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In this work, we present an atomic-scale investigation of L10-FePt particles that are partly or fully embedded in a single-crystalline MgO matrix. Hundreds of particles in different orientations, of different sizes, and with different side contact facets are statistically and quantitatively analyzed. It is found that the presence of side contact facets does not introduce any misorientation in particles with the c axis out-of-plane (OP), even in those of small sizes. In addition, a markedly higher proportion of in-plane (IP) variants is found in smaller particles of sizes less than 10 nm, and most IP variants and the IP part in multi-variants have a large area of side contact facets or are even fully embedded. Those results can be explained by the fact that the transformation strain and interface strain jointly affect the particle orientation, and the competition between total strain energy in the film plane and in lateral planes plays a key role in determining particle orientation. Thus, a suggestion on the L10-FePt nanoparticle film production can be proposed that a moderate area of side contact facets may help keep a perfect OP orientation in the OP particles without increasing the proportion of IP variants. Additionally, our work can provide reference information on the variant orientation preference during a post-annealing process in nanoparticle films on a rough substrate or embedded in a matrix as well as in core–shell material systems. [ABSTRACT FROM AUTHOR]

Efficiently interfacing photonic with semiconductor qubits plays an important role in future quantum communication applications. In this paper, we model a photon to exciton interface based on an optically active gate-defined quantum dot (OAQD) embedded in a carefully designed photonic crystal cavity constraining its emission profile via the Purcell effect while maintaining a low enough quality factor to allow for electrical tuning of the emission wavelength. By matching the in-plane k-vector of a cavity mode and the reciprocal lattice constant of the photonic crystal, vertical emission is obtained. A back-reflection mirror located below the cavity and integrated as part of an already predefined process flow allows for not only the increasing of the light extraction efficiency but also the tailoring of the extracted beam profile to match that of a single mode fiber. We numerically show that a photon emitted by the OAQD can be coupled to the targeted free-space Gaussian beam with a probability above 50%, limited by electrode absorption. Further efficiency improvement up to 90% is possible by using indium tin oxide instead of gold as a gate material. [ABSTRACT FROM AUTHOR]

The electron energy-loss magnetic chiral dichroism (EMCD) technique has been generally applied to single-phase magnetic crystals while rarely used for composite structures. It is mainly due to the lack of in-depth understanding of EMCD in the latter case where an additional phase may present under or above the investigated magnetic phase in the electron beam path. Here, we report EMCD signals acquired on a 15-nm-thick magnetic iron film with different thicknesses of the MgO substrate underlayer. By comparison, for areas with total thicknesses of t = 0.59 λ and t = 1.02 λ expressed with the mean free inelastic path of electron λ , the relative dichroic signals at the Fe ‐ L 3 edge are 3.8 % ± 1.0 % and 3.5 % ± 1.6 % , respectively, demonstrating no significant difference within the error range. However, the dichroic signal intensity at the Fe ‐ L 2 edge peak is 77.6% larger in the thinner area of t = 0.59 λ. Accordingly, the extracted m L / m s ratio of Fe 3 d moments is 63% smaller in the thinner area even after the plural scattering is removed. Then, we confirm that the presence of an additional nonmagnetic phase under a magnetic iron crystal can noticeably affect the quantified value of the m L / m s ratio of iron moment determined from the EMCD measurements. Furthermore, the larger thickness of the underlayer may result in relatively higher valuation of the m L / m s ratio of the upper layer. A correction method, considering the different influence of the underlayer on the Fe ‐ L 3 and L 2 edges, is in demand for developing potential applications of the EMCD technique to such composite nanomaterial systems. [ABSTRACT FROM AUTHOR]

A change in the dimensionality of an energy band in a semiconductor is done by reducing the dimension of its physical size. Here, we show that by spatially deforming a two-layer heterostructure into a wrinkled pattern, the minimum of the energy profile transforms from a two-dimensional plane at the hetero-interface into a one-dimensional path that lies along the wrinkled edge. This change alters the carrier path, causing the carriers to travel along a one-dimensional sinusoidal path, which may lead to an application. The present investigation shows that the dimensionality of the energy profile can be engineered by changing the morphology of the epilayers and provides insight into possible applications of the wrinkled pattern. [ABSTRACT FROM AUTHOR]

In this work, we use ultrafast optical pump-optical probe spectroscopy to probe the polaron dynamics in La0.7Ca0.3MnO3 (LCMO) thin films. The temporal evolution in transient reflectivity change ΔR/R exhibits two relaxing components: a fast component with a time constant of subpicosecond and a slow component with time constant ranging from tens of picoseconds to hundreds of picoseconds. The amplitude of the fast component, though has been seldom discussed before, exhibits the similar temperature dependence with that of the resistivity and the neutron scattering intensity due to nanoscale correlated polarons. The results strongly suggest that the fast photoinduced reflectivity change may have been due to the photoexcitation and trapping process of correlated Jahn–Teller polarons in the paramagnetic and ferromagnetic phases and, thus, implies the presence of electronic inhomogeneity in LCMO manganites. [ABSTRACT FROM AUTHOR]

