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PubMed2006

Apparently complex high-pressure phase of gallium as a simple modulated structure.

The phase of gallium GaII, with symmetry C222(1) and 104 atoms per unit cell, has been recently reported as an example of structural complexity under high pressure. It is shown here that this phase is a simple modulated distortion of an average structure of Fddd symmetry with all atoms structurally equivalent. The modulation can be described with only 4 parameters and satisfies symmetry properties described by a centrosymmetric superspace group. The structural distortion is dominated by a frozen transversal mode associated with a single irreducible representation of Fddd, with a wave vector on the line Q, at an edge of the Brillouin zone. The average structure can be related with an hcp configuration through simple sliding of hcp layers, reminiscent of the hcp-bcc Bürgers mechanism.

Journal Article↗

PubMed2000

A dicationic gallium-oxo-hydroxide cage compound

The crystal structure of hexa-&mgr;-hydroxo-dodecamethylocta-&mgr;(3)-oxo-dodecagallium(III) bis[tetrakis(pentafluorophenyl)borate(III)] chlorobenzene disolvate dihydrate, [Ga(12)(CH(3))(12)(&mgr;(3)-O)(8)(&mgr;-OH)(6)](C(24)F(20)B)(2). 2C(6)H(5)Cl.2H(2)O, is reported. The gallium-oxo-hydroxide dication is located on an inversion center and adopts a cage structure composed of 12 fused Ga(3)O(3) rings and is associated with the hydrate molecules and the [B(C(6)F(5))(4)](-) anions through hydrogen bonds and one O-H.pi-ring interaction. Disordered chlorobenzene solvent molecules are also present in the crystal structure.

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PubMed2002

GaFPO(3)(C(6)H(5)): a new fluorinated gallium phenylphosphonate with a layered network.

Crystals of gallium fluorophenylphosphonate were synthesized hydrothermally at 453 K under autogenous pressure. The solid crystallizes in the monoclinic system and its structure is built up by the connection of zigzag chains of edge-sharing GaO(4)F(2) octahedra to phenylphosphonate groups. This results in the formation of a layered structure, in which the phenyl groups point upward and downward from the inorganic sheet. The Ga atoms occupy the special positions 4a (inversion center) and 4e (twofold axis).

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PubMed2005

RbGa3(P3O10)2: a new gallium phosphate isotypic with RbAl3(P3O10)2.

Rubidium trigallium bis(triphosphate), RbGa3(P3O10)2 has been synthesized by solid-state reaction and studied by single-crystal X-ray diffraction at room temperature. This compound is the first anhydrous gallium phosphate containing both GaO4 tetrahedra (Ga1) and GaO6 octahedra (Ga2 and Ga3). The three independent Ga atoms are located on sites with imposed symmetry 2 (Wickoff positions 4a for Ga1 and 4b for Ga2 and Ga3). The GaO4 and GaO6 polyhedra are connected through the apices to triphosphate groups and form a three-dimensional host lattice. This framework presents intersecting tunnels running along the [001] and <110> directions, where the Rb2+ cations are located on sites with imposed symmetry 2 (Wickoff position 4a). The structure also exhibits remarkable features, such as infinite helical columns created by the junction of GaO4 and PO4 tetrahedra.

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PubMed2005

A layered fluorinated gallium phosphate organically templated by propane-1,3-diaminium, an analog of the aluminophosphate MIL-12: Ga2(PO4)F5.C3H12N2.

Crystals of the oxyfluorinated gallium phosphate MIL-12 (digallium phosphate pentafluoride propane-1,3-diaminium), (C3H12N2)[Ga2(PO4)F5], were synthesized hydrothermally at 453 K under autogenous pressure using propane-1,3-diamine as the structure-directing agent. The title compound is isomorphous with the aluminium phosphate having the MIL-12 structural type. The structure is built up from a two-dimensional anionic network intercalated by the diamine species. The inorganic layer is composed of corner-linked GaO2F4 octahedra and PO4 tetrahedra. The diprotonated diamine group is located on a mirror plane, between the inorganic sheets, and interacts preferentially via hydrogen bonding through the ammonium groups and the terminal F and bridging O atoms of the inorganic layer. One of the Ga atoms lies on an inversion centre and the other lies on a mirror plane, as does the P atom, two of the phosphate O atoms and one of the F atoms.

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PubMed2001

EXAFS study on liquid gallium under high pressure and high temperature.

