Ga Bonds Research Articles

Theoretical prediction of hexagonal ternary phase Mo2Ga2C and its evolution to layered carbide Mo2C

The stable structure of Mo2Ga2C was determined by using a combination of crystal structure searching technique and first-principles calculations. Mo2Ga2C crystallizes a hexagonal layered structure of space group P63/ m m c (No. 194), which is the typical structure of conventional M n+1AX n phases. The dynamical and mechanical stability of the predicted structure is confirmed by the phonon dispersion and elastic constants, respectively. The structural stability of Mo2Ga2C is investigated by analyzing the stability of chemical bonds under tensile and shear deformations. Layered structural stability of Mo2Ga2C is determined by the strength of covalent Mo–Ga bond under tensile and shear strains. The stress–strain relationships of Mo2Ga2C are evaluated and compared with Mo2GaC. Two-dimensional layered Mo2C can be obtained by the selective removal of Ga atoms from Mo2Ga2C. Theoretical prediction of monolayer Mo2C is metallic, and has potential application as anode and thermoelectric material.

Impact of swift heavy ion irradiation on as-grown gallium nitride epilayers by MOCVD technique

The as-grown GaN by Metalorganic Chemical Vapor Deposition was utilized to study the irradiation effects on GaN epilayers. The stopping range of ions in the matter is studied to choose the energy range for irradiation. The grown epilayers were irradiated with light and heavy ions of O7+ and Ag12+ by varying ion fluence. The X-ray Diffraction confirmed the wurtzite crystal structure for pristine and all the irradiated GaN epilayers. Atomic force microscopy showed high surface roughness for heavy ion irradiation when compared with light ion. Micro-Raman analysis was carried out through the Lorentz line fitting and calculated the carrier concentration and phonon lifetime. In light and heavy ion irradiation, the carrier concentration enhances with defect formations. X-ray Photoelectron Spectroscopy analysis showed that light ion irradiation caused oxygen bonding, while heavy ion irradiation led to the Ga–Ga bond shift, revealing film degradation.

Layered GaGe2Te: structure and chemical bonding

AbstractThe structure of the new compound GaGe2Te has been determined using nanofocused synchrotron radiation. The trigonal structure (space group P m1, a=4.0443(3) Å, c=14.923(2) Å, V=211.38(4) Å3; Z=2) consists of Ge bilayers sandwiched by Ga−Te layers. Ge and Ga are tetrahedrally coordinated. The layer packages are separated by a van der Waals gap with a Te−Te distance of 4.1502(7) Å. The structure resembles that of GaGeTe but features an additional Ge atom layer. Despite small scattering contrast of Ga and Ge, precise high‐resolution data enable unequivocal atom assignment as confirmed by R values of different models. DFT calculations suggest only a small extent of charge transfer, which is confirmed by both Bader and Mulliken charges. Thus, bonding within the layer packages is predominantly covalent, especially between Ga and Ge. Formal oxidation states according to GaIIIGe(0)Ge−ITe−II, i. e. assuming rather ionic Ge−Ga bonds, convey a much less realistic situation than GaIIGe2(0)Te−II, which is in line with GaGeTe.

Ga–C and Ga–Ga bond formation using a NON-ligated gallyl nucleophile

We report an improved synthesis of the NON-donor stabilized potassium gallyl dimer [K{Ga(NON)}]2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene) from (NON)GaI and potassium naphthalenide that avoids issues associated with over-reduction of the metal centre. The use of [K{Ga(NON)}]2 in the synthesis of Ga–E bonds has been explored through its reactions with a range of electrophiles. The reaction with (NON)GaI to give {Ga(NON)}2 via Ga–Ga bond formation mirrors the behaviour of the corresponding aluminyl compound, while Ga–C bond formation via nucleophilic attack on 1-bromopentane to give (NON)Ga(n-pentyl) avoids the retention of KBr often encountered in the formation of (more Lewis acidic) AlIII compounds. Attempted formation of a Mg–Ga bond, e.g. via the reaction of [K{Ga(NON)}]2 with (NacnacMes)MgI(OEt2), generates instead the unsymmetrical digallane(4), (NacnacMes)Ga(μ2-N,N'-NON)GaI, consistent with enhanced lability of Ga (over Al) within the NON-ligand scaffold.