A two-step treatment by argon (Ar) and hydrogen plasma beam scanning was developed to modify the surface bonds of a hydrogenated amorphous carbon (a-C:H) film on indium tin oxide glass. The modified a-C:H film is an excellent layer for liquid crystal alignment, on which the pretilt angle of a nematic liquid crystal (ZLI-2293) can be adjusted by the two-step scanning treatment. The chemical bonding characteristics of the as-scanned a-C:H films were measured using micro-Raman and x-ray photoemission spectroscopies. The antiparallel cells were filled with the nematic liquid crystal on the as-scanned a-C:H film to measure the pretilt angle. Experimental results indicate that the carbon dangling bonds are generated through a bond-breaking process during the Ar plasma beam scanning step (first step). The hydrogen plasma beam scanning step (second step) can passivate some of the carbon dangling bonds that are generated in the first step. The pretilt angle decreases as the hydrogen plasma beam scanning time increases. The decrease of pretilt angle is due to the formation of C–H bonds that passivate the a-C:H film and limit the formation of C–O bonds in air. [ABSTRACT FROM AUTHOR]

A plasma beam scanning treatment has been developed to modify the surface of the hydrogenated amorphous carbon (a-C:H) film on the indium tin oxide glass. The plasma beam scanning treatment makes the a-C:H film an excellent layer for liquid-crystal alignment. The qualities of a-C:H films were characterized by using atomic force microscope, micro-Raman spectroscopy, and field-emission scanning electron microscope. The ultrathin a-C:H films were deposited at 50% CH4/(H2+CH4) gas ratio, 100 W radio-frequency power, and a gas pressure of 10 mtorr for 15 min by capacitive-coupled plasma chemical-vapor deposition method. The twist nematic cells were filled with liquid crystal (ZLI-2293) on the a-C:H film treated with different nitrogen plasma beam scanning time. The grooving mechanism is considered not responsible for the liquid-crystal (LC) alignment. Raman spectra suggest that a bond-breaking process of aromatic rings occurs in the a-C:H film. The O1s, C1s, and N1s core-level spectra support that the nitrogen plasma beam scanning treatment induces a bond-breaking process of aromatic rings to create available carbon dangling bonds for the formation of C–O bonds. The newly formed C–O bonds are “directional,” which favor the LC alignment on the a-C:H film. [ABSTRACT FROM AUTHOR]

A general, quantitative relationship between the photon-transport mean free path (l*) and resin sensitivity (DP) in multiple-scattering alumina/monomer suspensions formulated for ceramic stereolithography is presented and experimentally demonstrated. A Mie-theory-based computational method with structure factor contributions to determine l* was developed. Planar-source diffuse transmittance experiments were performed on monodisperse and bimodal polystyrene/water and alumina/monomer systems to validate this computational tool. The experimental data support the application of this l* calculation method to concentrated suspensions composed of nonaggregating particles of moderately aspherical shape and log-normal size distribution. The values of DP are shown to be approximately five times that of l* in the tested ceramic stereolithography suspensions. [ABSTRACT FROM AUTHOR]

Single phase TiO[sub 2] thin films, of either rutile or anatase structure, have been prepared on SrTiO[sub 3](STO)(100) substrates by in situ pulsed laser deposition (PLD). Thermodynamically unfavorable, for films deposited on STO(100) substrate directly, pure anatase TiO[sub 2](001) films were formed even when a rutile TiO[sub 2] (110) substrate was used as a target. On the other hand, pure rutile TiO[sub 2](110) films were obtained by oxidizing PLD TiN films in-situ at temperatures higher than 700 °C. The optimized deposition conditions for preparing TiN and TiO[sub 2] films were reported. The crystalline structure, surface morphology, and electronic structure of these films were examined. A mechanism of the process of film formation is also proposed. [ABSTRACT FROM AUTHOR]

We present time-resolved electron energy loss spectroscopy measurement of isothermal desorption of NH3 and ND3 from Cu(001) as a function of coverage. The desorption process is characterized by pseudo-first-order kinetics. The pseudo-first-order rate constant increases approximately exponentially as a function of adsorbed ammonia coverage. The results of an analysis based on a quasiequilibrium approximation which expresses the desorption rate in terms of a virial expansion in adsorbate coverage are reported. This demonstrates that the intermolecular interactions are dominated by short range repulsive lateral interactions, in qualitative accord with expectations of dipolar interactions. The results also suggest the existence of longer-range attractive interactions. [ABSTRACT FROM AUTHOR]

