Incommensurate-commensurate transition via domain wall evaporation in an overlayer

Abstract

A new mechanism is proposed in a two-dimensional system for the transition from an incommensurate phase containing walls of striped symmetry to a commensurate phase via evaporation of the domain walls into a gas of point-like defects (PD). The point-like defect can be a vacancy, interstitial or a composite defect like domain wall loop. The precise nature of the PD is not important in the limit of vanishing DW density. The incommensurate-commensurate transition via domain wall evaporation (DWE transition) occurs under the condition of fixed overlayer coverage, and can be of either first or second order. We study the possible types of the phase diagram in the case of DWE. Experimental examples are discussed. In the case of the second-order DWE transition the domain wall density ρ w behaves near Tc like ρw ∝ (Tc − T ).

Characterizing Surfaces of Garnet and Steel, and Adsorption of Organic Additives

“…This phenomenon is not uncommon for adsorbed layers. 71,72 Preliminary sum frequency generation spectroscopy data, obtained from polished garnet surfaces dosed with DMP-30, BPA, BEHP, and PA, has indicated the presence of adsorbed layers, with molecular conformations consistent with the areas per molecule calculated from the adsorption isotherms on garnet powder described herein. Further studies are planned to investigate the effect of the polishing process on the nature of the garnet surface, and to determine the conformations of the different functional groups in the adsorbed molecules.…”

“…Instead, the saturation coverage is determined by the molecular adsorbed overlayer, with the different organic species considered to adopt different conformations, to pack as closely as the experimental conditions would allow on the substrate surface. This phenomenon is not uncommon for adsorbed layers. , …”

Impurity-induced changes of overlayer symmetry and of phase transitions

“…Both transitions, i.e. melting of the domain wall lattice at T m (l) and complete domain wall evaporation at T e , are predicted to be functions of the domain wall lattice period l [10,19]. For melting of three and more sublattices, T m (l) always has a finite limit when l → ∞.…”

“…For the interpretation of our experimental data that two successive phase transitions occur, namely continuous melting of the domain wall lattice followed evaporation of the domain walls into point-like defects, it is instructive to make a comparison with theoretical considerations. The thermodynamics of the coexistence of point defects and domain walls at constant particle concentration have been studied by us earlier [19]. For the domain wall evaporation mechanism a dependence of the inverse average wall distance, l, on temperature below T e , the transition temperature to the phase free of domain walls,…”

Pokrovsky-Talapov commensurate-incommensurate transition in the CO/Pd(100) system

“…16 Chemisorbed systems are very often governed by sharp domain walls; 17,18 however, it is often impossible to control the chemical potential, which renders a direct comparison between theory and experiment rather difficult. In the recent past, a different mechanism of a CIT via domain wall evaporation has been discussed for several chemisorbed systems like Ba/Mo͑110͒, Te/Mo͑110͒, and S/Ru͑0001͒, 19 which under certain circumstances renders the transition first order. Chiral transitions have been observed for the pϭ3 case for Si͑113͒ ͑Refs.…”