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\begin{figure}[H] |
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\includegraphics[width=\linewidth]{EPS_ProgressionOfDoubleLayerFormation} |
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\caption{The Pt(557) / 50\% CO system at a sequence of times after |
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initial exposure to the CO: (a) 258~ps, (b) 19~ns, (c) 31.2~ns, and |
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(d) 86.1~ns. Disruption of the (557) step-edges occurs quickly. The |
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doubling of the layers appears only after two adjacent step-edges |
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touch. The circled spot in (b) nucleated the growth of the double |
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step observed in the later configurations.} |
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\label{fig:reconstruct} |
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\end{figure} |
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\efloatseparator |
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|
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\begin{figure}[H] |
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\includegraphics[width=\linewidth]{Portrait_DiffusionComparison_1} |
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\caption{Diffusion constants for mobile surface atoms along directions |
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parallel ($\mathbf{D}_{\parallel}$) and perpendicular |
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($\mathbf{D}_{\perp}$) to the (557) step-edges as a function of CO |
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surface coverage. Diffusion parallel to the step-edge is higher |
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than that perpendicular to the edge because of the lower energy |
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barrier associated with traversing along the edge as compared to |
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completely breaking away. The two reported diffusion constants for |
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the 50\% Pt system arise from different sample sets. The lower values |
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correspond to the same 40~ns amount that all of the other systems were |
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examined at, while the larger values correspond to a 20~ns period } |
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\label{fig:diff} |
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\end{figure} |
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\efloatseparator |
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|
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\begin{figure}[H] |
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\includegraphics[width=\linewidth]{COpaths} |
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\caption{Configurations used to investigate the mechanism of step-edge |
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breakup on Pt(557). In each case, the central (starred) atom is |
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pulled directly across the surface away from the step edge. The Pt |
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atoms on the upper terrace are colored dark grey, while those on the |
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lower terrace are in white. In each of these configurations, some |
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number of the atoms (highlighted in blue) had a CO molecule bound in |
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a vertical atop position. The energies of these configurations as a |
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function of central atom displacement are displayed in Figure |
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\ref{fig:SketchEnergies}.} |
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\label{fig:SketchGraphic} |
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\end{figure} |
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\efloatseparator |
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|
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\begin{figure}[H] |
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\includegraphics[width=\linewidth]{Portrait_SeparationComparison} |
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\caption{Energies for displacing a single edge atom perpendicular to |
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the step edge as a function of atomic displacement. Each of the |
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energy curves corresponds to one of the labeled configurations in |
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Figure \ref{fig:SketchGraphic}, and are referenced to the |
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unperturbed step-edge. Certain arrangements of bound CO (notably |
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configurations g and h) can lower the energetic barrier for creating |
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an adatom relative to the bare surface (configuration a).} |
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\label{fig:SketchEnergies} |
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\end{figure} |
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\efloatseparator |
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|
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\begin{figure}[H] |
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\includegraphics[width=\linewidth]{EPS_rxnCoord} |
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\caption{Points along a possible reaction coordinate for CO-mediated |
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edge doubling. Here, a CO-bound adatom burrows into an established |
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step edge and displaces an edge atom onto the upper terrace along a |
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curvilinear path. The approximate barrier for the process is |
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20~kcal/mol, and the complete process is exothermic by 15~kcal/mol |
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in the presence of CO, but is endothermic by 3~kcal/mol without.} |
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\label{fig:lambda} |
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\end{figure} |
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\efloatseparator |
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|
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\begin{figure}[H] |
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\includegraphics[width=\linewidth]{EPS_doubleLayerBreaking} |
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\caption{Dynamics of an established (111) double step after removal of |
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the adsorbed CO: (A) 0~ps, (B) 100~ps, and (C) 1~ns after the removal |
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of CO. The presence of the CO helped maintain the stability of the |
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double step. Nearly immediately after the CO is removed, the step |
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edge reforms in a (100) configuration, which is also the step type |
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seen on clean (557) surfaces. The step separation involves |
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significant mixing of the lower and upper atoms at the edge.} |
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\label{fig:breaking} |
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\end{figure} |
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\efloatseparator |
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