The kinetics of NH3 and ND3 desorption from Cu(001) surface have been measured by time-resolved electron energy loss spectroscopy. The desorption precess is observed to be characterized by pseudo-first-order kinetics. The desorption energy and the prefactor have been determined for both NH3 and ND3. The prefactors are unusually low as compared to those observed for simple diatomic molecules. Moreover, we observed an unusual behavior consistent with an isotope kinetic compensation effect. Both of these observations can be explained within the context of transition state theory by the interplay between isotopic masses and the shifts of frustrated vibrational modes of adsorbed molecules. Our results imply that the conventional Arrhenius form would not be precisely applicable to molecular desorption, if a large enough temperature range could be measured, particularly for hydrogen-containing molecules. [ABSTRACT FROM AUTHOR]

Deals with a study which investigated submicron indium phosphide transferred electron devices. Method used to model the direct current characteristics of near-micron structures; Background on the physical origins of the length effect in submicron structures; Description of the static characteristics of transferred electron devices.

Presents a theoretical study of electron transport in the resonant-tunneling diode under the effects of an in-plane magnetic field. Description of the theoretical model; Results; Conclusions.

Presents information on a study which considered front formation and steady-state front motion in a one-dimensional polymer system undergoing case-II diffusion. Analysis of the problem with a steady-state moving front; Results of the study; Conclusions.

Presents information on a study which considered the swelling of a polymer glass by sorption of a small molecule penetrant in a regime characterized by so-called case-II diffusion. Methodology of the study; Results and discussion.

We present time-resolved electron energy loss spectroscopy (EELS) results for the desorption of submonolayer coverages of H2O and D2O from Ag(011). The measurements were performed isothermally and effectively at constant coverage. At coverages above a few percent of a monolayer, we observe that the desorption is characterized by zero-order kinetics. That is, the desorption rate is independent of coverage. We hypothesize that this results from the formation of two-dimensional water islands on the surface at all coverages and temperatures measured. The desorption process is governed in part by the dissociation of water from the edges of these islands. Rapid diffusion on the surface maintains a quasiequilibrium between the molecules bound to islands and isolated adsorbed water molecules, thereby leading to pseudo-zero-order kinetics. This result is interpreted upon general thermodynamic grounds, and also using a simple kinetic model which leads to pseudo-zero-order desorption kinetics. An unusual hydrogen kinetic isotope effect is reported which lends support to our interpretation. [ABSTRACT FROM AUTHOR]

The macro-size magnetic colloidal particles in both distilled water and oleic acid were prepared by using Fe[sub 3]O[sub 4] ferrofluids (SMG018), the sodium dodecyl sulfate (SDS), and distilled water or oleic acid. The optical transmission of these ferrofluid emulsions has been investigated as functions of concentration of SDS between 0.64 and 3.73 wt %, incident optical wavelengths between 450 and 750 nm, and applied magnetic fields up to 141 Oe. The optical transmission shows maximum with concentration of SDS near 3.13 and 1.90 wt % for samples in distilled water and oleic acid, respectively. In general, under an applied magnetic field, the size of the magnetic colloidal particles for samples in oleic acid is smaller than that of samples in distilled water; however, the concentration of the magnetic colloidal particles is the opposite. This can be explained due to the different aggregation ability of the magnetic colloidal particles in both distilled water and oleic acid. The optical transmission of the samples is observed to be reversed proportional to the area covered by the magnetic colloidal particles. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To reduce seismic and environmental vibration noise, ultra-low-frequency vertical vibration isolation systems play an important role in absolute gravimetry. For this purpose, an isolator based on a two-stage beam structure is proposed and demonstrated. The isolator has a simpler and more robust structure than the present ultra-low-frequency vertical active vibration isolators. In the system, two beams are connected to a frame using flexural pivots. The upper beam is suspended from the frame with a normal hex spring and the lower beam is suspended from the upper one using a zero-length spring. The pivot of the upper beam is not vertically above the pivot of the lower beam. With this special design, the attachment points of the zero-length spring to the beams can be moved to adjust the effective stiffness. A photoelectric detector is used to detect the angle between the two beams, and a voice coil actuator attached to the upper beam is controlled by a feedback circuit to keep the angle at a fixed value. The system can achieve a natural period of 100 s by carefully moving the attachment points of the zero-length spring to the beams and tuning the feedback parameters. The system has been used as an inertial reference in the T-1 absolute gravimeter. The experiment results demonstrate that the system has significant vibration isolation performance that holds promise in applications such as absolute gravimeters. [ABSTRACT FROM AUTHOR]

Presents a study which examined the optical, electrical and magnetic properties of neodymium iron boron films. Experimental methods; Observations of the oscillatory behavior with thickness of the films; Anomalous behaviors near the Curie temperature.

