Gallium Atoms Research Articles

Ionothermal synthesis, characterization of a new layered gallium phosphate with an unusual heptamer SBU

A new layered gallium phosphate Ga3(PO4)4(C2N2H8)·(H2C2N2H8)2·Cl (compound 1), has been ionothermally synthesized in the presence of deep eutectic solvent (DES) comprising mixtures of choline chloride and 2-imidazolidone (IMI). Single-crystal X-ray diffraction analysis reveals that compound 1 shows 2D layered framework with 10-ring windows, which is constructed from unusual heptamer second building units (SBUs). The ethylenediamine (en) units deriving from the decomposition of IMI, play a dual role as bidentate ligands coordinated with 6-fold coordinate gallium atoms and the templates. Additionally, compound 1 shows photoluminescence property in solid state at room temperature.

Molecular Group 13 Metallaborates Derived from M-O-M Cleavage Promoted by BH3.

The reaction of metalloxanes [{MeLM(OH)}2(μ-O)] [M = Al (1), Ga (2); MeL = CH{CMe(NAr)}2-, Ar = 2,4,6-Me3C6H2, Me = methyl] with an excess of BH3·D (D = tetrahydrofuran (THF), SMe2) affords annular metallaborate systems achieved through M-O-M cleavage. Compound 1 led exclusively to the formation of eight-membered ring systems [{MeLAl(μ-O){B(OnBu)}(μ-O)}2] (3) and [{MeLAl(μ-O)(BH)(μ-O)}2] (6), while for 2 the unprecedented six-membered ring systems [{(MeLGa)2(μ-O)}(μ-O)2{B(OnBu)}] (4) and [(MeLGa)(μ-O)2{(BOnBu)2(μ-O)}] (5) were observed. The use of BH3·THF with 1 and 2 led to the concomitant THF ring-opening reaction, while with BH3·SMe2 in THF no such reaction was observed. The metallaborates [MeLAl{OB(pinacol)}(OH)] (7) and [{MeLGa(OB(pinacol))}2(μ-O)] (8) were synthesized from pinacolborane and the corresponding metalloxane, providing structural evidence that supports the reaction pathways proposed for the formation of 3-6. Density functional theory studies were performed on 3-5 to assess the effect of the metal exchange between aluminum and gallium atoms on the energy of the general ring structures.

Adsorption of H2 on Ga24N24 cluster; A density functional theory investigation

Molecular adsorption of hydrogen on Ga24N24 cluster is explored using Density Functional Theory. It is shown that the adsorption of H2 molecules on gallium atoms surface of the cluster is a quasi-molecular adsorption with Ead = −19.7 kJ mol−1, which is favorable for hydrogen-storage materials. This adsorption is nearly position-independent but is not dissociative. The natural bond orbital analysis, reduced density gradient scatter graphs as well as Fukui functions and density of states spectra confirm the weak interaction between σ-bonding electrons of H2 molecule with the gallium atom of the cluster. The results may open a window to new hydrogen-storage devices at moderate pressures.

Nanometer scale composition study of MBE grown BGaN performed by atom probe tomography

Laser assisted atom probe tomography is used to characterize the alloy distribution in BGaN. The effect of the evaporation conditions applied on the atom probe specimens on the mass spectrum and the quantification of the III site atoms is first evaluated. The evolution of the Ga++/Ga+ charge state ratio is used to monitor the strength of the applied field. Experiments revealed that applying high electric fields on the specimen results in the loss of gallium atoms, leading to the over-estimation of boron concentration. Moreover, spatial analysis of the surface field revealed a significant loss of atoms at the center of the specimen where high fields are applied. A good agreement between X-ray diffraction and atom probe tomography concentration measurements is obtained when low fields are applied on the tip. A random distribution of boron in the BGaN layer grown by molecular beam epitaxy is obtained by performing accurate and site specific statistical distribution analysis.

