Nanoscale oxide growth on Al single crystals at low temperatures: Variable charge molecular dynamics simulations

Abstract

We investigate the oxidation of aluminum low-index surfaces ͓͑100͒, ͑110͒, and ͑111͔͒ at low temperatures ͑300-600 K͒ and three different gas pressure values. We use molecular dynamics ͑MD͒ simulations with dynamic charge transfer between atoms where the interaction between atoms is described by the Es+ potential composed of the embedded atom method ͑EAM͒ potential and an electrostatic contribution. In the considered temperature range and under different gas pressure conditions, the growth kinetics follow a direct logarithmic law where the oxide thickness is limited to a value of ϳ3 nm. The fitted curves allow us to determine the temperature and the pressure dependencies of the parameters involved in the growth law. During the adsorption stage, we observe a rotation of the oxygen pair as a precursor process to its dissociation. In most cases, the rotation aligns the molecule vertically to the Al surface. The separation distance after dissociation ranges from 3 to 9 Å. Atomistic observations revealed that the oxide presents a dominant tetrahedral ͑AlO 4 ͒ environment in the inner layer and mixed tetrahedral and octahedral ͑AlO 6 ͒ environments in the outer oxide region when the oxide thickness reaches values beyond ϳ2 nm.

Oxidation of nanocrystalline aluminum by variable charge molecular dynamics

“…Indeed, these authors mentioned a short "transition" initial stage before the direct logarithmic law [21,22]. Based on the present work,…”

“…Oxidation of Al nanoclusters [19,20] or single-crystal surfaces of Al [21,22] for pressure ranging from 10 to 40 times the normal state were studied by variable charge molecular dynamics (VCMD) approaches. Under their oxidation conditions, these works clearly characterized the formation of an amorphous oxide layer.…”

“…It was used to study nanocrystalline metal-oxide properties [16][17][18] or processes involved in the oxidation of metallic substrates [12,13,[19][20][21][22].…”

In situ anodization of aluminum surfaces studied by x-ray reflectivity and electrochemical impedance spectroscopy

“…2 Surface science studies have provided detailed information on the initial formation of the protective oxide at low or ambient temperature using highly controlled ultra high vacuum (UHV) conditions and well-prepared single crystal surfaces [3][4][5][6][7][8][9][10][11] as well as by using theoretical means. 12 Many applications for Al require increased corrosion protection for better durability. This can be obtained by increasing the thickness of the protective oxide by electrochemical means using anodization.…”

Effect of oxygen gas pressure on the kinetics of alumina film growth during the oxidation of Al(111) at room temperature

“…The amorphous alumina films formed by low-temperature oxidation can be well described locally by a close packing of oxygen anions with the Al cations distributed over the octahedral and tetrahedral interstices [10]. The alumina films formed at low temperature exhibit a deficiency of Al cations (as compared to γ-Al 2 O 3 ) [11][12][13].…”