Electronic and structural study of Pt-modified Au vicinal surfaces: a model system for Pt–Au catalysts

Abstract

Two single crystalline surfaces of Au vicinal to the (111) plane were modified with Pt and studied using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in ultra-high vacuum environment. The vicinal surfaces studied are Au(332) and Au(887) and different Pt coverage (θPt) were deposited on each surface. From STM images we determine that Pt deposits on both surfaces as nanoislands with heights ranging from 1 ML to 3 ML depending on θPt. On both surfaces the early growth of Pt ad-islands occurs at the lower part of the step edge, with Pt ad-atoms being incorporated into the steps in some cases. XPS results indicate that partial alloying of Pt occurs at the interface at room temperature and at all coverage, as suggested by the negative chemical shift of Pt 4f core line, indicating an upward shift of the d-band center of the alloyed Pt. Also, the existence of a segregated Pt phase especially at higher coverage is detected by XPS. Sample annealing indicates that the temperature rise promotes a further incorporation of Pt atoms into the Au substrate as supported by STM and XPS results. Additionally, the catalytic activity of different PtAu systems reported in the literature for some electrochemical reactions is discussed considering our findings.

Promotion Effect of Platinum on Gold’s Reactivity: A High-Resolution Photoelectron Spectroscopy Study

“…Figure 4 shows a sphere model of the Pt/Au(332) surface structure with different scenarios that may arise upon Pt deposition on Au(332) depending on the Pt surface loading. For instance, at very low coverage, the incoming Pt atoms can be exchanged with Au atoms both in the terrace and at the step edge, with the more favorable position being the step edge position due to the uncoordinated nature of these type of atoms, as we were able to corroborate with STM 16 . Thus, the displaced Au atoms begin to form 2D agglomerates where new Pt atoms can condense, forming nanoislands of mixed composition.…”

“…The effect of adding Pt on Au(332) is a transition from monolayer (ML) to bilayer (BL) heights of the nanoislands, as demonstrated by us in a previous report using scanning tunnelling microscopy 16 . Thus, component 2 could be ascribed to the topmost atomic layer of bi-layered nanoislands, with the atomic layer beneath being responsible for component 1.…”

“…The morphology of the Pt/Au(332) surface was studied and recently reported in a previous paper 16 . In that report we showed that the growth of Pt nanostructures proceeds via an island formation mechanism.…”

Efficient Plasmon-Mediated Energy Funneling to the Surface of Au@Pt Core–Shell Nanocrystals

“…The above picture of the surface is consistent with prior studies of Pt deposition on Au substrates. At low coverage, Pt is known to form 2D islands on Au, 88 with Pt embedded in the surface and subsurface layer to form a bimetallic interface. [88][89][90]91,92 Scanning tunneling microscopy of Pt evaporated on Au (111) shows that Pt embeds in the surface layer at ϑ < 0.03, and forms alloyed islands above this coverage with the Pt concentration of the islands increasing to 50% by the point of island coalescence.…”

Methanol oxidation on Au(332): an isothermal pulsed molecular beam study

“…Previous structural investigations have shown that the steps may contain kinks depending on the crystal miscut. 24 On this surface, pulsed molecular beam (MB) experiments under well-defined single collision conditions are conducted to investigate the kinetics of the methanol oxidation under isothermal conditions. As gold single crystal surfaces cannot activate molecular oxygen under ultra-high vacuum conditions, pulses of atomic oxygen supplied by a thermal cracker were used to allow for the oxidation reactions.…”