Regulating the Metallic Cu–Ga Bond by S Vacancy for Improved Photocatalytic CO2 Reduction to C2H4

AbstractArtificial photosynthesis, which converts carbon dioxide into hydrocarbon fuels, is a promising strategy to overcome both global warming and energy crisis. Herein, the geometric position of Cu and Ga on ultra‐thin CuGaS2/Ga2S3 is oriented via a sulfur defect engineering, and the unprecedented C2H4 yield selectivity is ≈93.87% and yield is ≈335.67 µmol g−1 h−1. A highly delocalized electron distribution intensity induced by S vacancy indicates that Cu and Ga adjacent to S vacancy form Cu–Ga metallic bond, which accelerates the photocatalytic reduction of CO2 to C2H4. The stability of the crucial intermediates (*CHOHCO) is attributed to the upshift of the d‐band center of ultra‐thin CGS/GS. The C–C coupling barrier is intrinsically reduced by the dominant exposed Cu atoms on the 2D ultra‐thin CuGaS2/Ga2S3 in the process of photocatalytic CO2 reduction, which captures *CO molecules effectively. This study proposes a new strategy to design photocatalyst through defect engineering to adjust the selectivity of photocatalytic CO2 reduction.

Sources of n-Type Conductivity in Single Crystal β-Ga2O3 and Monoclinic WO3 Nanoparticles

The source of the commonly observed unintentional n-type conductivity in wide-band-gap oxides is controversial. For high-quality β-Ga2O3 single crystals, the physical characteristics of H-containing defects are studied by solid-state nuclear magnetic resonance (ssNMR) and Fourier transform infrared (FT-IR) spectroscopy. NMR observation demonstrated that the hydrogen atoms occur exclusively in the positive charge state, and three trapped protons are housed in two “half vacancies” left by the Ga vacancy to form a VGa–H2+1 complex. Protons trapped in the vacancies are hardly ever able to diffuse out due to the strong hydrogen bonds they establish, even at relatively high temperatures. The hydrogen atoms in one of the two “half vacancies” are the bridged protons in Ga–O(H2)–Ga bonds, the hydrogen atoms can readily donate electrons to the conduction band, and these hydrogen atoms become the shallow donors. The VGa–H2+1 complex provides high-quality β-Ga2O3 single crystals with the extra-stability and the n-type conductivity. For monoclinic WO3 nanoparticles, NMR, FT-IR, and EPR results show that the bridged proton in W–O(H2)–W groups was assumed to be responsible for the so-called “hidden” hydrogen, which can be converted into a shallow donor in the course of sample processing. Our results provide a guide to more refined experimental studies of point defects and impurities in wide-band-gap oxides and their influence on the control of n-type conductivity.

Comparative studies of interatomic potentials for modeling point defects in wurtzite GaN

In this paper, a new version of the Stillinger–Weber (SW) potential for wurtzite GaN is presented, by which we systematically explore the structural and thermodynamical properties of native point defects and their complexes. In parallel, the semi-empirical Modified Embedded-Atom Method (MEAM) potential is selected for comparison. The SW and MEAM potentials are assessed by the reproduction of the fundamental properties of wurtzite GaN and by the ability to describe the inversion domain boundaries and the wurtzite–rocksalt phase transition. Then the structural search of native point defects and their complexes in GaN is implemented using both SW and MEAM potentials with the benchmark of Density Functional Theory (DFT) calculations. Besides vacancies and antisites, four N and five Ga interstitials are confirmed by refining the DFT calculations, among which two N split interstitials N+−N⟨21̄1̄0⟩ and N+−Ga⟨011̄0⟩, and two Ga split interstitials, Ga+−Ga⟨011̄0⟩−g and Ga+−N⟨011̄0⟩, are observed for the first time. The SW potential correctly predicts the octahedral occupation GaOct to be the most stable Ga interstitial, while the MEAM potential predicts the ground state of the N+−N⟨011̄0⟩ split interstitial (N+−N⟨011̄0⟩−g) as the most stable N interstitial. However, neither of the two potentials could simultaneously generate the most stable configurations of N and Ga interstitials. The investigations of point defect complexes reveal that N octahedral Frenkel [FrenkelOct(N)] and paired antisite (NGaGaN) defects are unstable and get converted into VN⊕N+−N⟨011̄0⟩−g configurations with different separations between VN and N+−N⟨011̄0⟩−g point defects based on the DFT calculations. The formation energies calculated by the DFT and SW potential demonstrate that Schottky, Ga octahedral Frenkel [FrenkelOct(Ga)], and VN⊕N+−N⟨011̄0⟩−g point defect complexes are energetically feasible and that they should not dissociate into two isolated point defects. In contrast, the MEAM potential predicts the dissociation to be exothermic for Schottky and VN⊕N+−N⟨011̄0⟩−g. Overall, the structural features concerned with N–N or Ga–Ga bonds relaxed by the SW potential are more consistent with DFT calculations than the MEAM counterpart.

