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Understanding the behavior of intrinsic defects and helium (He) in tungsten oxides is useful for the application of tungsten (W) in a fusion environment because of the oxidation of W surfaces. The formation and diffusion energies of intrinsic defects and He in monoclinic γ-WO3 have been investigated using first-principles density functional theory calculations. The formation energy and diffusion activation energy of O defects are lower than W defects. O vacancy prefers to diffuse along the ⟨ 001 ⟩ direction, then followed by ⟨ 010 ⟩ and ⟨ 100 ⟩ directions; however, the W vacancy is immobile at temperatures lower than 2000 K. The stability of Schottky defects (SDs) is sensitive to their geometry and orientation. W interstitials prefer to move along the [100] direction, while O interstitials jump around W atoms rather than through the W quasi-cubic centers. He interstitial atoms are predicted to have a high solubility and an anisotropic diffusion mechanism in γ-WO3. In addition, the effect of biaxial strain on the solubility and diffusivity of He interstitials was investigated. He interstitials prefer to reside at individual sites rather than clusters. He atoms are weakly trapped by single vacancies or SDs. Vacancies assist the local migration of nearby He. Correspondingly, He self-clustering and bubble formation are less likely to form in γ-WO3 relative to bcc W. The energetics obtained in this work can be used to predict the microstructure evolution of the WO3 layer on a W substrate exposed to He plasmas at different temperatures. [ABSTRACT FROM AUTHOR]

This work investigates the detailed difference between dielectric function models, the Mermin model and the full Penn algorithm (FPA) model, for the determination of an electron inelastic mean free path (IMFP) with optical energy loss function (ELF), as an extension of our previous study [Da et al., Surf. Interface Anal. 51, 627 (2019)] by using the simple Drude-type ELF. In the conventional normal Mermin (NM) model, the approximations of ELF by the Drude equation will introduce inevitable fitting error. In order to enhance the accuracy of the NM model, our previous proposed extended Mermin model [Da et al., Phys. Rev. Lett. 113, 063201 (2014)], which is renamed as a super-extended Mermin algorithm (SE-MA) now, is employed to eliminate the error by expanding the definition of Drude oscillators used in the NM. In the SE-MA, the Drude-like oscillators allow the existence of negative strengths to express the fine structures of phonon–electron scattering and the plasmon lifetime broadening effect. Because in our previous study, the simple Drude-type ELF cannot include these complex structures, in this work, the electron IMFPs are calculated for five realistic materials, Al, Si, Cu, Au, and MgO. The difference between IMFPs calculated by the SE-MA model and the FPA model is material dependent and is significant in the low energy region, which is analyzed by using the Fano plot. This is due to the more important role played by the plasmon lifetime broadening effect. [ABSTRACT FROM AUTHOR]

Ferroelectricity and magnetism seldom coexist due to mutual exclusiveness. Recent attempts have been made to achieve the coexistence of ferroelectricity and magnetism in polar magnets. In this paper, we investigated the magnetic properties, dielectric relaxation, and magnetodielectric (MD) effect of polar Dy2Cu2O5 ceramic. At the antiferromagnetic ordering temperature, the dielectric constant (ɛ) curves exhibit a spontaneous change in slope, indicating strongly coupled charge and spin degrees of freedom. With increase in the magnetic field intensity, the simultaneous suppression of the dielectric anomaly and the antiferromagnetic transformation demonstrates the existence of the MD effect. It is important to note that ɛ varies nonmonotonically with the magnetic field. Below the magnetic ordering temperature, ɛ increases continuously before the metamagnetic transition and then decreases after that. The results are discussed in terms of the magnetic field-induced change of spin configuration and spin–phonon coupling. Moreover, two dielectric relaxation-related steps are observed, which are correlated with the electrons hopping within and among the zigzag chains of Cu2+, respectively. This work helps understand the dielectric behavior and the MD effect in materials with complicated spin structures. [ABSTRACT FROM AUTHOR]

In this paper, mesoporous nitrocellulose (NC)/graphene oxide (GO) composite aerogel is manufactured by a sol-gel method followed by supercritical carbon dioxide drying. The effects of GO on the microstructure, decomposition, and thermal conductivity are studied. The laser absorption, laser ignition property, and combustion performance of NC aerogel and NC/aerogel are also investigated. The results indicate that NC/GO aerogel is established by the combination of NC nano-fibers and GO sheets, and the aerogels are mesoporous with average pore size at 40 nm. Moreover, the thermal stability of aerogels is decreased by the nano-structure of NC, and the laser absorption is significantly increased by the nano-porous structure and the adoption of GO. In addition, the laser ignition and combustion efficiency are also greatly improved by the nano-porous aerogel structure and the incorporation of evenly uniformly dispersed GO sheets with high photothermal conversion efficiency and thermal conductivity. Laser ignition times reduced by 73.7% and 99.6% are obtained, and flame propagation rates up to 4.7 and 12.3 times are observed for NC aerogel and NC/5 wt. % GO aerogel, respectively. [ABSTRACT FROM AUTHOR]

