Gallium Atoms Research Articles

Reactions of trialkyl aluminum and trialkyl gallium with the N-tert-butyl amide of succinic acid: Molecular and supramolecular structures of the products

The reaction of the N-tert-butyl amide of succinic acid with tBu3M (M = Al, Ga) resulted in the formation of the new complexes [AltBu2{N(H)(tBu)C(O)CH2CH2COO}] (1), [MtBu2{N(H)(tBu)C(O)CH2CH2COO}(tBu3M)] [M = Al (2), M = Ga (3), and [GatBu2{N(H)(tBu)C(O)CH2CH2COO}]2 (4). The aluminum complexes 1 and 2 contained seven-membered C4O2Al rings with the Al atom bonded to the oxygen atom and coordinated to the nitrogen atom. The reaction of tBu3Ga with the N-tert-butyl amide of succinic acid resulted in the formation of a mixture of 3 and 4. The gallium complex 3 was isostructural to 2, whereas the gallium atoms in the dinuclear compound 4 were bonded to the carboxylate oxygens only forming a central Ga2C2O4 ring. X-ray studies showed that the crystalline solid obtained after crystallization from the post-reaction mixture was composed of crystals of compound 3 and co-crystals of 3 and 4. In all reactions, only the OH protons of the ligand reacted with tBuM groups with an alkane evolution, while NH protons remained unreactive. The reaction of tBu3Ga with the N-tert-butyl amide of succinic acid in a 2:1 M ratio of the reagents in the presence of water proceeded with the formation of the unprecedented compound [(GatBu2)2(OH){N(H)(tBu)C(O)CH2CH2COO}] (5) as the only product. Compound 5 was also obtained in the hydrolysis reaction of the mixture of compounds 3 and 4 isolated from the post-reaction mixture of tBu3Ga with the N-tert-butyl amide of succinic acid. The molecular and molecular packing in the crystal structures of 1–3 and 5 were determined by single-crystal X-ray diffraction. Crystal structure examinations showed laminar structures of 1, 3, and 5 and a packed crystal network of 2.

Development of a fluorescence based flux sensor for thin film growth and nanoparticle deposition.

An optical flux sensor, based on the fluorescence properties of materials and nanoparticles, has been developed to control the deposition rate in thin film deposition systems. Using a simple diode laser and a photomultiplier tube with a light filter, we report the detection of gallium atoms and CdSe-ZnS quantum dots. This setup has a high sensitivity and reproducibility.

Bonding and structure in network glasses

The aim of this paper is to foster greater use of the concepts of electrostatic bond strength and bond valence in the interpretation of glass structure. Methods of applying these concepts to diffraction data to investigate the atomic bonding environments in network glasses are presented, and illustrated using neutron diffraction results on lead gallate glasses, which show that gallium atoms are tetrahedrally coordinated by oxygen, and lead atoms have an average oxygen coordination number between three and four. It is of great value to consider the oxygen anion-centred coordination numbers, as well as the cation-centred coordination numbers. Due to the requirement for charge balance, the dominant coordination for oxygen in lead gallate glasses is 3-coordinated, with both OGa2Pb and OGaPb2 motifs. A small fraction (~1–2%) of the oxygen atoms are bonded to four cations, either as OGa2Pb0+2 or OGaPb1+2. By means of a valence sum function, it is shown that that the number of long (~2.8Å) Pb-O bonds is not significant, and thus the number of Pb atoms on symmetric sites (with a stereochemically inactive lone pair of electrons) is not significant. It is shown that, even though glasses and crystals obey the same bonding rules, the structure of a glass can differ from that of a closely related crystal.