Migration mechanisms and diffusion barriers of vacancies in Ga2O3

We employ the nudged elastic band and the dimer methods within the standard density functional theory (DFT) formalism to study the migration of the oxygen and gallium vacancies in the monoclinic structure of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$. We identify all the first nearest neighbor paths and calculate the migration barriers for the diffusion of the oxygen and gallium vacancies. We also identify the metastable sites of the gallium vacancies which are critical for the diffusion of the gallium atoms. The migration barriers for the diffusion of the gallium vacancies are lower than the migration barriers for oxygen vacancies by 1 eV on average, suggesting that the gallium vacancies are mobile at lower temperatures. Using the calculated migration barriers we estimate the annealing temperature of these defects within the harmonic transition state theory formalism, finding excellent agreement with the observed experimental annealing temperatures. Finally, we suggest the existence of percolation paths which enable the migration of the species without utilizing all the migration paths of the crystal.

Multi‐Center vs. Two‐Center Bonding within the Hetero‐Polyanion in Eu2GaPt2 and its Prototype Ca2SiIr2

The compound Eu2GaPt2 was synthesized from the elements in a sealed tantalum tube. Its Ca2SiIr2‐type crystal structure was refined from single‐crystal X‐ray diffraction data: space group C2/c, a = 9.8775(6), b = 5.8621(6), c = 7.9677(5) Å, β = 102.257(4)°, RF = 0.039, 1344 observed reflections, and 25 variable parameters. The platinum (iridium) atoms in Eu2GaPt2 and Ca2SiIr2 form linear chains of dumbbells [2c(Pt–Pt) or 2c(Ir–Ir) bonds, respectively]. These chains are interconnected to 2D polyanions in Eu2GaPt2 by the gallium atoms forming 4c(Ga–Pt–Ga–Pt) or by silicon atoms forming 2c(Si–Ir) bonds in Ca2SiIr2. The polyanion bonds to the europium (calcium) matrix via the pseudo lone‐pairs at the gallium (silicon) atoms.

Adsorption and desorption of hydrogen at nonpolar GaN(11¯00) surfaces: Kinetics and impact on surface vibrational and electronic properties

The adsorption of hydrogen at nonpolar GaN(1-100) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab-initio thermodynamics show, that the H-free surface is energetically favored. To validate these theoretical predictions experiments at room temperature and under ultrahigh vacuum conditions were performed. They reveal that molecular hydrogen does not dissociatively adsorb at the GaN(1-100) surface. Only activated atomic hydrogen atoms attach to the surface. At temperatures above 820 K, the attached hydrogen gets desorbed. The adsorbed hydrogen atoms saturate the dangling bonds of the gallium and nitrogen surface atoms and result in an inversion of the Ga-N surface dimer buckling. The signatures of the Ga-H and N-H vibrational modes on the H-covered surface have experimentally been identified and are in good agreement with the DFT calculations of the surface phonon modes. Both theory and experiment show that H adsorption results in a removal of occupied and unoccupied intragap electron states of the clean GaN(1-100) surface and a reduction of the surface upward band bending by 0.4 eV. The latter mechanism largely reduces surface electron depletion.

Zinc-blende MnN bilayer formation on the GaN(111) surface

Atomic layers of manganese nitride, deposited on the cubic gallium nitride (111) surface, are investigated using spin polarized periodic density functional theory calculations. The adsorption of a manganese atom has been evaluated at different high symmetry sites. Incorporation into the GaN substrate by replacing gallium atoms drives the formation of a site in which the displaced Ga atom forms bonds with Ga atoms at the surface. This energetically favorable configuration shows a ferromagnetic alignment. Surface formation energy calculations demonstrate that when a full Mn ML is incorporated into the GaN structure, a Ga ML on top of a MnN bilayer may be formed for very Ga-rich conditions. On the other hand, when a full Mn ML is deposited on top of the nitrogen terminated surface, an epitaxial MnN bilayer is formed with antiferromagnetic characteristics. Density of states and partial density of states are reported to show the antiferromagnetic alignment in both structures. This behavior is mainly induced by the Mn-d orbitals.

