Coarsening phenomena of metal nanoparticles and the influence of the support pre-treatment: Pt/TiO2(110)

• Published in: Surface science Vol. 606; no. 11-12; pp. 908 - 918
• Main Authors: Behafarid, F., Roldan Cuenya, B.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.06.2012; Elsevier
• Subjects: Coarsening; Computer simulation; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion; Diffusion-coalescence; Exact sciences and technology; Nanoparticle; Nanoparticles; Ostwald ripening; Physical vapor deposition; Physics; Platinum; Sintering; Sintering simulation; STM; TiO2; Titanium dioxide; Ostwald ripening; Platinum; Nanoparticle; Sintering simulation; Diffusion-coalescence; STM; Coarsening; TiO2; Inorganic compounds; Transition element compounds; Surface diffusion; Nanoparticles; 110; Scanning tunneling microscopy; Simulation; Sintering; Transition elements; TiO; Coalescence; Diffusion; Titanium oxide
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2012.01.022

One of the technologically most important requirements for the application of oxide-supported metal nanoparticles (NPs) in the fields of molecular electronics, plasmonics, and catalysis is the achievement of thermally stable systems. For this purpose, a thorough understanding of the different pathways underlying thermally-driven coarsening phenomena, and the effect of the nanoparticle synthesis method, support morphology, and degree of support reduction on NP sintering is needed. In this study, the sintering of supported metal NPs has been monitored via scanning tunneling microscopy combined with simulations following the Ostwald ripening and diffusion-coalescence models. Modifications were introduced to the diffusion-coalescence model to incorporate the correct temperature dependence and energetics. Such methods were applied to describe coarsening phenomena of physical-vapor deposited (PVD) and micellar Pt NPs supported on TiO2(110). The TiO2(110) substrates were exposed to different pre-treatments, leading to reduced, oxidized and polymer-modified TiO2 surfaces. Such pre-treatments were found to affect the coarsening behavior of the NPs. No coarsening was observed for the micellar Pt NPs, maintaining their as-prepared size of ~3nm after annealing in UHV at 1060°C. Regardless of the initial substrate pre-treatment, the average size of the PVD-grown NPs was found to increase after identical thermal cycles, namely, from 0.5±0.2nm to 1.0±0.3nm for pristine TiO2, and from 0.8±0.3nm to 1.3±0.6nm for polymer-coated TiO2 after identical thermal treatments. Although no direct real-time in situ microscopic evidence is available to determine the dominant coarsening mechanism of the PVD NPs unequivocally, our simulations following the diffusion-coalescence coarsening route were in significantly better agreement with the experimental data as compared to those based on the Ostwald-ripening model. The enhanced thermal stability of the micellar NPs as compared to the PVD clusters might be related to their initial larger NP size, narrower size distribution, and larger interparticle distances. [Display omitted] ► Coarsening of Pt NPs on TiO2 is studied and simulated for three different systems. ► Modifications in the diffusion coalescence model: correct temperature dependence. ► Physically meaningful energetics for adatom formation in NPs is incorporated. ► More efficient simulation methods for coarsening phenomena are described. ► Diffusion-coalescence was found to be the dominant coarsening pathway for evaporated NPs.