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Metallic glasses have the potential to become transformative materials, but this is hindered by the lack of ability to accurately predict which metallic alloys will form good glasses. Current approaches are limited to empirical rules that often rely on parameters that are unknown until the glasses are made, rendering them not predictive. In this Perspective, properties of metallic liquids at elevated temperatures and how these might lead to better predictions for glass formation are explored. A central topic is liquid fragility, which characterizes the different dynamics of the liquids. What fragility is and how it might be connected to the liquid structure is discussed. Since glass formation is ultimately limited by crystallization during cooling, recent advances in crystal growth and nucleation are also reviewed. Finally, some approaches for improving glass stability and glass rejuvenation for improved plasticity are discussed. Building on a summary of results, some key questions are raised and a prospective for future studies is offered. [ABSTRACT FROM AUTHOR]

In this paper, the strain gradient is introduced to tune the semiconducting performance of piezoelectric semiconductor (PSC) nanowires by changing their cross sections. A one-dimensional model of the PSC nanowire with a non-homogeneous cross section under axial extension is established. The combined influences of piezoelectricity and flexoelectricity resulting from the strain gradient are taken into account. Approximate closed-form solutions for the distribution of carriers and electromechanical fields of the PSC nanowire are given. The effects of strain gradient, flexoelectricity, and initial carrier concentration on the distribution of carriers, electric field, electric potential, and displacement are discussed. It is observed that non-homogeneous PSC nanowires show strong size-dependent behaviors in connection with their cross-sectional diameters. The strain gradient and flexoelectric effect enhance the electromechanical coupling effect. This research provides a new way to tune inner carrier distributions and electromechanical characteristics for piezoelectric semiconductor devices. [ABSTRACT FROM AUTHOR]

The polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs), which are grown in inverted tetrahedral pyramids, are studied. It is seen that the emitted light is detected for two mutually perpendicular linear polarization directions in the less conventional cleaved-edge geometry.

Various experiments, including the atomic force microscopy and cathodoluminescnece measurements are used to analyze the influence of long-range substrate roughness in the photoluminescnece spectra of GaAs/ AlGaAs V-groove quantum wires (QWRs). The results demonstrate the effect of long-range substrate roughness on the QWR features.

We present a detailed structural investigation of self-assembled indium gallium nitride nanodots grown on c-plane aluminum nitride templates by the droplet heteroepitaxy technique in a plasma assisted molecular beam epitaxy reactor. Various growth parameters, including the total coverage of the metal species, relative and total metal effusion fluxes, and nitridation temperature were investigated. Analyses of in situ reflection high-energy electron diffraction patterns and comparison with simulations showed that the resulting crystal structure was a mixture of wurtzite and twinned zinc blende phases, with the zinc blende phase increasingly dominant for lower metal coverages and lower nitridation temperatures, and the wurtzite phase increasingly dominant for higher nitridation temperature. Studies by field emission scanning electron microscopy and atomic force microscopy revealed that the nanodots exhibit trimodal size distributions, with the dot morphologies of the intermediate size mode often resembling aggregations of distinct clusters. Nanodots grown at higher nitridation temperatures had larger inter-dot spacings, with hexagonal in-plane ordering observable at a sufficiently high temperature. Using grazing incidence small angle X-ray scattering, we determined the nanodots to be approximately truncated cone shaped, and extracted the mean radius, height, and inter-dot distance for each distribution. Microstructural investigations of the nanodots by cross-sectional transmission electron microscopy indicated that the majority of the dots were formed in dislocation-free regions, and confirmed that the intermediate size dots were approximately truncated cone shaped and consisted of both zinc blende and wurtzite regions. Mapping of the elemental distributions by energy dispersive X-ray spectroscopy in scanning transmission electron microscopy mode indicated highly nonuniform indium distributions within both small and intermediate size dots which are potentially indicative of indium clustering and kinetically controlled nanoscale phase separation rather than the spinodal decomposition associated with bulk diffusion. The observed enrichment in indium concentration towards the tops of the nanodot layers could be ascribed to the compositional pulling effect. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the time-dependent behavior of quantum cellular automata (QCA) with imperfections. A chain of quantum cells with the imperfections introduced by variations of intercellular distances, stray charges and variations of intercell tunneling strengths was investigated. Results demonstrate that the imperfections may easily impair the switching characteristics of semiconductor based QCAs.

The time evolution of the polarization of chains of quantum-dot cells called quantum cellular automata as a result of the switching of a driver cell for the particular cases of linear chains and L-shaped configurations were studied. Each cell is composed of four quantum dots on the four corners of the square and has two electrons. Dissipation processes were observed to result in satisfactory response characteristics. For the two cases investigated, there were no metastable states.

The study of the quantum bound states in a double-bend quantum channel of finite length reveals that one quasibound state below the first conductance plateau exists for the quantum channel. The study is performed by the mode matching technique. The quantum channels connect two 2D electron gas reservoirs and have a conductance G which is calculated as the function of Fermi energy.

