on the emission current, consistent with the growth results that the 20 nm case has the lowest CNF density. On the other hand, the CNF length of the 40 nm case is longer than that of the 30 nm one, while the densities are nearly the same; as a result, Ethreshold for the 30 nm case is higher. [ABSTRACT FROM AUTHOR]

This work systematically investigates the influence of InAs growth conditions and superlattice parameters on the optical properties of InAs/GaAs quantum dot (QD) superlattice structures grown by molecular beam epitaxy. Using surface photovoltage spectroscopy, one directly obtains the absorption spectra up to the highest confined QD levels at room temperature. Based on photoluminescence measurements at different excitation wavelengths, a feature below the fundamental transition is attributed to the transition from uncoupled dots in the bottom layers. The QD transition energy shift was found to be correlated with material intermixing, driven by enhanced strain strength with the increase of layer number and the decrease of spacer thickness, and the growth rate of InAs. A blueshift observed in low growth rate samples is indicative of greatly enhanced intermixing. For QD superlattices grown at a relatively high deposition rate of InAs, the material intermixing effect is gradually enhanced with increasing layer numbers, which will compensate the electronically coupled effect and will prevent further energy shift toward the lower energy side. The absorption wavelengths in 10- and 30-period InAs/GaAs QD superlattices with higher growth rates are near 1.32 μm. The results suggest that these QD superlattice structures can be used as promising active media for long-wavelength QD lasers operating at room temperature. [ABSTRACT FROM AUTHOR]

300⊗300 μm2 crack-free GaN/AIN multilayers of 2 μm in thickness have been successfully grown on the Si(111) substrate patterned with the SixNy mesh by metal-organic chemical-vapor deposition. The in-plane stress exhibits a U-shape distribution across the ‘window’ region, supported by the Raman shift of the GaN E2(TO) mode. This indicates a stress relaxation abruptly occurring near the edge of the window region due to the freestanding surface (1101) or (1122). The in-plane stress is almost relaxed at the corner of the window region due to three freestanding surfaces (1101), (1122), and (1011). The maximum in-plane stress is located near the surface of the multilayers at the center of the window region, supported by the Raman measurements and the failure observations. The role of the SixNy mesh in the stress relaxation is discussed. [ABSTRACT FROM AUTHOR]

The objective of this work was to understand the effect of the movable electrode (the tip of an atomic force microscope) on a piezoelectric-induced (PEI) image. Local polarization is induced on a lead zirconate titanate (PZT) thin film using an atomic force microscope (AFM), by applying dc voltage between the movable electrode and the Pt bottom electrode. The polarized PZT film is then characterized by the AFM using a two-pass method, in which both the topography and PEI image are obtained. The surface morphology is recorded in the first pass under contact mode with a fixed setpoint. A PEI image is obtained in the second pass in piezo-response mode. In this mode, the sample surface is scanned by applying ac voltage between the AFM tip and the Pt bottom electrode at sample displacement. PEI images of various sample displacement, corresponding to different stress exerted by the tip on the sample surface, are obtained and analyzed using force–sample displacement curves. It is found that PEI images can be detected if the tip adheres to the sample. The asymmetry of the A cos θ signal is improved as the force changes from repulsive to attractive. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effects on the local structure due to self-irradiation damage of Ga stabilized δ-Pu stored at cryogenic temperatures have been examined using extended x-ray absorption fine structure (EXAFS) experiments. Extensive damage, seen as a loss of local order, was evident after 72 days of storage below 15 K. The effect was observed from both the Pu and the Ga sites, although less pronounced around Ga. Isochronal annealing was performed on this sample to study the annealing processes that occur between cryogenic and room temperature storage conditions, where damage is mostly reversed. Damage fractions at various points along the annealing curve have been determined using an amplitude-ratio method, a standard EXAFS fitting, and a spherical crystallite model, and provide information complementary to the previous electrical resistivity- and susceptibility-based isochronal annealing studies. The use of a spherical crystallite model accounts for the changes in EXAFS spectra using just two parameters, namely, the crystalline fraction and the particle radius. Together, these results are discussed in terms of changes to the local structure around Ga and Pu throughout the annealing process and highlight the unusual role of Ga in the behavior of the lowest temperature anneals. [ABSTRACT FROM AUTHOR]

