Sputtering Of Dimers Research Articles

Atomistic simulations of Be irradiation on W: mixed layer formation and erosion

In the recent ITER-Like Wall experiment at JET, tungsten (W) and beryllium (Be) are used as the first wall plasma-facing materials. Due to the plasma–wall interactions, these materials will erode, be transported, re-deposit and mix. We present the first computational, atomistic, systematic study on the W–Be material mixing under fusion-relevant conditions. To this end, W surfaces were irradiated by Be, varying the impacting energy and angle, followed by annealing the mixed W–Be layers. At low energies, a Be layer is deposited on W, suppressing the W erosion. The materials mix as the W atoms migrate towards the Be layer due to the heat of mixing. Be2 and BeW molecules eroded, both physically (dimer sputtering) and chemically (sputter etching). All the mixed layers show an underlying hcp-like Be structure and the Be : W ratios are close to those in the intermetallic phases (Be2W—Be12W). However, no crystalline alloy structure formed, even after annealing. Further, we present a geometrical model for the angular dependence of the Be reflection, which strongly affects the W sputtering.

Comments on “Sputtering of dimers off a silicon surface” by M.I. Nietiadi et al.

The conclusions in a recent paper by Nitiadi et al. on the sputtering of neutral Si-dimers are critically commented.

Sputtering of dimers off a silicon surface

We present experimental and molecular-dynamics simulation results of the sputtering of a Si surface by 2keV Ar ions. Results on both the monomer and dimer distributions are presented. In simulation, these distributions follow a generalized Thompson law with power exponent n=2 and n=3, respectively. The experimental data, obtained via plasma post-ionization in an SNMS (secondary neutral mass spectrometry) apparatus, show good agreement with respect to the dimer fraction, and the relative energy distributions of dimers and monomers. The consequences for the dimer sputtering mechanism are discussed.

A molecular dynamics study of ion-induced defects on a silicon stepped surface

Computer simulations of the type molecular dynamics (MD) are used to study the effects of a secondary generation of recoils on a silicon stepped surface. Dimers and subsurface atoms are displaced with a low kinetic energy ( E k⩽10 eV) and the evolution of the irradiated region is simulated with classical MD using standard three-body potentials. Two main types of defects have been found. These are vacancies, generated by sputtering of dimers and of second layers atoms, and interstitials due to the displacements of third-layer atoms. The dependence of these defects on the structural properties of the surface and the effects of E k and of the lattice temperature have been analyzed.

Theoretical energy distributions of atoms sputtered from elastic collision spikes by monomer and dimer ion bombardment

The energy spectra of atoms sputtered from metal targets by bombardment with heavy monomer and dimer ions have been investigated on the basis of a standard model for elastic collision spikes. In particular we calculated the energy distributions for a Au sample bombarded by 4 keV I+ and 8 keV I 2 + ions. The results were compared with the recent time of flight measurements performed by de Vries and coworkers. It was shown that the model described accurately most of the experimental observations: the count rates and the relative cascade to spike ratios for both I+ and I 2 + projectiles, and the energy spectrum for dimer sputtering. The spectrum for monomer bombardment, however, was shifted towards lower energies in comparison to the experimental one. The possible source of this discrepancy is discussed.

On the energy distribution of sputtered clusters

Abstract Our previous model on dimer sputtering is extended to the formation of larger clusters. The general formalism for the calculation of the momentum distribution function of these clusters is given. A simple analytical expression is obtained for the distribution function of any cluster in the high energy limit. Comparison of this expression with experimental data on the energy and angle distribution of Wk + clusters at high energies shows good agreement. The experimental results on K2 and KI sputtering with low energies are recompared with the theory. For the ionic crystal KI, evidence is obtained that sputtering of non adjacent K and I atoms from the lattice gives an important contribution to dimer formation. The role of the binding energy Eb , of the particles with respect to the surface is discussed.