Columnar (001) FePt-ZrO2-C films with large coercivity, small grain size, and high aspect ratio were obtained. By doping ZrO2 into FePt film at high sputtering temperature, tetragonal (002) textured ZrO2 was formed and distributed at the grain boundaries of FePt grains, resulting in the formation of columnar structured FePt films. The perpendicular anisotropy of FePt films was degraded since some (200) FePt grains were formed directly on the (002) textured ZrO2. With a small amount of carbon doping into FePt-ZrO2 35 vol.% films, the perpendicular anisotropy was improved. However, FePt grains were still interconnected. Upon further increasing concentration of ZrO2, (001) textured FePt-ZrO2 40 vol.%-C 5 vol.% films with well isolated grains in average diameter of 5.5 nm and very good columnar structure were obtained. [ABSTRACT FROM AUTHOR]

Polycrystalline YMn2-xTixO5 (x=0.00-0.05) samples with partial substitution of Mn by Ti are prepared in order to modulate the multiferroicity of YMn2O5. It is revealed that the substituting Ti ions are in the Ti4+ valence state and prefer to occupy the Mn4+ sites. The lattice structure has slight volume expansion upon the Ti substitution, although the symmetry remains unchanged. A proper Ti4+ substitution surprisingly allows significant enhancement of ferroelectric polarization and appearance of weak ferromagnetism. It is suggested that the substitution induced Ti4+O6 octahedra and modulated exchange-striction are possibly responsible for the enhanced ferroelectricity and improved ferromagnetism. [ABSTRACT FROM AUTHOR]

Two series of samples of single-layer IrMn and IrMn/FePd bilayer films, deposited on a single-crystal MgO substrate at different IrMn deposition temperatures (Ts=300-700 °C), were investigated using magnetron sputtering. L12 ordering was revealed for the 30nm-thick IrMn epitaxial (001) films with Ts⩾400 °C, determined by synchrotron radiation x-ray diffractometry (XRD). XRD results also provide evidence of the epitaxial growth of the IrMn films on MgO substrate. Increasing Ts from 400 to 700 °C monotonically increases the ordering parameter of L12 phases from 0.17 to 0.81. An in-plane exchange bias field (Heb) of 22Oe is obtained in a 10nm-thick FePd film that is deposited on the disordered IrMn films. As the L12 ordering of the IrMn layers increases, the Heb gradually decreases to 0Oe, meaning that the exchange bias behavior vanishes. The increased surface roughness, revealed by atomic force microscopy, of the epitaxial IrMn layers with increasing Ts cannot be the main cause of the decrease in Heb due to the compensated surface spins regardless of the disordered and ordered (001) IrMn layers. The change of antiferromagnetic structure from the A1 to the L1H2 phase was correlated with the evolution of Heb. [ABSTRACT FROM AUTHOR]

In this study, FeMn was introduced as an antiferromagnetic (AFM) layer to couple with a singlelayered Co49Pt51 alloy thin film, and it was compared with a Co49Pt51/IrMn bilayer system in exchange bias (EB) effect, to explore the mechanism of spontaneous perpendicular exchange bias (PEB), which has been recently observed in CoPt/IrMn bilayers. Bilayers of CoPt/IrMn and CoPt/ FeMn were prepared under the same conditions by sputtering at room temperature without any inducing field. Although PEB was observed in as-grown CoPt/FeMn bilayers, the loop shape and PEB behavior were found to exhibit different characteristics from those of CoPt/IrMn bilayers. The CoPt (5 nm)/FeMn (10 nm) bilayer has a sheared loop that is similar to a double-shifted loop and a much lower squareness ratio (SQR=0.52) and exchange bias field (He=180 Oe) than the CoPt (5 nm)/IrMn (10 nm) system, which has a rectangular loop shape and a high SQR of 0.97 and large He of 290 Oe. The two systems present entirely different dependences of PEB on the thickness of the AFM layer. CoPt/IrMn exhibits behavior that is typical of most EB systems, but for CoPt/ FeMn, this dependence is more complicated with an unusual peak at an AFM layer thickness of 10 nm. Based on the dissimilar loop shapes and dependences of PEB on AFM thickness, the mechanisms of the spontaneously established PEB in these two systems are considered to differ. Investigations of cross-sectional transmission electron microscopy revealed no apparent difference between the interfacial microstructures of the two systems. X-ray diffraction studies demonstrated the <111> texture of both systems. Therefore, different interfacial spin configurations may be responsible for the dissimilar PEB behaviors in these two FM/AFM bilayer systems. [ABSTRACT FROM AUTHOR]

The charge carriers type in antimony-doped ZnO (ZnO:Sb) microwires was studied using the hot probe technique. The wires were grown by a simple thermal evaporation method. Contrary to the expected p-type behavior reported for Sb doped ZnO thin films and nanowires, our hot probe measurements of representative single Sb-doped ZnO wires show a stable n-type behavior. The hot probe technique is a simple and efficient way to determine the charge carrier type from thermoelectric measurements on a single semiconductor wire and could offer an alternative to Hall effect measurements. The technique relies on creating a temperature gradient across the wire (i.e., heating one side of the wire relative to the other) and monitoring the resulting open-circuit voltage between the two ends. We also performed Energy Dispersive X-ray Spectroscopy measurements to identify and monitor the elemental composition in these ZnO:Sb wires. [ABSTRACT FROM AUTHOR]

