Anomalous inter-layer atomic transport and the low-temperature amplification of surface instability in Al(111)

TL;DR

This study uses molecular dynamics simulations to reveal how impurity atoms like Pt can rapidly penetrate Al(111) surfaces at low temperatures through anomalous inter-layer transport, involving ballistic injection and surface atom ejection.

Contribution

It uncovers the atomic-scale mechanisms of impurity injection and surface instability in Al(111), highlighting the role of atomic size mismatch and transient collective motions.

Findings

Pt atoms are injected below the surface at low temperatures.

Surface atoms are ejected during impurity injection, causing disorder.

Atomic size mismatch influences intermixing and surface instability.

Abstract

Anomalous inter-layer atomic transport of deposited impurity atoms on Al(111) has been found by constant temperature molecular dynamics simulations. The low-energy deposition of Pt on Al(111) leads to oscillatory adsorbate-substrate interaction and to a low-temperature ballistic injection of the deposited particles to below the topmost layer. The ultrafast injection of a Pt atom coincides with the ejection of a substrate atom to the surface (ballistic replacement or exchange mechanism). This is in agreement with the experimental findings in which thin film rich in Al has been found on the surface after deposition of few MLs of Pt. We attribute the anomalous inter-layer transport to the size-mismatched impurity/host interaction and we point out the role of atomic size mismatch in biasing towards intermixing. The deposition induced low-temperature disordering of surface Al atoms with few transient Al adatoms has also been observed. The ultrafast injection of the impurity particles to the substrate is assisted by the transient out-of-plane and lateral circulating motion of few surface atoms arranged nearly in a hexagonal symmetry. The atomic injection of Pt can be regarded as a superexchange process driven by the transient and collective motion of few surface atoms. A chaotic surface state assisted mechanism could also be a possible explanation of the unexpected phenomenon.