Preparation and Characterization of Ni5Ga3 for Methanol Formation via CO2 Hydrogenation

A nickel–gallium catalyst (Ni5Ga3) with superior catalytic performance for the hydrogenation of CO2 into methanol was prepared by co-precipitation, and calcined for 7 h at 600 °C in a flowing stream of air containing hydrogen. On the basis of measurements of X-ray photoelectron spectra (XPS), the fraction of integrated area of Ga2O3 over the Ni5Ga3 surface decreased significantly from 75.24 to 53.24%. Spectra showing X-ray absorption near-edge structure (XANES) indicate that the oxidation state of gallium atoms shifted from Ga(0) to Ga(III) indicating that Ga is a reactive component. Extended X-ray absorption fine structure (EXAFS) showed that the first shells of gallium and its adjacent atoms in fresh and used Ni5Ga3 were Ga–Ga and Ga–O, respectively. The coordination number, 5.56, of Ga atoms in used Ni5Ga3 was larger than that, 5.31, in the fresh catalyst; the bond Ga–O of length 1.94 A is shorter than the bond Ga–Ga of length 1.98 A. These results of XPS and XANES/EXAFS analyses indicate that the reactive gallium in Ni5Ga3 is first oxidized to Ga2O3 and then carbonated to GaCO3 over the catalyst surface during the formation of methanol. That formation was demonstrated through the appearance of specific peaks at 3681, 2982, 1345, and 1053 cm−1 for the absorption of methanol in infrared spectra recorded in situ. At 250 °C and 50 bar, the greatest conversion of CO2 was 95.7% and the greatest yield of methanol was 72.2%. In terms of the formation of dimethyl ether, the optimal reaction temperature with greatest selectivity (47.6%) and yield (27.8%) was 350 °C. Most importantly, the conversions of CO2 at 150, 250 and 350 °C were much larger than the equilibrium conversions, 47.6, 47.8 and 47.2%, of CO2, which indicates that Ni5Ga3 prevented the formation of water so that methanol could be produced continuously. For the formation of methanol with Ni5Ga3, the optimal Gibbs energy was 4.23 kJ mol−1; the equilibrium constant was 0.378 h−1.

A first principle study on oxygen adsorption and incorporation on the (1 0 0) surface of [0 0 1]-oriented GaN nanowires

Oxygen adsorption and incorporation on the (1 0 0) surface of [0 0 1]-oriented GaN nanowires are investigated through first principle calculations. Results indicate that oxygen adsorption configurations are much more stable than oxygen incorporation. With increasing oxygen coverage, the surface of oxygen adsorption and incorporation become more stable and unstable, respectively. Besides, significant changes of surface structure occur after oxidization of the GaN nanowire surface, including changes in the thickness of the topmost bilayer and the distance between layers. Relaxation of the surface structure becomes more prominent with increasing oxygen coverage for adsorption cases. Compared with adsorption, the effects of incorporation on surface structures are more obvious. Furthermore, by comparison of band structures of clean surfaces and oxidized surfaces, both oxygen adsorption and incorporation will hinder the escape of photoelectrons due to the increase of the work function. Ultimately, calculations of Mulliken charge distribution and bond population suggest that oxygen impurities can obtain electrons from surface gallium and nitrogen atoms. The bond population of Ga–O for adsorption cases are larger than Ga–N, while that of incorporation cases is lower than Ga–N. All these calculations indicate that oxidization has significant impacts on the surface characteristics of GaN nanowires. Surface oxidization is harmful to the photoemission of optoelectronic devices fabricated by GaN nanowires. These results may contribute to the removal of surface oxides of GaN nanowires, but require further verification by experimental observation.