Numerous studies are used to investigate the polarization fatigue suppression behavior of the ferroelectric [Pb.sub.1-x][Ba.sub.x]([Zr.sub.0.52][Ti.sub.0.48])[O.sub.3] (PBZT) thin films, prepared by the sol-gel method. The results reveal that Ba doping of the substances leads to enhanced ion stability and suppressed oxygen vacancies, which ultimately results in an improved fatigue endurance of the substance.

The recombination dynamics of neutral donor bound excitons (DoX: I4, I6/6a) and near band edge defect-related emission in solution grown ZnO nanorods are investigated using steady state and time-resolved photoluminescence (PL) measurements. The effects of annealing are also studied. Low temperature steady state PL shows a systematic removal of the I4 line after annealing at 450 °C and the subsequent domination of I6a in these PL spectra. Additionally, the time decay of the I4, I6/6a, free exciton (FX), and basal plane stacking fault-related (BSF) PL transitions are studied as a function of annealing temperature. For the various annealing temperatures studied, the PL decay is described by a bi-exponential profile with a fast component (contribution from the surface) and slow component (related to bulk recombination). The fast component dominates in the case of as-grown and low temperature annealed samples (anneal temperatures up to 300 °C), suggesting the presence of surface adsorbed impurities. For samples annealed above 400 °C, the effects of the surface are reduced. The sample annealed at 850 °C produced an overall enhancement of the crystal quality. The underlying mechanisms for the observed PL characteristics are discussed based on near surface band bending caused by surface impurities. [ABSTRACT FROM AUTHOR]

The multiferroic RMn2O5 family, where R is rare-earth ion or Y, exhibits rich physics of multiferroicity which has not yet well understood. DyMn2O5 is a representative member of this family. The ferroelectric polarization of DyMn2O5 is claimed to be magnetically relevant and have more than one component. Therefore, the polarization reversal upon the sequent magnetic transitions is expected. We investigate the evolution of the ferroelectric polarization upon a partial substitution of Mn3+ by nonmagnetic Al3+ in order to tailor the Mn3+-Mn4+ interactions and then to modulate the polarization in DyMn2–x/2Alx/2O5. It is revealed that the polarization can be successfully reversed by Al-substitution via substantially suppressing the Mn3+-Mn4+ interactions, while the Dy3+-Mn4+ interactions can sustain against the substitution until a level as high as x=0.2. In addition, the independent Dy spin ordering is shifted remarkably down to an extremely low temperature due to the Al3+ substitution. The present work unveils the possibility of tailoring the Mn3+-Mn4+ and Dy3+-Mn4+ interactions independently, and thus reversing the ferroelectric polarization. [ABSTRACT FROM AUTHOR]

FePt (10, 20, 40, and 60 nm) films were fabricated on four different single crystal substrates [MgO (001), KTaO3 (001), SrTiO3 (001), and LaAlO3 (001)], and the effects of lattice mismatch on the microstructure and magnetic properties of FePt films were systematically investigated. The X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results showed that the different lattice mismatch between the substrates and FePt films resulted in the different crystallographic texture and microstructure of the FePt films. Under the tensile strain between the FePt and substrates (MgO, KTaO3, SrTiO3), the FePt films preferred to form L10 FePt (001) texture. The perpendicular anisotropy of the FePt films grown on MgO was larger than that grown on KTaO3 and SrTiO3. For the FePt films grown on the LaAlO3 substrate, both FePt (110) and (001) orientations were found, which indicated the presence of tensile and compressive strain, respectively. With the reduction of the lattice mismatch between the FePt (10 nm) and substrate from 5.8% (MgO) to 2.4% (KTaO3), and 0.1% (SrTiO3), the microstructure of the FePt films changed gradually from granular to continuous films (SEM and TEM results). The microstructure of the 10 nm FePt film grown on LaAlO3 substrate showed granular structure. [ABSTRACT FROM AUTHOR]

The recent realization of silicon core optical fibers has the potential for novel low insertion loss rack-to-rack optical interconnects and a number of other uses in sensing and biomedical applications. To the best of our knowledge, incoherent light source based rapid photothermal processing (RPP) was used for the first time to anneal glass-clad silicon core optical fibers. X-ray diffraction examination of the silicon core showed a considerable enhancement in the length and amount of single crystallinity post-annealing. Further, shifts in the Raman frequency of the silicon in the optical fiber core that were present in the as-drawn fibers were removed following the RPP treatment. Such results indicate that the RPP treatment increases the local crystallinity and therefore assists in the reduction of the local stresses in the core, leading to more homogenous fibers. The dark current-voltage characteristics of annealed silicon optical fiber diodes showed lower leakage current than the diodes based on as-drawn fibers. Photons in UV and vacuum ultraviolet (VUV) regions play a very important role in improving the bulk and carrier transport properties of RPP-treated silicon optical fibers, and the resultant annealing permits a path forward to in situ enhancement of the structure and properties of these new crystalline core optical fibers. [ABSTRACT FROM AUTHOR]