Interest exists in utilizing boron (B) wall conditioning of fusion tokamaks containing tungsten (W) plasma facing components, in order to improve plasma confinement. To understand the interactions of B with W surfaces, first-principles density functional theory calculations have been performed to model the adsorption, diffusion, and solution of B near the W(100), W(110), and W(111) surfaces. The results show that B within a distance of 0.6 nm above the surfaces is adsorbed to the surfaces without activation barriers. B atoms are strongly adsorbed on the W(100) surface with an adsorption energy of 7.80 eV, which is 1.22 and 1.35 eV larger than on the W(110) and W(111) surfaces. B diffusion on the W(100), W(110), and W(111) surfaces has an activation energies of 2.08, 1.12, and 1.47 eV, respectively; while, diffusion from the adsorption sites into the bulk requires 2.2–2.3 eV. The B solution energy below a clean W(100) surface is the lowest, followed by the W(111) and W(110) surfaces. B clustering and B-induced surface deformation as a function of B coverage has been investigated. B on the W(100) surface occupy epitaxial sites at coverages of 0–1.25 ML, but form clusters at higher coverages. B clustering on the W(110) and W(111) surfaces is expected throughout the adsorption process. Compared to a clean surface, B atoms on the W(100) reduce the surface effect on the B solution energy below the surface, while the presence of B on the W(110) and W(111) surfaces generally decreases or increases the B solution energy below surfaces, respectively. [ABSTRACT FROM AUTHOR]

Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system. [ABSTRACT FROM AUTHOR]

The interaction of xenon (Xe) bubbles with small self-defects in uranium dioxide (UO2) has been studied using molecular statics simulations. The results show that the pressure and size of bubbles have a minimal impact on the heterogeneity of the interaction between a charge neutral Xe bubble and charged point defects, while the local charge distribution around the bubble overwhelmingly determines the interaction strength and critical interaction distance. The charge effect on the interactions between Xe bubbles and defects was further confirmed by assessing the point defect interaction energies with negatively or positively charged Xe bubbles. The Xe density, or pressure, has a much smaller effect on the interaction energy between charged bubbles and small defects at least for low and medium pressure bubbles. The interactions between charged Xe bubbles and point defects basically follow the Coulomb electrostatic interaction law, which is independent of the empirical potentials employed for the Xe–UO2 system in this work. [ABSTRACT FROM AUTHOR]

A systematic study has been performed based on a Monte Carlo simulation for the investigation of secondary electron yields, backscattering coefficients, and total electron yields for eight compound semiconductor materials, i.e., AlN, TiN, VN, VC, GaAs, InAs, InSb, and PbS, at different incident electron energies in the range 0.1–10 keV. Our Monte Carlo simulation model is based on the Mott cross section for electron elastic scattering as calculated by a partial wave method and a dielectric functional approach to electron inelastic scattering with the full Penn algorithm. We used Palik's optical data for lower photon energies below 100 eVs and Henke's data for higher photon energies. The cascade production of secondary electrons in electron inelastic scattering and low energy is included in the simulation. The simulated results of electron backscattering coefficients are compared with the experimental data available in the literature. Considering the fact that the experimental data for these compound materials are not available, we have compared them with experimental data for elements having the nearest mean atomic numbers. The simulation predicted much larger backscattering coefficient values than the empirical Staub formula. [ABSTRACT FROM AUTHOR]

We have performed a systematic Monte Carlo simulation of primary and secondary electron trajectories to predicate the mean escape depth of secondary electron emission for six compound semiconductors, i.e., TiN, VN, GaAs, InAs, InSb, and PbS. Mott's cross section is used for the description of electron elastic scattering in the simulation model, and the full-Penn's dielectric function approach is adopted for the modeling of electron inelastic scattering, where the energy loss function obtained with the optical data is contributed from phonon excitation, interband transition of the loosely bound valance electrons, and inner-shell electron excitations. We have calculated the excitation depth distribution function, emission depth distribution function, and their combining effect in probability depth distribution function at different primary energies for the excited and emitted secondary electrons in these materials. The calculation leads to the primary energy dependence of mean escape depth whose values are found in the range of 0.4–1.4 nm for these materials. [ABSTRACT FROM AUTHOR]

Hydrogen (H) solution, migration, and binding to vacancies near the tungsten/tungsten carbide (W/WC) interfaces based on hcp WC or bcc W (W/WCb and Wb/WC) have been studied by first-principles simulations to provide insights into the effect of C on H behavior in W exposed to C deposition in fusion reactors. The H behavior near the W/WC interfaces is related to the tensile or compressive strain due to the lattice match and interfacial effects. Near the W/WCb interface, the H solution energy in hcp WC increases approaching the interface, while it decreases from the W side to the interface. The configuration change of the W slab significantly decreases the H solution energy but has only a modest effect on the H migration energy barrier in comparison with the values in bcc W. The interface enhances the H binding to vacancies in WC layers. Both the interface and configuration adjustment of the W slab reduce the H binding to vacancies on the W side of the interface. Near the Wb/WC interface, H solution energies in both WC and W slabs weakly decrease approaching the interface. The configuration change of the WC slab significantly increases the H solution energy and binding energy to vacancies but decreases the H migration energy barrier in comparison with the values in hcp WC. The H energetics near the W/WC interfaces indicate the likelihood of H localization and diffusion in the W side of the interface, rather than diffusing through the interface into WC layers. [ABSTRACT FROM AUTHOR]