To investigate the perforating characteristics of Zr-based bulk metallic glass fragments against thin steel target, ballistic experiments were carried out to measure ballistic the limit velocities of fragments perforating against different thicknesses of targets. The fragments were driven by a 57 mm one-stage light gas gun to impact the thin steel target. The numerical model of Zr-based bulk metallic glass fragments perforating against thin steel target was established using Autodyn2D commercial software, and the perforating process and perforating mechanism were analyzed by numerical simulation. The semi-empirical model to predict the ballistic limit velocity was fitted. An energy model for calculating the residual velocity of a fragment was derived based on the conservation of energy. The theoretical results of the semi-empirical model and the energy model are in good agreement with experiment results and simulation results. And the energy model has good applicability without fitting the parameters for different target thicknesses. [ABSTRACT FROM AUTHOR]

We have investigated space and astrophysical phenomena in nonrelativistic laboratory plasmas with long high-power lasers, such as collisionless shocks and magnetic reconnections, and have been exploring relativistic regimes with intense short pulse lasers, such as energetic ion acceleration using large-area suspended graphene. Increasing the intensity and repetition rate of the intense lasers, we have to handle large amounts of data from the experiments as well as the control parameters of laser beamlines. Artificial intelligence (AI) such as machine learning and neural networks may play essential roles in optimizing the laser and target conditions for efficient laser ion acceleration. Implementing AI into the laser system in mind, as the first step, we are introducing machine learning in ion etch pit analyses detected on plastic nuclear track detectors. Convolutional neural networks allow us to analyze big ion etch pit data with high precision and recall. We introduce one of the applications of laser-driven ion beams using AI to reconstruct vector electric and magnetic fields in laser-produced turbulent plasmas in three dimensions. [ABSTRACT FROM AUTHOR]

We report the observation of mid-infrared room-temperature electroluminescence from a p-i-n Ge/Ge0.922Sn0.078/Ge double heterostructure diode. The device structure is grown using low-temperature molecular beam epitaxy. Emission spectra under various injection current densities in the range of 318 A/cm2-490 A/cm2 show two distinct profiles peaked at 0.545 eV (2.275 μm) and 0.573 eV (2.164 μm), corresponding to indirect and direct bandgaps of the Ge0.922Sn0.078 active layer, respectively. This work represents a step forward towards the goal of an efficient direct-bandgap GeSn light-emitting device on a Si substrate by incorporating higher Sn content of 7.8% in a diode structure that operates at lower current densities. [ABSTRACT FROM AUTHOR]

A potential Seebeck microprobe apparatus is described such that a profile of Seebeck coefficients can be detected on a material sample surface for thermopower investigations. Due to its spatially resolved limit on detecting small inhomogeneities of dopants or composition changes, we here propose a constructive combination of numerical modeling and practical measurement to improve the spatial resolution by deconvolution algorithm. The relevant transfer function, obtained from numerical calculations, was successfully applied on real measurement data. Besides, an improvement in detecting the 1.5 μm inhomogeneity has been achieved by applying one transfer function of the known tip setup on a set of Seebeck line scan signals, obtained with 6 μm tip-sample contact length, 3 μs signal capture time after contact, and 0.75 μm scan period. The result showed that a system theoretical approach in terms of deconvolution algorithm could theoretically enhance the spatial resolution anyway, but is practically limited by the systemic preconditions (tip size, signal capture time, and scan period) and the signal to noise ratio of the captured thermovoltages. Therefore, we provide a clear understanding of systemic preconditions and their impacts on the detection of small inhomogeneities and thus the performance in the thermopower analysis. [ABSTRACT FROM AUTHOR]

Direct numerical simulations using high-resolution total variation diminishing (TVD) scheme are performed for studying the shock enhancement of two-dimensional confined (spatially growing) supersonic mixing flows. Several specially designed mixing enhancement schemes are examined with emphasis placed on the study of the fundamental aspects involved in the shock-induced mixing enhancement process. The merits associated with these mixing enhancement schemes are evaluated based on a cost/effectiveness criterion, in which the cost paid for the total pressure loss encountered and the improvement in mixing gained are considered together. The results suggest that mixing enhancement using shock waves can only be effective if the stimulation is spatially persistent, and begins from the very upstream. Being motivated by this observation, an idea of using wavy-wall configuration to generate the desirable periodic shock stimulation is proposed and investigated. The computed results show that, by an appropriate manipulation of the parameters including wall wavelength, relative phase shift between the top and bottom walls, as well as the amplitude of the waviness, considerable improvement in mixing efficiency can be achieved. [ABSTRACT FROM AUTHOR]