Miscut dependent surface evolution in the process of N-polar [formula omitted] growth under N-rich condition

The evolution of surface morphology during the growth of N-polar (0001¯) GaN under N-rich conditions is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2° and 4°. The results are compared with experimentally observed surface morphologies of (0001¯) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(0001¯) surface where both types of atoms, nitrogen and gallium, attach to the surface and diffuse independently shows that at relatively high rates of the step flow (miscut angle <2°) the low mobility of gallium adatoms causes surface instabilities and leads to experimentally observed roughening while for low rates of the step flow (miscut 4°), smooth surface can be obtained. In the presence of almost immobile nitrogen atoms under N-rich conditions crystal growth is realized by the process of two-dimensional island nucleation and coalescence. Larger crystal miscut, lower growth rate or higher temperature results in similar effect of the surface smoothening. We show that the surface also smoothens for the growth conditions with very high N-excess. In the presence of large number of nitrogen atoms the mobility of gallium atoms changes locally thus providing easier coalescence of separated island.

Infrared-active modes in Ag3Ga5S9 and Ag3In5S9 single crystals: An influence of trivalent cation substitution

Infrared reflection spectra are registered in the frequency range of 50–2000cm−1 for Ag3Ga5S9 and Ag3In5S9 single crystals grown by Bridgman method. Four infrared-active modes are detected in spectra. By replacing the gallium atoms by indium ones in Ag3Ga5S9 crystal, the observed bands shift to low frequencies. Spectral dependence of optical parameters; real and imaginary parts of the dielectric function, the function of energy losses, refractive index, absorption index and absorption coefficient were calculated from reflectivity experiments. The frequencies of transverse and longitudinal optical modes and oscillator strength were also determined. The highest frequency bands observed in an infrared spectra of studied crystals were tentatively assigned to the antiphase vibration of the trivalent cation and anion sublattices.

Ni4 and Ni3Ga clusters as building units in Ca3Ni4Ga4 and Sr3Ni3□Ga4

Abstract The gallides Ca3Ni4Ga4 and Sr3Ni3Ga4 were synthesized from arc-melted NixGay precursor alloys and the respective alkaline earth metal in sealed niobium tubes in an induction furnace. Redetermination of the Ca3Ni4Ga4 structure from X-ray single crystal diffractometer data confirmed the X-ray powder data: Na3Pt4Ge4 type, I4̅3m, a=740.6(1) pm, wR2=0.0245, 169 F2 values, 9 variables. The nickel atoms build tetrahedral Ni4 clusters (256 pm Ni–Ni) that are end-on coordinated by gallium atoms (234 pm Ni–Ga). These [Ni4Ga4] units show a bcc packing and leave cavities Ca@Ga4Ni4Ga4 for the calcium atoms. Sr3Ni3Ga4 crystallizes with a new structure type: R3m, a=1039.8(2), c=698.2(1) pm, wR2=0.1048, 636 F2 values, 23 variables. The structure shows twinning by inversion with a domain ratio of 79/21. The structures of Sr3Ni3Ga4 and Ca3Ni4Ga4 are related by a group–subgroup scheme (R3m is a translationengleiche subgroup of I4̅3m). The 8c Ni and Ga subcell sites split into site 3a and 9b each. This allows formation of ordered Ni3Ga tetrahedra (264 pm Ni–Ga) along with ordered gallium vacancies.

Monoorgano-gallium and –indium complexes derived from dianionic tridentate ONO Schiff bases: Synthesis, crystal structures and photoluminescence

Reactions of triorgano-gallium and –indium etherates with N′-(2-hydroxybenzylidine)benzohydrazide and N′-(2-hydroxy-3-methoxybenzylidine)benzohydrazide in refluxing benzene afforded complexes of composition [{RM}{–O(C6H3R′-3)CHN–NC(C6H5)O–}] (MGa, In; RMe, Et; R′H, OMe). These complexes have been characterized by elemental analysis, IR, UV-vis, and NMR (1H and 13C{1H}) spectroscopy. The molecular structures of [{MeGa}{–O(C6H4)CHN–NC(C6H5)O–}]2 (1), [{MeGa}{–O(C6H3–OMe)CHN–NC(C6H5)O–}]2 (2) and [{EtGa}{–O(C6H3–OMe)CHN–NC(C6H5)O–}]2 (6) were established by X-ray crystallography. These complexes adopt a dimeric structure with phenolate oxygen bridges with the gallium atom acquiring a distorted square pyramidal configuration. These complexes are emissive in toluene solution at room temperature.