First-principles investigation of a-line Shockley partial dislocations in wurtzite GaN: core reconstruction and electronic structure

Αtomistic simulations based on density functional theory were performed to investigate Shockley partial dislocations, parallel to the <11–20> direction, in wurtzite gallium nitride. The cores of both 30° and 90° Shockley partial dislocations, their possible reconstructions and their electronic structures were analyzed and compared systematically. Shockley partial dislocations were found to have a variety of core structures while exhibiting different bonding states like: deformed Ga–N bonds, Ga–Ga and N–N homo-nuclear bonds, as well as Ga– and N–dangling bonds. We have demonstrated that the core reconstruction of these dislocations is not always energetically favourable in wurtzite GaN, as it is the case in elemental semiconductors. It results from interplay between the energy gain from eliminating dangling and forming homo-nuclear bonds and the energy excess from the induced strain of hetero-nuclear Ga–N bonds within the core. Depending on their core configurations, Shockley partial dislocations are expected to have different electronic behaviours in wurtzite GaN, as they can act either as sources of parasitic luminescence or non-radiative recombination centres, or give pathways to leakage currents. We have demonstrated that deep states associated with dislocations are not due to the dangling bonds, as generally believed, but rather to Ga–Ga bonds in their cores, and that N–N bonds do not lead to any gap states. These results are of high relevance as guidelines in defect engineering strategies aiming at producing dislocations with a particular electronic behaviour in wurtzite GaN.

C-H and Si-H Activation Reactions at Ru/Ga Complexes: A Combined Experimental and Theoretical Case Study on the Ru-Ga Bond.

Treatment of [Ru(COD)(MeAllyl)2 ] and [Ru(COD)(COT)] with GaCp* under hydrogenolytic conditions leads to reactive intermediates which activate Si-H or C-H bonds, respectively. The product complexes [Ru(GaCp*)3 (SiEt3 )H3 ] (1) and [Ru(GaCp*)3 (C7 H7 )H3 ] (2) are formed with HSiEt3 or with toluene as the solvent, respectively. While 1 was isolated and fully characterized by NMR, MS, IR and SC-XRD, 2 was too labile to be isolated and was observed and characterized in situ by using mass spectrometry, including labelling experiments for the unambiguous assignment of the elemental composition. The structural assignment was confirmed by DFT calculations. The relative energies of the four isomers possible upon toluene activation at the ortho-, meta-, para- and CH3 -positions have been determined and point to aromatic C-H activation. The Ru-Ga bond was analyzed by EDA and QTAIM and compared to the Ru-P bond in the analogue phosphine compound. Bonding analyses indicate that the Ru-GaCp* bond is weaker than the Ru-PR3 bond.

Role of Oxygen and Fluorine in Passivation of the GaSb(111) Surface Depending on Its Termination

The mechanism of the chemical bonding of oxygen and fluorine on the GaSb(111) surface depending on its termination is studied by the projector augmented-waves method within density functional theory. It is shown that on an unreconstructed (111) surface with a cation termination, the adsorption of fluorine leads to the removal of surface states from the band gap. The binding energy of fluorine on the cation-terminated surface in the most preferable Ga-T position is lower by ~0.4 eV than that of oxygen, but it is significantly lower (by ~0.8 eV) on the anion-terminated surface. We demonstrate that the mechanism of chemical bonding of electronegative adsorbates with the surface has an ionic–covalent character. The covalence of the O–Sb bond is higher than the F–Sb one, and it is higher than both O–Ga and F–Ga bonds. Trends in the change in the electronic structure of the GaSb(111) surface upon adsorption of fluorine and oxygen are discussed. It is found that an increase in the oxygen concentration on the Sb-terminated GaSb(111) surface promotes a decrease in the density of surface states in the band gap.

GaAsBi: From Molecular Beam Epitaxy Growth to Devices

On the background of a molecular beam epitaxy (MBE) machine viewport, a simplified representation of the Bi surface hopping mechanism is depicted for a GaAs surface exposed to an oscillating Bi flux. The exact behaviour of Bi on a growing surface is still the subject of some debate and oscillating fluxes appear to enhance Bi incorporation, potentially due to the increased likelihood of Bi – Ga bonds forming. These mechanisms are discussed in the Review by Robert D. Richards, Abdul R. Mohmad, and co-workers (see article number 2100330).