The transient absorbance of poly(4-methyl-1-pentene) (PMP) irradiated with gamma rays at elevated temperatures has been investigated. The absorbance in the ultraviolet and visible range increases with gamma ray dose. A bathochromic shift in transmission spectra emerges significantly upon irradiation. A first-order generation model is proposed to analyze the kinetics of color centers during annealing. The activation energy of the color center increases with increasing gamma ray dose. The equilibrium behavior of color centers in PMP is similar to that of vacancies in metals, and the formation energy of color centers in PMP decreases with increasing gamma ray dose. However, annealable color centers are not observed in this study. [ABSTRACT FROM AUTHOR]

The effects of a TiN intermediate layer on the epitaxial growth and magnetic properties of FePt films were investigated. It was found that 5 nm TiN can effectively block the diffusion of a CrRu underlayer into a FePt magnetic layer and the magnetic dead layer on the TiN layer was negligible. Compared with an FePt film grown on a MgO intermediate layer, FePt film grown on a TiN interlayer exhibited very high out-of-plane coercivity and very narrow opening-up of in-plane hysteresis loop. With doping 40 vol. % SiNx in FePt film the grain size was reduced to 5.5 nm and the magnetic properties, such as high out-of-plane coercivity and line-like in-plane hysteresis loop, were retained. [ABSTRACT FROM AUTHOR]

We investigated the role of helium ambient gas on the dynamics of C2 species formation in laser-produced carbon plasma. The plasma was produced by focusing 1064 nm pulses from an Nd:YAG laser onto a carbon target. The emission from the C2 species was studied using optical emission spectroscopy, and spectrally resolved and integrated fast imaging. Our results indicate that the formation of C2 in the plasma plume is strongly affected by the pressure of the He gas. In vacuum, the C2 emission zone was located near the target and C2 intensity oscillations were observed both in axial and radial directions with increasing the He pressure. The oscillations in C2 intensity at higher pressures in the expanding plume could be caused by various formation zones of carbon dimers. [ABSTRACT FROM AUTHOR]

This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its [formula] A-plane parallel to the [formula] R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having [formula] planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with [formula] planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut (∼0.5°) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects in the (1126) GaN films. [ABSTRACT FROM AUTHOR]

Homogeneous thick film (∼0.10 mm) of high dielectric K0.05Ti0.02Ni0.93O; abbreviated as KTNO/polyvinylidene fluoride (PVDF) composite has been prepared by hot-molding technique. The frequency and temperature dependent dielectric behavior of this composite has been studied by varying the KTNO volume fraction (fKTNO). Near the percolation threshold (fKTNO=0.40), a large enhancement of effective dielectric permittivity ([variant_greek_epsilon]eff∼400 which is 40 times higher than that of pure PVDF) with low loss (∼0.20 at 1 kHz) is observed. The experimental [variant_greek_epsilon]eff data have been fitted with different theoretical models and found to follow percolation theory successfully. Such a high [variant_greek_epsilon]eff and low loss flexible dielectric material appears to be suitable for technological applications. [ABSTRACT FROM AUTHOR]

It has been reported both experimentally and theoretically that the Ba2+-doping at the A-site of quantum paraelectric SrTiO3 suppresses the quantum fluctuations by activating the ferroelectric mode, while the Ru4+-doping at the B-site plays the opposite role. For a double-impurity doped SrTiO3, i.e., Sr1-xBaxTi1-yRuyO3, where the two types of opposite effects compete with each other, we propose an improved transverse-field Ising model in order to investigate the effect of the double-impurity doping on the quantum phase transitions and critical behaviors. The calculated quantum behavior is quite well consistent with experimental measurements. A linear relationship between the quantum critical doping concentrations for Ba2+ and Ru4+ is predicted, subsequently validated qualitatively by an anharmonic oscillator model. [ABSTRACT FROM AUTHOR]

Magnetic properties of hexagonal YMnO3 nanoparticles were systematically investigated. It is found that zero-field cooled and field-cooled magnetization display divergences at low temperature and a spin-glass temperature of TSG of 43 K are undergone. The thermoremanent magnetization further confirms the spin-glass feature of the YMnO3, which is related to the surface effects resulting in uncompensated spin and suppression of antiferromagnetic order. In particular, the exchange-bias effect is attributed to an exchange coupling between an antiferromagnetic core and the spin-glassy shell or ferromagnetic surface spins of the nanoparticles, which depends on the cooling field, is very interesting for nanomagnetic devices applications. [ABSTRACT FROM AUTHOR]