Theoretical investigation of GaN carbon doped

In this work we used first principles calculations in the frame of density functional theory (DFT) in order to study the structural and electronic properties of GaN doped with carbon. The computational calculations were carried out by a method based on plane waves pseudopotentials, as implemented in the Quantum Espresso code. In the wurtzite type GaN supercell the nitrogen atoms were replaced by carbon atoms (C by N) and then also the gallium atoms by carbon atoms (C by Ga). The carbon concentrations in the GaN volume was set as x=25, 50 y 75%. For each concentration x of carbon the formation energy was calculated for the substitutions C by N and CxGa. We found that it is more energetically favourable that the carbon atoms occupy the positions of the nitrogen atoms (C by N), because in all the x concentrations of carbon the formation energies were lower than that in the substitutions (C by Ga). It was found that the new compounds CxGaN1-x have higher bulk moduli. So they are very rigid. This property makes them good candidates for applications in hard coatings or devices for high power and temperatures. Analysis of the density of states show that the new CxGaN1-x ternary compound have metallic behaviour that comes essentially from the hybridization states N-p and C-p cross the Fermi level.

Reactions of Terphenyl-Substituted Digallene AriPr4GaGaAriPr4 (AriPr4 = C6H3-2,6-(C6H3-2,6-iPr2)2) with Transition Metal Carbonyls and Theoretical Investigation of the Mechanism of Addition

The neutral digallene AriPr4GaGaAriPr4 (AriPr4 = C6H3-2,6-(C6H3-2,6-iPr2)2) was shown to react at ca. 25 °C in pentane solution with group 6 transition metal carbonyl complexes M(CO)6 (M = Cr, Mo, W) under UV irradiation to afford compounds of the general formula trans-[M(GaAriPr4)2(CO)4] in modest yields. The bis(gallanediyl) complexes were characterized spectroscopically and by X-ray crystallography, which demonstrated that they were isostructural. In each complex, the gallium atom is two-coordinate with essentially linear geometry, which is relatively rare for gallanediyl-substituted transition metal species. The experimental data show that the gallanediyl ligand :GaAriPr4 behaves as a good σ-donor but a poor π-acceptor, in agreement with prior theoretical analyses on related systems. In addition, the monogallanediyl complex Mo(GaAriPr4)(CO)5 was synthesized by reacting AriPr4GaGaAriPr4 with two equivalents of Mo(CO)5NMe3 in THF solution. The mechanism of the reaction between AriPr4GaGaAriPr4 and Cr(CO)6 was probed computationally using density functional theory. The results suggest that the reaction proceeds via an intermediate monogallanediyl complex, Cr(GaAriPr4)(CO)5, that can be generated via two pathways, one of which involves the dimeric AriPr4GaGaAriPr4, that are possibly competing. AriPr4GaGaAriPr4 was also shown to react readily under ambient conditions with Co2(CO)8 to give the monosubstituted dicobalt complex Co2(μ-GaAriPr4)(μ-CO)(CO)6 by X-ray crystallography. The :GaAriPr4 unit bridges the Co–Co bond unsymmetrically in the solid state. No evidence was found for incorporation of more than one :GaAriPr4 unit into the dicobalt complex.

Axial Ligand Effects on the Structures of Self-Assembled Gallium-Porphyrin Monolayers on Highly Oriented Pyrolytic Graphite.

