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Atomistic modeling of the directed-assembly of bimetallic Pt-Ru nanoclusters on Ru(0001)-supported monolayer graphene
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10.1063/1.4798348
/content/aip/journal/jcp/138/13/10.1063/1.4798348
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/13/10.1063/1.4798348

Figures

Image of FIG. 1.
FIG. 1.

Schematics showing various regions within the MLG/Ru(0001) moiré cell: (a) superimposed on an STM image of MLG. Reprinted with permission from A. L. V. de Parga, F. Calleja, B. Borca, M. C. G. Passeggi, Jr., J. J. Hinarejos, F. Guinea, and R. Miranda, Phys. Rev. Lett. 100, 056807 (2008). Copyright 2008 American Physical Society; (b) Indicating the coordinate system used to describe the adsorption energy below.

Image of FIG. 2.
FIG. 2.

Experimental data for the filling factor (FF) versus coverage θ: (a) Pt deposition on MLG/Ru(0001) at T = 309 K; (b) Ru deposition on MLG/Ru(0001) at T = 305 K. Plots show that FF3 is roughly proportional to θ. Deposition fluxes F are in the range 0.01–0.1 ML/min.

Image of FIG. 3.
FIG. 3.

1D schematic of the form of the variation of the adsorption energy, E ads, across the MLG/Ru(0001) moiré cell (shown in Fig. 1(b) ) which was incorporated into our model. The fine-scale variation is shown by a highly oscillatory thin curve. The 2D coarse variation of the adsorption energy at adsorption sites (green dashed curve) is described by in the small triangle corresponding to 1/6 of the fcc half moiré cell with x- and y-axes shown in Fig. 1(b) , and by in 1/6 of the hcp half moiré cell. The adsorption energy at the transition state for hopping between adsorption sites, E TS (red dashed curve), is assumed to be elevated above these values by a fixed amount, E d0.

Image of FIG. 4.
FIG. 4.

Dependence of FF on basic model parameters, E d0 and Δ = δ. A contour is shown for constant FF = 0.21 in the E d0-Δ plane evaluated for T = 307 K, flux F = 0.034 ML/min, and θ = 0.05 ML. The direction of greatest increase of FF is also shown.

Image of FIG. 5.
FIG. 5.

Dependence of FF on Δ = δ for various E d0. Other parameters: F = 0.034 ML/s, T = 307 K, θ = 0.05 ML. The horizontal line denotes the experimental FF value for Pt. The non-monotonic increase of FF for small values of decreasing Δ (evident for larger E d0) corresponds to the onset of NC nucleation in hcp regions (as well as in fcc regions).

Image of FIG. 6.
FIG. 6.

(a) and (b) STM images of NC distributions for Pt deposition followed by Ru deposition (Ru@Pt) under conditions described in the text. Image size: 35 × 35 nm2. (c) and (d) KMC simulation of NC distributions for Pt deposition followed by Ru deposition (Ru@Pt) under conditions described in the text. Image size: 89 × 53 nm2. Pure Pt (Ru) NCs are green (red), and mixed NCs have a green core and red ring.

Image of FIG. 7.
FIG. 7.

Ru@Pt deposition process. (a) Size distributions for the Pt NCs after Pt deposition, and both pure Ru and mixed NCs after Ru deposition. Inset: schematic of NC formation. (b) Joint probability distribution for mixed NCs with various numbers of Pt and Ru atoms. Red (blue) denotes higher (lower) population as indicated in the scale. (c) Distribution of Ru atoms in mixed NCs.

Image of FIG. 8.
FIG. 8.

NC height distributions FF(h): (a) Experimental distribution after Pt and after Ru@Pt deposition. (b) Corresponding KMC results where in bars for Ru@Pt indicate separate contributions from mixed and pure Ru NCs.

Image of FIG. 9.
FIG. 9.

(a) and (b) STM images of NC distributions Ru deposition followed by Pt deposition (Pt@Ru) under conditions described in the text. Image size: 35 × 35 nm2. (c) and (d) KMC simulation of NC distributions Ru deposition followed by Pt deposition (Pt@Ru) under conditions described in the text. Image size: 89 × 53 nm2. Pure Ru (Pt) NCs are red (green), and mixed NCs have a red core and green ring.

Image of FIG. 10.
FIG. 10.

Pt@Ru deposition process. (a) Size distributions for Ru NCs after Ru deposition; and both pure Pt and mixed NCs after Pt deposition. Inset: schematic of NC formation. (b) Joint probability distribution for mixed NCs with various numbers of Pt and Ru atoms. Red (blue) denotes higher (lower) population as indicated in the scale. (c) Distribution of Pt atoms just in mixed NCs.

Image of FIG. 11.
FIG. 11.

NC height distributions, FF(h): (a) Experimental distribution after Ru and after Pt@Ru deposition. (b) Corresponding KMC results where in bars for Pt@Ru indicate separate contributions from mixed and pure Pt NCs.

Image of FIG. 12.
FIG. 12.

Quasi-continuous and corresponding discrete atomic-layer height distributions for pure Ru NCs with a Ru coverage of 0.12 ML and a FF of 47%.

Tables

Generic image for table
Table I.

Experimental data for FF and FF(h) for pure Pt, pure Ru, and mixed Pt-Ru NCs. The NC height h = 1, 2, 3, … (in unit of layers).

Generic image for table
Table II.

Results from KMC simulations for FF mimicking the experimental deposition procedure. The top two rows describe the deposition first of Pt followed by that of Ru (Ru@Pt). The bottom five rows describe the deposition first of Ru followed by that of Pt (Pt@Ru). Actually for Pt@Ru, in both experiment and KMC simulation, the initial deposition of Ru was performed in increments: the first 0.030 ML deposited at a lower flux of 0.0085 ML/min, and the last 0.012 ML at the higher flux given in the table.

Generic image for table
Table III.

DFT values of adsorption energies E ads(fcc) and E ads(hcp) (in eV) at fcc and hcp sites and their differences for an isolated Pt or Ru adatom on Pt(111) or Ru(0001) surface. Parameters for the DFT analysis using the VASP code: 43–45 2 × 2 supercell, 10 ML substrate, 19 × 19 k-mesh, updated PAW-PBE potentials. 46 For more computational details about DFT calculations of adsorption energy, see our previous work. 47

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/content/aip/journal/jcp/138/13/10.1063/1.4798348
2013-04-01
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Atomistic modeling of the directed-assembly of bimetallic Pt-Ru nanoclusters on Ru(0001)-supported monolayer graphene
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/13/10.1063/1.4798348
10.1063/1.4798348
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