Nuclear weapons testing generates large volumes of glassy materials that influence the transport of dispersed actinides in the environment and may carry information on the composition of the detonated device. We determine the oxidation state of U and Fe (which is known to buffer the oxidation state of actinide elements and to affect the redox state of groundwater) in samples of melt glass collected from three U.S. nuclear weapons tests. For selected samples, we also determine the coordination geometry of U and Fe, and we report the oxidation state of Pu from one melt glass sample. We find significant variations among the melt glass samples and, in particular, find a clear deviation in one sample from the expected buffering effect of Fe(II)/Fe(III) on the oxidation state of uranium. In the first direct measurement of Pu oxidation state in a nuclear test melt glass, we obtain a result consistent with existing literature that proposes Pu is primarily present as Pu(IV) in post-detonation material. In addition, our measurements imply that highly mobile U(VI) may be produced in significant quantities when melt glass is quenched rapidly following a nuclear detonation, though these products may remain immobile in the vitrified matrices. The observed differences in chemical state among the three samples show that redox conditions can vary dramatically across different nuclear test conditions. The local soil composition, associated device materials, and the rate of quenching are all likely to affect the final redox state of the glass. The resulting variations in glass chemistry are significant for understanding and interpreting debris chemistry and the later environmental mobility of dispersed material. [ABSTRACT FROM AUTHOR]

The impact of proton irradiation on the threshold voltage (VT) of AlGaN/GaN heterostructures is systematically investigated to enhance the understanding of a primary component of the degradation of irradiated high electron mobility transistors. The value of VT was found to increase monotonically as a function of 1.8MeV proton fluence in a sub-linear manner reaching 0.63V at a fluence of 1×1014 cm-2. Silvaco Atlas simulations of VT shifts caused by GaN buffer traps using experimentally measured introduction rates, and energy levels closely match the experimental results. Different buffer designs lead to different VT dependences on proton irradiation, confirming that deep, acceptorlike defects in the GaN buffer are primarily responsible for the observed VT shifts. The proton irradiation induced VT shifts are found to depend on the barrier thickness in a linear fashion; thus, scaling the barrier thickness could be an effective way to reduce such degradation. [ABSTRACT FROM AUTHOR]

We examined the crystal structure of the new thermoelectric material LaOBiS2-xSex, whose thermoelectric performance is enhanced by Se substitution, by using powder synchrotron X-ray diffraction and Rietveld refinement. The emergence of metallic conductivity and enhancement of the thermoelectric power factor of LaOBiS2-xSex can be explained with the higher in-plane chemical pressure caused by the increase of Se concentration at the in-plane Ch1 site (Ch = S, Se). High-temperature X-ray diffraction measurements for optimally substituted LaOBiSSe revealed anomalously large atomic displacement parameters (Uiso) for Bi and Ch atoms in the BiCh2 conduction layers. The anisotropic analysis of the atomic displacement parameters (U11 and U33) for the in-plane Bi and Ch1 sites suggested that Bi atoms exhibit large atomic displacement along the c-axis direction above 300 K, which could be the origin of the low thermal conductivity in LaOBiSSe. The large Bi vibration along the c-axis direction could be related to in-plane rattling, which is a new strategy for attaining low thermal conductivity and phonon-glass-electron-crystal states. [ABSTRACT FROM AUTHOR]

A droplet that moves on a solid substrate with a velocity higher than a certain critical velocity disintegrates, i.e., leaves behind residual droplets. Infrared laser illumination can be used to increase the droplet mobility and suppress the shedding of droplets. By means of two-dimensional numerical simulations, we studied the effect of a non-uniform temperature distribution on the dynamics of straight receding contact lines. A streamfunction-vorticity model is used to describe the liquid flow in the vicinity of the receding contact line. The model takes into account the thermocapillary shear stress and the temperature-dependent liquid viscosity and density. A second, coupled model describes the laser-induced displacement of the contact line. Our results show that the reduction of the liquid viscosity with increasing temperature is the dominant mechanism for the increase of the critical velocity. Thermocapillary shear stresses are important primarily for low substrate speeds. [ABSTRACT FROM AUTHOR]

The shape of a droplet moving on a solid substrate is largely determined by the mobility of its contact line. Above a certain critical velocity, the droplet typically disintegrates and leaves residual liquid behind. We studied experimentally how localized infrared laser illumination can stabilize it against the progressive loss of liquid. We systematically varied the substrate velocity, the laser power, and the laser spot position and found that the critical velocity of the droplet can be substantially increased. These results are potentially important for increasing throughput in immersion lithography systems. [ABSTRACT FROM AUTHOR]