The diffusion and self-clustering nucleation behavior of hydrogen (H) without vacancies below tungsten (W) surfaces are important for understanding the retention of deuterium (D) in W crystals exposed to high-flux and low-energy D plasma. The H migration energy and binding energy of H to self-clusters near the W(100), W(110), and W(111) surfaces have been investigated by first-principles computer simulations using density functional theory. H diffusion from adsorption sites on the W(100), W(110), and W(111) surfaces into solute sites in the bulk requires energies of at least 1.21, 1.78, and 1.80 eV, respectively, while 0.27, 0.31, and 0.24 eV for the reverse process. In addition, the lateral diffusion of H between two subsurface layers below the W surfaces has been investigated. Two H atoms at a depth of 0.08 nm below the W(110) surface have the highest binding energy, followed by H atom pairs below the W(111) and W(110) surfaces. The nucleation and stability of H clusters depend on the surface orientation. A planar configuration between the first nearest neighbor {100} planes is energetically favorable for H self-clustering below the W(100), W(110), and W(111) surfaces. The thermal stability of a platelet containing 16 H atoms below the W surfaces at 300 and 600 K was also studied by ab initio molecular dynamics simulations, which indicate that the H platelet below a W(111) surface is more stable than that below either the W(100) or the W(110) surface. [ABSTRACT FROM AUTHOR]

The effect of post-growth annealing (PGA) on dot-in-well (DWELL) structures grown on Si substrates has been studied. The photoluminescence (PL) measurements showed that, compared to the DWELL structures directly grown on GaAs, the PGA process induces a distinct difference in the tuning of the emission properties. Then, transmission electron microscopy imaging of the samples revealed that PGA improved the uniformity of quantum dots (QDs) while the size of the QDs increased, in agreement with a corresponding red shift and a decrease of the full width at half maximum in the PL emission spectrum. Finally, energy-dispersive x-ray linescan provided a quantitative analysis of the composition change of DWELL grown on Si in the as-grown, 700 °C annealed, and 800 °C annealed samples. The change in the InL/GaK concentration ratio became gradual between the QDs and surrounding materials after 800 °C annealing. The analysis of the optical properties, morphology evolution, and compositional change of the QDs as a function of the annealing temperature showed good agreement. [ABSTRACT FROM AUTHOR]

Understanding the interaction between hydrogen (H) and helium-vacancy (He-V) complexes in tungsten (W) is important for the development of plasma-facing materials in fusion reactors. H trapping by HexVy complexes in bulk W, as well as the H solution behavior and H trapping by HexV complexes near W(100), W(111), and W(110) surfaces, has been investigated by first-principles computer simulations using density function theory. The results show that the sequential H binding energies to HexV complexes in bulk W decrease with the increasing number of H and He. For the HexV2 complexes in bulk W, H prefers to trap at interstitial sites near the junction of the di-vacancy, where the H can minimize the isosurface of optimal charge density. The most stable interstitial sites for H below W surfaces are dependent on the surface orientation. Our calculations indicate that H atoms tend to prefer a depth of 0.3 nm below the W(100) and W(111) surfaces due to the surface reconstruction. The binding energy of H to a HeV complex near W surfaces has the most significant orientation dependence below the W(111) surface, followed by the W(100) and W(110) surfaces. Compared with the bulk value, the largest difference in the average binding energy of H to the stable HexV complexes at the three W surfaces is about 0.2 eV. Furthermore, the effect of surfaces on the H binding energy to HexV complexes can be ignored for depths greater than 0.65 nm. [ABSTRACT FROM AUTHOR]

Density function theory calculations have been performed to study the stability of small helium-vacancy (He-V) complexes near tungsten (W) surfaces of different orientations. The results show that the stability of vacancies and He-V complexes near W surfaces depends on surface orientation. However, as the depth below the surface increased beyond about 0.65–0.8 nm, the stability of He-V complexes is similar to the bulk. The formation energies of single vacancies and di-vacancies at depths less than 0.2 nm below the W(110) surface are higher than for W(100) or W(111) surfaces, but have lower energies at depths between 0.2 and 0.65 nm. The formation energies of He-V complexes below W surfaces are sensitive to the geometric orientation of the He and vacancy, especially below the W(111) surface. Within about 0.2 nm of the top layer of the three W surfaces, neither a vacancy nor a di-vacancy can trap He. Because of the lower formation energy of He-V complexes and higher He binding energy to vacancies below the W(110) surface, the He desorption from the W(110) surface is less likely to occur than from the W(100) and W(111) surfaces. Our results provide fundamental insight into the differences in surface morphology changes observed in single W crystals with different surface orientations under He plasma exposure. [ABSTRACT FROM AUTHOR]

