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\begin{document} |
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\title{Molecular Dynamics simulations of the surface reconstructions |
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of Pt(557) and Au(557) under exposure to CO} |
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\author{Joseph R. Michalka} |
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\author{Patrick W. McIntyre} |
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\author{J. Daniel Gezelter} |
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\email{gezelter@nd.edu} |
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\affiliation[University of Notre Dame]{251 Nieuwland Science Hall\\ |
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Department of Chemistry and Biochemistry\\ University of Notre |
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Dame\\ Notre Dame, Indiana 46556} |
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\keywords{} |
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\begin{document} |
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%% |
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%Introduction |
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% Experimental observations |
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% Causes of 2_layer reordering in Pt |
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%Summary |
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%% |
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%Title |
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\title{Molecular Dynamics simulations of the surface reconstructions |
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of Pt(557) and Au(557) under exposure to CO} |
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\author{Joseph R. Michalka, Patrick W. McIntyre and J. Daniel |
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Gezelter\footnote{Corresponding author. \ Electronic mail: gezelter@nd.edu} \\ |
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Department of Chemistry and Biochemistry,\\ |
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University of Notre Dame\\ |
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Notre Dame, Indiana 46556} |
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%Date |
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\date{Mar 5, 2013} |
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%authors |
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% make the title |
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\maketitle |
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\begin{doublespace} |
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\begin{abstract} |
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We examine surface reconstructions of Pt and Au(557) under |
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performed until the energy difference between subsequent steps |
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was less than $10^{-8}$ Ry. Nonspin-polarized supercell calculations |
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were performed with a 4~x~4~x~4 Monkhorst-Pack {\bf k}-point sampling of the first Brillouin |
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zone.\cite{Monkhorst:1976,PhysRevB.13.5188} The relaxed gold slab was |
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zone.\cite{Monkhorst:1976} The relaxed gold slab was |
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then used in numerous single point calculations with CO at various |
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heights (and angles relative to the surface) to allow fitting of the |
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empirical force field. |
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\multirow{2}{*}{\textbf{Pt-CO}} & \multirow{2}{*}{-1.9} & -1.4 \bibpunct{}{}{,}{n}{}{,} |
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(Ref. \protect\cite{Kelemen:1979}) \\ |
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& & -1.9 \bibpunct{}{}{,}{n}{}{,} (Ref. \protect\cite{Yeo}) \\ \hline |
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\textbf{Au-CO} & -0.39 & -0.40 \bibpunct{}{}{,}{n}{}{,} (Ref. \protect\cite{TPD_Gold}) \\ |
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\textbf{Au-CO} & -0.39 & -0.40 \bibpunct{}{}{,}{n}{}{,} (Ref. \protect\cite{TPDGold}) \\ |
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\hline |
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\end{tabular} |
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\label{tab:co_energies} |
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1200~K were performed to confirm the relative |
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stability of the surfaces without a CO overlayer. |
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The different bulk melting temperatures (1337~K for Au |
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and 2045~K for Pt) suggest that any possible reconstruction should happen at |
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The different bulk melting temperatures (1337~K for Au\cite{Au:melting} |
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and 2045~K for Pt\cite{Pt:melting}) suggest that any possible reconstruction should happen at |
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different temperatures for the two metals. The bare Au and Pt surfaces were |
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initially run in the canonical (NVT) ensemble at 800~K and 1000~K |
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respectively for 100 ps. The two surfaces were relatively stable at these |
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original (557) lattice. Previous work by Williams et al.\cite{Williams:1991, Williams:1994} |
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highlights the repulsion that exists between step-edges even |
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when no direct interactions are present in the system. This |
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repulsion exists because the entropy of the step-edges is constrained |
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repulsion arises because the entropy of the step-edges is constrained, |
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since step-edge crossing is not allowed. This entropic repulsion |
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does not completely define the interactions between steps, |
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which is why some surfaces will undergo step coalescence, |
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where additional attractive interactions can overcome the |
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repulsion\cite{Williams:1991} and others will not. The presence |
