We comment and discuss the findings and conclusions of a recent theoretical study of the diffraction of He atoms from a monolayer of Xe atoms adsorbed on the graphite (0001) surface [Khokonov et al., Surf. Sci. 496(2002)L13]. By revisiting the problem we demonstrate that all main conclusions of Khokonov et al. that pertain to the studied system are at variance with the available experimental and theoretical evidence and the results of multiple scattering calculations presented in this comment.
We present results of a theoretical study of 4He films adsorbed on graphite, based on the continuous space worm algorithm. In the first layer, we find a domain-wall phase and a (7/16) registered structure between the commensurate (1/3) and the incommensurate solid phases. For the second layer, we find only superfluid and incommensurate solid phases. The commensurate phase found in previous simulation work is only observed if first layer particles are kept fixed; it disappears upon explicitly including their zero-point fluctuations. No evidence of any supersolid phase is found.
We introduce a simple nearest-neighbor spin model with multiple metastable phases, the number and decay pathways of which are explicitly controlled by the parameters of the system. With this model we can construct, for example, a system which evolves through an arbitrarily long succession of metastable phases. We also construct systems in which different phases may nucleate competitively from a single initial phase. For such a system, we present a general method to extract from numerical simulations the individual nucleation rates of the nucleating phases. The results show that the Ostwald rule, which predicts which phase will nucleate, must be modified probabilistically when the new phases are almost equally stable. Finally, we show that the nucleation rate of a phase depends, among other things, on the number of other phases accessible from it.
We overview recent results on intrinsic frictional properties of adsorbed monolayers, composed of mobile hard-core particles undergoing continuous exchanges with a vapor phase. In terms of a dynamical master equation approach we determine the velocity of a biased impure molecule - the tracer particle (TP), constrained to move inside the adsorbed monolayer probing its frictional properties, define the frictional forces exerted by the monolayer on the TP, as well as the particles density distribution in the monolayer.
Grand canonical Monte Carlo simulations have been performed to determine the adsorption behavior of Ar and Kr atoms on the exterior surface of a rope (bundle) consisting of many carbon nanotubes. The computed adsorption isotherms reveal phase transitions associated with the successive creation of quasi-one dimensional lines of atoms near and parallel to the intersection of two adjacent nanotubes.
We present a comparative assessment of the features of inelastic atom-surface scattering spectra that are produced by several different forms of linear and nonlinear phonon coupling to the projectile atom. Starting from a simple theoretical model of atom-surface scattering and employing several recently developed exact numerical and approximate analytical methods we calculate and compare the scattering probabilities ensuing from each form of interaction and from each calculational scheme. This enables us to demonstrate that in the regime of thermal energy atom scattering from surfaces the dominant contributions to the zero-, one- and multi-phonon excitation probabilities obeying unitarity arise from linear coupling treated to all orders in the interaction.
A. Siber
,B. Gumhalter
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(2003)
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"Diffraction of He atoms from Xe monolayer adsorbed on the graphite (0001) revisited: The importance of multiple scattering processes"
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Antonio Siber
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