Rare-earth titanate cubic pyrochlore Ho2Ti2O7 ceramics are prepared by the standard solid state reaction. The magnetic, dielectric, and ferroelectric behaviors are measured in order to investigate the multiferroic behaviors of Ho2Ti2O7. Upon the gradual spin ordering sequence with decreasing temperature, a ferroelectric transition with a small polarization is identified. We discuss the origin of ferroelectricity and its possible correlation with the spin order at low temperature. [ABSTRACT FROM AUTHOR]

Rare-earth titanate cubic pyrochlore Ho2Ti2O7 ceramics are prepared by the standard solid state reaction. The magnetic, dielectric, and ferroelectric behaviors are measured in order to investigate the multiferroic behaviors of Ho2Ti2O7. Upon the gradual spin ordering sequence with decreasing temperature, a ferroelectric transition with a small polarization is identified. We discuss the origin of ferroelectricity and its possible correlation with the spin order at low temperature. [ABSTRACT FROM AUTHOR]

Nanocomposite α-Fe/Nd2Fe14B alloys with high coercivity were prepared by melt spinning. The influence of Ti addition on the microstructure and magnetic properties of these nanocomposite alloys were investigated. Ti addition has proved to result in relevant improvements in the microstructure and magnetic properties, especially in the coercivity Hc. It is shown that the magnetic properties of α-Fe/Nd2Fe14B nanocomposite are improved by an additional 5 at. % Ti, in particular, Hc from 595 up to 1006 kA/m, and (BH)max from 126.7 up to 135.3 kJ/m3. The coercivity mechanism of the α-Fe/Nd2Fe14B nanocomposite magnets was analyzed by studying the behavior of Hc(T)/Ms(T) versus HNmin(T)/Ms(T) (Kronmüller plot) and the dependence of Mirrev(H)/2Mr on the reverse field H. The results of this analysis show that nucleation is the dominating mechanism for the magnetization reversal in these nanocomposites. The Kronmüller plot gives evidence for a reduction in the exchange coupling resulting in an increase in the coercivity. [ABSTRACT FROM AUTHOR]

Si nanowires grown by the vapor-liquid-solid (VLS) mechanism were fabricated using Au-catalyst nanoparticles and silane (SiH4) gas on Si substrates. Au was deposited on the substrate surface both by electron-beam evaporation and Au-colloid deposition. Both kinking defects and vertical nanowire epitaxy on Si <111> substrates were found to be directly related to SiH4 flow rate. A correlation between Au-colloid dilution and the nanowire growth rate was also observed, with the growth rate increasing with increasing concentrations of Au-catalyst particles on the wafer surface. Systematic experiments relating the nanowire growth rate to the proximity of nearest-neighbor Au particles and Au reservoirs were carried out, and the results were found to be in good agreement with a SiH4 reaction model, which associates decomposition to form SiH2 with higher nanowire growth rates. Implications toward the realization of VLS-grown single nanowire transistors are discussed. [ABSTRACT FROM AUTHOR]

We investigate in detail the migration kinetics of oxygen vacancies (OVs) in Ba-doped Pb(Zr0.52Ti0.48)O3 (PZT) ferroelectrics by complex impedance spectroscopy. The temperature dependent dc-electrical conductivity σdc suggests that Ba doping into PZT can lower significantly the density of OVs, leading to the distinctly decreased σdc and slightly enhanced activation energy U for the migration of OVs, thus benefiting the polarization fatigue resistance. Furthermore, the polarization fluctuation induced by the relaxation of OVs is reduced by the Ba doping. The Cole–Cole fitting to the dielectric loss manifests strong correlation among OVs, and the migration of OVs appears to be a collective behavior. [ABSTRACT FROM AUTHOR]

Using the first-principle calculations, we investigate in detail the structure instability resulting from softening of the polar zone-center phonon mode [ferroelectric (FE) instability] and nonpolar zone-boundary mode [antiferrodistortive (AFD) instability] in cubic BaZrO3 (BZO) under hydrostatic pressure P from -20 to 90 GPa. The hydrostatic pressure enhances the AFD instability, while it suppresses and then enhances the FE instability. A sequence of FE→cubic→AFD→AFD/FE phase transitions with increasing P is predicted. A careful examination of the pressure dependence of full phonon dispersions and interatomic force constants in real space reveals the microscopic key interactions in driving the transitions. With increasing pressure P, the drastically evolving short-range forces suppress the FE instability induced by the long-range dipole-dipole forces under low pressure, and enhance both the AFD and FE instability under high pressure. We investigate the dielectric properties of cubic BZO under hydrostatic pressure. The dielectric constant as a function of pressure shows a minimum contributed from the TO1 mode with the lowest frequency. We argue that this pressure dependence of the dielectric constant mainly originates from fluctuations of the SR forces. [ABSTRACT FROM AUTHOR]