New multicell model for describing the atomic structure of La3Ga5SiO14 piezoelectric crystal: Unit cells of different compositions in the same single crystal

Accurate X-ray diffraction study of langasite (La3Ga5SiO14) single crystal has been performed using the data obtained on a diffractometer equipped with a CCD area detector at 295 and 90.5 K. Within the known La3Ga5SiO14 model, Ga and Si cations jointly occupy the 2d site. A new model of a “multicell” consisting of two different unit cells is proposed. Gallium atoms occupy the 2d site in one of these cells, and silicon atoms occupy this site in the other cell; all other atoms correspondingly coordinate these cations. This structure implements various physical properties exhibited by langasite family crystals. The conclusions are based on processing four data sets obtained with a high resolution (sin θ/λ ≤ 1.35 A–1), the results reproduced in repeated experiments, and the high relative precision of the study (sp. gr. P321, Z = 1; at 295 K, a = 8.1652(6) A, c = 5.0958(5) A, R/wR = 0.68/0.68%, 3927 independent reflections; at 90.5 K, a = 8.1559(4) A, c = 5.0913(6) A, R/wR = 0.92/0.93%, 3928 reflections).

In situ flashes of gallium technique for oxide-free epiready GaSb (100) surface

The authors report a novel in situ technique for desorption of native oxides from GaSb (100) substrates. In the proposed approach, flashes of atomic gallium (FLAG) are irradiated onto a heated substrate to convert the nonvolatile Ga2O3 to volatile Ga2O. The conventional thermal oxide desorption (TOD) technique was compared with the proposed FLAG technique. Reflection high energy electron diffraction was used to monitor the oxide desorption. Oxide desorption by the FLAG technique was observed at 470 °C, which is ∼80 °C lower than the TOD technique (550 °C). Atomic force microscopy of the GaSb buffer grown using the FLAG technique reveals an atomically smooth surface. Unipolar barrier midwave infrared detectors based on InAs/GaSb type II superlattices were grown using the two approaches. The dark current from a representative FLAG device measured at T = 77 K and Vb = −0.1 V was 5.28 × 10−6 A/cm2 compared with a reference TOD device which had a dark current of 8.96 × 10−4 A/cm2 measured under identical conditions. The quantum efficiency at λ = 4.5 μm, T = 77 K, Vb = 0 V was measured to be 51% for the FLAG detector and 24% for the reference TOD detector. The FLAG technique was tested on several substrates of varying thickness of the native oxide. Also, the number of Ga-flashes was optimized to get a good starting epiready surface. The authors believe that they have established a promising technique for the in situ preparation of an epiready growth surface without the need for any ex situ treatment.

Synthesis of Aggregation-Induced Emission-Active Conjugated Polymers Composed of Group 13 Diiminate Complexes with Tunable Energy Levels via Alteration of Central Element.

Conjugated polymers containing boron and gallium diiminate complexes were prepared with various electron-donating comonomers via pre- and post-complexation methods, respectively. From a comparison of emission quantum yields between solution and film states, it was seen that all polymers containing group 13 elements possessed an aggregation-induced emission property. Additionally, the frontier orbital energies and the optical and electrochemical properties of the polymers can be tuned by altering a central element at the complex moieties as well as by changing a comonomer unit. In particular, it was demonstrated that the gallium atom can contribute to stabilizing the energy levels of the lowest unoccupied molecular orbitals, resulting in narrow band gaps of the conjugated polymers. This study presents the potential of gallium not only for preparing solid-state emissive conjugated polymers but also for fabricating low-band gap materials by employing the conjugated ligand.

