Small Amount Of Ga Research Articles

Transition from thin film to nanostructure in low pressure chemical vapor deposition growth of β-Ga2O3: Impact of metal gallium source

Highly crystalline β-Ga2O3 has been grown on a c-plane (0001) sapphire substrate using low-pressure chemical vapor deposition. This work has been focused on the impacts of the Gallium (Ga) concentration on the surface morphology of the β-Ga2O3 films. Formation of thin film, nanostructure, and the combination of both have been observed. However, no changes have been noticed on the X-ray diffraction peaks of β-phase with an increase in Ga vapor concentration, though different crystal orientation of the nanostructures has been found in the sample with relatively high Ga amount. The average crystallite size which has been calculated using Scherrer's formula shows an increment with Ga concentration. The bandgap has also been found to be altered with the metal concentration. The crystal quality of the nanostrctures evaluated from the Raman measurements shows good quality with low internal strain and low defects density. A small amount of Ga will tend towards the thin film growth whereas a high amount of Ga leads to the formation of different types of nano-structure on the β-Ga2O3 thin film. We propose that the nanostructures are formed through vapor-solid and vapor-liquid-solid mechanisms under the self-catalytic approach.

Sustainable Production of Acetonitrile from Microalgae via Catalytic Fast Pyrolysis with Ammonia over Ga/HZSM-5 Catalysts

We report on catalytic fast pyrolysis microalgae under ammonia atmosphere into acetonitrile over Ga/HZSM-5, which provides a long-term sustainable option for acetonitrile production and microalgae valorization. The effect of various catalysts, reaction conditions and species of microalgae on acetonitrile production was explored systematically. Under the optimized conditions, the maximum carbon yield of acetonitrile from Chlorella vulgaris was 23.4%, and the selectivity of acetonitrile in bio-oil was up to 77.2%. The possible reaction pathways were proposed according to the comprehensive experimental investigation on the conversion of model compounds and intermediates (proteins, carbohydrates, lipids, amino acids, carboxylic acids, furans, and amines). High-resolution transmission electron microscopy (TEM) analysis showed that Ga was present mainly at the outer surface of zeolite crystals, and a small amount of Ga was doped into the zeolite crystals.

Comparison of Ag and Ga alloying in low bandgap CuInSe2-based solar cells

Solar cells based on CuInSe2 (CIS) with absorber bandgap 1.0 eV are excellent candidates for a bottom cell in a tandem solar cell. This work investigates the effect of alloys of Ag and small amounts of Ga as an approach to improve the efficiency of CIS-based solar cells with bandgap less than 1.1 eV. Ga and Ag influence the surface morphology of the absorber layer, and Ag alloyed solar cells also have an increased concentration of Ag relative to Cu at the surface. Despite these structural and compositional differences compared to CuInSe2, the device with the highest efficiency incorporates a mixture of Ga and Ag alloying to form (Ag,Cu)(In,Ga)Se2, where Ga addition improves the open circuit voltage and Ag addition improves the short circuit current. Ag improves current collection from long wavelength light due to the larger space charge width of Ag alloyed solar cells. However, Ag alloyed devices demonstrate lower VOC due to an interface recombination mechanism.

High refractive index dispersion of compositionally optimized Ge-Ga-Sb-S sulfide glass for use as molded lens in the long-wavelength infrared range

In an effort to endow Ge-Sb-S sulfide glass with capability to transmit the long-wavelength infrared (LWIR) photons as well as to possess highly dispersive refractive indexes over the LWIR spectral range, we have compositionally adjusted ternary Ge-Sb-S glass prior to tuning quaternary Ge-X-Sb-S (X = Ga, Bi, In or Sn) glass. Among the constituent atoms of ternary Ge-Sb-S glass, Ge content turned out to exert the strongest influence not only on thermal and mechanical properties but also on infrared transmission edge. Specifically, glass transition temperature and Vickers hardness tended to be directly proportional to Ge content, but infrared transmission edge was blue-shifted upon increase of Ge content, simultaneously producing an additional multiphonon absorption peak at ~ 9 µm. As such, Ge-Sb-S glass containing Ge atoms less than ~ 15 at% was considered to feature applicability in LWIR range, which on the other hand suffers from relatively poor thermal and mechanical properties. In our experimental attempts on quaternary sulfide glasses performed to mitigate such deteriorations, presence of relatively small amount of Ga appeared to be most effective among the elements employed in this study as the fourth constituent. Moreover, only Ga atoms improved thermal stability with significantly increasing crystallization temperature. Quaternary Ge-Ga-Sb-S glass compositionally optimized in this study was then verified to be much more dispersive than typical Se-based chalcogenide glasses in the LWIR region.

