Coexistence of two diffusion mechanisms: W on W(100)

Abstract

We utilized the field ion microscope and density functional theory to investigate surface diffusion and surface adsorption of W on W(100). We demonstrated experimental proof for the occurrence of the exchange diffusion mechanism on W(100) and its coexistence with adatom jump. From our study it is evident that the primary mechanism of motion is atom exchange which is activated on the time scale of seconds at a temperature of around 650 K and is associated with an activation energy of 1.6 eV. Additionally, at a temperature around 700 K we observe a second surface diffusion mechanism with the activation energy estimated as ß2.1 eV, which we associate with adatom jump. Our findings are in excellent agreement with DFT investigations. We have performed the adsorption-desorption experiments as a method helping with determining the morphology of a W(100) surface.

Efficient and accurate determination of lattice-vacancy diffusion coefficients via non equilibriumab initiomolecular dynamics

“…In this paper, we show that, for cases in which atomic migration takes place over a single energy barrier (assumption typically valid for point-defect diffusion in crystal lattices [18][19][20][21] and adatom dynamics on surfaces [22,23]), equilibrium jump rates can be efficiently retrieved by fitting accelerated rates obtained within a sharply nonlinear jump rate vs force trend. To this aim, the CD algorithm is applied in NE-AIMD simulations of monovacancy jump in bcc Mo, here chosen as a model system.…”

Tungsten migration energy barriers for surface diffusion: a parameterization for KMC simulations

“…Comparing the nontethered NEB calculated barriers in table 1 with DFT values from the literature, listed in the same table, suggest that the interatomic potential by Marinica et al [19] may predict the barriers with up to ∼30% errors, although the order of the barrier values are the same as calculated with DFT. It can also be noted that the Marinica potential does not predict the "zigzag" reconstruction of the W{100} at temperatures below 250 K, which has been observed in experiments and DFT calculations [23][24][25], and would give slightly higher barrier values, as shown in table 1. The potential also slightly underestimate the surface energy of the {100} surface, compared to DFT, as shown in table 3.…”

“…Migration energy barriers for three different processes, calculated with NEB, with and without the use of tethering, and compared to DFT values. The DFT values in parenthesis are calculated for a "zigzag" reconstructed {100} surface, which may occur below 250 K [23][24][25] (see discussion in section 4). The attempt frequencies are estimated from MD diffusion simulations and by the harmonic approximation (HA) of the non-tethered data.…”

Growth mechanism for nanotips in high electric fields

“…In this paper we use a bcc lattice and a W parameterization, described in [49], which includes firstand second-nearest jumps. The parameterization also includes a third-nearest neighbour diagonal exchange process, which has been found important for the {100} surface [49,50].…”