Predicting Fracture Propensity in Amorphous Alumina from Its Static Structure Using Machine Learning.

Structural, optical and mechanical properties of amorphous and crystalline alumina thin films

The effect of thermal annealing on the properties of thin alumina films prepared by low pressure metal-organic chemical vapour deposition

Pulsed laser deposited alumina thin films

Properties of alumina films prepared by low-pressure metal-organic chemical vapour deposition

Predicting the early-stage creep dynamics of gels from their static structure by machine learning

The hydrogenolysis of methylcyclopentane on platinum model catalysts: Particle size effect due to a reaction occurring at the phase boundary metal-support

The incorporation of a siliceous impurity during the anodic oxidation of aluminum in a sodium tartrate electrolyte

Thin films of amorphous alumina were prepared on fused silica substrates by e-beam evaporation technique without any deliberate substrate heating. The effects of thermal annealing of alumina films on the structural and optical properties were investigated for annealing temperatures of 600°C, 800°C, 950°C, 1050°C and 1130°C. The present study focuses on investigating the thermal and mechanical stability of the films and phase and structural transformations as a function of heat treatment. With increasing temperature, different crystallographic phases were observed to grow in the films. The most dominant phases were γ and δ alumina which were stable upto 1100°C. Optical properties of the films were measured by UV-visible optical spectroscopy and refractive index value was measured to be 1.66 ± 0.01 for an amorphous film. The refractive index increased to 1.78 ± 0.01 (at a wavelength of 700 nm) on crystallization of amorphous coatings.

ABSTRACTSelf supporting thin films of amorphous alumina and zirconia were irradiated with light and heavy ions at various temperatures(25–430°C). Irradiation was found to result in the formation of 10–30 nm large grains well below conventional crystallization temperatures. These grains were quite stable against subsequent thermal growth. Crystallization, grain size, and growth depended on ion species as well as on ‘stabilizing’ additives (yttria or Pt).

Electron microscopy of [formula omitted] model catalysts : II. Sintering in atmospheres of H 2, O 2 and Ar

Thin films of amorphous alumina of thickness ∼350 nm were prepared on silicon wafer by DC cathode reactive sputtering. The effects of thermal annealing on the structural properties were investigated at annealing temperatures of 600°C, 800°C, 1100°C and 1220°C. X-ray diffraction showed that crystallization starts at 800°C and produces δ and θ alumina phases, the latter phase grows with heat treatment and the film was predominantly δ-phase with small amount of a-phase after annealing at 1220°C. AFM studies found that the surface of thin films smoothened upon crystallization.

Amorphous aluminum oxide (alumina) thin films are of interest as inert chemical barriers for various applications. However, the existing literature on the aqueous stability of atomic layer deposited (ALD) amorphous alumina thin films remains incomplete and, in some cases, inconsistent. Because these films have a metastable amorphous structure─which is likely partially hydrated in the as-deposited state─hydration and degradation behavior likely deviate from what is expected for the equilibrium, crystalline Al2O3 phase. Deposition conditions and the aqueous solution composition (ion content) appear to influence the reactivity and stability of amorphous ALD alumina films, but a full understanding of why these alumina films hydrate, solvate, and/or dissolve in near-neutral pH = 7 conditions, for which crystalline Al2O3 is expected to be stable, remains unsolved. In this work, we conduct an extensive X-ray photoelectron spectroscopy investigation of the surface chemistry as a function of water immersion time to reveal the formation of oxyhydroxide (AlOOH), hydroxide (Al(OH)3), and possible carbonate species. We further show that brief postdeposition exposures of these ALD alumina films to an air plasma anneal can significantly enhance the film's stability in near-neutral pH aqueous conditions. The simplicity and effectiveness of this plasma treatment may provide a new alternative to thermal annealing and capping treatments typically used to promote aqueous stability of low-temperature ALD metal oxide barrier layers.

Inelastic electron tunneling spectroscopy has been used to probe the irreversible chemisorption at 295 K of phenol, catechol, resorcinol and hydroquinone on thin amorphous alumina films in Al/Al2O3/Pb sandwich structure tunneling junctions. This spectroscopy yields a representation of the vibronic excitations of the chemical bonds in the adspecies. Phenol chemisorbs predominantly as C6H5O- on Al+3 sites with a very small amount of associative chemisorption at high coverages. Catechol and resorcinol both adsorb predominently as the di-ion C6H4O2-2, whereas hydroquinone chemisorbs both as the di-ion and as the single ion 1, 4-C6H4(OH)O- at high surface coverages. Hydrogen bonding is observed among the adsorbates and between the adsorbates and the OH groups on the partially hydroxylated Al2O3 surface. The experimental results are explicable in terms of the geometry and chemical properties of the adsorbates and the oxide surface.

Influence of titanium and vanadium on the hydrogen transport through amorphous alumina films

Alumina surface coatings are commonly applied to layered oxide cathode particles for lithium-ion battery applications. Atomic layer deposition (ALD) is one such surface coating technique, and ultrathin alumina ALD films (<2 nm) are shown to improve the electrochemical performance of LiNixMnyCo1-x-yO2 materials, with groups hypothesizing that a beneficial Li-Al-O product is being formed during the alumina ALD process. However, the atomic structure of these films is still not well understood, and quantifying the interface of ultrathin (∼1 nm) ALD films is an arduous experimental task. Here, we perform molecular dynamics simulations of amorphous alumina films of varying thickness in contact with the (0001) LiCoO2 (LCO) surface to quantify the film nanostructure. We calculate elemental mass density profiles through the films and observe that the Li-Al-O interphase extends ∼2 nm from the LCO surface. Additionally, we observe layering of Al and O atoms at the LCO-film interface that extends for ∼1.5 nm. To access the short-range order of the amorphous film, we calculated the Al coordination numbers through the film. We find that while [4]Al is the prevailing coordination environment, significant amounts of [6]Al exist at the interface between the LiCoO2 surface and the film. Taken together, these principal findings point to a pseudomorphic Li-Al-O overlayer that approximates the underlying layered LiCoO2 lattice but does not exactly replicate it. Additionally, with sufficient thickness, the Li-Al-O film transitions to an amorphous alumina structure. We anticipate that our findings on the ALD-like, Li-Al-O film nanostructure can be applied to other layered LiNixMnyCo1-x-yO2 materials because of their shared crystal structure with LiCoO2. This work provides insight into the nanostructure of amorphous ALD alumina films to help inform their use as protective coatings for Li-ion battery cathode active materials.