Molecular dynamics studies of temperature effects on low energy helium bombardments on tungsten surfaces

MD simulations have been conducted to study the effect of temperature on low energy (<200 eV) helium bombardments on tungsten surfaces. The reflection coefficients, energy distributions and depth distributions of helium atoms were calculated at various time points. Collisions between helium atoms and target atoms are found to be the main mechanism for the reflection of the helium atoms before 0.2 ps, after which the thermal movement of the atoms is found to play the dominant role. An important temperature effect is that increasing temperature may induce a rapid slowing down of incident helium atoms. This effect makes the reflection energy distributions quite different from those that are predicted without accounting for temperature effects. Moreover, the helium atoms thermally moving to the substrate surface are found to be hindered to escape from the surface, and the accumulation of the helium atoms near the surface may occur.