EXAFS (Extended X-ray Absorption Fine Structure) spectra of liquid gallium near the Ga K-edge have been collected in wide pressure and temperature ranges. Reliable short-range pair distribution functions have been determined using advanced ab-initio calculations (GNXAS) taking into account the medium and long-range structure obtained by previous neutron and x-ray-scattering studies.

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PubMed2001

XAFS study on gallium ions implanted in silicon carbide.

Local structure of gallium ions implanted in silicon carbide has been investigated using extended X-ray absorption fine structure on the Ga K-edge. The crystallinity of the implantation layer is compared in the samples prepared under several different conditions of implantation temperature and post-implantation annealing. It is found that significant damage is induced by the implantation at room temperature, but the crystallinity recovers by the subsequent annealing at high temperature at 1600 degrees C. On the other hand, the best crystallinity is obtained by the implantation at high temperature of 500 degrees C. but the annealing results in degrading the crystallinity. This indicates an influence of the post-implantation annealing at high temperature on the crystallinity in atomic level, which relates to the secondary defects in lattice observed by electron microscope.

Journal Article↗

PubMed2002

Metal strip reflectivity and NSPUDT orientations in langanite, langasite, and gallium phosphate.

New materials of the trigonal 32 class have received much attention recently, due to their quartz-like temperature behavior and the promise of higher electromechanical coupling coefficients. The magnitude and phase of the reflection coefficient of the metal strips that form the SAW transducers and reflector structures is a critical parameter that allows proper device designs and optimal material surface orientation. This paper describes an investigation of the magnitude and phase of the SAW metal strip reflectivity in some new materials and along new orientations. The materials are langanite, langasite, and gallium phosphate. The results are presented as contour plots of the magnitude and phase of the reflection coefficient. In addition, the phase velocity, temperature coefficient of delay, electromechanical coupling coefficient, and power flow angle are given, thus allowing proper orientation selection for SAW device designs. The results presented highlight the reflection coefficient calculations in the selection of natural single-phase unidirectional transducer orientations (NSPUDT) for these new materials. As a result of the present work, reflection coefficient magnitudes five times larger than those of the well-known quartz NSPUDT orientation (Euler angles: 0 degrees 132.75 degrees 25 degrees) can be obtained with the new materials, for orientations where the optimum NSPUDT reflection coefficient phase criterion is met. The new materials discussed here provide an opportunity to design shorter- and higher-bandwidth devices due to: the increased electromechanical coupling coefficient; the higher reflection coefficient; and the lower phase velocities; while maintaining the excellent temperature insensitivity characteristic of quartz. The orientation regions suggested in this paper for the new materials are thus very promising for low-loss, high-performance consumer and communications SAW designs, such as NSPUDT filters, resonator-based filters, and other devices that can benefit from a high metal strip reflectivity.

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PubMed2006

Determination of the electromechanical coupling factor of gallium orthophosphate (GaPO4) and its influence on resonance-frequency temperature dependencies.

The quartz homeotype gallium orthophosphate (GaPO4) is a representative of piezoelectric single crystals of large electromechanical coupling factor. It is known that its coupling factor kappa26 associated with the resonators vibrating in the thickness-shear mode is approximately two times greater than that of quartz. This property increases the spacing between the series and parallel resonance frequencies of resonators, as well as the difference between the resonance frequency temperature dependencies of the fundamental and harmonic resonance frequencies of resonators vibrating in the thickness-shear mode. In this paper, the methods for determination of the coupling factor kappa26 are presented, and the computed values are compared with the measured ones. The influence of the coupling factor to the resonance-frequency temperature dependencies of the fundamental and third harmonics of selected rotated Y-cut GaPO4 resonators vibrating in the thickness-shear mode is presented. The purely elastic case for a laterally unbounded plate, which corresponds closely to the limiting case of high harmonic resonance frequency-temperature behavior was assumed for the calculations. The computed temperature coefficients for the Y-cut orientation and calculated turnover point temperatures TTP for different (YX1) orientations are presented.

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PubMed1993

Enhancement of ultrasonically induced cell damage by a gallium-porphyrin complex, ATX-70.