The dielectric relaxation and magnetocapacitance effect of one-dimensional spin frustrated compound Ca3Co2O6 are investigated. The steplike magnetocapacitance effect is observed and one to one corresponds to the steplike magnetization. We explain this phenomenon from the spin configuration dependent dielectric response. The simulation results using the Monte Carlo method are in good agreement with experimental data at low temperature. The close correspondence between the magnetic and dielectric properties indicates that the coupling is the intrinsic character of Ca3Co2O. The steplike magnetocapacitance effect may find potential applications in data storage and sensors. [ABSTRACT FROM AUTHOR]

Aligned CdS nanowire arrays have been fabricated directly on a Cd foil via a simple solvothermal method. The metal Cd foil serves as both the Cd source and substrate during fabrication of the aligned CdS nanowire arrays. The morphology, structure, and composition of the samples are characterized by x-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy, and selected-area electron diffraction, and the results reveal the formation of aligned single-crystalline CdS nanowires with uniform diameters of 20–40 nm. The photoluminescence and Raman spectra disclose the optical properties of the products and the possible growth mechanism is suggested. The electron field emission properties are also investigated and analyzed. The screening effect is observed to play a vital role in the electron field emission properties due to the coalescent ends of the nanowires. The simple synthesis methodology in conjunction with the good field emission and optical properties makes the materials both scientifically and technologically interesting. [ABSTRACT FROM AUTHOR]

The conduction relaxations of polycrystalline La0.5Ca0.5Mn0.95Fe0.05O3 upon imposing rectangle electric current pulses (with minute time scale) are studied in details. We observe clear “overshooting” features of the conduction relaxation at both the front and rear edges of the current pulse so long as the pulse is sufficiently high. The Joule heating effect and the intrinsic stabilization of the ferromagnetic metal phase by the current pulse are linked in understanding our observations, and these effects may be applicable for resistance switching function. [ABSTRACT FROM AUTHOR]

The low temperature dielectric and ferroelectric properties of SrTiO3, with constant averaged A-site ionic size but different A-site disorder degrees induced by A-site cation size mismatching through the codoping of Ca and Ba, are investigated. Upon the increasing A-site disorder degree, the dielectric property shows different behaviors from individually Ca- or Ba-doped SrTiO3 where the averaged A-site ionic size varies linearly with the doping. The transition from the quantum paraelectric state to relaxorlike ferroelectric state and eventually to normal ferroelectric state upon the increasing A-site disorder degree is revealed. The physics underlying these phenomena is discussed based on the A-site size mismatch effect. [ABSTRACT FROM AUTHOR]

Bi5Ti3FeO15 bulk ceramic and thin film samples are prepared using the sol-gel method. The dielectric, ferroelectric, and magnetic behaviors of these samples are measured in order to investigate the possible multiferroic effect. The superparamagnetic behavior with dominant antiferromagnetic (AFM) interaction background for the as-prepared Bi5Ti3FeO15 samples is revealed. The clearly identified magnetocapacitance effect at low temperature is argued to originate from the suppression of the AFM interaction by external magnetic field. [ABSTRACT FROM AUTHOR]

In this paper, we report the growth of GaN quantum dot superlattices (QDSLs) with AlN barriers on (0001) sapphire substrates by molecular beam epitaxy at relatively high temperature (770 °C) using the modified Stranski-Krastanov growth mode. Observations with atomic force microscopy show that the height distribution of the dots depends strongly on the number of GaN monolayers (MLs) grown on the AlN barriers. Specifically, the height distribution consists of two Gaussian distributions (bimodal) for coverages of 3 or 4 ML, and becomes a single Gaussian distribution for 5 and 6 ML of coverage. Furthermore, the density of quantum dots increases with the degree of coverage and saturates at 2×1011 dots/cm2. An increase in the number of stacks in the superlattice structure with 4 ML coverage also leads to a more pronounced bimodal height distribution. Electron microscopy observations indicate that the GaN QDs are truncated pyramids faceted along the {1103} planes and suggest that larger dots are associated with threading dislocations which presumably provide low-energy nucleation sites. Transmission electron microscopy studies also indicate that most of the larger dots are nucleated next to edge-type dislocations, while most of the smaller dots are located in dislocation-free regions. These GaN QDSLs were also studied by grazing-incidence small angle x-ray scattering and grazing-incidence x-ray diffraction methods. The average lateral deviation and the vertical correlation length between QD positions for two successive layers were determined to be 1.4 nm and 190 nm, respectively. A GaN QD growth model is proposed to explain the phenomenon. [ABSTRACT FROM AUTHOR]

Both experimental studies and molecular dynamics (MD) simulations reveal a unique atomic-scale growth mechanism during crystallization of an amorphous alloy Zr65Ni25Ti10. By using a high-resolution transmission electron microscope incorporated with nanobeam diffraction technique, we have clearly seen imperfect ordered packing of nano-ordered clusters (NOCs) with a size of 1–2 nm embedded in this amorphous material. Under a very large undercooling condition, NOCs essentially act as preexisting nuclei that can grow directly into nanocrystals during annealing treatments. The growth mechanism includes three distinct steps in succession: formation of quasi-ordered structure with one-dimensional (1D) periodicity, and then 2D periodicity, and finally forming 3D nanocrystals. These three growth steps are cross-linked, and atomic movements are also accommodated by a rotation of atomic planes. This growth mechanism is unambiguously verified by MD simulation. [ABSTRACT FROM AUTHOR]

