Thermal decomposition of trimethylindium and indium trisguanidinate precursors for InN growth: An ab initio and kinetic modeling study.

Indium nitride (InN) is an interesting material for future electronic and photonic-related applications, as it combines high electron mobility and low-energy band gap for photoabsorption or emission-driven processes. In this context, atomic layer deposition techniques have been previously employed for InN growth at low temperatures (typically <350 °C), reportedly yielding crystals with high quality and purity. In general, this technique is assumed to not involve any gas phase reactions as a result from the time-resolved insertion of volatile molecular sources into the gas chamber. Nonetheless, such temperatures could still favor the precursor decomposition in the gas phase during the In half-cycle, therefore altering the molecular species that undergoes physisorption and, ultimately, driving the reaction mechanism to pursue other pathways. Thence, we herein evaluate the thermal decomposition of relevant In precursors in the gas phase, namely, trimethylindium (TMI) and tris(N,N'-diisopropyl-2-dimethylamido-guanidinato) indium (III) (ITG), by means of thermodynamic and kinetic modeling. According to the results, at T = 593 K, TMI should exhibit partial decomposition of ∼8% after 400 s to first generate methylindium and ethane (C2H6), a percentage that increases to ∼34% after 1 h of exposure inside the gas chamber. Therefore, this precursor should be present in an intact form to undergo physisorption during the In half-cycle of the deposition (<10 s). On the other hand, the ITG decomposition starts already at the temperatures used in the bubbler, in which it slowly decomposes as it is evaporated during the deposition process. At T = 300 °C, the decomposition is a fast process that reaches 90% completeness after 1 s and where equilibrium, at which almost no ITG remains, is achieved before 10 s. In this case, the decomposition pathway is likely to occur via elimination of the carbodiimide ligand. Ultimately, these results should contribute for a better understanding of the reaction mechanism involved in the InN growth from these precursors.

Understanding carbon dioxide capture on metal-organic frameworks from first-principles theory: The case of MIL-53(X), with X = Fe3+, Al3+, and Cu2.

Metal-organic frameworks (MOFs) constitute a class of three-dimensional porous materials that have shown applicability for carbon dioxide capture at low pressures, which is particularly advantageous in dealing with the well-known environmental problem related to the carbon dioxide emissions into the atmosphere. In this work, the effect of changing the metallic center in the inorganic counterpart of MIL-53 (X), where X = Fe3+, Al3+, and Cu2+, has been assessed over the ability of the porous material to adsorb carbon dioxide by means of first-principles theory. In general, the non-spin polarized computational method has led to adsorption energies in fair agreement with the experimental outcomes, where the carbon dioxide stabilizes at the pore center through long-range interactions via oxygen atoms with the axial hydroxyl groups in the inorganic counterpart. However, spin-polarization effects in connection with the Hubbard corrections, on Fe 3d and Cu 3d states, were needed to properly describe the metal orbital occupancy in the open-shell systems (Fe- and Cu-based MOFs). This methodology gave rise to a coherent high-spin configuration, with five unpaired electrons, for Fe atoms leading to a better agreement with the experimental results. Within the GGA+U level of theory, the binding energy for the Cu-based MOF is found to be Eb = -35.85 kJ/mol, which is within the desirable values for gas capture applications. Moreover, it has been verified that the adsorption energetics is dominated by the gas-framework and internal weak interactions.

X-ray Photoelectron Fingerprints of High-Valence Ruthenium-Oxo Complexes along the Oxidation Reaction Pathway in an Aqueous Environment.

Recent advances in operando-synchrotron-based X-ray techniques are making it possible to address fundamental questions related to complex proton-coupled electron transfer reactions, for instance, the electrocatalytic water splitting process. However, it is still a grand challenge to assess the ability of the different techniques to characterize the relevant intermediates, with minimal interference on the reaction mechanism. To this end, we have developed a novel methodology employing X-ray photoelectron spectroscopy (XPS) in connection with the liquid-jet approach to probe the electrochemical properties of a model electrocatalyst, [RuII(bpy)2(py)(OH2)]2+, in an aqueous environment. There is a unique fingerprint of the extremely important higher-valence ruthenium-oxo species in the XPS spectra along the oxidation reaction pathway. Furthermore, a sequential method combining quantum mechanics and molecular mechanics is used to illuminate the underlying physical chemistry of such systems. This study provides the basis for the future development of in-operando XPS techniques for water oxidation reactions.

A quantum chemistry study for ionic liquids applied to gas capture and separation.

In recent years, the global climate change is in evidence and it is almost a consensus that it is caused by the greenhouse gases emissions. An alternative to reduce these emissions is carbon capture and storage (CCS), which employs solvents based on amine compounds. In this scene, ionic liquids (IL) have been investigated to a greater extent for this application. In this work, we make an evaluation of interactions between gases (CO2, SO2, and H2S) and anion/cation from IL, as well as cation-anion interactions. For this, quantum calculations under vacuum were performed at the B3LYP/6-311+G** level of theory and using the M06-2X functional, where dispersion effects are considered. Among the well-studied systems based on imidazolium cations and fluorinated anions, we also studied the tetraalkylammonium, tetraalkylphosphonium, ether-functionalized imidazolium based systems, and tetrahexylammonium bis(trifluoromethanesulfonyl)imide, [THA][Tf2N], as a potential prototype. The ion pairs evaluated include [Tf2N](-)-based IL, with alkyl chain varying from [C1mim](+) to [C8mim](+) and [C1mim](+)-based IL. We found that the anion becomes more available to interact with gas with the weakening of the cation-anion interaction. [THA][Tf2N] has a binding energy of -274.89 kJ/mol at the B3LYP/6-311+G** level of theory, which is considered energetically interesting to gas capture applications.