We propose a barrierless mechanism for describing the oxidation of Al(111) in which oxygen atoms located on the outer surface extract aluminum atoms of the surface layers through local cooperation of other pre-adsorbed oxygen atoms. We show the details of this complex chemical process that kinetically competes with the non-destructive formation of an oxygen monolayer onto the Al surface, thus elucidating the initial aluminum oxidation regime. We demonstrate that further stripping of the complete surface Al layer is consistent with both (i) the formation of a defective alumina structure and (ii) an oxide capping layer preventing further oxidation at low temperature.
The surface chemistry associated with the synthesis of energetic nanolaminates controls the formation of the critical interfacial layers that dominate the performances of nanothermites. For instance, the interaction of Al with CuO films or CuO with Al films needs to be understood to optimize Al/CuO nanolaminates. To that end, the chemical mechanisms occurring during early stages of molecular CuO adsorption onto crystalline Al(111) surfaces are investigated using density functional theory (DFT) calculations, leading to the systematic determination of their reaction enthalpies and associated activation energies. We show that CuO undergoes dissociative chemisorption on Al(111) surfaces, whereby the Cu and O atoms tend to separate from each other. Both Cu and O atoms form islands with different properties. Copper islanding fosters Cu insertion (via surface site exchange mechanism) into the subsurface, while oxygen islands remain stable at the surface. Above a critical local oxygen coverage, aluminum atoms are extracted from the Al surface, leading to oxygen-aluminum intermixing and the formation of aluminum oxide (γ-alumina). For Cu and O co-deposition, copper promotes oxygen-aluminum interaction by oxygen segregation and separates the resulting oxide from the Al substrate by insertion into Al and stabilization below the oxide front, preventing full mixing of Al, Cu, and O species.
A phosphoryl Ru(II) polypyridyl complex was prepared in a one-pot process. Theoretical analysis suggests that the phosphoryl ligand may be viewed as a strong σ-donor anionic phosphine L-type ligand. State-of-the-art free-energy profile calculations on the excited states demonstrate that both favorable thermodynamic and kinetic factors are responsible for the remarkable room temperature luminescence properties of the phosphoryl complex.
Vapor deposited multilayered aluminum/oxide and bimetallics are promising materials for Micro Electro Mechanical System technologies as energy carriers, for instance, microinitiators or heat microsources in biological or chemical applications. Among these materials, the Al/Ni couple has received much attention both experimentally and theoretically. However, the detailed relation between the chemical composition of the intermixed interfacial regions and its impact on the ignition capabilities remains elusive. In this contribution, we propose a two-fold strategy combining atomistic density functional theory (DFT) calculations and a macroscopic 1D model of chemical kinetics. The DFT calculations allow the description of the elementary chemical processes (involving Al, Ni atoms and vacancies basic ingredients) and to parameterize the macroscopic model, in which the system is described as a stack of infinite layers. This gives the temporal evolution of the system composition and temperature. We demonstrate that the amount of vacancies, originating from the deposition process and the Al and Ni lattice mismatch, plays a critical role on both the ignition time and the temperature. The presence of vacancies enhances the migration of atoms between layers and so dramatically speeds up the atomic mixing at low temperatures far below ignition temperature, also pointing to the relation between experimental deposition procedures and ageing of the nanolaminates. V
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