Fundamentals of Au(111) Surface Dynamics: Coarsening of Two-Dimensional Au Islands

Abstract

Au(111) surfaces play a central role in many applications, yet studies of fundamental aspects of their dynamics are limited. Thus, using Scanning Tunneling Microscopy (STM) at 300 K, we analyze the coarsening of first-layer 2D Au islands directly on the Au(111) substrate, and also of second-layer 2D Au islands. Specifically, we monitor the decay of Au first-layer islands with areas of about 100-500 nm 2 in the vicinity of larger islands or extended step edges over a period of approximately 40 hours-the relevant time scale for this process. Experimentally observed behavior is captured by analytic theory for terrace-diffusion-limited decay incorporating DFT results for the Au terrace diffusion barrier and the adatom formation energy. Experimental observations of second layer island decay were also compared with appropriate analytic theory and stochastic simulations, thereby determining the effective Ehrlich-Schwoebel barrier for Au on Au(111).

Enhanced Nanostructure Dynamics on Au(111) with Adsorbed Sulfur due to Au−S Complex Formation

“…However, significant fluctuations in experimental data (due to the stochastic nature of detachment and attachment events at the island perimeter which underly decay) limit the utility of such an analysis. Additional evidence for TD‐limited OR is provided elsewhere [38] . TD‐limited OR is expected as such behavior is also observed for other coinage metal(111) surfaces in the absence of additives [39–41] .…”

“…We caution that there is some uncertainty in energy estimates from DFT analysis, but one can be confident that Au 4 S 4 and AuS 2 have the lowest E act , well below that for Au. We note that previous analyses [38,43] for Au adatom diffusion on Au(111) have produced E d values somewhat above the 0.10 eV value listed in Table I, and this would lead to an E act value somewhat above 0.75 eV. It might also be noted that the Au 3 S 3 trimer complex purportedly observed by Kurokawa et al [19] .…”

“…A study of Au diffusion on the reconstructed surface just using a semi‐empirical glue potential did find higher diffusion barriers as well as anisotropy compared to unreconstructed Au(111) [42] . However, modeling of coarsening behavior on the sulfur‐free Au(111) surface recovered experimental observations using a low Au diffusion barrier of 0.12 eV corresponding to a bulk terminated surface [38] . Thus, we adopt the view that coarsening is not predominantly affected by the presence or absence of the reconstruction.…”

“…The feature that decay of island area is non‐linear is the classic signature of terrace diffusion (TD) limited OR (as opposed to the linear decay associated with attachment‐limited OR, where there is an additional barrier for attachment). Behavior can be fit by the form A∼(t 0 –t) 2/3 , where t 0 is the time of disappearance [38] . However, significant fluctuations in experimental data (due to the stochastic nature of detachment and attachment events at the island perimeter which underly decay) limit the utility of such an analysis.…”

“…S‐free coarsening of 2D metal (M) islands on M(111) with M=Au, Cu, and Ag always occurs via TD‐limited OR, but with different rates. Thus, shrinking islands of comparable size in similar environments have different survival times [38–41] . Decay of islands for Au is somewhat slower than for Cu, and far slower than for Ag.…”