An aqueous solution of carbon nanotubes, treated by a concentrated nitric/sulfuric acid mixture to disentangle the nanotubes, was utilized as the working medium in a two-phase closed thermosyphon to investigate its performance. In comparison with the thermosyphon filled with a distilled water medium, the one filled with carbon nanotube suspension has a high evaporation section wall temperature, incipience temperature, and excursion, as well as thermal resistance. The carbon nantotubes’ nanofluid deteriorates the performance of the gravity-assisted heat pipe. Measurements employing the maximum bubble pressure method demonstrate that suspending carbon nanotubes in bulk water gives rise to increased surface tension. In addition, the contact angle of suspension obtained with the sessile drop method on a copper plate is much smaller than that of water. Alterations of solid-liquid-vapor interfacial properties, arising from the addition of carbon nanotubes, change the boiling mechanism and thus deteriorate the boiling heat transfer. [ABSTRACT FROM AUTHOR]

Time-resolved photoluminescence (PL) near 540 nm, taken from barium titanate (BaTiO3) ultrafine powders of ∼80, 90, and 110 nm in size, was measured at 11 K. Two-exponential functions were found to fit the decay curves well, and the decay lifetimes were composed of one short, about 10 ns, and one long, about 200 ns, time constants, respectively. Results also indicate that the PL peaks show a small blueshift with decreasing BaTiO3 particle size. The decay process consists of the recombination of self-trapped excitons (long lifetime decay) and of the electrons in the surface states with the holes in the valence band (short lifetime decay). The short lifetime component makes comparable contribution to the decay intensity of PL with the long lifetime one. [ABSTRACT FROM AUTHOR]

The polarization switching fatigue behaviors of tetragonal Pb(Zr0.1Ti0.9)O3(PZT0.1) thin films deposited on Pt-coated silicon wafers by the sol-gel method are investigated by testing the fatigue endurance at different temperatures and by measuring the small-signal dielectric loss associated with the fatigued samples. It is observed that the fatigue endurance can be significantly improved at low temperature, while the low-temperature fatigue becomes more serious with increasing magnitude of the electrical pulses for fatigue testing. The fatigued thin films exhibit much bigger dielectric loss than the fresh films over the whole temperature range, due to the domain pinning by the aggregated defects (oxygen vacancies). In addition, the temperature dependence of the fatigue resistance performance of the thin films can be well described by the exponential law. The long-range diffusion and aggregation of the defects and the consequent domain pinning as one of main origins for switching fatigue in the PZT0.1 thin films are demonstrated. [ABSTRACT FROM AUTHOR]

Dispersed nickel sulfate (NiSO4) microclusters on Si substrates were fragmented by pulsed excimer laser irradiation to serve as catalysts for carbon nanotube/nanofiber (CNT/CNF) growth. At proper fluences, NiSO4 clusters were pulverized into nanoparticles. The sizes of clusters/nanoparticles were found to be dependent on laser fluence and laser pulse number. By increasing the laser fluence from 100 to 300 mJ/cm2, the size of disintegrated particles decreased drastically from several micrometers to several nanometers. It was found that laser-induced disintegration of as-dispersed NiSO4 clusters was mainly due to physical fragmentation by transient thermal expansion/contraction. Thermal melting of nanoparticles in a multipulse regime was also suggested. Hot-filament chemical vapor deposition (HFCVD) was used for growth of CNTs from the pulsed-laser treated catalysts. For samples irradiated at 100 and 200 mJ/cm2, CNFs were dominant products. These CNFs grew radially out of big NiSO4 clusters, forming dendritic CNF bunches. For samples irradiated at 300 mJ/cm2, dense multiwalled carbon nanotubes (MWCNFs) with uniform diameters were obtained. It is suggested that elemental Ni was formed through thermal decomposition of NiSO4 clusters/nanoparticles during HFCVD. The size and the shape of the Ni aggregation, which were determined by the initial size of NiSO4 clusters/nanoparticles, might affect the preference in the synthesis of CNTs or CNFs. [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]

Carbon nanotube (CNT) bulk samples were fabricated by spark plasma sintering (SPS), which, as a rapid consolidation technique, preserved the phase structure and diameter of cylindrical tubules of the CNTs even at high temperatures of up to 2000 °C. The thermal conductivity of the resultant bulk samples was measured by the conventional laser-flash method, and the corresponding thermal conductivity was found to be as low as 4.2 W/m/K at room temperature. This low thermal conductivity of the CNT bulk materials was explained on the basis of multiple physical elements including intensive tube–tube interactions. CNT bulk materials may find potential applications as thermoelectric materials that require low thermal conductivity, but high electrical conductivity. [ABSTRACT FROM AUTHOR]