To search for half-metallic materials for spintronic applications, instead of using an expensive trial-and-error experimental scheme, it is more efficient to use first-principles calculations to design materials first, and then grow them. In particular, using a priori information of the structural stability and the effect of the spin--orbit interaction (SOI) enables experimentalists to focus on favorable properties that make growing half-metals easier. We suggest that using acoustic phonon spectra is the best way to address the stability of promising half-metallic materials. Additionally, by carrying out accurate first-principles calculations, we propose two criteria for neglecting the SOI so the half-metallicity persists. Based on the mechanical stability and the negligible SOI, we identified two half-metals, β-LiCrAs and β-LiMnSi, as promising half-Heusler alloys worth growing. [ABSTRACT FROM AUTHOR]

A series of polycrystalline YMn1-xRuxO3 (0≤x≤0.2) samples were prepared by traditional solidstate reaction method. Effects of doping on the microstructures and magnetic properties were investigated. Microstructural results reveal that samples crystallize in a single hexagonal structure with P63cm group for x≤0.1. Lattice parameters a, c, and unit-cell volume of YMn1-xRuxO3 are found to increase with doping content, which are ascribed to the larger radius of Ru3+ than that of Mn3+. Weak ferromagnetism is found and is enhanced with increasing doping concentration x. The bond angles of Mn-O3-Mn and Mn-O4-Mn are changed in the opposite trends, which break the Mn-Mn exchange interaction, thus the antiferromagnetic ordering. The MnO5 bipyramid is found to be relieved and the trimerization of Mn ions is weakened. These structural modifications result in the increase of weak ferromagnetism ordering in samples. [ABSTRACT FROM AUTHOR]

NiAs-type manganese telluride (MnTe) films with preferred crystallographic plane of (110) were prepared on Si/SiO2 substrates by pulsed laser deposition. X-ray diffraction(XRD) of the films was studied at different temperatures. The XRD peak of MnTe (110) films shifts to higher angle with decreasing temperature, showing the decrease of the lattice parameter. Resistivity of the films was studied in the temperature range of 2-350 K. The bump between 150 and 250 K was observed in the films, which may be related to the special s-d and p-d overlaps induced by the compressed lattice. The magnon drag effect near its Néel temperature TN and enlarged magnetic-elastic coupling below 100 K were observed and analyzed in details. [ABSTRACT FROM AUTHOR]

Transmission electron microscopic studies of Cu ion-implanted Cu nanoclusters reveals that ion beam current defines size and arrangement of Cu clusters. Optical absorption spectra show a size-dependent surface plasmon resonance in the nonlinear coefficients of two-photon absorption and refraction. The nonlinear and linear optical properties of these nanoclusters are used in nonlinear optical devices.

NaZn13-type La(Fe0.94Co0.06)11.8Si1.2 alloys were manufactured to investigate the influence of their microstructural change on magnetic refrigeration performance during magnetic field cycling. The magnetic refrigeration performance measurements indicate that both the large magnetic entropy change value (ΔS=14.1 J kg-1 K-1) and maximum adiabatic temperature change (Δ=2.2K) are favorable for the alloys to be superior candidate of magnetic refrigerants. However, the alloys exhibit nearly 10% decrease of ΔS and ΔT when they performed cycling ten-thousand times. More than thousand times of cycles induce local stress and grain cleavages presented by the accumulation of irreversible microstructure changes such as micro-cracks and sub-boundaries. According to the domain observation for the alloys with different field cycles, these microstructure characteristics accompany with the reconfiguration of the local magnetic domains and increase of domain wall energy, which are considered to be the reason of the decrease of ΔS. [ABSTRACT FROM AUTHOR]

A sort of composite solder was produced by adding Y2O3 nanoparticles in Sn3.0Ag0.5Cu solder. The microstructure and tensile strength of solder joint were investigated. It was found that the size of intermetallic compounds and tensile strength of solder joint were notably influenced by the nanoparticles. The growth behaviors of intermetallic compounds Ag3Sn and Cu6Sn5 were suppressed due to the addition of Y2O3 nanoparticles. The tensile test results revealed that the strength of composite solder joint was higher than that of solder joint without nanoparticles addition. It is indicated that Y2O3 nanoparticles should play important roles in strengthening of joint by hampering dislocation movement. [ABSTRACT FROM AUTHOR]

Al-doped ZnO thin films (AZO) have been deposited on amorphous glass substrates by DC sputtering at different substrate temperatures Ts. X-Ray diffraction results reveal that AZO thin films have a hexagonal wurtzite structure with (002) preferred orientation. (002) peaks indicate that the crystalline structure of the films is oriented with c-axis perpendicular to the substrate. Three-dimensional (3D) atomic force microscopy images of AZO thin films deposited on glass substrate at 200 °C, 300 °C, and 400 °C, respectively, shows the improvement of the crystallinity and the homogeneity of AZO thin films with Ts which is in agreement with the noise measurements. The noise was characterized between 1 Hz and 100 kHz and we have obtained 1/f spectra. The noise is very sensitive to the crystal structure especially to the orientation of the crystallites which is perpendicular to the substrate and to the grain boundaries which generate a high current flow and a sharp increase in noise. Through time, Rsh and [αμ]eff increase with the modification of the crystallinity of AZO thin films. Study of noise aging shows that the noise is more sensitive than resistivity for all AZO thin films. [ABSTRACT FROM AUTHOR]

