Diffusion of adsorbed particles on surfaces with channeled atomic corrugation
We review experimental data on surface diffusion of electropositive adsorbates (alkali, alkaline-earth and rare-earth elements) on substrates with strongly anisotropic («channeled») atomic corrugation. The substrates were (112) surfaces of tungsten and molybdenum. The adatoms under study form rarefied chain structures at low coverages, dense commensurate structures at medium coverages and uniaxially incommensurate structures at coverages approaching a close-packed monolayer. At sufficiently low temperatures, the adsorbate diffusion on the channeled surfaces has a quasi-one-dimensional character (proceeds actually only along the channels). Its rate is strongly dependent on the coverage and exhibits a pronounced correlation with the phase transitions occurring in the overlayers when the coverage varies. All the adsorbates studied show an enhancement of the diffusion rate in the region of the commensurate-incommensurate phase transition. This feature is ascribed to the operation of a collective mechanism of surface diffusion effected by the movements of domain walls, which separate commensurate domains and have properties of topological solitons. At sub- and superstoichiometric coverages, vacancy and interstitial solitons are formed, respectively. They show different mobilities. We also present experimental results illustrating sensitivity of the diffusion kinetics to surface defects, and anomalous diffusion characteristics observed under some conditions.
KeywordsDomain Wall Surface Diffusion Adsorbed Particle Topological Soliton Coverage Profile
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