Direct numerical simulations using the high-resolution TVD scheme are performed for the study of two-dimensional confined spatially growing supersonic mixing layers. Numerical simulations, being forced by the linear instability wall modes, are justified by comparing the calculated results with both theoretical and experimental data. The numerically visualized downstream compression/expansion wave system explains the so-called ‘‘strange waves’’ observed in experiments and are found to be responsible for the rapid growth of the mixing layer in that region. The existence of shock waves would lead to mixing enhancement by accelerating the process of extracting turbulent kinetic energy from the mean stream. However, the phenomenon of shock-induced mixing improvement is found quite local around the shock impingement area, and often is followed by a saturation in turbulent energy absorption which impedes the further growth of the shear layer in the immediate downstream region. For the present cases considered, the subharmonic instability modes are not dominant, and the baroclinic-torque effect is comparatively less important for the vorticity development. These observations suggest that compressibility effects may behave in a considerably different manner as the underlying instability mechanism changes from the subsonic Kelvin–Helmholtz type to the present supersonic wall instability type. [ABSTRACT FROM AUTHOR]

The drop size distribution was measured from back-lighted spark photographs at the edge of steady sprays in the immediate vicinity of the nozzle exit. The conditions of these liquid-into-gas sprays were such that the outer surface of the liquid jets broke up into small drops at the nozzle exit. The objective was to elucidate the mechanism of breakup. At room temperature, n-hexane and n-tetradecane at pressures from 2.86 to 9.76 MPa were injected into gaseous nitrogen at 1.48 to 2.86 MPa through three straight cylindrical nozzles of different diameters, 127 and 335 μm, and length-to-diameter ratios, 4 and 10. In all cases, the drop sizes could be fitted satisfactorily with a chi-square distribution with degree of freedom equal to 28. The Sauter mean drop diameter and other average diameters were found to decrease with increasing injection velocity and decreasing liquid surface tension, to be insensitive to nozzle diameter and length, and to increase slightly with increasing gas density. The trends and magnitudes are in agreement with those predicted by the supplemented aerodynamic theory of surface breakup if it is assumed that between the jet surface where the drops are formed, that is not visible, and the edge of the spray, where the measurements were made, drops undergo collisions and coalescence. In this region of dense sprays, drop coalescence leads to a rapid increase in drop size, particularly in high gas densities. [ABSTRACT FROM AUTHOR]

A new high-resolution electron energy-loss spectrometer based on the dispersion compensation (DC) concept has been designed, built, and tested. The parallel processing inherent in DC has allowed us to attain signal levels two orders of magnitude in excess of conventional designs while operating at comparable resolution. This is consistent with expectations based on simple model calculations. The resolving power of the spectrometer is not as good as theoretically predicted probably due to uncontrolled beam angle effects. Initial tests on a variety of systems are presented. We analyze the strengths and weaknesses of the design and suggest future improvements. [ABSTRACT FROM AUTHOR]

The properties of Cr-doped GaN epilayers grown by rf-plasma-assisted molecular beam epitaxy were studied. The deep acceptor nature of Cr was used to grow semi-insulating GaN epilayers on sapphire substrates for electronic device applications. The room-temperature (RT) sheet resistivity of the epilayers reached 1010 Ω/square. The activation energy of dark conductivity was about 0.48 eV. Step-graded AlxGa1-xN/GaN (x=0.3-0.2) superlattices (SLs) were designed to filter dislocations. Transmission electron microscopy images showed that the SLs can dramatically reduce dislocation density. Al0.35Ga0.65N/GaN heterostructure grown on Cr-doped semi-insulating GaN epilayer exhibited a RT mobility of 960 cm2/V s and sheet carrier density of 2.1×1013 cm-2. [ABSTRACT FROM AUTHOR]

The effect of gate voltage on hot-carrier induced degradation in drain extended high-voltage metal-oxide-semiconductor (MOS) transistors with thick gate oxide (100 nm) structure is presented. Different from the conventional low-voltage n-type MOS transistors, under a fixed drain voltage, devices stressed at a higher Vgs result in a greater maximum transconductance and on-resistance degradation. Under higher Vgs, the increase in channel hot-carrier injection is responsible for the greater Gm,max degradation. On the other hand, Kirk effect induced increase in drain avalanche hot carriers near the drain as well as higher electric field in the channel is responsible for the greater Ron degradation. [ABSTRACT FROM AUTHOR]

In this study, we present an easy way to create layered-nanoplatelets with well-defined geometry by controlling the cracking process of nanostructured multilayers. The geometrical dimension of layered-nanoplatelets is determined by the multilayer intrinsic size, the total strain, and the elastic mismatch between the substrate and multilayers, which was analyzed by statistical approach. Fracture behaviors characterized by critical strain to nucleate microcrack, fracture toughness, and evolution of fragment width were also studied for nanostructured Cu/Cr multilayers with modulation period (λ) spanning from of 5 to 250 nm and were quantified based on linear elastic theory and shear-lag theory. An optimal modulation period seems to be likely favorable for maximizing the ductility, strength, and fracture toughness of the nanolayered materials. [ABSTRACT FROM AUTHOR]