Strain-engineered phase boundaries in epitaxial bismuth ferrite films has been investigated via thermodynamics analysis in good agreement with both experimental and first principle studies, and a novel orthorhombic-rhombohedral (OR) phase boundary is found to exist under tensile misfit strain. In contrast to more widely studied tetragonal-rhombohedral phase boundary in bismuth ferrite where enhanced piezoelectric response is largely attributed to extrinsic mechanism, the OR phase boundary is found to show enhanced intrinsic piezoelectric response, and the change of the polarization slope at phase boundary is found to be the key to the enhancement. Difference between strain-engineered phase boundaries and classical morphotropic phase boundary in lead zirconate titanate is also noticed. [ABSTRACT FROM AUTHOR]

Metal-semiconductor-metal ultraviolet photodetectors were fabricated by using the sputtered Ga-doped ZnO (GZO) thin films on sapphire substrate as an active layer. Current-voltage (I-V) and opto-electrical characteristics of the devices were investigated. It is found that the peak optical responsivity of the devices can be significantly improved by selecting appropriate thermal annealing temperature, i.e., from 12.0 A/W (annealed at 500 °C) and 54.0 A/W (700 °C). Furthermore, dark current of the devices drops by two orders of magnitude after annealing process. The significant improvement in performance of the device is ascribed to the removal of massive defect centers of the GZO thin films and increase of Schottky barrier height between the GZO and metal electrodes after thermal annealing at appropriate temperatures. [ABSTRACT FROM AUTHOR]

The recently discovered three-dimensional topological insulator Bi2Te3 is studied as function of pressure in terms of crystal structures, resistance, and Hall coefficient. The superconductivity is found in phase I (ambient phase) Bi2Te3 with Tc ∼ 3 K, which is related to the topological features. The evolution of crystal structure with pressure is investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring at about 8 GPa, 13 GPa, and 16 GPa, respectively. Furthermore, the high pressure phases of Bi2Te3 are also superconducting but with much higher Tc ∼ 8 K. The superconducting transitions are compared with those for Bi, Te elements. A global phase diagram of Bi2Te3 as function of pressure up to 30 GPa is obtained. [ABSTRACT FROM AUTHOR]

A monolithic, epitaxially-integrated, vertically-aligned, multi-band photodetector architecture has been demonstrated via the successful growth and fabrication of metamorphic back-to-back n-i-p/p-i-n In0.61Ga0.39P/In0.14Ga0.86As visible/near-IR dual-detector devices. The back-to-back diode design enables simultaneous and independent operation of detectors in both bands with low optical cross talk (<-10 dB outside the 690-720 nm range) and complete electrical isolation between the sub-detectors. The high electronic quality of the resultant metamorphic materials was confirmed via deep level transient spectroscopy, which revealed total trap concentrations of 5 × 1012 cm-3 for the In0.14Ga0.86As and 2 × 1014 cm-3 for the In0.61Ga0.39P sub-detectors, enabling low, room temperature reverse bias (-2 V) dark current densities of 4 × 10-8 A cm-2 and 7 × 10-12 A cm-2, respectively. High responsivity and specific detectivity values, at a working bias of -2 V, were measured: 0.41 A/W and 8.6 × 1011 cm Hz1/2/W for the In0.14Ga0.86As sub-detectors (at 980 nm), and 0.30 A/W and 2.0 × 1014 cm Hz1/2/W for the In0.61Ga0.39P sub-detectors (at 680 nm). The successful integration of high-quality lattice-mismatched materials, combined with the excellent sub-detector performances, demonstrate the potential for extending such a multi-band photodetector technology to achieve simultaneous detection of a wide range of wavelength bands with tunable cut-off wavelengths. [ABSTRACT FROM AUTHOR]

Correlation between the elastic modulus (B) and the Raman shift (Δω) of TiO2 and their responses to the variation of crystal size, applied pressure, and measuring temperature have been established as a function depending on the order, length, and energy of a representative bond for the entire specimen. In addition to the derived fundamental information of the atomic cohesive energy, binding energy density, Debye temperature and nonlinear compressibility, theoretical reproduction of the observations clarified that (i) the size effect arises from the under-coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth; (ii) the thermally softened B and Δω results from bond expansion and bond weakening due to vibration; and, (iii) the mechanically stiffened B and Δω results from bond compression and bond strengthening due to mechanical work hardening. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantitative information as such from any single measurement alone. [ABSTRACT FROM AUTHOR]