Enhancement of ultrasonically induced cell damage by a gallium-porphyrin complex [ATX-70, 2,4-bis(1-decyloxyethyl)-Ga(III)-1,3,5,8- tetramethylporphryin-6,7-dipropionyl diaspartic acid] was investigated. The rate of damage to isolated sarcoma 180 cells in air-saturated suspension induced by 2 MHz ultrasound irradiation was enhanced more than four times by 80 microM ATX-70 in contrast to only twice by the same concentration of hematoporphyrin (Hp). The enhancement was almost completely inhibited in the presence of 10 mM histidine in the suspension, but not at all by 100 mM mannitol, which suggests that the enhanced cell damage was mostly mediated by singlet oxygen. Ultrasonically induced active oxygen generation in an air-saturated aqueous solution of ATX-70 was studied by detecting the electron spin resonance signals of 2,2,6,6,-tetramethyl-4-piperidone-N-oxyl produced by the reaction of 2,2,6,6-tetramethyl-4-piperidone with the generated active oxygen species. The rate of ultrasonically induced nitroxide generation was enhanced five times by 80 microM ATX-70 in contrast to only twice by Hp. The enhancement was inhibited significantly in the presence of 10 mM histidine in the suspension, but not at all by 100 mM mannitol. The singlet oxygen generation in air-saturated aqueous solution was further confirmed by the bleaching of N,N-dimethyl-4-nitrosoaniline in the presence of imidazole. The ultrasonically induced bleaching rate was enhanced six times by ATX-70, in contrast to only twice by Hp.

Animals↗

PubMed2001

Pharmacokinetic study of a gallium-porphyrin photo- and sono-sensitizer, ATX-70, in tumor-bearing mice.

The tissue distribution of a gallium-porphyrin photo- and sono-sensitizer, 7,12-bis(1-decyloxyethyl)-Ga(III)-3,8,13,17-tetramethylporphyrin-2,18-dipropionyldiaspartic acid, ATX-70, was pharmacokinetically examined in tumor-bearing mice. The drug was administered intravenously to CDF(1) mice implanted with Colon 26 carcinoma. Blood and tissue samples were collected for up to 72 h after administration. The drug concentration was determined by high-performance liquid chromatography (HPLC) with fluorescence detection. ATX-70 was found to accumulate in tumors at a relatively high concentration that peaked between 2 h and 6 h after administration. However, modest concentrations of ATX-70 also remained in healthy tissues for up to 6 h. We examined the distribution of ATX-70 in the tumor in comparison with other tissues from the viewpoint of minimizing possible side effects of laser or ultrasound exposure while maintaining the treatment effect. About 24 h after administration, the tumor / plasma concentration ratio peaked, and relatively high tumor / skin and tumor / muscle concentration ratios were seen.

Adenocarcinoma↗

PubMed2006

Marginal adaptation and micro-porosity of class II restorations of a high copper amalgam and a palladium-free gallium-based alloy.

The aim of the current investigation was to compare the marginal adaptation and internal porosity of a gallium (Ga)-based alloy (Galloy) with a high copper amalgam (Permite C DP) when used in moderately sized conventional class II cavities. Ten dentists placed two restorations of each material in standardized class II cavities in typodont teeth set in a phantom head. The proximal surfaces of the restored teeth were subsequently examined using an optical microscope and colour photographs were taken. The teeth were then serially sectioned before being re-examined microscopically and re-photographed. Three dentists rated the photographs of the restorations on two occasions, 2 weeks apart, for marginal adaptation and internal porosity using a six and five point scoring criteria, respectively. Inter- and intra-examiner agreements were assessed with weighted kappa statistics. The Ga-based alloy exhibited inferior marginal adaptation and a significantly higher level of porosity and internal defects compared with the dental amalgam. Marginal defects were mainly concentrated at the gingival third of the proximal boxes for both alloys. The poor marginal adaptation and extensive internal porosity detected for the Ga-based alloy was attributed to the difficulty in the alloy condensation related mainly to the 'stickiness' of the alloy to the condensers and to the rapid change in the plasticity of the alloy during condensation. This could possibly be a factor in the post-operative complications reported with the clinical use of this alloy.

Copper↗

PubMed2003

Phonon dispersions of fcc delta-plutonium-gallium by inelastic x-ray scattering.

We report an experimental determination of the phonon dispersion curves in a face-centered cubic (fcc) delta-plutonium-0.6 weight % gallium alloy. Several unusual features, including a large elastic anisotropy, a small-shear elastic modulus C', a Kohn-like anomaly in the T1[011] branch, and a pronounced softening of the [111] transverse modes, are found. These features can be related to the phase transitions of plutonium and to strong coupling between the lattice structure and the 5f valence instabilities. Our results also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory calculations for delta-plutonium.

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PubMed1996

Homogeneous Linewidths in the Optical Spectrum of a Single Gallium Arsenide Quantum Dot

The homogeneous linewidths in the photoluminescence excitation spectrum of a single, naturally formed gallium arsenide (GaAs) quantum dot have been measured with high spatial and spectral resolution. The energies and linewidths of the homogeneous spectrum provide a new perspective on the dephasing dynamics of the exciton in a quantum-confined, solid-state system. The origins of the linewidths are discussed in terms of the dynamics of the exciton in zero dimensions, in particular, in terms of lifetime broadening through the emission or absorption of phonons and photons.