Phase dynamics, structural, and magnetic properties of a Mn2.6Ga1−xSnx alloy series

Although Mn-Ga alloys are discussed as novel permanent magnetic materials, there are several drawbacks, including the high price of Ga and the yet too small saturation magnetization to name a few. We used several guidelines to motivate the replacement of Ga by Sn to tackle these issues and explored the phase formation, structural and magnetic properties of a Mn2.6Ga1−xSnx alloy series. The structure of Sn-rich samples is dominated by the corresponding hexagonal and orthorhombic phases, while the structure of Ga-rich samples shows additional contributions from the tetragonal DO22 structure. However, formation of the tetragonal phase happens only upon an appropriate annealing procedure. In contrast to the discussion in the literature, our experiments do not hint on the tetragonal DO22 structure being metastable, but rather indicate the DO22 structure being an equilibrium phase. In general, the experimentally found phase fractions impact on the magnetic properties and hard magnetic properties are downgraded very rapidly even if only a small amount of Ga is substituted by Sn. This indicates that the DO22 phase found only in the Ga-rich samples is indeed the one which is most relevant for realization of high magnetic anisotropy.

Effect of Ga doping on the thermoelectric performance of Cu3SbSe4

The Cu3SbSe4 compound is an environmentally friendly and low-cost medium-temperature thermoelectric material, which is featured by its low thermal conductivity. The disadvantage of this compound lies in its intrinsic poor electrical transport property. In order to improve the electrical conductivity of Cu3SbSe4, in this work we are to increase its carrier concentration by one to two orders of magnitude though elemental doping. The sample composition of Cu2.95GaxSb1-xSe4 is designed to increase the hole carrier concentration by introducing Cu vacancies and substituting Ga3+ for Sb5+. The Cu2.95GaxSb1-xSe4 (x=0, 0.01, 0.02 and 0.04) samples are prepared by melting-quench method. The X-ray diffraction analysis indicates that the obtained samples are of single-phase with the tetragonal famatinite structure, and the energy-dispersive X-ray spectroscopy results show that the actual compositions of the samples are very close to their nominal compositions. The effect of Ga doping on the thermoelectric performance of Cu3SbSe4 compound is investigated systematically by electrical and thermal transport property measurements. According to our experimental results, the hole concentration of the sample is efficiently increased by substituting Sb with a small amount of Ga (x=0.01), which can not only substantially improve the electrical conductivity but also suppress the intrinsic excitation of the sample. The maximum power factor reaches 10 μW/cm·K2 at 625 K for the Ga doped sample with x=0.01, which is nearly twice as much as that of the sample free of Ga. Although the carrier concentration further increases with increasing Ga content, the hole mobility decreases dramatically with the Ga content increasing due to the increased hole effective mass and point defect scattering. Thus, the electrical transport properties of the samples deteriorate at higher Ga content, and the maximum power factors for the samples with x=0.02 and 0.04 reach 9 and 8 μW/cm·K2 at 625 K, respectively. The lattice thermal conductivities of the samples basically comply with the T-1 relationship, suggesting the phonon U-process is the dominant scattering mechanism in our samples. For the samples with x=0 and 0.01, the lattice thermal conductivities at high temperature deviate slightly from the T-1 curve due to the presence of intrinsic excitation. However, these deviations are eliminated for the samples with x=0.02 and 0.04 because the bipolar effect is effectively suppressed with the increasing of Ga content. Thus, Ga doping can reduce the bipolar thermal conductivity at high temperature by increasing the hole carrier concentration. Furthermore, the point defects introduced by Ga doping can also enhance the scattering of high-frequency phonons, leading to slightly reduced lattice thermal conductivities of Ga-doped samples at higher temperature. Finally, a maximum ZT value of 0.53 at 664 K is achieved in Ga-doped sample, which is 50% higher than that of the sample free of Ga.

