Non-equilibrium effects in profile evolution measurements of surface diffusion

Nikunen, P.; Vattulainen, Ilpo; Ala-Nissilä, Tapio

doi:10.1016/s0039-6028(99)01204-2

Cited by 17 publications

(18 citation statements)

References 27 publications

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“…The results are then compared with the full spreading case where the initial coverage ϭ1. 26 We find that while nonequilibrium effects are still clearly present, D C ( ) as determined from the partial spreading case approaches its asymptotic equilibrium behavior much more rapidly than in the case of full spreading. We also find that the spreading and diffusion rates in directions parallel and perpendicular to rows of ogygen atoms are significantly different within the ordered p(2ϫ1) phase.…”

Section: Introductionmentioning

confidence: 64%

“…29 In the present study we concentrate on the coverage dependence of D C at a temperature of Tϭ590 K to allow direct comparison to the equilibrium results for D C ( ), 27,28 and to results obtained from Boltzmann-Matano analysis of full spreading. 26 At T ϭ590 K, starting from the coverage ϭ 1 2 corresponding to the ideal p(2ϫ1) phase, the system undergoes a continuous phase transition around Ϸ0.37 to a disordered ͑DO͒ phase at low coverages. 30 We wish to emphasize that the model has been extensively studied, and a complete set of equilibrium data for diffusion coefficients and other relevant quantities at various temperatures can be found elsewhere.…”

Section: Model and Methodsmentioning

confidence: 99%

“…We have recently shown 26 through Monte Carlo simulations of a lattice-gas model of O/W͑110͒ that nonequilibrium effects can play a noticeable role under conditions where there are several ordered phases present at different coverages. In Ref.…”

Section: Introductionmentioning

confidence: 99%

“…In Ref. 26, we focused on the temporal behavior of D C ( ) as the system approaches equilibrium starting from a step function density profile at a full initial coverage of ϭ1. We demonstrated that the effective D C ( ) and the corresponding diffusion barriers obtained in this fashion depend strongly on the time regime chosen for analysis of the density profiles, and may deviate significantly from results obtained from equilibrium simulations especially within ordered phases and close to phase transition boundaries.…”

Section: Introductionmentioning

confidence: 99%

“…This is essentially due to the interplay between spreading and phaseordering kinetics, and is manifested in the particle number fluctuations that differ significantly from their equilibrium value. 26 In the present work, we consider the influence of nonequilibrium effects in partial spreading experiments where the initial coverage is less than unity. In particular, we consider the temporal behavior of the effective collective diffusion coefficient D C ( ) within and below the ideal p(2ϫ1) phase in the lattice-gas model of O/W͑110͒.…”

Section: Introductionmentioning

confidence: 99%

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Density profile evolution and nonequilibrium effects in partial and full spreading measurements of surface diffusion

Nikunen

Vattulainen

Ala-Nissilä

2001

The Journal of Chemical Physics

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We study the nature of nonequilibrium effects in the collective diffusion coefficient DC(θ) vs the coverage θ as extracted from Boltzmann–Matano analysis of spreading coverage profiles. We focus on the temporal behavior of the profiles and study how the corresponding nonequilibrium effects in DC(θ) depend on the initial density gradient and the initial state from which the spreading starts. To this end, we carry out extensive Monte Carlo simulations for a lattice-gas model of the O/W(110) system. Studies of submonolayer spreading from an initially ordered p(2×1) phase at θ=12 reveal that the spreading and diffusion rates in directions parallel and perpendicular to rows of oxygen atoms are significantly different within the ordered phase. Aside from this effect, we find that the degree of ordering in the initial phase has a relatively small impact on the overall behavior of DC(θ). Also, although we find that nonequilibrium effects are clearly present in submonolayer spreading profiles, DC(θ) determined from such data approaches its asymptotic equilibrium behavior much more rapidly than in the case of full spreading. Nevertheless, in both cases there are noticeable deviations from equilibrium results that persist even at very long times and are strongest in ordered phases and in the vicinity of phase boundaries. These conclusions are confirmed by complementary studies of the temporal behavior of the order parameter φ(θ). Finally, we use DC(θ) and φ(θ) to determine the locations of phase boundaries and find such data to be clearly time dependent during full spreading. We conclude that nonequilibrium effects seem to be an inherent feature in profile evolution studies of surface diffusion in all cases where ordering plays a prominent role. This warrants particular care to be taken with profile spreading experiments.

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Section: Introductionmentioning

confidence: 64%