Stability and mobility of tungsten clusters on tungsten (110) surface: Ab initio and atomistic simulations

Abstract

Quantifying the surface transport properties of tungsten (W) is of prime importance to understand the formation of nano-fuzz in fusion plasma-facing conditions. The stability and mobility of W adatom clusters (Wn, n = 2-9) on the W(110) surface has been investigated by computer simulations, including ab initio calculations using density functional theory (DFT) and molecular statics (MS) simulations with multiple W interatomic potentials. The DFT results demonstrate that the sequential binding energy generally increases with number of W adatoms, except for the 5th and 7th W adatoms. The most common elemental migration steps of Wn (n>2) clusters are observed to consist of monomer and dimer hops, while larger Wn clusters can also diffuse by dissociation and recombination of smaller clusters. The threshold migration energy of W9 is the highest, then followed by W8, W4, and W6, while W3, W5, and W7 have similar migration energies. Compared to DFT, each interatomic potential evaluated overestimates the binding energies of Wn clusters. The embedded-atom potential developed by Juslin and Wirth adequately predicts the threshold migration energy of Wn (n>2) clusters, although it predicts different underlying migration mechanisms. The results show that interaction mechanism between W adatoms controls the stability and mobility of Wn clusters on the W(110) surface.