Monolayers of five-coordinate gallium octaethylporphyrin complexes (Ga(OEP)X; X = Cl, Br, I, O3SCF3, CCPh) on highly oriented pyrolytic graphite were studied at the solid-liquid (1-phenyloctane) interface using scanning tunneling microscopy (STM) to probe the dependence of their properties on the nature of the axial X ligand. Density functional theory calculations of the gas-phase structures of the free molecules reveal that the gallium atom is positioned above the plane of the porphyrin macrocycle, with this pyramidal distortion increasing in magnitude according to X = O3SCF3 (displacement = 0.35 Å) < Cl, Br, I (∼0.47 Å) < CCPh (0.54 Å). All compounds exhibit pseudohexagonal close-packed structures in which the porphyrin is oriented coplanar with the surface and the axial ligand is oriented perpendicular to it, and with unit-cell parameters that are within experimental error of each other (a, b = 1.34 (3)-1.39 (2) nm, Γ = 66 (2)-68 (1)°). In contrast to these close similarities, the stabilities of the monolayers are sensitive to the nature of the axial ligand: the monolayers of Ga(OEP)(O3SCF3) and Ga(OEP)(CCPh) exhibit damage during the STM experiment upon repeated scanning and upon toggling the sign of the bias potential, but monolayers of Ga(OEP)Cl, Ga(OEP)Br, and Ga(OEP)I do not. A second important ligand-influenced property is that Ga(OEP)I forms bilayer structures, whereas the other Ga(OEP)X compounds form monolayers exclusively under identical conditions. The top layer of the Ga(OEP)I bilayer is oriented with the iodo ligand directed away from the surface, like the bottom layer, but the molecules pack in a square, lower-density geometry. The comparatively large polarizability of the iodo ligand is suggested to be important in stabilizing the bilayer structure.

Catalytic conversion of light hydrocarbons to propylene over MFI-zeolite/metal-oxide composites

Zeolite-based composite catalysts for producing propylene efficiently by cracking of light hydrocarbons were developed in the present study to meet future demand for propylene and utilize various light hydrocarbons (e.g., light-naphtha, condensates recovered from natural gas and olefinic hydrocarbons obtained from GTL-process). The composite catalysts, consisting of Al-MFI zeolites containing iron and gallium atoms (Fe–Ga–Al-MFI) at optimized ratio and aluminum-oxide binder (Al2O3), were employed for cracking of n-hexane or 1-hexene using fixed-bed-type reactor at around 550 °C. Since the Fe–Ga–Al-MFI zeolites caused acidity suitable for generating light olefins selectively, high propylene yields (18–41 wt%) were obtained by suppressing formation of aromatics at mild temperatures. The present catalyst exhibited high propylene productivity and catalytic stability simultaneously in the steam-cracking of hydrocarbons at suitable steam ratio. Moreover, in the cracking of n-hexane without dilution over the present catalyst, high propylene yields of ca. 18 wt% were maintained for at least 80 h due to its high resistance to coke formation in spite of severe conditions, suggesting that simplified cracking process for on-purpose propylene production from light hydrocarbons is feasible in fixed-bed mode by using the present composite catalysts.

Gallium isopropoxide: Synthesis, properties, “coordination polymerism”. New pentanuclear gallium oxoisopropoxochloride

Conditions for the synthesis of gallium isopropoxide (I) by anodic dissolution of the metal in i-PrOH (in the presence of Bu4NBr supporting electrolyte) and by exchange reaction of GaCl3 with i-PrONa were studied. In the latter case, the crude product was a waxy substance (II) infinitely soluble in the alcohol and hydrocarbons and containing 12–30% Cl, which cannot be removed by adding an excess of i-PrONa due to the formation of insoluble NaGa(OPr-i)4. During 1.5–2 months, II is solidified to give non-melting nonvolatile amorphous product (III) poorly soluble in the alcohol. Upon heat treatment of II in vacuum, compound I is distilled off as an oily liquid consisting, according to mass spectrometry, of [Ga(OPr-i)3]2 dimer molecules. It can be retained for a long period of time in the presence of the [Ga(OPr-i)3]4 tetramer crystals. The existence of oligomeric molecules of different size up to polymers (“coordination polymerism”) in the materials is related to the possibility of tetrahedral or octahedral coordination of the metal atom. From concentrated solutions of components, the oxoalkoxochloride [Ga5(µ5-O)(µ-OPr-i)8Cl5] (IV) is crystallized. Its molecule is a flattened tetragonal pyramid. The equatorial plane formed by four gallium atoms has the µ5-O group at the center. The axial Ga atom has an octahedral coordination. All eight sides of the pyramid are drawn together by the µ-OPr-i groups, and the chlorine atoms occupy the terminal positions. (CIF file CCDC no. 693282.)

