Infrared Spectra of Indium Hydrides in Solid Hydrogen and Neon

Role of Ambient Hydrogen in HiPIMS-ITO Film during Annealing Process in a Large Temperature Range

Indium tin oxide (ITO) thin films were prepared by high power impulse magnetron sputtering (HiPIMS) and annealed in hydrogen-containing forming gas to reduce the film resistivity. The film resistivity reduces by nearly an order of magnitude from 5.6 × 10^-3 Ω·cm for the as-deposited film to the lowest value of 6.7 × 10^-4 Ω·cm after annealed at 700 °C for 40 min. The role of hydrogen (H) in changing the film properties was explored and discussed in a large temperature range (300-800 °C). When annealed at a low temperature of 300-500 °C, the incorporated H atoms occupied the oxygen sites (H_o), acting as shallow donors that contribute to the increase of carrier concentration, leading to the decrease of film resistivity. When annealed at an intermediate temperature of 500-700 °C, the H_o defects are thermally unstable and decay upon annealing, leading to the reduction of carrier concentration. However, the film resistivity keeps decreasing due to the increase in carrier mobility. Meanwhile, some locally distributed metallic clusters formed due to the reduction effect of H₂. When annealed at a high temperature of 700-800 °C, the metal oxide film is severely reduced and transforms to gaseous metal hydride, leading to the dramatic reduction of film thickness and carrier mobility at 750 °C and vanish of the film at 800 °C.

Reduction Behavior of Cubic In2O3 Nanoparticles by Combined Multiple In Situ Spectroscopy and DFT

Indium oxide (In₂O₃) has emerged as a highly active catalyst for methanol synthesis by CO₂ hydrogenation. In this work we elucidate the reduction behavior and oxygen dynamics of cubic In₂O₃ nanoparticles by in situ Raman and UV-vis spectra in combination with density functional theory (DFT) calculations. We demonstrate that application of UV and visible Raman spectroscopy enables, first, a complete description of the In₂O₃ vibrational structure fully consistent with theory and, second, the first theoretical identification of the nature of defect-related bands in reduced In₂O₃. Combining these findings with quasi in situ XPS and in situ UV-vis measurements allows the temperature-dependent structural dynamics of In₂O₃ to be unraveled. While the surface of a particle is not in equilibrium with its bulk at room temperature, oxygen exchange between the bulk and the surface occurs at elevated temperatures, leading to an oxidation of the surface and an increase in oxygen defects in the bulk. Our results demonstrate the potential of combining different in situ spectroscopic methods with DFT to elucidate the complex redox behavior of In₂O₃ nanoparticles.

Periodic Trends Manifested through Gas-Phase Generation of Anions Such as [AlH4]-, [GaH4]-, [InH4]-, [SrH3]-, [BaH3]-, [Ba(0)(η2-O2CH)1]-, [Pb(0)H]-, [Bi(I)H2]-, and Bi- from Formates

Metal-hydride anions of main group elements, such as BaH₃ ^- and InH₄ ^-, were generated by dissociating formate adducts of the respective metal formates. Upon activation, these adducts fragment by formate-ion ejection or by decarboxylation. For adducts of alkali-metal formates, the formate-ion ejection is the preferred pathway, whereas for those of alkaline-earth and group 13-15 metals, the expulsion of CO₂ is the more favorable pathway. Decarboxylation is deemed to yield a metal-hydrogen bond presumably by a hydride transfer to the metal atom. For example, the decarboxylation of Al(η-OCOH)₄ ^- and Ga(η-OCOH)₄ ^- generated AlH₄ ^- and GaH₄ ^-, respectively. The initial fragment-ion with a H-M bond formed in this way from adducts of the heavier metals of group 13 (Ga, In, and Tl) undergo a unimolecular reductive elimination, ascribable to the "inert-pair" effect, to lower the metal-ion oxidation state from +3 to +1. As group 13 is descended, the tendency for this reductive elimination process increases. PbH₃ ^-, generated from the formate adduct of lead formate, reductively eliminated H₂ to form PbH^-, in which Pb is in oxidation state zero. In the energy-minimized structure [H-Pb(η²-H₂)]^-, proposed as an intermediate for the process, a H₂ molecule is coordinated with PbH^- as a dihapto ligand. The formate adducts of strontium and barium produce monoleptic ions such as [M(0)(η²-O₂CH)₁]^-, in which the formate ion is chelated to a neutral metal atom. The bismuth formate adduct undergoes a double reductive elimination process whereby the oxidation state of Bi is reduced from +3 to +1 and then to -1. Upon activation, the initially formed [H-Bi-H]^- ion transforms to an anionic η²-H₂ complex, which eliminates dihydrogen to form the bismuthide anion (Bi^-).