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PubMed2001

Spatially resolved spin-injection probability for gallium arsenide.

We report a large spin-polarized current injection from a ferromagnetic metal into a nonferromagnetic semiconductor, at a temperature of 100 Kelvin. The modification of the spin-injection process by a nanoscale step edge was observed. On flat gallium arsenide [GaAs(110)] terraces, the injection efficiency was 92%, whereas in a 10-nanometer-wide region around a [111]-oriented step the injection efficiency is reduced by a factor of 6. Alternatively, the spin-relaxation lifetime was reduced by a factor of 12. This reduction is associated with the metallic nature of the step edge. This study advances the realization of using both the charge and spin of the electron in future semiconductor devices.

Journal Article↗

PubMed1991

Effects of low-power gallium aluminium arsenide diode laser irradiation on the development of synapses in the neonatal rat hippocampus.

The effect of low-power gallium aluminium arsenide diode laser irradiation on the development of synapses was studied in the radiatum layer and the lacunosum-molecular layer of field CA3 of the neonatal rat hippocampus. Neonatal rats were irradiated with a low-power diode laser (830 nm, 60 mW) at two points located above the hippocampi, for 15 s, respectively, twice per day from birth (day 1) to day 5. The mean body weights of the laser-irradiated animals were found to be lower than those of the control animals, the deficit at day 20 being 22.6%. Moreover, the density of synaptic junctions stained by ethanolic phosphotungstic acid per unit area of the radiatum layer and the lacunosum-molecular layer of the neonatal rat hippocampus was significantly reduced at day 20. It was suggested that the low-power diode laser irradiation affected the development of synapses in the neonatal rat brain.

Age Factors↗

PubMed2002

Effect of terbium gallium garnet crystal orientation on the isolation ratio of a Faraday isolator at high average power.

We present a comprehensive and systematic investigation of the fundamental physical limitations of Faraday isolation performance at high average powers that are due to thermally induced birefringence. First, the operation of various Faraday isolator designs by use of arbitrary orientation of cubic magneto-optic crystals is studied theoretically. It is shown that, for different Faraday isolator designs, different crystal orientations can optimize the isolation ratio. Second, thermo-optic and photoelastic constants for terbium gallium garnet crystals grown by different manufacturers were measured. Measurements of self-induced depolarization are made for various orientations of crystallographic axes. The measurements are in good agreement with our theoretical predictions. Based on our results, it is possible to select a crystal orientation that optimizes isolation performance at high average powers, resulting in a 5-dB enhancement over nonoptimized orientations.

Journal Article↗

PubMed2003

Development of a gallium-doped germanium far-infrared photoconductor direct hybrid two-dimensional array.

To our knowledge, we are the first to successfully report a direct hybrid two-dimensional (2D) detector array in the far-infrared region. Gallium-doped germanium (Ge:Ga) has been used extensively to produce sensitive far-infrared detectors with a cutoff wavelength of approximately equal to 110 microm (2.7 THz). It is widely used in the fields of astronomy and molecular and solid spectroscopy. However, Ge:Ga photoconductors must be cooled below 4.2 K to reduce thermal noise, and this operating condition makes it difficult to develop a large format array because of the need for a warm amplifier. Development of Ge:Ga photoconductor arrays to take 2D terahertz images is now an important target in such research fields as space astronomy. We present the design of a 20 x 3 Ge:Ga far-infrared photoconductor array directly hybridized to a Si p-type metal-oxide-semiconductor readout integrated circuit using indium-bump technology. The main obstacles in creating this 2D array were (1) fabricating a monolithic Ge:Ga 2D array with a longitudinal configuration, (2) developing a cryogenic capacitive transimpedance amplifer, and (3) developing a technology for connecting the detector to the electronics. With this technology, a prototype Ge:Ga photoconductor with a direct hybrid structure has shown a responsivity as high as 14.6 A/W and a minimum detectable power of 5.6 x 10(-17) W for an integration time of 0.14 s when it was cooled to 2.1 K. Its noise is limited by the readout circuit with 20 microV/Hz(1/2) at 1 Hz. Vibration and cooling tests demonstrated that this direct hybrid structure is strong enough for spaceborne instruments. This detector array will be installed on the Japanese infrared satellite ASTRO-F.

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