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Microscopic diffusion processes of NO on the Pt(997) surface
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10.1063/1.2822136
/content/aip/journal/jcp/128/5/10.1063/1.2822136
http://aip.metastore.ingenta.com/content/aip/journal/jcp/128/5/10.1063/1.2822136

Figures

Image of FIG. 1.
FIG. 1.

(a) A schematic drawing of the Pt(997) surface. (b) A lattice used in the present KMC simulations. Circles of thin lines represent the fcc- and hcp-hollow sites of the terrace, and those of heavy lines represent the bridge sites of the step, respectively. The coordinates of points on the terrace and the step are represented by and , respectively. and are the Cartesian coordinates on a terrace; is 0 (fcc site) or 1 (hcp site). is used to distinguish the terraces. For example, the points labeled “A” and “B” in the lattice are represented as (1, 4, 1, 0) and (3, 0), respectively. One terrace is formed by the points of . In this study, the KMC simulations were performed with a lattice of points with a periodic boundary condition.

Image of FIG. 2.
FIG. 2.

Two models of potential energy shape in the KMC simulation. Sites 1 and 2 are hollow sites of the terrace and 3 is a bridge site of the step, respectively. is the rate constant to migrate from a hollow site to a neighbor hollow site on the terrace. (a) A Schematic drawing of the Pt(997) surface around the step and the potential energy surface with Schwoebel barrier . [(b) and (c)] Two models of the potential energy surface for the present KMC simulation. In the models, the rate constant from 2 to 3 is assumed to be the same as that on the terrace, while that from 1 to 3 is also assumed to be the same as that on the terrace [; (b) model A] or zero [; (c) model B]. On the terrace, the same value of the rate constant is assigned to each direction.

Image of FIG. 3.
FIG. 3.

IRAS spectra of 0.017 ML NO on Pt(997) as a function of heating temperature. (a) A spectrum after a NO gas injection at . (b) After heating the substrate to and cooling down to . (c) After heating the substrate to and cooling down to .

Image of FIG. 4.
FIG. 4.

A series of TR-IRAS spectra of NO on Pt(997) after a NO gas injection. (coverage: 0.02 ML; temperature: ).

Image of FIG. 5.
FIG. 5.

The change of the fractional coverage of each NO species in Fig. 4 as a function of the elapsed time (coverage: 0.02 ML; temperature: ): dots—OT species; cross—HT species; triangles—BS species; lines—fitted lines based on the first order kinetics. In this result, and were 0.0056 and 0.89, respectively.

Image of FIG. 6.
FIG. 6.

An Arrhenius plot of the hopping process from on-top sites. In all of the measurements in the plot, the coverage is about 0.02 ML. From the gradient and intercept of the linear fitting line, the activation barrier and the preexponential factor are estimated to be and , respectively.

Image of FIG. 7.
FIG. 7.

IRAS spectra of 0.026 ML NO on Pt(997) as a function of heating temperature. (a) After a NO gas injection at . (b) After heating the substrate to and cooling down to . (c) After heating the substrate to and cooling down to .

Image of FIG. 8.
FIG. 8.

A result of multipeak fitting for the peak of the BS species in Fig. 7(b) by Voigt function. The top of each component is located at 1623 and , respectively.

Image of FIG. 9.
FIG. 9.

A series of TR-IRAS spectra of NO on Pt(997) after a NO gas injection (coverage: 0.017 ML; temperature: ).

Image of FIG. 10.
FIG. 10.

The change of the fractional coverage of each NO species in Fig. 9 as a function of the elapsed time (coverage: 0.017 ML; temperature: ): dot—HT species; triangle—BS species; lines—fitted lines based on the KMC simulation. (a) Model A. (b) Model B.

Image of FIG. 11.
FIG. 11.

The change of the fractional coverage of each NO species as a function of the elapsed time (coverage: 0.05 ML; temperature: ): dot—HT species; triangle—BS species; lines—fitted lines by the KMC simulation. (a) Model A. (b) Model B.

Image of FIG. 12.
FIG. 12.

An Arrhenius plot of the hopping process from hollow sides. The coverage range is from 0.012 to 0.055 ML. From the gradient and intercept of the fitting line, the activation barrier an the preexponential factor are estimated at and , respectively.

Image of FIG. 13.
FIG. 13.

IRAS spectra of 0.027 ML NO on Pt(997) as a function of the heating temperature. NO molecules were adsorbed at . In each spectra, the measurements were carried out in the indicated temperature.

Image of FIG. 14.
FIG. 14.

Probable diffusion routes to the bridge site of the upper step. Route A: From the upper terrace; route B: from the lower terrace. The starting point is set at an on-top site in this figure as an example. : These adsorption energies are taken from Ref. 18.

Tables

Generic image for table
Table I.

Abbreviated expressions for NO molecules at the adsorption sites. For example, the abbreviation “HT” means hollow sites of the terrace. : Hollow sites of the terrace contain fcc and hcp sites, but they are assumed to be identical in this study. Therefore in this table, hopping parameters, which relate to the hollow sites, are the average between the fcc and hcp sites.

Generic image for table
Table II.

The fitting parameters of the KMC simulations of model A with experimental results in the temperature range from 100 to . is the interaction energy between HT species; is the probability that NO is on the step at .

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/content/aip/journal/jcp/128/5/10.1063/1.2822136
2008-02-05
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Microscopic diffusion processes of NO on the Pt(997) surface
http://aip.metastore.ingenta.com/content/aip/journal/jcp/128/5/10.1063/1.2822136
10.1063/1.2822136
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