| 364 |
|
1200~K were performed to confirm the relative |
| 365 |
|
stability of the surfaces without a CO overlayer. |
| 366 |
|
|
| 367 |
< |
The different bulk melting temperatures (1337~K for Au |
| 368 |
< |
and 2045~K for Pt) suggest that any possible reconstruction should happen at |
| 367 |
> |
The different bulk melting temperatures (1337~K for Au\cite{Au:melting} |
| 368 |
> |
and 2045~K for Pt\cite{Pt:melting}) suggest that any possible reconstruction should happen at |
| 369 |
|
different temperatures for the two metals. The bare Au and Pt surfaces were |
| 370 |
|
initially run in the canonical (NVT) ensemble at 800~K and 1000~K |
| 371 |
|
respectively for 100 ps. The two surfaces were relatively stable at these |
| 419 |
|
original (557) lattice. Previous work by Williams et al.\cite{Williams:1991, Williams:1994} |
| 420 |
|
highlights the repulsion that exists between step-edges even |
| 421 |
|
when no direct interactions are present in the system. This |
| 422 |
< |
repulsion exists because the entropy of the step-edges is constrained |
| 422 |
> |
repulsion arises because the entropy of the step-edges is constrained, |
| 423 |
|
since step-edge crossing is not allowed. This entropic repulsion |
| 424 |
|
does not completely define the interactions between steps, |
| 425 |
|
which is why some surfaces will undergo step coalescence, |
| 426 |
|
where additional attractive interactions can overcome the |
| 427 |
< |
repulsion\cite{Williams:1991} and others will not. The presence |
| 428 |
< |
of adsorbates can affect these step interactions, potentially |
| 427 |
> |
repulsion\cite{Williams:1991} and others will not. The presence and concentration |
| 428 |
> |
of adsorbates, as shown in this work, can affect these step interactions, potentially |
| 429 |
|
leading to a new surface structure as the thermodynamic minimum. |
| 430 |
|
|
| 431 |
|
\subsubsection{Double layers} |
| 442 |
|
effect that adsorbate coverage has on edge breakup and on the |
| 443 |
|
surface diffusion of metal adatoms. While both systems displayed |
| 444 |
|
step-edge wandering, only the 50\% Pt surface underwent the |
| 445 |
< |
doubling seen by Tao et al. within the time scales studied here. |
| 446 |
< |
Over longer periods (150~ns) two more double layers formed |
| 445 |
> |
doubling seen by Tao et al.\cite{Tao:2010} within the time scales studied here. |
| 446 |
> |
Over longer periods, (150~ns) two more double layers formed |
| 447 |
|
on this interface. Although double layer formation did not occur |
| 448 |
|
in the other Pt systems, they show more step-wandering and |
| 449 |
|
general roughening compared to their Au counterparts. The |
| 465 |
|
of ignoring the dynamics of the system. Previous experimental work by Pearl and |
| 466 |
|
Sibener\cite{Pearl}, using STM, has been able to capture the coalescing |
| 467 |
|
of steps on Ni(977). The time scale of the image acquisition, |
| 468 |
< |
$\sim$70 s/image provides an upper bound for the time required for |
| 468 |
> |
$\sim$70~s/image provides an upper bound for the time required for |
| 469 |
|
the doubling to occur. In this section we give data on dynamic and |
| 470 |
|
transport properties, e.g. diffusion, layer formation time, etc. |
| 471 |
|
|
| 642 |
|
of Pt atoms was then examined to determine possible barriers. Because |
| 643 |
|
the movement was forced along a pre-defined reaction coordinate that may differ |
| 644 |
|
from the true minimum of this path, only the beginning and ending energies |
| 645 |
< |
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 |
| 645 |
> |
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 |
| 646 |
|
locations can lead to lowered barriers for Pt breaking apart from the step-edge. |
| 647 |
|
Additionally, as highlighted in Figure \ref{fig:lambda}, the presence of CO makes the |
| 648 |
|
burrowing and lifting of adatoms favorable, whereas without CO, the process is neutral |
| 666 |
|
\caption{} |
| 667 |
|
\label{fig:lambdaTable} |
| 668 |
|
\end{figure} |
| 669 |
+ |
|
| 670 |
+ |
|
| 671 |
|
|
| 672 |
+ |
\begin{table}[H] |
| 673 |
+ |
\caption{} |
| 674 |
+ |
\centering |
| 675 |
+ |
\begin{tabular}{| c || c | c | c | c |} |
| 676 |
+ |
\hline |
| 677 |
+ |
\textbf{System} & 0.5~\AA & 2~\AA & 4~\AA & 6~\AA \\ |
| 678 |
+ |
\hline |
| 679 |
+ |
A & 6.38 & 38.34 & 44.65 & 47.60 \\ |
| 680 |
+ |
B & -20.72 & 0.67 & 17.33 & 24.28 \\ |
| 681 |
+ |
C & 4.92 & 27.02 & 41.05 & 47.43 \\ |
| 682 |
+ |
D & -16.97 & 21.21 & 35.87 & 40.93 \\ |
| 683 |
+ |
E & 5.92 & 30.96 & 43.69 & 49.23 \\ |
| 684 |
+ |
F & 8.53 & 46.23 & 53.98 & 65.55 \\ |
| 685 |
+ |
\hline |
| 686 |
+ |
\end{tabular} |
| 687 |
+ |
\label{tab:rxcoord} |
| 688 |
+ |
\end{table} |
| 689 |
|
|
| 690 |
+ |
|
| 691 |
|
\subsection{Diffusion} |
| 692 |
|
The diffusion parallel to the step-edge tends to be |
| 693 |
|
much larger than that perpendicular to the step-edge. The dynamic |
