78 research outputs found
Interpretation of surface diffusion data with Langevin simulations: a quantitative assessment
No full textDiffusion studies of adsorbates moving on a surface are often analyzed using 2D Langevin simulations. These simulations are computationally cheap and offer valuable insight into the dynamics, however, they simplify the complex interactions between the substrate and adsorbate atoms, neglecting correlations in the motion of the two species. The effect of this simplification on the accuracy of observables extracted using Langevin simulations was previously unquantified. Here we report a numerical study aimed at assessing the validity of this approach. We compared experimentally accessible observables which were calculated using a Langevin simulation with those obtained from explicit molecular dynamics simulations. Our results show that within the range of parameters we explored Langevin simulations provide a good alternative for calculating the diffusion procress, i.e. the effect of correlations is too small to be observed within the numerical accuracy of this study and most likely would not have a significant effect on the interpretation of experimental data. Our comparison of the two numerical approaches also demonstrates the effect temperature dependent friction has on the calculated observables, illustrating the importance of accounting for such a temperature dependence when interpreting experimental data
Crucial electronic contributions to measures of surface diffusion by He atom scattering
No full textWe examine theoretically recent He atom scattering measurements of Na/Cu(001), identifying a nontrivial relation between the dynamics of the electron distribution and that of the Na ions. The magnitude of the calculated variations in the charge density, and their dependence on the local density of adsorbates, account for the correlated three-dimensional (3D) motion experimentally observed. The results of this study further highlight the sensitivity of helium scattering to the electron distribution of the sample and point out the role of electronic contributions in high-resolution measures of surface dynamics
Linewidths in bound state resonances for helium scattering from Si(111)-(1x1)H
No full textHelium-3 spin-echo measurements of resonant scattering from the Si(111)–(1 × 1)H surface, in the energy range 4–14 meV, are presented. The measurements have high energy resolution yet they reveal bound state resonance features with uniformly broad linewidths. We show that exact quantum mechanical calculations of the elastic scattering, using the existing potential for the helium/Si(111)–(1 × 1)H interaction, cannot reproduce the linewidths seen in the experiment. Further calculations rule out inelastic and other mechanisms that might give rise to losses from the elastic scattering channels. We show that corrugation in the attractive part of the atom–surface potential is the most likely origin of the experimental lineshapes
A refined He–LiF(001) potential from selective adsorption resonances measured with high-resolution helium spin-echo spectroscopy
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A magnetically focused molecular beam source for deposition of spin-polarised molecular surface layers
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Probing molecule–surface interactions through ultra-fast adsorbate dynamics: propane/Pt(111)
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