Research was conducted to study internal losses in optically pumped type-II lasers with InAs/GaSb/Ga(sub 1-x)InxSb/GaSb superlattice active regions. The superlattice lasers produced maximum peak output powers of up to 6.5 W per facet at 100 K and 3.5 per face at 180 K. Temperature-dependent intervalence absorption computations indicated that losses of the magnitude can easily occur if one does not avoid resonances in all regions of the Brillouin zone.

The neutron imaging system at the National Ignition Facility is an important diagnostic tool for measuring the two-dimensional size and shape of the source of neutrons produced in the burning deuterium-tritium plasma during the stagnation phase of inertial confinement fusion implosions. Very few two-dimensional projections of neutron images are available to reconstruct the threedimensional neutron source. In this paper, we present a technique that has been developed for the 3D reconstruction of neutron and x-ray sources from a minimal number of 2D projections. We present the detailed algorithms used for this characterization and the results of reconstructed sources from experimental data collected at Omega. [ABSTRACT FROM AUTHOR]

Artificial magnetic spin-ice nanostructures provide an ideal platform for the observation of magnetic monopoles. The formation of a magnetic monopole is governed by the motion of a magnetic charge carrier via the propagation of domain walls (DWs) in a lattice. To date, most experiments have been on the static visualization of DW propagation in the lattice. In this paper, we report on the low field dynamics of DW in a unit spin-ice structure measured by magnetoresistance changes. Our results show that reversible DW propagation can be initiated within the spin-ice basis. The initial magnetization configuration of the unit structure strongly influences the direction of DW motion in the branches. Single or multiple domain wall nucleation can be induced in the respective branches of the unit spin ice by the direction of the applied field. [ABSTRACT FROM AUTHOR]

The impact of annealing of proton irradiation-induced defects in n-type GaN devices has been systematically investigated using deep level transient and optical spectroscopies. Moderate temperature annealing (>200-250 °C) causes significant reduction in the concentration of nearly all irradiation-induced traps. While the decreased concentration of previously identified N and Ga vacancy related levels at EC-0.13 eV, 0.16 eV, and 2.50 eV generally followed a first-order reaction model with activation energies matching theoretical values for NI and VGa diffusion, irradiation-induced traps at EC-0.72 eV, 1.25 eV, and 3.28 eV all decrease in concentration in a gradual manner, suggesting a more complex reduction mechanism. Slight increases in concentration are observed for the N-vacancy related levels at EC-0.20 eV and 0.25 eV, which may be due to the reconfiguration of other N-vacancy related defects. Finally, the observed reduction in concentrations of the states at EC-1.25 and EC-3.28 eV as a function of annealing temperature closely tracks the detailed recovery behavior of the background carrier concentration as a function of annealing temperature. As a result, it is suggested that these two levels are likely to be responsible for the underlying carrier compensation effect that causes the observation of carrier removal in proton-irradiated n-GaN. [ABSTRACT FROM AUTHOR]

Investigates the origin of temperature-sensitive hole current at low voltage regime in ultrathin gate oxide. Correlation of the gate and source/drain currents at low gate voltage regime; Dependence of the currents on temperature above 250 Kelvin; Observation of the temperature dependence on both negative and positive polarities.

Presents a study which proposed a method to measure the lifetime of excess electron-hole pairs generated by laser beams. Importance of the lifetime of the excess carriers in a semiconductor; Measurement principles; Components of the noise measurement system.

The magnetic anisotropy of the multilayered structures strongly depends on the structures of the interface and the uniaxial character of these multilayers decreases largely due to intermixing of the layers and as a result less magnetic anisotropic films are produced. Magneto-optic Kerr rotation, measured at a suitable photon wavelength where the rotation depends on induced polarization of nonferromagnetic constituents, gives a rough measurement for the extent of intermixing.

The poling of lophine-type chromophores in soluble and insoluble polyimides having different poling geometries was studied. Lopin chromophore was poled either parallel or perpendicular to the polymer film plane and the decay of poling was evaluated under several temperatures. The chromophore's poling behavior with other polymeric hosts was also examined. Results show that the poling decay times for all the systems considered in the study are strongly correlated with the glass transition temperature of the guest-host system.