About electrochemical stability and biocompatibility of two types of CoCr commercial dental alloys

The present paper is an investigation of two commercial Co‐Cr dental alloys, named Wirobond 280 and Wirobond C. The two alloys have similar composition; the difference is made by the small amount of Ga and Mn existing in Wirobond 280. The electrochemical behavior of the alloys was tested in the artificial Erikson saliva at different temperatures between 25 and 55 °C. The electrochemical methods used have been the potentiodynamic polarization and the electrochemical impedance spectroscopy. The investigation have been performed in the presence of two different fluoride ions concentrations and permitted to compute corrosion rate and the energy activation. In order to complete the tests the cell response has been studied in vitro. The stability of Wirobond 280 alloy is correlated with the greater cell viability and with a smaller level of ROS in comparison with the Wirobond C alloy. Regarding fluoride doping effect, based on the experimental data, we can conclude that NaF increases the corrosion rate of the Wirobond 280 and decrease the corrosion rate in the case of the Wirobond C. The study established that the Wirobond 280 alloy is the one with best properties.

Effect of Ga addition on Ca-deficient Ca3Co4Oy thermoelectric materials

Ca3−xGaxCo4Oy polycrystalline thermoelectric ceramics with small amounts of Ga have been synthesized by the classical solid state method. XRD data have shown that all the Ga has been incorporated into the Ca3Co4O9 and Ca3Co2O6 thermoelectric phases and no Ga-containing secondary phases have been produced. Moreover, for Ga contents ≥0.07, the Ca3Co2O6 phase disappears. Apparent density measurements have revealed that all samples are very similar, with densities around 70% of the theoretical one. Electrical resistivity decreases in all Ga-doped samples, compared with the pure ones, while the Seebeck coefficient is practically the same for all samples, except for the 0.12 and 0.15 Ga substituted ones, at high temperatures which present slightly higher values. Both factors in the 0.15 Ga-substituted samples lead to power factor values around 0.35mW/K2m at 800°C which is about 70% higher than the values obtained for the undoped samples.

Evolution of Superconducting Properties of LiFeAs Single Crystals Doped with Magnetic or Nonmagnetic Impurities

The effect of magnetic Co 2+ and nonmagnetic Ga 3+ impurities on the crystal structure and superconduct- ing properties of LiFeAs single crystals has been investi- gated. A large Tc decrease of about 4.8 K/at% is observed in Ga-doped LiFeAs. This rate is higher than that of the material doped with magnetic Co impurities (∼3.7 K/at%). The greater Tc suppression in the Ga case is likely due to the pair breaking associated with the significant changes in the crystal structure of the doped material. The increase of the critical current densities in intermediate magnetic fields (H ⊥ ab) indicates that a very small amount of Ga (0.5 at%) acts as an effective pinning site for flux pinning enhance- ment in the material. The analysis of the temperature and field dependencies of the magnetic relaxation is consistent with the collective pinning model for the Co-doped mate- rial, while the magnetic relaxation measurements combined with the peak position of the critical current density in the B-T phase diagram of Ga-doped LiFeAs suggest an elastic- plastic transition of the vortex lattice at higher temperatures and fields.

Temperature dependent lifetime of Dy3+: 1.3 μm emission in Ge–As–S glass containing very small amount of Ga and CsBr

The lifetime of 1.3μm emission from Dy3+-doped Ge–As–S glass containing very small amount of Ga and CsBr reveals interesting temperature dependence; with the addition of Ga/CsBr up to ∼0.2mol% the lifetime decreases with increasing temperature. When the concentration of Ga/CsBr reaches ∼0.3mol%, however, the lifetime remains relatively constant regardless of temperature change. For further addition up to ∼0.5mol%, the lifetime increases as temperature rises. This uncommon behavior is explained through our understanding of the different temperature dependences of multiphonon relaxation and spontaneous emission rates associated with the thermally coupled Dy3+: (6H9/2, 6F11/2) manifolds in our modified chalcogenide glass.

Density functional theory study on the electronic structure ofn- andp-type doped SrTiO3at anodic solid oxide fuel cell conditions

The electronic conductivity and thermodynamic stability of mixed $n$-type and $p$-type doped SrTiO${}_{3}$ have been investigated at anodic solid oxide fuel cell (SOFC) conditions using density functional theory (DFT) calculations. In particular, constrained ab initio thermodynamic calculations have been performed to evaluate the phase stability and reducibility of various Nb- and Ga-doped SrTiO${}_{3}$ at synthesized and anodic SOFC conditions. The density of states (DOS) of these materials was analyzed to study the effects of $n$- and $p$-doping on the electronic conductivity. In agreement with experimental observations, we find that the transformation from 20$%$ Nb-doped Sr-deficient SrTiO${}_{3}$ to a non-Sr-deficient phase occurs at high temperature and low oxygen partial pressure, which leads to a significant improvement in electronic conductivity. A mixed ionic/electronic conductor is obtained when doping 20$%$ Nb-doped SrTiO${}_{3}$ with small amounts of Ga (10$%$) in a reducing environment and high temperature. Doping with higher concentrations of Ga, e.g., 20$%$, diminishes the electronic conductivity of the material. These findings suggest that independent of the specific dopant, mixed ionic/electronic conductivity can be obtained in perovskite oxides under reducing conditions and high temperatures by doping the B-site with small amounts of both $n$-type and $p$-type dopants.