A complete study is given in this paper on the structural properties of Ba(Sr,Ti)O3 (BST) thin films which present various preferred orientations: (111) and (001) fiber and epitaxial textures. The films are deposited in situ at 800 °C by sputtering on Si/SiO2/TiOx/Pt substrates and the orientation is controlled by monitoring the concentration of O2 in the reactive plasma or by prior deposition of a very thin TiOx buffer layer between BST films and substrates. The epitaxial films are obtained on (001)-alpha-Al2O3 substrates covered with TiOx buffer layers. In order to analyze finely the preferred orientations, the texture, the microstructural features, and the anisotropy-related quantities such as residual stresses in the films, the conventional Bragg-Brentano θ - 2θ x-ray diffraction diagrams is shown not to be sufficient. So, we systematically used x-ray combined analysis, a recently developed methodology which gives access to precise determination of the structure (cell parameters and space group) of the films, their orientation distributions (texture strengths and types) and mean crystallite sizes, their residual stresses. This fine structural analysis shows important modifications between the film qualities which induce differences in BST films electrical behavior, permittivity, loss tangent, and tunability. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5,prepared by suction casting the molten alloy into a copper mold under an argon atmosphere, have been investigated. The results show that clusters with size 3-5 nm are found to be embedded in the amorphous matrix of as-cast bulk amorphous Nd60Fe20Al5Co10B5 alloy. The Nd60Fe20Al5Co10B5 alloy shows hard magnetic behavior at room temperature, with an intrinsic coercivity of 360 kA/m and a remanence of 69.39 mT. The magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5 has been investigated on the major hysteresis loop, and simple logarithmic time dependence is observed. A value for the fluctuation field of 8.24 kA/m is obtained. Analysis based on a Henkel plot is used to confirm the existence of magnetic interaction among clusters. The coercivity mechanism responsible for the hard magnetic behavior of bulk amorphous Nd60Fe20Al5Co10B5 alloy is also discussed. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) and contact angle measurements have been made to characterize patterned organic light-emitting-diode (OLED) substrates comprising indium-tin-oxide and a photoresist, both of which are modified by treatment with oxygen and tetrafluoromethane in a radiofrequency (13.56 MHz) low-power (∼1 W) capacitively coupled plasma as a function of time. Correlations between the surface chemical compositions from XPS and the contact angle, θ, are evaluated in order that the wettability of very small areas may be predicted. Very clear correlations for both the indium-tin-oxide and the photoresist surfaces are obtained enabling the prediction of the contact angles for these plasma-treated OLED materials from XPS data to a standard uncertainty of 9% in cos θ. These correlations need to be extended to a wider range of compositions in order to establish the physicochemical properties of particular surface functional groups that control water contact angles by this method. [ABSTRACT FROM AUTHOR]

ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity. [ABSTRACT FROM AUTHOR]

The functional dependence of stress, elastic modulus, melting point, and their interdependence on the identities (bond order, nature, length, and strength) of a representative bond of the specimen has been established for deeper insight into the transition from the conventional Hall-Petch relationship (HPR) to the inverse HPR (IHPR) for nanostructured TiO2. Theoretical reproduction of the observed inverse HPR suggests that the intrinsic competition between the energy-density gain (elastic modulus enhancement) and the cohesive-energy remnant (melting point depression) in the grain boundaries originates and the extrinsic competition between the activation and the inhibition of atomic dislocations activates the IHPR. [ABSTRACT FROM AUTHOR]

Patterned organic light-emitting-diode substrates were treated by oxygen (O2) and tetrafluoromethane (CF4) radio-frequency (rf, 13.56 MHz) plasmas of low-power (close to 1 W) that were capacitively-coupled. An unexpected wettability contrast (water contact angle difference up to 90°) between the indium-tin-oxide anode and the bank resist regions was achieved, providing excellent conditioning prior to the ink-jet printing. This selectivity was found to be adjustable by varying the relative exposure time to the O2 and CF4 sequential plasmas. Static contact angle measurements and extensive x-ray photoelectron spectroscopy analyses showed that the wetting properties depend on the carbon and fluorine chemical functional groups formed at the outermost surface layers, whereas atomic force microscopy images did not show a morphological change. Plasma optical emission spectroscopy and ion mass spectroscopy suggested that surface functionalization was initiated by energy transfer from ionic species (O+, O2+, CF+, CF2+, and CF3+) and excited neutrals (O* and F*). The absolute ion fluxes measured on the substrates were up to 1014 cm-2 s-1 and the ion energies up to 20 eV, despite the low powers applied during the process. [ABSTRACT FROM AUTHOR]

Ab initio calculations based on density functional theory have been performed to determine the properties of self-interstitial atoms (SIAs), vacancies, and single H and He atoms in hcp-Er. The results show that the most stable configuration for a SIA is a basal octahedral configuration, while the octahedral (O), basal split, and crowdion (C) interstitial configurations are less stable, followed by the split <0001> dumbbell and tetrahedral configurations. For both H and He defects, the formation energy of an interstitial atom is less than that of a substitutional atom in hcp-Er. Furthermore, the tetrahedral interstitial position is more stable than an octahedral position for both He and H interstitials. The hybridization of the He and H defects with Er atoms has been used to explain the relative stabilities of these defects in hcp-Er. [ABSTRACT FROM AUTHOR]

