Anomalous Fast Dynamics of Adsorbate Overlayers near an Incommensurate Structural Transition

Abstract

We investigate the dynamics of a compressively strained adsorbed layer on a periodic substrate via a simple two-dimensional model that admits striped and hexagonal incommensurate phases. We show that the mass transport is superfast near the striped-hexagonal phase boundary and in the hexagonal phase. For an initial step profile separating a bare substrate region (or ''hole'') from the rest of a striped incommensurate phase, the superfast domain wall dynamics leads to a bifurcation of the initial step profile into two interfaces or profiles propagating in opposite directions with a hexagonal phase in between. This yields a theoretical understanding of the recent experiments for the Pb=Sið111Þ system.

Mass transport of adsorbates near a discontinuous structural phase transition

“…3 and the time evolution of the radius of the expanding HoI-SI interface in Fig. 4 are qualitatively consistent with MD simulations of an atomistic model 7 and with experimental observations for the Pb/Si(111) system 8 . A sign of the decay of the HoI region at long times could be the partial recovery of density in the hexagonal phase found in the experiment.…”

“…It focuses on the domain wall pattern and not the density variation inside the commensurate domains at a microscopic scale. It shares with the conventional PFC model the advantage that numerical work can be performed for system sizes orders of magnitude larger than in microscopic MD simulation studies 7 . Our results for the mass transport mechanism are qualitatively similar to the previous MD work of an atomistic model 7 .…”

“…It shares with the conventional PFC model the advantage that numerical work can be performed for system sizes orders of magnitude larger than in microscopic MD simulation studies 7 . Our results for the mass transport mechanism are qualitatively similar to the previous MD work of an atomistic model 7 . Taken together, they clearly demonstrate that the essential ingredient for the mass transport with a bifurcation of the initial profile is the presence of two incommensurate phases with a first order transition between the two incommensurate phases involving a discontinuity in the coverage.…”

“…The most striking feature of this system is that the observed rate of island growth implies a rate of mass transport orders of magnitude faster than that from the usual atomic diffusion mechanism [2][3][4] . Theoretical models [5][6][7] indicate that domain wall motion in an incommensurate phase can provide the basic mechanism for such fast dynamics. This anomalous fast mass transport dynamics was subsequently confirmed in another experimental study following the refilling of a hole region in the adsorbate layer in real time 8 .…”

C60-induced Devil's Staircase transformation on a Pb/Si(111) wetting layer

“…Although theoretical models with long-range elastic interaction included have studied some aspects of the pattern formation 15 and collective diffusion 16 in this compressed 2D system, essential information about the atomic level energy landscape in terms of single vs. multi-atom processes is still lacking.…”