Synthesis of Plate-like Zinc Oxide Particles by the Transcription of Precursor's Shape

Plate-like zinc contained precursors such as simonkoleite or basic sulphate were successfully synthesized by using equilmolar of Zn2+ / hexamethylenetetramine (HMT) acted as precursors, ethylene glycol(EG) as dispersant and surfactant additive, respectively. The reaction solution was sealed in a glass bottle and heated at 95°C for 3h. The zinc contained precursors possessed layered structure and plate-like morphology were successfully synthesized by controlling the zinc ions concentration, reaction temperature, organic solvent additives, anion additives. It was found that plate-like simonkolleite transformed to plate-like ZnO after calcination in air at 400°C, while it transformed to rod-like ZnO under hydrothermal conditions above 140°C. The additive of ethylene glycol decreased the particle size and affected the particle size distribution. The conductivity of the pressured powders was improved by small amount of Ga and Al doping followed by H2 reduction treatment at 500°C for 1h.

Compositional effects on fluorescence lifetime of Dy 3+ ions embedded in chalcogenide Ge–As–S glasses containing very small amount of Ga and CsBr

We have investigated the fluorescence lifetimes of Dy 3+: 1.3 μm emission in the chalcogenide Ge–As–S glasses with different compositions but identically containing 0.5 mol% Ga and 0.5 mol% CsBr. The measured lifetimes turn out to be sensitive not only to the concentrations of Ga and CsBr but also to compositional variations in the Ge–As–S host glasses. The lifetime is enhanced conspicuously in glass of the S-sufficient compositions, relative to the stoichiometric GeS 2–As 2S 3 composition, while this effect is not significant in the S-exact and S-deficient compositions. We employ Ga K-edge EXAFS analysis to support that the local structural environments of Ga in the modified chalcogenide glasses are closely correlated with the lifetime enhancement effect.

Surface termination of the NdGaO 3(1 1 0)

Auger electron spectroscopy using excitation via grazing impact of protons was applied to determine the elemental composition of the topmost and near-surface layers of a NdGaO 3(1 1 0) substrate. The preparation conditions of vicinal NdGaO 3 substrates were optimized by varying the annealing temperature, time, and gas atmosphere. Well prepared surfaces show regularly arranged, atomically smooth terraces with single-atomic steps. The surfaces were always NdO terminated with a small amount of Ga (2–4%) atoms on the surface. A Ga and O depletion layer with a thickness of about 4 nm has been detected at optimized preparation conditions.

Vacancy ordering and lithium insertion in III2VI3 nanowires

Superlattice structures resulting from vacancy ordering have been observed in many materials. Here we report vacancy ordering behavior in III2VI3 nanowires. The formation of layer-like structural vacancies has been achieved during the synthesis of In2Se3 nanowires through a vapor-transport route. Doping In2Se3 nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for (In x Ga1−x )2Se3 nanowires. Lithium atoms can fill in the layer-like structural vacancies of In2Se3 nanowires and generate new types of vacancy and lithium atom ordering superlattices. The screw-patterned vacancies of (In x Ga1−x )2Se3 nanowires show reversible lithium insertion. Our results contribute to the understanding of structure property correlations of III2VI3 materials used in lithium ion storage, photovoltaics, and phase change memory.

Electrical characteristics of metal-oxide-semiconductor capacitors on p-GaAs using atomic layer deposition of ultrathin HfAlO gate dielectric

Properties of ultrathin HfAlO gate dielectrics on sulfur-passivated p-GaAs were investigated using capacitance-voltage and current-voltage measurement techniques and angle-resolved x-ray photoelectron spectroscopy. By optimizing the individual layer thickness of atomic-layer deposited Al2O3 and HfO2 and the postdeposition anneal (PDA) conditions, a low equivalent oxide thickness of 1.6 nm, low gate leakage of 2.6×10−3 A/cm2 at Vg=Vfb−1 V, and excellent frequency dispersion characteristics were obtained. No interfacial As–O bonding and only a small amount of Ga–O bonding were detected after PDA at 500 °C. These results reveal a good quality dielectric interface on GaAs without an additional interface passivation layer.

