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Register a new userAdsorbate-induced substrate relaxation and the adsorbate-adsorbate interaction
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We formulate the theory of the perturbation caused by an adsorbate upon the substrate lattice in terms of a local modification of the interatomic potential energy around the adsorption site, which leads to the relaxation of substrate atoms. We apply the approach to CO chemisorption on close-packed metal surfaces, and show that the adsorbate-adsorbate interaction and a variety of other properties can be well described by a simple model.
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The effects of visible and infrared light on potassium atoms embedded in a nanoporous glass matrix are investigated. Photodesorption by visible light enhances the atomic mobility and causes the formation of metallic nanoparticles. Two different populations of metastable clusters with absorption bands in the near-infrared and infrared are grown as a consequence of illumination. Atoms can move between the two groups through sequences of adsorption/desorption events at the pore surface. Irradiation with infrared light, instead, does not significantly enhance the atomic diffusion inside the pores. However, it induces relevant modifications of the substrate, thus changing its interaction with the assembled clusters. Consequently, infrared light alters the dynamics of the system, affecting also the evolution of non-resonant nanoparticles populations, even after the illumination sequence. These results provide new insights on the photo-induced modifications of the substrate-adsorbate interaction in nano-sized confined systems.
We propose a mechanism to control the interaction between adsorbates on graphene. The interaction between a pair of adsorbates---the change in adsorption energy of one adsorbate in the presence of another---is dominated by the interaction mediated by graphenes pi-electrons and has two distinct regimes. Ab initio density functional, numerical tight-binding, and analytical calculations are used to develop the theory. We demonstrate that the interaction can be tuned in a wide range by adjusting the adsorbate-graphene bonding or the chemical potential.
We present a study of resonant vibrational coupling between adsorbates and an elastic substrate at low macroscopic coverages. In the first part of the paper we consider the situation when adsorbates form aggregates with high local coverage. Based upon our previously published theory, we derive formulas describing the damping rate of adsorbate vibrations for two cases of such aggregation: (i) adsorbates attached to step edges and (ii) adsorbates forming two-dimensional islands. We have shown that damping is governed by local coverage. Particularly, for a wide range of resonant frequencies, the damping rate of adsorbates forming well separated islands is described by the damping rate formula for a periodic overlayer with the coverage equal to the local coverage in the island. The second part of the paper is devoted to facilitating the evaluation of damping rates for a disordered overlayer. The formula describing the damping rate involves the parameter $beta$ which is related to the local density of phonon states at the substrate surface and does not allow a closed-form representation. For substrates of isotropic and cubic symmetries, we have developed a good analytical approximation to this parameter. For a vast majority of cubic substrates the difference between the analytical approximation and numerical calculation does not exceed 4%.
We show that strong coupling between graphene and the substrate is mitigated when 0.8 monolayer of Na is adsorbed and consolidated on top graphene-on-Ni(111). Specifically, the {pi} state is partially restored near the K-point and the energy gap between the {pi} and {pi}* states reduced to 1.3 eV after adsorption, as measured by angle-resolved photoemission spectroscopy. We show that this change is not caused by intercalation of Na to underneath graphene but it is caused by an electronic coupling between Na on top and graphene. We show further that graphene can be decoupled to a much higher extent when Na is intercalated to underneath graphene. After intercalation, the energy gap between the {pi} and {pi}* states is reduced to 0 eV and these states are identical as in freestanding and n-doped graphene. We conclude thus that two mechanisms of decoupling exist: a strong decoupling through intercalation, which is the same as one found using noble metals, and a weak decoupling caused by electronic interaction with the adsorbate on top.
In studies of dynamical systems, helium atoms scatter coherently from an ensemble of adsorbates as they diffuse on the surface. The results give information on the co-operative behaviour of interacting adsorbates and thus include the effects of both adsorbate-substrate and adsorbate-adsorbate interactions. Here, we discuss a method to disentangle the effects of interactions between adsorbates from those with the substrate. The result gives an approximation to observations that would be obtained if the scattering was incoherent. Information from the experiment can therefore be used to distinguish more clearly between long-range inter-adsorbate forces and the short range effects arising from the local lattice potential and associated thermal excitations. The method is discussed in the context of a system with strong inter-adsorbate interactions, sodium atoms diffusing on a copper (111) surface.
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