Single crystals of Bi2-xPbxSr2Co2Oy (0 ≤ x ≤ 0.55) have been grown using optical floating-zone method. The chemical compositions were determined using combined electron probe microanalysis and iodometric titration. Physical properties including electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were measured using single crystal specimens. Successful hole doping through Pb substitution is confirmed through combined iodometry titration, electrical transport, and Seebeck coefficient measurements. Significant reduction on both in-plane resistivity and thermal conductivity was found as a result of Pb substitution to the Bi site. The thermoelectric figure-of-merit ZT for x ∼ 0.55 is raised 20 folds from the undoped sample at room temperature. [ABSTRACT FROM AUTHOR]

A pulsed laser deposition system with a rotating reflector, which can generate an extended plume with a diameter of about 40 mm, has been proven to be viable in producing large area YBa2Cu3O7 (YBCO) thin films. Films with uniformity of thickness and electrical properties to within a few percents were obtained. By making a further modification on this laser scanning system, YBCO films with various thicknesses can be deposited in situ on several pieces of substrates under essentially identical deposition conditions, and particularly, in a continuous fashion. The atomic force microscopy (AFM) images reveal that films grown on NdGaO3 follow the Stranski–Krastanov (layer then island growth) mode, while films grown on as-polished MgO and on annealed MgO follow the Volmer–Weber (islands without layer growth) mode and step-flow mode, respectively. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the heterojunctions of solid Carbon 70 and crystalline silicon. Information on the rectifying properties of carbon and silicon compounds; Number of movable-ion charges in the solid C70 compound; Details on how the dielectric constant of the C70 compound can be identified.

An easily fabricated xenon-IV ion laser is described. The various parameters considered are the gas pressures, the excitation voltages, and the repetition rates. Based on our results we believe that there exists an optimal excitation voltage and an optimal repetition rate for achieving largest lasing power and good reliability. [ABSTRACT FROM AUTHOR]

The Brownian-type molecular dynamics simulation is revisited and applied to study the thermal and geometric properties of four mono- and two polyvalent metallic clusters. For the thermal property, we report the specific heat at constant volume CV and study the solid-liquid-like transition by scrutinizing its characteristic. For the geometric property, we calculate the root mean square relative bond-length fluctuation δ as a function of increasing temperature. The thermal change in δ reflects the movement of atoms and hence is a relevant parameter in understanding the phase transition in clusters. The simulated results for the CV of alkali and aluminum clusters whose ground state structures exhibit icosahedral symmetry generally show one phase transition. In contrast, the tetravalent lead is quite often seen to exhibit two phase transitions, a premelting process followed by a progressive melting. In connection with the premelting scenario, it is found here that those (magic number) clusters identified to be of lesser stability (among other stable ones) according to the second energy difference are clusters showing a greater possibility of undergoing premelting process. This energy criterion applies to aluminum clusters nAl=28 and 38. To delve further into the thermal behavior of clusters, we have analyzed also the thermal variation of δ(T) and attempted to correlate it with CV(T). It turns out that the premelting (if exist) and melting temperatures of the smaller size clusters (n≤50) extracted from CV do not always agree quantitatively with that deduced from δ. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Unoccupied states of the (110) YBa[sub 2]Cu[sub 3]O[sub 6.9] (YBCO) thin films were investigated by the Eab and Ec polarized O 1 s x-ray absorption near edge structure (XANES) spectroscopy. With correction of the self-absorption effect, the Eab O 1 s XANES spectra of the (110) YBCO films obtained from the normal incidence geometry and grazing incidence geometry are very similar. After the self-absorption correction, the Ec spectrum of the (110) YBCO film obtained from the normal incidence geometry is almost identical to that of the (001) YBCO film obtained from the grazing incidence geometry. Hole distribution over the different oxygen sites has been derived. The hole number in the apical sites in some thin films obtained in the present investigation is larger than that from the previous x-ray absorption studies of single crystals and from the theoretical calculations. The comparison of the XANES spectra between the (001) and (110) YBCO thin films is also presented. [ABSTRACT FROM AUTHOR]

Studies the magnetoresistance of nickel alloy multilayered films. Preparation of the sample; Discussion on the results of the study.

