Molecular dynamics calculations for low-energy helium atoms on a nickel surface

Abstract

We have reproduced, by means of molecular dynamics simulations, the behaviour of helium atoms impinging on a nickel {loo} surface at finite temperature ( T = 0.3T,, where T, is the bulk melting temperature) with incident energies ranging from 0.1 to 50 eV. We have evaluated the reflection coefficients as a function of incident energy for given incidence angle, (Y = 0". Several reflection mechanisms have been individuated in the higher-energy range (10 s Ei, s 50 eV). Furthermore, we discuss the role of the thermal spike associated with displacement cascades in the process of creation of surface defects. We describe the structural modifications induced on the metal lattice by the simultaneous presence of helium atoms and lattice point defects. The evaluation of the energies required to form these defective configurations confirms the strong tendency of helium to migrate to defective regions rather than to defect-free ones.

Molecular dynamics simulations of atomic carbon on tungsten surface

“…An interesting feature is that in our simulations in low energy range from 0.5 eV to 1 eV, the energy reflection coefficient is very close to the particle reflection coefficient, which means that the scattered particles almost do not lose the kinetic energy after reflection. From the reflected energy distribution for 0.5 eV and 1 eV carbon atoms incident on tungsten surface, we also found that the reflected particles may have energy slightly higher than the incident energy attributed perhaps to the lattice phonon absorption [14]. Fig.…”

“…This means that the surface structure has a pronounced effect on the projectiles' back-scattering behavior. Two types of reflection processes have been observed in this work: (1) direct reflection for the projectiles directly back-scattered after interacting with only a few atoms in the first or second layer; (2) delayed reflection for the projectiles with relatively high kinetic energies that penetrate deep into the bulk, and still flee to the surface, following a temporary residence time [14]. As for the amorphous cell, the random network may act as a labyrinth for the projectiles intruding into it.…”

Atomistic simulation of the interaction of slow protons with an iron surface

“…1 due to particles that gain energy in the interaction with the surface are a fmite-temperature effect already observed in the MD simulation of ref. [3], concerning helium atoms impinging on a nickel surface at T = 500 K, and decrease with increasing incident energy. fig.…”

“…In this work we have performed a computer experiment, analogous to that of ref. [3], devoted to the interaction of helium ions with a nickel surface: it consists in studying the behaviour of a big number of protons thrown on an iron surface, one at a time, and estimating both the main thermodynamic and structural parameters of the lattice and the dynamical properties of the projectiles by means of time averages.…”

Parallel Algorithms for Molecular Dynamics Simulation of Irradiation Effects in Crystals

“…around it. The cutoff R, was <'host'n between the third and fourth order Iwighbors so as to a\oid problems arising from finite temperature simulation in conjunction with short ranl!e interactions [11].…”