Effects of temperature and surface orientation on migration behaviours of helium atoms near tungsten surfaces

TL;DR

This study uses molecular dynamics simulations to explore how temperature and surface orientation affect helium atom migration behaviors near tungsten surfaces, revealing different escape mechanisms and trapping phenomena.

Contribution

It provides new insights into helium migration and trapping on tungsten surfaces, especially highlighting the complex behavior on W{111} surfaces and temperature-dependent escape rates.

Findings

He atoms escape quickly from W{100} and W{110} surfaces without accumulation.

Trap mutations on W{111} hinder helium escape and depend on temperature.

Helium escape rate on W{111} is non-monotonic with temperature.

Abstract

Molecular dynamics simulations were performed to study the dependence of migration behaviours of single helium atoms near tungsten surfaces on the surface orientation and temperature. For W{100} and W{110} surfaces, He atoms can quickly escape out near the surface without accumulation even at a temperature of 400 K. The behaviours of helium atoms can be well-described by the theory of continuous diffusion of particles in a semi-infinite medium. For a W{111} surface, the situation is complex. Different types of trap mutations occur within the neighbouring region of the W{111} surface. The trap mutations hinder the escape of He atoms, resulting in their accumulation. The probability of a He atom escaping into vacuum from a trap mutation depends on the type of the trap mutation, and the occurrence probabilities of the different types of trap mutations are dependent on the temperature. This finding suggests that the escape rate of He atoms on the W{111} surface does not show a monotonic dependence on temperature. For instance, the escape rate at T=1500 K is lower than the rate at T=1100 K. Our results are useful for understanding the structural evolution and He release on tungsten surfaces and for designing models in other simulation methods beyond molecular dynamics.