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O: Fachverband Oberflächenphysik

O 20: Nanostructures at Surfaces II

O 20.10: Vortrag

Montag, 31. März 2014, 18:15–18:30, WIL B321

Cluster Nucleation and Growth from a Highly Supersaturated 2D Phase: Ag/Fe₃O₄(001) — •Roland Bliem¹, Lukas Perneczky¹, Zbynek Novotny¹, David Fobes², Zhiqiang Mao², Michael Schmid¹, Ulrike Diebold¹, and Gareth Parkinson¹ — ¹Vienna University of Technology, Vienna, Austria — ²Tulane University, New Orleans, Louisiana, USA

The nucleation and growth of Ag clusters at the (√2×√2)R45^∘-Fe₃O₄(001) surface was studied using scanning tunneling microscopy (STM). This surface functions as a robust adsorption template, stabilizing a complete array of Ag adatoms with a nearest-neighbor distance of 0.84 nm to temperatures as high as 670 K. As the coverage exceeds 1 ML, the number of Ag adatoms exceeds the number of available adsorption sites and the system enters a supersaturated state. Cluster nucleation occurs spontaneously at room temperature and, with mild annealing, the nuclei grow at the expense of the surrounding material. This behavior cannot be reconciled with any of the established growth modes. From an analysis of the denuded zones, or “vacancy trails”, associated with each cluster, three distinct growth processes are discerned. Cluster nuclei are mobile and diffuse to step edges, capturing otherwise stable Ag adatoms encountered along their path. With the clusters immobilized, adatom diffusion and capture takes over as the dominant process. Above 720 K, the (√2×√2)R45^∘ reconstruction is lifted, and the system evolves rapidly to large (>10 nm) nanoparticles, consistent with the thermodynamic preference for 3D crystallites.