The structural origin of the 15 μm residual absorption in the BaGa4Se7 crystal

The 15 μm residual absorption of the BaGa4Se7 crystal is related to the OSe defect and originates from the deforming vibration of Ga–O–Ga bonds.

Synthesis and computational aspects of Al(II)-Al(II) and Ga(II)-Ga(II) dihalides based on an amidinate scaffold.

Amidinate compounds with stabilized aluminium(II) and gallium(II) elements of composition L2M2X2 (3 and 4) have been prepared from their LMX2 (1 and 2) precursor, where M = Al (1 and 4) and Ga (2 and 3); L = PhC(NiPr2C6H3)2 (1 and 4) and PhC(NtBu)2 (2 and 3); and X is I (1 and 4) and Cl (2 and 3) and insights into their bonding are gained. The M-M bond lengths are reported along with the single-crystal X-ray structures of 1-4.

Field-induced electron transfer in magnetostrictive material Fe81Ga19

The effect of magnetic fields on the local structure of the Fe81Ga19 alloy was investigated by X-ray absorption fine spectroscopy (XAFS) technique. The results demonstrate that 0.6 T magnetic fields lead to the increasing of the 3d, 4s and 4p electrons of Fe atoms, but the decreasing of the 4p electrons of Ga atoms. The electron transfer from Ga to Fe with applying magnetic fields is revealed. The magnetic fields increase the Fe–Ga bond length. The role of the Fe–Ga bond in determining the magnetostriction is revealed.

Low‐temperature phase of Ga3Ir: Crystal structure and chemical bonding

Abstractlt‐Ga3Ir is a low‐temperature phase in the Ga−Ir system, which is stable below 530 °C. The sample of lt‐Ga3Ir was obtained after annealing at 400 °C for 96 hours. The crystal structure of lt‐Ga3Ir was solved using 3D‐ED electron diffraction data obtained by SA‐EDT diffraction tomography, optimized by quantum‐mechanical techniques and refined from the X‐ray powder diffraction data: structure type Fe3C, space group Pnma, a=6.9073(4) Å, b=7.7275(4) Å and c=4.8536(2) Å, Z=4, Pearson symbol oP16. The striking feature of the chemical bonding is the absence of the two‐atomic Ga−Ga bonds. The two‐atomic Ga1−Ir and Ga2−Ir, as well as the three atomic Ga1−Ga2−Ir bonds, form the bonding pattern.

Structural studies of ligand stabilized Ni/Ga clusters by means of vibrational spectroscopy and theoretical calculations

AbstractIn order to explain the different catalytic activity in hydrogenation of two new intermetallic Ni/Ga clusters, [Ga7](NiCp*)6 (1A) and [NiGa6](NiCp*)6 (1B) (Cp* = C5Me5), investigations of structure–function relationship have been performed based on Raman and infrared (IR) spectroscopy and theoretical (density functional theory [DFT] and normal coordinate) calculations. Full interpretation of the Raman, far‐IR, and mid‐IR spectra of these dark colored solids has been proposed. Based on the overview of metal–Cp* complexes, all the 14 characteristic Cp*− skeletal fundamental modes have been identified. By comparison of the NiCp* stretching and tilting external modes (350–380 cm−1), their force constants, and bond lengths, cluster 1B exhibited slightly stronger metal–ligand bonding. Vibrations of Ga7 and NiGa6 cluster cores showed that the stretching wavenumbers and force constants of NiGa (100–350 cm−1) and GaGa (60–250 cm−1) bonds are higher for cluster 1B, in agreement with the shorter averaged experimental and calculated bond lengths of GaGa bonds (2.873 and 2823 Å for clusters 1A and 1B, respectively). Cluster hydrogenation experiments with H2 and D2 showed strong NiH and ND stretching features (at 1750 and 1260 cm−1, respectively), and at the same time, characteristic bands of self‐hydrogenated Cp*H and remained nondegraded clusters have been detected. The extent of HD exchange in cluster deuteration was obtained about 1.5 times more effective with cluster 1B than cluster 1A. The stronger hydrogen or deuterium uptake by cluster 1B and the more intensive self‐hydrogenation of Cp* clearly support the higher hydrogenation activity of cluster 1B compared with that of 1A.