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of adsorbates can affect these step interactions, potentially |
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repulsion\cite{Williams:1991} and others will not. The presence and concentration |
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of adsorbates, as shown in this work, can affect these step interactions, potentially |
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leading to a new surface structure as the thermodynamic minimum. |
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\subsubsection{Double layers} |
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effect that adsorbate coverage has on edge breakup and on the |
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surface diffusion of metal adatoms. While both systems displayed |
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step-edge wandering, only the 50\% Pt surface underwent the |
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doubling seen by Tao et al. within the time scales studied here. |
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Over longer periods (150~ns) two more double layers formed |
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doubling seen by Tao et al.\cite{Tao:2010} within the time scales studied here. |
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Over longer periods, (150~ns) two more double layers formed |
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on this interface. Although double layer formation did not occur |
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in the other Pt systems, they show more step-wandering and |
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general roughening compared to their Au counterparts. The |
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of ignoring the dynamics of the system. Previous experimental work by Pearl and |
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Sibener\cite{Pearl}, using STM, has been able to capture the coalescing |
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of steps on Ni(977). The time scale of the image acquisition, |
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$\sim$70 s/image provides an upper bound for the time required for |
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$\sim$70~s/image provides an upper bound for the time required for |
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the doubling to occur. In this section we give data on dynamic and |
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transport properties, e.g. diffusion, layer formation time, etc. |
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of Pt atoms was then examined to determine possible barriers. Because |
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the movement was forced along a pre-defined reaction coordinate that may differ |
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from the true minimum of this path, only the beginning and ending energies |
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are displayed in Table \ref{tab:energies} with the corresponding beginning and ending reaction coordinates in Figure \ref{fig:lambdaTable}. These values suggest that the presence of CO at suitable |
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are displayed in Table \ref{tab:rxcoord} with the corresponding beginning and ending reaction coordinates in Figure \ref{fig:lambdaTable}. These values suggest that the presence of CO at suitable |
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locations can lead to lowered barriers for Pt breaking apart from the step-edge. |
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Additionally, as highlighted in Figure \ref{fig:lambda}, the presence of CO makes the |
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burrowing and lifting of adatoms favorable, whereas without CO, the process is neutral |
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\caption{} |
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\label{fig:lambdaTable} |
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\end{figure} |
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\begin{table}[H] |
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\caption{} |
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\centering |
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\begin{tabular}{| c || c | c | c | c |} |
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\hline |
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\textbf{System} & 0.5~\AA & 2~\AA & 4~\AA & 6~\AA \\ |
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\hline |
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A & 6.38 & 38.34 & 44.65 & 47.60 \\ |
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B & -20.72 & 0.67 & 17.33 & 24.28 \\ |
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C & 4.92 & 27.02 & 41.05 & 47.43 \\ |
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D & -16.97 & 21.21 & 35.87 & 40.93 \\ |
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E & 5.92 & 30.96 & 43.69 & 49.23 \\ |
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F & 8.53 & 46.23 & 53.98 & 65.55 \\ |
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\hline |
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\end{tabular} |
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\label{tab:rxcoord} |
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\end{table} |
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\subsection{Diffusion} |
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% \end{tabular} |
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% \end{table} |
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\section{Acknowledgments} |
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\begin{acknowledgement} |
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Support for this project was provided by the National Science |
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Foundation under grant CHE-0848243 and by the Center for Sustainable |
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Energy at Notre Dame (cSEND). Computational time was provided by the |
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Center for Research Computing (CRC) at the University of Notre Dame. |
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\end{acknowledgement} |
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\newpage |
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\bibliography{firstTryBibliography} |
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\end{doublespace} |
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%\end{doublespace} |
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%\includegraphics[height=3.5cm]{timelapse} |
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\end{document} |