Spectroscopic Ellipsometry Study of the Dielectric Function of Cu(In<sub>1–x</sub>Ga<sub>x</sub>)<sub>3</sub>Se<sub>5</sub> Bulk Compounds: Identification of Optical Transitions

Using Spectroscopic Ellipsometry (SE), the optical properties of Cu(In1−xGax)3Se5 bulk compounds, grown by the Bridgman method, were analyzed by varying x composition (0 ≤ x ≤ 1). Energy levels above the gap in the band scheme were determined by measuring the complex dielectric function at room-temperature for energies between 1.5 and 5.5 eV using a variable angle of incidence ellipsometer. The transitions values E1, E2 and E3 were observed above the gap for different samples of Cu(In1−xGax)3Se5 alloy. When a gallium atom replaces an indium atom, one assumes globally that the levels related to selenium and copper are unchanged. Conversely, the levels corresponding to the conduction band are shifted towards higher energies. Thus, the gap increases as the composition of gallium increases. Spectroscopic Ellipsometry (SE) gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum. Several other characterization methods like Energy Dispersive Spectrometry (EDS), hot point probe method, X-ray diffraction, Photoluminescence (PL), Optical response (Photoconductivity) were presented in this paper. The Cu(In1−xGax)3Se5 have an Ordered Vacancy Chalcopyrite-type structure with lattice constants varying as a function of the x composition. The band gap energy of Cu(In1−xGax)3Se5 compounds is found to vary from 1.23 eV to 1.85 eV as a function of x.

Crystal structure of bis(triphenylphosphonium) hexabromodigallate(II) in the correct space group: Conformational complexity in a heteroethane

AbstractThe crystal structure of [Ph3PH]2[Ga2Br6], previously described as having a disordered anion in the space group R3¯, has been re-determined in the correct space group P3¯, where it is fully ordered. Interestingly, two-thirds of the [Ga2Br6]2− dianions have an intermediate conformation with a Br–Ga–Ga–Br torsion angle of 36.91 (1)°, while the remaining is staggered as required from adopting a site with inversion symmetry. In the lattice, [Ph3PH]+ ions lie along the same threefold axes as the dianions and are oriented such that the P–H bond is directed towards a gallium atom. The phosphonium ions lie back-to-back and interact with relatively strong T-interactions between phenyl rings on adjacent cations. DFT calculations at the B3LYP/6–311+G(fd,) level have been used to determine the barriers to rotation in [Ga2X6]2− ions. For X = Cl and X = Br, the barriers are found to be very small, with values of 4.3 and 5.1 kJ mol−1 for the two halogens.

Optoelectronic Properties and the Electrical Stability of Ga-Doped ZnO Thin Films Prepared via Radio Frequency Sputtering.

In this work, Ga-doped ZnO (GZO) thin films were deposited via radio frequency sputtering at room temperature. The influence of the Ga content on the film’s optoelectronic properties as well as the film’s electrical stability were investigated. The results showed that the film’s crystallinity degraded with increasing Ga content. The film’s conductivity was first enhanced due to the replacement of Zn2+ by Ga3+ before decreasing due to the separation of neutralized gallium atoms from the ZnO lattice. When the Ga content increased to 15.52 at %, the film’s conductivity improved again. Furthermore, all films presented an average transmittance exceeding 80% in the visible region. Regarding the film’s electrical stability, GZO thermally treated below 200 °C exhibited no significant deterioration in electrical properties, but such treatment over 200 °C greatly reduced the film’s conductivity. In normal atmospheric conditions, the conductivity of GZO films remained very stable at ambient temperature for more than 240 days.

Contacting Mechanically Exfoliated β-Ga2O3 Nanobelts for (Opto)electronic Device Applications

We systematically investigated the properties of metal contacts deposited on exfoliated β-Ga2O3 nanobelts. Unintentionally doped β-Ga2O3 was mechanically exfoliated from bulk β-Ga2O3 crystal and transferred onto SiO2/Si substrate having a back gate configuration. Electrodes were formed by depositing Ti/Au or Ni/Au onto the transferred β-Ga2O3 nanobelts, followed by rapid thermal annealing (RTA) with different ambient gases and temperatures. Using scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), it was shown that titanium reacts with oxygen to form titanium oxide, which has ohmic behavior. In contrast, nickel does not form an ohmic contact despite 600°C thermal treatment. The lower oxygen partial pressure in a nitrogen atmosphere as compared to air results in more oxygen vacancies within the Ga2O3 nanobelts during RTA and a negative threshold voltage shift. A decreased current level after high temperature annealing can be ascribed to significant outward diffusion of oxygen and gallium atoms and to oxidation of the metal electrode. Our results can pave a route to demonstrating high performance β-Ga2O3 nanobelt-based (opto)electronic devices.