Cationic Heterobimetallic Mg(Zn)/Al(Ga) Combinations for Cooperative C–F Bond Cleavage

AbstractLow‐valent (MeBDI)Al and (MeBDI)Ga and highly Lewis acidic cations in [(tBuBDI)M+⋅C6H6][(B(C6F5)4−] (M=Mg or Zn,MeBDI=HC[C(Me)N‐DIPP]2,tBuBDI=HC[C(tBu)N‐DIPP]2, DIPP=2,6‐diisopropylphenyl) react to heterobimetallic cations [(tBuBDI)Mg–Al(MeBDI)+], [(tBuBDI)Mg–Ga(MeBDI)+] and [(tBuBDI)Zn–Ga(MeBDI)+]. These cations feature long Mg–Al (or Ga) bonds while the Zn–Ga bond is short. The [(tBuBDI)Zn–Al(MeBDI)+] cation was not formed. Combined AIM and charge calculations suggest that the metal–metal bonds to Zn are considerably more covalent, whereas those to Mg should be described as weak AlI(or GaI)→Mg2+donor bonds. Failure to isolate the Zn–Al combination originates from cleavage of the C−F bond in the solvent fluorobenzene to give (tBuBDI)ZnPh and (MeBDI)AlF+which is extremely Lewis acidic and was not observed, but (MeBDI)Al(F)‐(μ‐F)‐(F)Al(MeBDI)+was verified by X‐ray diffraction. DFT calculations show that the remarkably facile C–F bond cleavage follows a dearomatization/rearomatization route.

Cationic Heterobimetallic Mg(Zn)/Al(Ga) Combinations for Cooperative C-F Bond Cleavage.

Low‐valent (MeBDI)Al and (MeBDI)Ga and highly Lewis acidic cations in [(tBuBDI)M+⋅C6H6][(B(C6F5)4 −] (M=Mg or Zn, MeBDI=HC[C(Me)N‐DIPP]2, tBuBDI=HC[C(tBu)N‐DIPP]2, DIPP=2,6‐diisopropylphenyl) react to heterobimetallic cations [(tBuBDI)Mg–Al(MeBDI)+], [(tBuBDI)Mg–Ga(MeBDI)+] and [(tBuBDI)Zn–Ga(MeBDI)+]. These cations feature long Mg–Al (or Ga) bonds while the Zn–Ga bond is short. The [(tBuBDI)Zn–Al(MeBDI)+] cation was not formed. Combined AIM and charge calculations suggest that the metal–metal bonds to Zn are considerably more covalent, whereas those to Mg should be described as weak AlI(or GaI)→Mg2+ donor bonds. Failure to isolate the Zn–Al combination originates from cleavage of the C−F bond in the solvent fluorobenzene to give (tBuBDI)ZnPh and (MeBDI)AlF+ which is extremely Lewis acidic and was not observed, but (MeBDI)Al(F)‐(μ‐F)‐(F)Al(MeBDI)+ was verified by X‐ray diffraction. DFT calculations show that the remarkably facile C–F bond cleavage follows a dearomatization/rearomatization route.

Effect of heteroepitaxial growth on LT-GaAs: ultrafast optical properties

Epitaxial low temperature grown GaAs (LT-GaAs) on silicon (LT-GaAs/Si) has the potential for terahertz (THz) photoconductive antenna applications. However, crystalline, optical and electrical properties of heteroepitaxial grown LT-GaAs/Si can be very different from those grown on semi-insulating GaAs substrates (‘reference’). In this study, we investigate optical properties of an epitaxial grown LT-GaAs/Si sample, compared to a reference grown under the same substrate temperature, and with the same layer thickness. Anti-phase domains and some crystal misorientation are present in the LT-GaAs/Si. From coherent phonon spectroscopy, the intrinsic carrier densities are estimated to be 1015 cm−3 for either sample. Strong plasmon damping is also observed. Carrier dynamics, measured by time-resolved THz spectroscopy at high excitation fluence, reveals markedly different responses between samples. Below saturation, both samples exhibit the desired fast response. Under optical fluences ⩾54 μJ cm−2, the reference LT-GaAs layer shows saturation of electron trapping states leading to non-exponential behavior, but the LT-GaAs/Si maintains a double exponential decay. The difference is attributed to the formation of As–As and Ga–Ga bonds during the heteroepitaxial growth of LT-GaAs/Si, effectively leading to a much lower density of As-related electron traps.

Reductive elimination of [AlH2]+ from a cationic Ga-Al dihydride.

Oxidative addition of TMEDA-supported [AlH2]+ to [{BDI}Ga] (BDI = {HC(C(CH3)N(2,6-iPr2-C6H3))2}) provides [{BDI}Ga(H)-Al(H)(tmeda)][B(C6H3-3,5-Me2)4] (TMEDA = N,N,N'N'-tetramethylethylenediamine) with a covalent metal-metal bond. The reaction is readily reversed by substituting TMEDA for an N-heterocyclic carbene or dissolving in THF.