A new technique for the decomposition of closely spaced interface and bulk deep trap states was presented. The technique utilizes temperature-dependent pulse-width deep level transient spectroscopy to separate two bulk trap states and one continuously distributed interface state in a Pt/CdS photodiode, thus allowing a more accurate measurement of the physical parametrs to be obtained.

An improved method for measuring the cross sections for carrier trapping at defects in semiconductors is described. This method, a variation of deep level transient spectroscopy (DLTS) used with bipolar transistors, is applied to hot carrier trapping at vacancy-oxygen, carbon-oxygen, and three charge states of divacancy centers (V2) in n- and p-type silicon. Unlike standard DLTS, we fill traps by injecting carriers into the depletion region of a bipolar transistor diode using a pulse of forward bias current applied to the adjacent diode. We show that this technique is capable of accurately measuring a wide range of capture cross sections at varying electric fields due to the control of the carrier density it provides. Because this technique can be applied to a variety of carrier energy distributions, it should be valuable in modeling the effect of radiation-induced generation-recombination currents in bipolar devices. [ABSTRACT FROM AUTHOR]

Size-selected Mon-, Wn-, and Fen - cluster anions are deposited on a weakly interacting substrate (highly oriented pyrolytic graphite) and studied ex-situ using atomic force microscopy. Depending on size, three growth modes can be distinguished. Very small clusters consisting of less than 10-30 atoms behave similar to atoms and coalesce into 3-dimensional bulk-like islands. Medium sized clusters consisting of hundreds of atoms do not coalesce and follow a Stanski-Krastanov growth pattern. At low coverage, an almost perfect monolayer is formed. This is a new finding different from all previous studies on deposited metal clusters. For clusters with several thousands of atoms, the growth pattern again changes. At low coverage, the substrate is dotted with individual clusters, while at high coverage, the surface becomes extremely rough. [ABSTRACT FROM AUTHOR]

Significant efforts towards understanding bi-magnetic core-shell nanoparticles are underway currently as they provide a pathway towards properties unavailable with single-phased systems. Recently, we have demonstrated that the magnetism of c-Fe2O3/CoO core-shell nanoparticles, in particular, at high temperatures, originates essentially from an interfacial doped iron-oxide layer that is formed by the migration of Co2+ from the CoO shell into the surface layers of the γ-Fe2O3 core [Skoropata et al., Phys. Rev. B 89, 024410 (2014)]. To examine directly the nature of the intermixed layer, we have used high-resolution transmission electron microscopy (HRTEM) and first-principles calculations to examine the impact of the core-shell intermixing at the atomic level. By analyzing the HRTEM images and energy dispersive spectra, the level and nature of intermixing was confirmed, mainly as doping of Co into the octahedral site vacancies of γ-Fe2O3. The average Co doping depths for different processing temperatures (150 °C and 235 °C) were 0.56 nm and 0.78 nm (determined to within 5% through simulation), respectively, establishing that the amount of core-shell intermixing can be altered purposefully with an appropriate change in synthesis conditions. Through first-principles calculations, we find that the intermixing phase of γ-Fe2O3 with Co doping is ferromagnetic, with even higher magnetization as compared to that of pure γ-Fe2O3. In addition, we show that Co doping into different octahedral sites can cause different magnetizations. This was reflected in a change in overall nanoparticle magnetization, where we observed a 25% reduction in magnetization for the 235 °C versus the 150 °C sample, despite a thicker intermixed layer. [ABSTRACT FROM AUTHOR]

This paper develops a discrete optimal control based on the multi-rate observer method for electromagnetic suspension systems in order to levitate the vehicle, maintaining the desired gap. The proposed multi-rate compensator consists of two parts which are the discrete Kalman filter and the optimal control law. The Kalman filter estimates all states with fast sampling rate time, using a slowly measured output from the gap sensor. The optimal control law is determined by linear matrix inequality optimization for the discrete time multiple input system obtained by the lifting operator. The proposed multi-rate controller has the advantages to guarantee the stability of the slow-rate optimal control and maintain the performance of fast-rate control. The simulation and experiment show the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