Synthesis, Characterization, Photophysical and DFT Studies of Coumarin Schiff Bases and Their Dimethylgallium Complexes

Reactions of trimethyl gallium ether adduct with five different coumarin Schiff bases in benzene yielded dimethyl gallium complexes of the general formula [Me2Ga{–O–(C9H3O–(2-O)–(4-Me))–CH=N–R}] (R = tBu, C6H5, C6H4Me-4, C6H4Cl-4 and C6H4Br-4). These complexes have been characterized by elemental analysis, IR, UV–vis, NMR (1H and 13C{1H}) spectroscopy. The molecular structures of three gallium complexes, viz. [Me2Ga{–O–(C9H3O–(2-O)–(4-Me))–CH=N–C6H5}], [Me2Ga{–O–(C9H3O–(2-O)–(4-Me))–CH=N–C6H4Me-4] and [Me2Ga{–O–(C9H3O–(2-O)–(4-Me))–CH=N–C6H4Br-4] were unequivocally established by single crystal X-ray crystallography. The gallium atom acquires a distorted tetrahedral geometry. These complexes exhibit emission in the visible region and their emission maxima are blue shifted with respect to that of the corresponding free ligand. DFT calculations reveal that the HOMO–LUMO gap value becomes slightly smaller with electron withdrawing substituent like Cl and Br.

Nature of gallium focused ion beam induced phase transformation in 316L austenitic stainless steel

The microstructural evolution and chemistry of the ferrite phase (α), which transforms from the parent austenite phase (γ) of 316L stainless steel during gallium (Ga) ion beam implantation in Focused Ion Beam (FIB) instrument was systematically studied as a function of Ga+ ion dose and γ grain orientations. The propensity for initiation of γ → α phase transformation was observed to be strongly dependent on the orientation of the γ grain with respect to the ion beam direction and correlates well with the ion channelling differences in the γ orientations studied. Several α variants formed within a single γ orientation and the sputtering rate of the material, after the γ → α transformation, is governed by the orientation of α variants. With increased ion dose, there is an evolution of orientation of the α variants towards a variant of higher Ga+ channelling. Unique topographical features were observed within each specific γ orientation that can be attributed to the orientation of defects formed during the ion implantation. In most cases, γ and α were related by either Kurdjumov-Sachs (KS) or Nishiyama-Wassermann (NW) orientation relationship (OR) while in few, no known OR's were identified. While our results are consistent with gallium enrichment being the cause for the γ → α phase transformation, some observations also suggest that the strain associated with the presence of gallium atoms in the lattice has a far field stress effect that promotes the phase transformation ahead of gallium penetration.

Features of spectra of low-energy neon ions scattered from gallium phosphide

Using mass-resolved ion scattering spectrometry, spectra of Ne+ ions scattered at an angle of 120° from the surface of GaP in the energy range of 0.4–1.96 keV have been studied in detail. In the spectra, in addition to the peaks of elastic binary Ne+/P and Ne+/Ga collisions, the peak of sputtered neon ions has been found, as well as the wide peak (a “hump”), the energy of which slightly depends on the energy of primary ions and the intensity considerably increases with an increase in this energy. In our opinion, the main contribution to this peak is made by neon ions that undergo multiple collisions with gallium and phosphorus atoms on the surface and deeper layers of the sample and keep their charge due to reionization processes.