Monte Carlo simulation of V/III flux ratio influence on GaAs island nucleation during MBE

The kinetic Monte Carlo simulation of GaAs/GaAs(001) molecular beam epitaxial growth considering V/III flux ratio influence on nucleating island characteristics is presented. It is shown that the island density increases with the surface coverage increase and reaches saturation after deposition of ∼0.1 monolayer of GaAs. The increase of V/III flux ratio from 3 to 40 leads to the increase of the island density from 1.9-1012 to 2.6-1012 cm-2. At the same time the average size decreases from 4.4 to 4.1 nm. The island size distribution function narrows with V/III flux ratio increase. This is attributed to the shortage of gallium atoms in comparison with deposited arsenic molecules that prevents large island formation and leads to the dramatic growth of little island concentration. The simulation demonstrates good agreement with experimental results.

Near-infrared photocathode In0.53Ga0.47As doped with zinc: A first principle study

In0.53Ga0.47As is an important material for the shortwave near-infrared negative electron affinity photocathodes. As we all known, doping is a necessary step for the formation of the negative electron affinity and zinc is a traditional substitutional element to generate the P-type semiconductor. The In0.53Ga0.44Zn0.03As and In0.50Ga0.47Zn0.03As were formed from In0.53Ga0.47As by a zinc atom substituting a gallium atom or an indium atom in the article. The atom structures, the band structures and the populations were studied by the first principle method for these two supercell models. Two problems, how the zinc-doping change the characters of intrinsic In0.53Ga0.47As and the differences between In0.53Ga0.44Zn0.03As and In0.50Ga0.47Zn0.03As, were solved by the research. Firstly, the atom structures were changed and the band gaps were narrowed after zinc doping. The ionicity was enhanced which is agreed with the character of P-type semiconductor. Secondly, there were small differences between the two supercells in electronic structures. Therefore, there is no need to consider which kind of atom to be substituted during the material growth for the near-infrared InGaAs photocathode.

Electron energy spectrum of two-dimensional hydroxysiloxane structures with defects of substitution of silanol groups with boron, aluminum, and gallium atoms

A computational scheme based on density functional theory, generalized to the case of periodic structures, is used to calculate the electron energy characteristics of two-dimensional hydroxysiloxane structures both of ideal structure and with defects induced by the substitution of surface silanol groups with GroupIII atoms (B, Al, Ga). The dependences of the energy-band parameters and the position of the chemical potential and optical absorption spectra on the defect concentration are analyzed in the energy range of absorbed photons ћω < 17 eV. It is shown that the energy of the electron transition from the np band to both the conduction band and to acceptor states resulting from the introduction of Group-III atoms into the hydroxysiloxane structure can be adjusted by varying the degree of substitution of silanol groups. The results can be used for the selection of film materials with the desired electron energy spectrum for microand nanoelectronics technology.