First-principle calculations are used to explore the use of magnetic degrees of freedom in catalysis. We use the Vienna Ab-Initio Simulation Package to investigate both L10-ordered FePt and CoPt bulk materials and perform supercell calculations for FePt nanoclusters containing 43 atoms. As the catalytic activity of transition-metal elements and alloys involves individual d levels, magnetic alloying strongly affects the catalytic performance, because it leads to shifts in the local densities of states and to additional peaks due to magnetic-moment formation. The peak shift persists in nanoparticles but is surface-site specific and therefore depends on cluster size. Our research indicates that small modifications in stoichiometry and cluster size are a useful tool in the search for new catalysts. [ABSTRACT FROM AUTHOR]

Equal-channel angular pressing (ECAP) is a well-established thermo-mechanical processing technique. This technique allows virtually unlimited strain and manipulation of texture by processing route, while the cross-section of the sample remains unchanged during processing. In order to clarify the effectiveness of ECAP on preparing anisotropic permanent magnets, the microstructure and magnetic properties of a melt-spun Nd13.5Fe73.8Co6.7B5.6Ga0.4 alloy processed at 773K for 300 s by ECAP were investigated. Macrotexture analysis carried out for the exit channel of ECAP shows that the basal plane of the tetragonal Nd2Fe14B crystal aligns parallel to the shear band, i.e., the c-axis texture formation normal to the shear band induced by the ECAP process. Due to this texture formation, the technical magnetization behaviour becomes anisotropic, and the remanent magnetization is clearly enhanced along the direction perpendicular to the shear band. This anisotropic microstructure is realized at a relatively low processing temperature of 773 K, well below the melting point of the Nd-rich intergranular phase. As a consequence of this lower processing temperature, the nanostructure of the melt-spun alloy remains approximately 20 to 30 nm, considerably smaller than the typical grain size obtained after conventional die-upsetting. Our study demonstrates that equal-channel angular pressing has a potential for realising anisotropic nanostructured magnets. [ABSTRACT FROM AUTHOR]

Superparamagnetic behavior of ultrathin CoFeB film grown on epitaxial BiFeO3 (BFO) thin film was investigated by using anomalous Hall effect (AHE) at different temperatures. A transition from superparamagnetism to blocked state was observed for CoFeB grown directly on SrTiO3 (STO) substrate, but absent for CoFeB grown on BFO from 30K to 300 K. By fitting normalized AHE data with Langevin equation, average grain sizes of the superparamagnetic CoFeB grown on STO and BFO were estimated. Considering the relationship between volume of nanoparticle and blocking temperature (TB), TB of CoFeB grown on BFO was above 30K which was not observed experimentally, indicating that in addition to surface roughness or oxidation, interfacial exchange coupling also played a role in the suppression of TB. By taking the interfacial exchange coupling between BFO and superparamagnetic CoFeB as an effective field, Bloch equations were introduced to study the relaxation process of superparamagnetic CoFeB. This suppression of TB was proposed to be attributed to a cooperative effect of interfacial exchange coupling as well as roughness or oxidation between BFO and superparamagnetic CoFeB. [ABSTRACT FROM AUTHOR]

Robustness of the geometric phase (GP) with respect to different noise effects is a basic condition for an effective quantum computation. Here, we propose a useful quantum system with real physical parameters by studying the GP of a pair of Stokes and anti-Stokes photons, involving Raman emission processes with and without photonic band gap (PBG) effect. We show that the properties of GP are very sensitive to the change of the Rabi frequency and time, exhibiting collapse phenomenon as the time becomes significantly large. The system allows us to obtain a state which remains with zero GP for longer times. This result plays a significant role to enhance the stabilization and control of the system dynamics. Finally, we investigate the nonlocal correlation (entanglement) between the pair photons by taking into account the effect of different parameters. An interesting correlation between the GP and entanglement is observed showing that the PBG stabilizes the fluctuations in the system and makes the entanglement more robust against the change of time and frequency. [ABSTRACT FROM AUTHOR]

