Interface-confined mixing and buried partial dislocations for Ag bilayer on Pt(111)

The trigonal strain-relief pattern formed by an Ag bilayer on Pt(111) is a prominent example for dislocation networks and their use as nanotemplates. However, its atomic structure has not been solved. Combining scanning tunneling microscopy, low-energy ion scattering, and x-ray photoelectron diffraction, we demonstrate that, unexpectedly, about 22% of the atoms exchange across the Ag/Pt interface, and that the partial dislocations defining the trigonal network are buried in the Pt interface layer. We present an embedded-atom-method simulation identifying the lowest energy structure compatible with all experimental findings.

Figure 1

(a) STM image showing the coexistence of the 2 ML SP and the pseudomorphic 1 ML after Ag deposition on Pt(111) at RT ($\Theta =1.9$ ML, $V_{\mathrm{t}}=-1.0$ V, $I_{\mathrm{t}}=0.5$ nA, $T_{\mathrm{STM}}=300$ K). (b) Atomic resolution image of the SP ($-5$ mV, 40 nA, 77 K). (c) STM image after annealing to 800 K showing the formation of the TN on 2 and 1 ML Ag regions ($\Theta =1.9$ ML, $-2.0$ V, 0.1 nA, 77 K). (d) Atomic resolution ($dz/dx$) image of the 1 ML Ag region shown in (c) ($-40$ mV, 40 nA, 77 K).

Figure 2

STM images of the 2 ML Ag TN revealing inhomogeneities on the atomic scale (a) $-10$ mV, 15 nA, 77 K and (b) $-1$ mV, 20 nA, 300 K.

Figure 3

(a) LEIS spectra of 2 ML Ag/Pt(111) deposited at RT (SP), after annealing to 800 K (TN), 7 ML Ag/Pt(111) deposited at RT, and pristine Pt(111). (b) LEIS spectra after sputtering of $\approx 0.37$ ML once from SP and once from TN.

Figure 4

XPD patterns of (a) Pt 4$f$ and (b) Ag 3$d$, both from the SP, and (c) Ag 3$d$ from the TN. (c) Comparison between experimental XPD profiles from the SP and TN [azimuths indicated in (b) and (c)] and SSC calculations of 2 ML Ag, of the EAM model of the TN shown in Fig. 5, and of 3 ML Ag.

Figure 5

Optimized structure for the $(25\times 25)$ TN as obtained by EAM calculations. (a) Pt interface layer incorporating Ag clusters highlighted in red. (b) Top Ag layer free of partials and consisting fully of Ag. (c) Cross section of the top six layers along the $\langle 11\overline{2}\rangle$ direction indicated in (b), Ag in red and Pt in green.