Ab initiostudy of Ga-GaN system: Transition from adsorbed metal atoms to a metal–semiconductor junction

Ab initio studies of a GaN(0001)-Ga system with various thicknesses of a metallic Ga layer were undertaken. The studied systems extend from a GaN(0001) surface with a fractional coverage of gallium atoms to a Ga-GaN metal–semiconductor (m–s) contact. Electronic properties of the system are simulated using density functional theory calculations for different doping of the bulk semiconductor. It is shown that during transition from a bare GaN(0001) surface to a m–s heterostructure, the Fermi level stays pinned at a Ga-broken bond highly dispersive surface state to Ga–Ga states at the m–s interface. Adsorption of gallium leads to an energy gain of about 4 eV for a clean GaN(0001) surface and the energy decreases to 3.2 eV for a thickly Ga-covered surface. The transition to the m–s interface is observed. For a thick Ga overlayer such interface corresponds to a Schottky contact with a barrier equal to 0.9 and 0.6 eV for n- and p-type, respectively. Bond polarization-related dipole layer occurring due to an electron transfer to the metal leads to a potential energy jump of 1.5 eV, independent on the semiconductor doping. Additionally high electron density in the Ga–Ga bond region leads to an energy barrier about 1.2 eV high and 4 A wide. This feature may adversely affect the conductivity of the n-type m–s system.

Density-functional investigation of gold cluster anions doped with gallium: Au n Ga– (1 ⩽ n ⩽ 8)

The equilibrium geometric, relative stabilities, electronic and magnetic properties of small AunGa– clusters (1 ⩽ n ⩽ 8), in comparison with pure gold cluster anions are investigated systematically within the framework of the first-principles density functional calculations at the PW91PW91 level. The calculations reveal that the impure gallium atom changes the structure of pure gold clusters. The most stable structures of AunGa– (4 ⩽ n ⩽ 8) prefer three-dimensional structures. The VDE, fragmentation energies and the secondorder difference energies and the HOMO–LUMO gaps for the lowest-energy structures of AunGa– and Au-n+1 (1 ⩽ n ⩽ 8) clusters show an even-odd oscillation along with the cluster size. Meanwhile the above results indicate the doping gallium atom enhance the stability of the clusters. It is must be pointed out that Au2Ga– cluster is the most stable. Finally, we research the natural population analysis (NPA) of Au-n+1 (1 ⩽ n ⩽ 8) clusters. The results indicate that Ga atom attracts electron from the Au atom except for the Au Ga–cluster.

Unexpected reactivity of “GaI” towards N,N′-diaryl-β-diketiminate tin(II) chloride: Synthesis, X-ray diffraction analysis and DFT studies

Reaction of the [HC(CMeNAr)2]SnCl (Ar=2,4,6-Me3C6H2) with “GaI” in THF provided an unexpected transhalogenation reaction product [HC(CMeNAr)2]SnI. The crystal structure shows a tin(II) ion with a distorted tetrahedral pyramidal geometry. Theoretical calculations, using density functional theory (B3LYP), suggest the probable reaction mechanism for transhalogenation. The activation energy for moving from reactant ([HC(CMeNAr)2]SnCl to product [HC(CMeNAr)2]SnI) is only 10.2kcal/mol. The chloride ion is displaced by the iodine ion, probably by the help of the gallium atom when it is coordinated to the chlorine atom.

Band gap and refractive index tunability in thallium based layered mixed crystals

Compositional variation of the band gap energy and refractive index of TlMeX2-type (Me = Ga or In and X = S or Se) layered mixed crystals have been studied by the transmission and reflection measurements in the wavelength range of 400–1100 nm. The analysis of absorption data of TlGa1-xInxSe2, TlGa(S1−xSex)2, TlGa1−xInxS2, and TlIn(Se1−xSx)2 mixed crystals revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps of mixed crystals decrease at the replacing of gallium atoms by indium and of sulfur atoms by selenium ones. Through the similar replacing of atoms (smaller atoms by larger ones) in the studied mixed crystals, the refractive index shows the quite opposite behavior.

The Blue LED Nobel Prize: Historical context, current scientific understanding, human benefit

The Blue LED Nobel Prize: Historical context, current scientific understanding, human benefit