Influence of Ga Content on Electrochemical Behavior of Mg-5 at%Hg Anode Materials

The effects of Ga content on the electrochemical behavior of Mg-5 at%Hg alloys which contain a small amount of Ga was investigated by the measurement of polarization curves and galvanostatic test. The microstructure of the alloys and the surface of the specimens corroded in galvanostatic test were observed by using scanning electron microscopy, energy spectrum analysis and X-ray diffraction analysis. It can be concluded that with the content of Ga increasing, the alloys come into Mg-Mg 3 Hg, Mg-Mg 7.2 (Hg, Ga) 2.8 and Mg-Mg 5 Ga 2 binary phase fields sequentially. The best electrochemical activity occur in the Mg-5 at%Hg -1 at%Ga alloy, with open circle potential -2.124V and mean potential -1.992 V. The corrosion resistance of the alloys is in the sequential order from big to small: Mg-5 at%Hg-5 at%Ga, Mg-5 at%Hg-22 at%Ga, Mg-5 at%Hg-1 at%Ga, Mg-5 at%Hg. The lowest corrosion current density is 0.418 mA·cm -2 . The activation mechanism of the magnesium alloy produced by Hg and Ga was concluded: the dissolution of Hg and Ga atoms leads to the back accumulation of liquid Hg and Ga, which makes a true metallic contact with a-Mg. Magnesium atoms diffuse through the liquid mercury and gallium to form magnesium amalgam and undergo severe oxidation at the amalgam/electrolyte interface. The reaction produces pure Hg and Ga again which continue the activation process.

Growth of InGaN layer on GaN templated Al 2 O 3 (0001) and Si (111) substrates by mixed‐source HVPE

The InGaN layers on GaN templated sapphire (0001) and Si (111) substrates are grown by mixed-source hydride vapor phase epitaxy (HVPE) method. As a new attempt in obtaining an InGaN layers, the growth of the thick InGaN layer is performed by putting small amount of Ga into the In source. The InGaN layer is compounded from chemical reaction between a NH3 and an Indium-gallium chloride formed by HCl flown over metallic In mixed with Ga. The InGaN layer is analyzed by X-ray photoelectron spectroscopy (XPS) to characterize the InGaN ternary crystal alloy. The optical property of the selective area growth (SAG) of the InGaN layer is investigated by the photoluminescence (PL) spectrum and the cathodoluminescence (CL) images. Indium compositions are estimated to be in the range 3-10%. In order to obtain the GaN layer on GaN templated Si (111) substrates, an InGaN layer is used as an intermediate layer. The PL and CL of the InGaN intermediate layer are measured at 300K. We find that the InGaN intermediate layer is possible to be one of the growth methods of thick GaN layer on Si substrates by HVPE method. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Microstructural studies and micromagnetic analysis of nanocrystalline NdFeCoMB (M = Ga, Ge) melt-spun ribbon

The effects of Ge and Ga additions on the microstructure and coercivity of melt-spun ribbons of Nd13.5 Fe(74.9−z) Co5.5 Mz B6 (z=0.0 to 0.54; M=Ge, Ga) alloys have been investigated. For the first time, a detailed microstructural study of nanometer-sized Nd-rich grain boundary phase enriched with small amounts of Ga and Ge was carried out using a three-dimensional atom probe (3DAP) technique. Ga partitions to thin uniform Nd-rich grain boundary phase, causing effective isolation of Nd2Fe14B grains. As a result, the coercivity increased. On the other hand, Ge caused the formation of Ge- and Nd-rich precipitates, resulting in the formation of dispersoids along the grain boundaries. Due to the poor isolation of the Nd2Fe14B grains, the coercivity decreased.

Effect of Mini Ga Doping in Nanocrystalline Nd<sub>4.5</sub>(Fe,Co)<sub>77.5</sub>B<sub>18</sub> Magnet on Coercivity

The microstructure and the coercivity of nanocomposite Nd4.5Fe76.5-xGaxCo1.0B18 (x=0~0.6at%)bonded magnets were studied. The results showed that addition of small amount of Ga in Nd4.5Fe76.5-xGaxCo1.0B18 made the grains finer and more uniform. A notable peak of coercivity was observed in the variational curve of coercivity with annealing time when Ga content was low (x=0.2). This phenomenon could be explained by the microstructure and the exchange coupling interaction of two-phase nanocomposite.