Matrix Infrared Spectra and Quantum Chemical Calculations of Ti, Zr, and Hf Dihydride Phosphinidene and Arsinidene Molecules

Laser ablated Ti, Zr, and Hf atoms react with phosphine during condensation in excess argon or neon at 4 K to form metal hydride insertion phosphides (H2P-MH) and metal dihydride phosphinidenes (HP═MH2) with metal phosphorus double bonds, which are characterized by their intense metal-hydride stretching frequencies. Both products are formed spontaneously on annealing the solid matrix samples, which suggests that both products are relaxed from the initial higher energy M-PH3 intermediate complex, which is not observed. B3LYP (DFT) calculations show that these phosphinidenes are strongly agostic with acute H-P═M angles in the 60° range, even smaller than those for the analogous methylidenes (carbenes) (CH2═MH2) and in contrast to the almost linear H-N═Ti subunit in the imines (H-N═TiH2). Comparison of calculated agostic and terminal bond lengths and covalent bond radii for HP═TiH2 with computed bond lengths for Al2H6 finds that these strong agostic Ti-H bonds are 18% longer than single covalent bonds, and the bridged bonds in dialane are 10% longer than the terminal Al-H single bonds, which show that these agostic bonds can also be considered as bridged bonds. The analogous arsinidenes (HAs═MH2) have 4° smaller agostic angles and almost the same metal-hydride stretching frequencies and double bond orders. Calculations with fixed H-P-Ti and H-As-Ti angles (170.0°) and Cs symmetry find that electronic energies increased by 36 and 44 kJ/mol, respectively, which provide estimates for the agostic/bridged bonding energies.

The stabilization of gallane and indane by a ring expanded carbene

7Dipp Complexes of the group 13 binary hydrides GaH3 and InH3 have been prepared. Both adducts possess excellent thermal stability in the solid state but decompose readily in solution at ambient temperature. The presence of short M-H···H-CAlkyl distances in the structures of both [MH3(7Dipp)] complexes is discussed.

Molecular single-bond covalent radii for elements 1-118

A self-consistent system of additive covalent radii, R(AB)=r(A) + r(B), is set up for the entire periodic table, Groups 1-18, Z=1-118. The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same fit. Both E-E, E-H, and E-CH(3) data are incorporated for most elements, E. Many E-E' data inside the same group are included. For the late main groups, the system is close to that of Pauling. For other elements it is close to the methyl-based one of Suresh and Koga [J. Phys. Chem. A 2001, 105, 5940] and its predecessors. For the diatomic alkalis MM' and halides XX', separate fits give a very high accuracy. These primary data are then absorbed with the rest. The most notable exclusion are the transition-metal halides and chalcogenides which are regarded as partial multiple bonds. Other anomalies include H(2) and F(2). The standard deviation for the 410 included data points is 2.8 pm.

One-Dimensional BeH2 Polymers: Infrared Spectra and Theoretical Calculations

Laser-ablated beryllium atoms react with H2 upon co-condensation in excess hydrogen and neon to form BeH2 and (BeH2)2, which are identified through isotopic substitution and DFT calculations. Unreacted Be atoms isolated in solid neon or hydrogen are excited to the 1P0 state and react further with H2 to enhance the BeH2 and (BeH2)2 concentrations and produce (BeH2)n polymers. The series of strong infrared-active parallel Be-H-Be bridge-bond stretching modes observed for (BeH2)n polymers suggests one-dimensional structures, and this conclusion is supported by DFT calculations. The computed polymerization energy per BeH2 unit is about 33 kcal/mol.