We present detailed numerical results on the ground state structures of metallic clusters. The Gupta-type many-body potential is used to account for the interactions between atoms in the cluster. Both the genetic algorithm technique and the basin hopping method have been applied to search for the global energy minima of clusters. The excellent agreement found in both schemes for the global energy minima gives credence to the optimized energy values obtained. For four monovalent and one polyvalent metals studied in this work and within the accuracy of the energies presented here, we find that the global energy minima predicted by the basin hopping method are the same as those values obtained by the genetic algorithm. Our calculations for the ground state energies of alkali metallic clusters show regularities in the energy differences, and the cluster growth pattern manifested by this same group of clusters is generally icosahedral, which is quite different from the close-packed and decahedral preferentially exhibited by the tetravalent lead clusters. Considering the inherent disparities in the electronic properties and the bulk structures in these metals (body-centered cubic for alkali metals and face-centered cubic for the lead metal), it is not unreasonable to conjecture that the valence electrons do play a subtle role in the conformation of metallic clusters. [ABSTRACT FROM AUTHOR]

The theory of substrate-mediated dispersion interactions is applied to analyze a set of quasiequilibrium measurements of adsorption isobars and desorption isotherms of the CH4/Ag(011) physisorption system. The theory provides for the construction of an adsorbate intermolecular potential from the gas phase potential, with the spacing between the metal surface and the adsorbed layer as the sole adjustable parameter. The best fits to the kinetic and thermodynamic data yield a consistent intermolecular potential, with a well depth of approximately two-thirds of the free space value. The limited dynamic range of the measurements does not permit a determination of the form of the intermolecular potential. However, the good agreement of the theory with both data sets lends strong support for the quasiequilibrium model, and supports the proposition that the properties of physisorbed layers can be predicted using gas phase potentials while accounting for substrate-mediated dispersion interaction effects. [ABSTRACT FROM AUTHOR]

Provides information on a study which examined rare-earth element erbium, which was deposited onto (100) oriented Zn-doped p-type InP to form Schottky barriers. Material attractive for high-speed optoelectronic and high power microwave devices; Prerequisite essential for the development of advanced devices; Measurements in the I-V-T method; Technique used for measuring the reverse bias capacitance-voltage characteristics.

It is shown that a small substitution of praseodymium for bismuth as in Pr0.05Bi1.95Sr2CaCu2.2O8.2+δ produces a significant increase, 13 K, in the onset temperature, 7 K in the temperature at which the whole specimen is superconducting, and 10 K in the transition-midpoint temperature relative to Bi2Sr2CaCu2.2O8.2+δ. Unfortunately the transition is broadened, 20 K versus 14 K. Doubling the amount of praseodymium substitution causes the occurrence of extraneous phase(s), the effect of which is seen only in the resistance versus temperature data, and does not indicate any additional significant increases in the aforementioned temperatures. [ABSTRACT FROM AUTHOR]

For the applications in precision measurement such as absolute gravimeter, we have designed and built an ultra-low frequency vertical vibration isolator based on LaCoste spring linkage. In the system, an arm with test mass is suspended by a mechanical extension spring, and one end of the arm is connected to the frame with flexible pivots. The displacement of the arm is detected by an optical reflection method. With the displacement signal, a feedback control force is exerted on the arm to keep it at the balance position. This method can also correct the systematic drift caused by temperature change. In order to study the vibration isolation performance of the system, we analyze the dynamic characteristics of the spring linkage in the general case, and present key methods to adjust the natural oscillating period of the system. With careful adjustment, the system can achieve a steady oscillation with a natural period up to 32 s. This isolator has been tested based on the T-1 absolute gravimeter. A statistical uncertainty of 2 µGal has been achieved within a typical 12 h measurement. The experimental results verify that the isolator has significant vibration isolation performance, and it is very suitable for applications in high precision absolute gravity measurement. [ABSTRACT FROM AUTHOR]

Microwave applicators are widely employed for materials heating in scientific research and industrial applications, such as food processing, wood drying, ceramic sintering, chemical synthesis, waste treatment, and insect control. For the majority of microwave applicators, materials are heated in the standing waves of a resonant cavity, which can be highly efficient in energy consumption, but often lacks the field uniformity and controllability required for a scientific study. Here, we report a microwave applicator for rapid heating of small samples by highly uniform irradiation. It features an anechoic chamber, a 24-GHz microwave source, and a linear-to-circular polarization converter. With a rather low energy efficiency, such an applicator functions mainly as a research tool. This paper discusses the significance of its special features and describes the structure, in situ diagnostic tools, calculated and measured field patterns, and a preliminary heating test of the overall system. [ABSTRACT FROM AUTHOR]

Phonon dynamics in Bi, Bi2Se2, and CuxBi2Se3 (x = 0, 0.1, 0.125) single crystals was investigated using femtosecond pump-probe spectroscopy. Two damped oscillations in measured transient reflectivity changes were observed, respectively, attributed to coherent optical and acoustic phonons. The frequency shift of the phonon modes in Bi-rich Bi2Se2 crystals indicates the intercalation of the additional Bi atoms into the Bi2Se3 matrix and formation of the Bi2 layer between the quintuple layers (QLs). The deformation of QLs in CuxBi2Se3 crystals was also found. These phonon dynamics results suggest that Cu atoms in CuxBi2Se3 crystals are predominantly intercalated between pair of QLs. [ABSTRACT FROM AUTHOR]