We provide an overview of progress on the exchange biasing of a ferromagnetic semiconductor (Ga1-xMnxAsd by proximity to an antiferromagnetic oxide layer (MnO). We present a detailed characterization study of the antiferromagnetic layer using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, transmission electron microscopy, and x-ray reflection. In addition, we describe the variation of the exchange and coercive fields with temperature and cooling field for multiple samples. [ABSTRACT FROM AUTHOR]

A model of the quasi-Debye loss mechanism in SrTiO3 and Ba0.6Sr0.4TiO3 perovskite ferroelectrics at microwave frequencies is presented. The field dependence and the size of the field-induced quasi-Debye loss contribution in SrTiO3 and Ba0.6Sr0.4TiO3 systems have been evaluated in the simple approximation of the isotropic phonon spectra of these materials. Good agreement between experimental and simulated results for the field dependence of dielectric loss for SrTiO3 ferroelectric material is observed for the weak dc fields [tunability n=[variant_greek_epsilon](0)/[variant_greek_epsilon](E)<2]. A significant feature in the field dependence of dielectric loss at microwave frequencies, a pronounced maximum, is predicted for SrTiO3 at higher values of the bias field (n≅2) whereas in Ba0.6Sr0.4TiO3 the field dependence of the loss is found to be monotonic. The influence of the quasi-Debye loss contribution on microwave performance of SrTiO3 and Ba0.6Sr0.4TiO3 ferroelectric materials is analyzed. It is concluded that the contribution of this mechanism is large enough to affect the performance of tunable microwave devices based on SrTiO3 ferroelectric materials, whereas in the case of Ba0.6Sr0.4TiO3 ferroelectrics the contribution of the quasi-Debye loss mechanism is found to be relatively small. [ABSTRACT FROM AUTHOR]

A method for producing gallium nitride (GaN) and gallium oxide (Ga2O3) nanoribbons by the combination of plasma immersion ion implantation of nitrogen into GaAs and rapid thermal annealing (RTA) has been investigated. Our approach uses a broad ion-impact energy distribution with variable implant doses to form a spread-out nitrogen depth profile and an amorphous surface layer. This approach circumvents the retained-dose limitation and low nitrogen content problems associated with ion beam implantation at fixed energy. Raman spectroscopy, transmission electron microscopy (TEM), x-ray diffraction and x-ray photoelectron spectroscopy were conducted on the samples. For the samples which had undergone RTA at 850 °C for 2 min, a Raman peak at 577 cm-1 associated with GaN was observed. The weak Raman intensity indicated that a small amount of GaN was present. Cross-sectional TEM imaging showed that the thickness of the region containing GaN was about 40 nm. When RTA was performed at 950 °C for 2 min, Ga2O3 nanoribbons were found on the GaAs sample surface instead. The ribbons were 0.1–2 μm in width, several tens of nanometers in thickness, and several tens of micrometers in length. Raman spectroscopy confirmed that the ribbons are single crystalline Ga2O3. In addition, the Ga2O3 ribbons were found to possess strong visible photoluminescence. The possible formation mechanism of these nanoribbons is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the dielectric properties of Cd[sub x]Zn[sub 1-x]Te (0.056≤x≤0.582) epilayers studied by capacitance and dissipation factor measurements at temperature 201 K

Optical excitation of covalent bond structures via plasmon-mediated local fields inside elemental gallium nanoparticles can explain the recently observed phenomenon of light-controlled gallium nanoparticle growth on silica substrates under very low intensity laser illumination. Alongside the previously reported mechanism of atomic desorption induced by electronic excitation, we introduce another parallel mechanism based on the suppression of adatom adsorption, and illustrate how both mechanisms lead to a narrowing of the size distribution of the particle during the growth process. [ABSTRACT FROM AUTHOR]

A full-band ensemble Monte Carlo simulation has been used to study the high-field carrier transport properties of 4H-SiC. The complicated band structure of 4H-SiC requires the consideration of band-to-band tunneling at high electric fields. We have used two models for the band-to-band tunneling; one is based on the overlap test and the other on the solution of the multiband Schrödinger equations. The latter simulations have only been performed for holes in the c-axis direction, since the computer capacity requirement are exceedingly high. Impact-ionization transition rates and phonon scattering rates have been calculated numerically directly from the full band structure. Coupling constants for the phonon interaction have been deduced by fitting of the simulated low-field mobility as a function of lattice temperature to experimental data. Secondary hot electrons generated as a consequence of hole-initiated impact ionization are considered in the study for both models of band-to-band tunneling. When the multiband Schrödinger equation model is used for holes in the c-axis direction, a significant change in the electron energy distribution is found, since the hole impact-ionization rate is very much increased with this model. The secondary electrons increase the average energy of the electron distribution leading to a significant increase in the electron-initiated impact-ionization coefficients. Our simulation results clearly show that both electrons and holes have to be considered in order to understand electron-initiated impact ionization in 4H-SiC. [ABSTRACT FROM AUTHOR]