We report a facile, two-step method for the micro-landscaping of Au nanoparticles(NPs) on reduced graphene oxide (rGO) film en route to micro-patterned Au(NPs)-rGO hybrid functional materials. This method employs a focused laser beam to first locally convert GO to rGO before immersing the micro-patterned GO-rGO film into HAuCl4 solution. The rGO micro-pattern, shaped by the focused laser beam, serves as nucleation sites for the reduction of Au ions. The reduction mechanism that governs the decoration of Au NPs on rGO films is akin to electroless deposition process. In this instance, surface charges that are formed during laser reduction of GO to rGO provide active nucleation sites for Au3+ ions to form Au NPs when HAuCl4 solution is introduced. The number density, the size, and size distribution of the Au NPs can thus be directly tuned and preferentially anchored onto the rGO micro-pattern by varying the incident laser power, the scanning speed of the laser, or the concentration of HAuCl4. The resulting hybrid materials can be used as a substrate for Surface Enhanced Raman Spectroscopy (SERS). Using Rhodamine 6G as the test subject, we found an improvement of SERS enhancement over bare rGO of up to four times, depending on the size of the Au NPs. [ABSTRACT FROM AUTHOR]

We report the formation of plutonium hydride in 2 at.% Ga-stabilized δ-Pu, with 1 at.% H charging. We show that magnetization measurements are a sensitive, quantitative measure of ferromagnetic plutonium hydride against the nonmagnetic background of plutonium. It was previously shown that at low hydrogen concentrations, hydrogen forms super-abundant vacancy complexes with plutonium, resulting in a bulk lattice contraction. Here, we use magnetization, X-ray, and neutron diffraction measurements to show that in addition to forming vacancy complexes, at least 30% of the H atoms bond with Pu to precipitate PuHx on the surface of the sample with x∼1.9. We observe magnetic hysteresis loops below 40K with magnetic remanence, consistent with ferromagnetic PuH1.9. [ABSTRACT FROM AUTHOR]

We outline the procedure of extending the Thévenin equivalence principle for classical electric circuits to reducing Aharonov-Bohm-based quantum networks into equivalent models. With examples, we show from first principles how the requirements are related to the electron band structure's Fermi level and the lattice spacing of the network. Quantum networks of varying degrees of coupling strength from four basic classifications of single and double entangled loops sharing symmetry and highly correlated band structures are used to demonstrate the concept. We show the limitations of how the principle may be applied. Several classes of examples are given and their equivalent forms are shown. [ABSTRACT FROM AUTHOR]

The results of the growth of thin (~3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation. [ABSTRACT FROM AUTHOR]

Ni3Fe/(Ni, Fe)O thin films with bilayer and nanocrystallite dispersion morphologies are prepared with a dual ion beam deposition technique permitting precise control of nanocrystallite growth, composition, and admixtures. A bilayer morphology provides a Ni3Fe-to-NiO interface, while the dispersion films have different mixtures of Ni3Fe, NiO, and FeO nanocrystallites. Using detailed analyses of high resolution transmission electron microscopy images with Multislice simulations, the nanocrystallites' structures and phases are determined, and the intermixing between the Ni3Fe, NiO, and FeO interfaces is quantified. From field-cooled hysteresis loops, the exchange bias loop shift from spin interactions at the interfaces are determined. With similar interfacial molar ratios of FM-to-AF, we find the exchange bias field essentially unchanged. However, when the interfacial ratio of FM to AF was FM rich, the exchange bias field increases. Since the FM/AF interface 'contact' areas in the nanocrystallite dispersion films are larger than that of the bilayer film, and the nanocrystallite dispersions exhibit larger FM-to-AF interfacial contributions to the magnetism, we attribute the changes in the exchange bias to be from increases in the interfacial segments that suffer defects (such as vacancies and bond distortions), that also affects the coercive fields. [ABSTRACT FROM AUTHOR]

Perpendicular recording media consisting of isolated Copt magnetic grains separated with a nonmagnetic oxide grain boundary, which could be prepared by sputtering a Ru interlayer and then cosputtering CoPt with an oxide material, with low adatom mobility is presented. It is found that an increase in the oxide volume fraction in the magnetic layer does not affect the saturation magnetization but significantly reduces the magnetocrystalline anisotropy of magnetic grains.

The various effects of MgO tunnel barrier thickness on magnetohysteresis of a perpendicularly magnetized magnetic tunnel junction are investigated. The results demonstrate the oscillating dependences of the high coercivity of pinned layer and the low coercivity of free layer on MgO thickness along with an out-of-phase feature between both layers' coercivity cyclic variation.

The effect of the size of nanosized thin-film iron dot on the growth of multiwall carbon nanotubes (MWNTs) is examined. MWNT growth is not supported by iron dots or catalytic particles, which are smaller than 140 nm.