Modulated reflectance (contactless electroreflectance (CER), photoreflectance (PR), and piezoreflectance (PzR)) has been applied to study direct optical transitions in bulk MoS2, MoSe2, WS2, and WSe2. In order to interpret optical transitions observed in CER, PR, and PzR spectra, the electronic band structure for the four crystals has been calculated from the first principles within the density functional theory for various points of Brillouin zone including K and H points. It is clearly shown that the electronic band structure at H point of Brillouin zone is very symmetric and similar to the electronic band structure at K point, and therefore, direct optical transitions at H point should be expected in modulated reflectance spectra besides the direct optical transitions at the K point of Brillouin zone. This prediction is confirmed by experimental studies of the electronic band structure of MoS2, MoSe2, WS2, and WSe2 crystals by CER, PR, and PzR spectroscopy, i.e., techniques which are very sensitive to critical points of Brillouin zone. For the four crystals besides the A transition at K point, an AH transition at H point has been observed in CER, PR, and PzR spectra a few tens of meV above the A transition. The spectral difference between A and AH transition has been found to be in a very good agreement with theoretical predictions. The second transition at the H point of Brillouin zone (BH transition) overlaps spectrally with the B transition at K point because of small energy differences in the valence (conduction) band positions at H and K points. Therefore, an extra resonance which could be related to the BH transition is not resolved in modulated reflectance spectra at room temperature for the four crystals. [ABSTRACT FROM AUTHOR]

We report the effects of thermal annealing on the characteristics of GeSn epilayers grown on Ge-buffered Si wafers with a high Sn content near a threshold value that affords a direct bandgap. On annealing at temperatures below 400 °C, the characteristics of the epilayer remain unchanged, compared to those of the as-grown samples. On annealing the samples at a temperature in the range of 440-540 °C, strain relaxation in the epilayer is observed, accompanied by generation of misfit dislocations at the GeSn/Ge interface. A further increase in annealing temperature beyond 580 °C causes not only a relaxation in strain but also a change in the microstructure of the epilayer. In addition, Sn forms clusters and segregates to the surface, resulting in a reduction in the Sn content of the epilayer. The present investigation shows changes in the characteristics of the film under thermal treatment, providing an insight into the physical properties of such devices. [ABSTRACT FROM AUTHOR]

High quality Zn0.92Cd0.08O/ZnO multiple quantum wells with smooth interfaces have been prepared on c-plane sapphire substrates by pulsed laser deposition. The periodic structure has been characterized by scanning transmission electron microscope and energy dispersive x-ray spectroscopy line scans. The temperature dependent photoluminescence of Zn0.92Cd0.08O/ZnO exhibits an inconspicuous S-shaped property due to a combined effect of the slightly disordered ZnCdO alloy. We can observe both quantum confinement effects and quantum-confinement Stark effect in the quantum wells. We can modulate the well emission energy from 2.90 to 3.085 eV by varying the well thickness at room temperature. [ABSTRACT FROM AUTHOR]

In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO-5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic-paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)-orthorhombic (O)-cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO-5%BT exhibits a R-C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO-5%BT remains less than 0.04 below 150 °C. [ABSTRACT FROM AUTHOR]

The magnetism-induced ferroelectricity in the E-type orthorhombic HoMnO3 (o-HMO) films grown on Nb-doped and undoped SrTiO3(001) substrates was studied. The temperature dependent magnetization in these films evidently exhibits an antiferromagnetic ordering around 44 K and an anomalous second magnetic ordering along the c-axis near 35 K. Interestingly, at this anomalous transition temperature, an associated ferroelectric polarization was probed by the P-E hysteresis measurements, indicating the intimated coupling between the ferroelectric response and the reordering of Mn spins, which has never been disclosed previously by dielectric constant measurements. [ABSTRACT FROM AUTHOR]

Both La0.375Pr0.25Ca0.375MnO3 (LPCMO) and La0.625Ca0.375MnO3 (LCMO) were found to exhibit coexistence of competing orders (phase separation) over a wide temperature range. However, substantial hysteretic behaviors in both of the temperature-dependent resistance [R(T)] and magnetization [M(T)] [also known as the persistent magnetic memory effect (PMME)] are only displayed in LPCMO. The results indicate that, in LPCMO, the size distribution of the coexisting charge-ordered insulating and metallic ferromagnetic (FM) phases plays a determinant role in the PMME effects in different temperature regimes. Moreover, due to the direct competition between the two coexisting phases, the system is most susceptible to the external applied field in the hysteretic temperature region. On the other hand, in LCMO, the phase transition between paramagnetic and FM is more like an isomorphic transition in pure materials, and thus does not show significant hysteresis. [ABSTRACT FROM AUTHOR]