Polycrystalline PrCuMn6O12 sample has been successfully synthesized. It has been characterized by x-ray diffraction (XRD), magnetic and magnetotransport measurements at ambient pressure, and transport property measurements under pressures. From the refinements of XRD data, a cubic phase and a trigonal phase with charge ordering state were identified at higher and lower temperatures, respectively. The temperature dependence of the resistance indicates that the phase transition is a first-order transition. Both effective paramagnetic moments of the trigonal and cubic phases can be explained by orbital moment freezing theory. The transport property of the trigonal phase has been fitted with Mott’s law for variable range hopping. Though the magnetoresistance value is not large, the pressure-induced resistance value change of PrCuMn6O12 is positive and achieves 264.8%. The cubic phase is suppressed under pressure and transformed to the trigonal phase at 15 kbar, indicating favor of the charge ordering state under pressure. [ABSTRACT FROM AUTHOR]

This paper reports that the pressure effects on the electronic transport properties of Mn3ZnN and Mn3Zn0.9Ge0.1N were measured under pressures up to 2.4 GPa. Cooling and warming cycles of the temperature-dependent magnetization curves of Mn3ZnN show a hysteresis phenomenon near the transition, implying a first order transition. The cracks which appear in the vicinity of magnetic transition at ambient pressure for Mn3ZnN and at applied pressures not more than 0.3 GPa for Mn3Zn0.9Ge0.1N are restrained under higher pressures. The paramagnetic-antiferromagnetic transition temperature TN decreases almost linearly at the rate of 1.9 and 51 K/GPa for Mn3ZnN and Mn3Zn0.9Ge0.1N respectively, which is explained by the model of TN discussed by Fruchart and the Labbé–Jardin tight-binding approximation model. [ABSTRACT FROM AUTHOR]

In situ high-pressure angle dispersive x-ray diffraction experiments using synchrotron radiation on inverse spinel structure Zn2SnO4 nanowires were carried out with a diamond anvil cell at room temperature. The crystal symmetry becomes lower at around 12.9 GPa and an intermediate phase with an orthorhombic structure occurs. At about 32.7 GPa, a phase transition occurs accompanying a high-pressure phase. In situ Raman scattering investigation was also performed to explore the phase transition. In the pressure range 15.5–32.8 GPa, the intermediate phase is also detected and a high-pressure phase is observed above 32.8 GPa. The high-pressure phase is considered to possess the ambient pressure structure of CaFe2O4. [ABSTRACT FROM AUTHOR]

CoSb3 nanocomposites with different contents of CoSb3 nanoparticles were prepared by mixing nanosized CoSb3 particles obtained via polyol method and micron-sized particles obtained via solid state reaction. X-ray diffractometer and field emission scanning electron microscope were used to characterize the prepared products. The thermoelectric properties of the nanocomposites with different amounts of nanoparticles as dispersants were measured from room temperature to around 500 °C. Due to the grain boundaries scattering, the lattice thermal conductivity was observed to decrease as the amount of nanoparticles increased. The electrical properties were also improved by the addition of nanoparticles. The ZT value of the nanocomposites with 10 wt % of nanoparticles was nearly doubled that of the sample without any nanoparticles. [ABSTRACT FROM AUTHOR]

Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 °C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 °C. [ABSTRACT FROM AUTHOR]

Lead zirconic titanate (PZT) microscale island (1 μm–100 nm) was fabricated by focused ion beam before its crystallization, followed by the annealing treatment at the crystallization temperature. Local electrical properties were evaluated by piezoresponse force microscopy technique. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases. Raman spectra and Kelvin force microscopy result both show that there are little degradations on the PZT surface after this amorphous etching process. The mechanism will be discussed in this paper. These results are very beneficial to the development of the ferroelectric film applications in the dynamic random access memory, ferroelectric random access memory, and micro-electro-mechanical system field. [ABSTRACT FROM AUTHOR]

The structures of Fe78M9B13 (M=Nb, Si, and Zr) melts have been studied by ab initio molecular dynamics simulation. The essential features of the structures are the same in these melts. Prism-type local atomic arrangements dominate around B atoms and icosahedral-like clusters are frequently found around Fe atoms. However, the structures of the three melts differ in the degree of structural distortion caused by introducing M atoms to the prisms. The structural and dynamical properties of these melts change with different M elements, suggesting that they are closely correlated with their glass formation. The degree of complexity of molten structure caused by the interactions among Fe, M, and B may play an important role in their glass forming ability. [ABSTRACT FROM AUTHOR]

Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid (VLS) method, a relatively high temperature approach, and the aqueous chemical growth (ACG) method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 μN on the SiC substrates and 114 μN on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15×10-12 and 2.337×10-12 J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 μN and 7.03×10-12 J on the SiC substrates, and 19 μN and 1.805×10-13 J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks. [ABSTRACT FROM AUTHOR]

Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition (CBD) method. The optical properties of the grown ZnO nanorods were investigated by time resolved photoluminescence spectroscopy. It was found that the effective decay time of the near bandgap recombination in the CBD grown ZnO nanorods strongly depends on the diameter of the ZnO nanorods. Typically, the decay curves obtained from these ZnO nanorods show a combination of two exponential decays. The experimental results show that the fast exponential decay is related to the surface recombination and the slow decay is related to the “bulk” decay. The measured decay time of the effective surface recombination decreases with decreasing diameter, while the bulk decay time remains unchanged. The results also show that an annealing treatment around 500 °C significantly reduces the surface recombination rate. A simple carrier and exciton diffusion equation is also used to determine the surface recombination velocity, which results in a value between 1.5 and 4.5 nm/ps. [ABSTRACT FROM AUTHOR]

The orthorhombic SrIrO3 perovskite was synthesized under 5 GPa and 1000 °C. It is paramagnetic below about 170 K and transfers to an unknown magnetism under higher temperature. A band type metal to insulator transition caused by a pseudogap was observed at about 44 K. Interestingly a positive magnetoresistance, i.e., resistance increased with applying magnetic field, was observed in the orthorhombic SrIrO3 perovskite below about 170 K. [ABSTRACT FROM AUTHOR]

The influence of structure characteristics on the ferromagnetism of Ni-doped ZnO (ZnO:Ni) thin films prepared by pulsed laser deposition has been investigated by magnetization and resistivity measurements. Structural and optical absorption analyses revealed that Ni has been incorporated into ZnO lattice as Ni2+ substituting for Zn2+ ions and the microstructure of the films becomes more inhomogeneous with increasing Ni content. The room temperature ferromagnetic (FM) behavior only occurs when Ni content is not high and the saturation magnetic moment per Ni atom decreases with increasing Ni content. No FM signal was detected for the film with 7 at. % Ni content. Interestingly, the carrier density decreases with the increase of Ni doping from 1 to 5 at. %, whereas an increase of carrier density is observed for 7 at. % doped film, which indicates that carrier density alone cannot account for the FM property in ZnO:Ni films. All the results demonstrated that the microstructure of ZnO:Ni films gets more deteriorated with increasing Ni content and it is unfavorable for the long-range FM order in the ZnO:Ni films. [ABSTRACT FROM AUTHOR]

High-pressure Raman scattering experiments were performed on the zircon-type RCrO4 (R=Nd, Dy) compounds with the space group I41/amd by using diamond anvil cell techniques at room temperature. These two compounds exhibit similar Raman behaviors. Pressure-induced structural phase transitions were observed at the onset of 1.3 and 4.1 GPa for R=Nd and Dy, respectively. Moreover, pressure-released Raman spectra indicate that the structural transitions are irreversible. The high-pressure new phases were convincingly confirmed to be the scheelite structure in I41/a symmetry based on the same Raman vibrations between the pressure-released DyCrO4 and the scheelite-type DyCrO4 synthesized at 6 GPa and 450 °C. In addition, we also calculated the bulk moduli according to Errandonea’s method as well as the mode Grüneisen parameters of RCrO4. [ABSTRACT FROM AUTHOR]

High-pressure Raman scattering experiments were performed on the zircon-type RCrO4 (R=Nd, Dy) compounds with the space group I41/amd by using diamond anvil cell techniques at room temperature. These two compounds exhibit similar Raman behaviors. Pressure-induced structural phase transitions were observed at the onset of 1.3 and 4.1 GPa for R=Nd and Dy, respectively. Moreover, pressure-released Raman spectra indicate that the structural transitions are irreversible. The high-pressure new phases were convincingly confirmed to be the scheelite structure in I41/a symmetry based on the same Raman vibrations between the pressure-released DyCrO4 and the scheelite-type DyCrO4 synthesized at 6 GPa and 450 °C. In addition, we also calculated the bulk moduli according to Errandonea’s method as well as the mode Grüneisen parameters of RCrO4. [ABSTRACT FROM AUTHOR]

The effects of using different interatomic potentials in molecular dynamics (MD) simulations of the formation of He-vacancy clusters within displacement cascades in α-Fe are investigated using two sets of potentials. Simulations of cascades produced by primary knock-on atoms of energy Ep=1–20 keV were performed in α-Fe containing a concentration of substitutional He atoms varying from 1 to 5 at. % at an irradiation temperature of 100 K. Although the effects of interatomic potentials on the nucleation of He-vacancy clusters induced by cascades are relatively small, the number and size of He-vacancy clusters produced are significantly different for the different potentials employed in this study. Thus, these differences may influence the microstructural evolution predicted in damage accumulation models that use the results from MD cascade simulations as input. The observed differences in postcascade configurations can be attributed mainly to the differences in the Fe–Fe and Fe–He potentials. [ABSTRACT FROM AUTHOR]

Resistivity measurements of Eu0.58Sr0.42MnO3 were carried out at different magnetic fields under ambient pressure and 1 GPa, respectively. The critical temperature TC of the ferromagnetic metallic state is 128.5 K under 1 GPa and 7 T. The antiferromagnetic insulating phase can be transformed into the ferromagnetic metallic phase by either magnetic field or pressure. Different from the effect of the magnetic field, a plateau is observed in the temperature dependence of the resistivity curve in the lower temperature under pressure, which indicates a phase separation. Magnetic phase diagrams at ambient pressure and 1 GPa are established. [ABSTRACT FROM AUTHOR]