Communication: Diverse nanoscale cluster dynamics: Diffusion of 2D epitaxial clusters

Area of Science:

• Surface science
• Materials science
• Computational physics

Background:

• Continuum formalisms describe macroscale behavior.
• Nanoscale cluster dynamics can deviate significantly from bulk properties.
• Edge atom hopping mediates diffusion in 2D homoepitaxial systems.

Purpose of the Study:

• Investigate the size-dependent diffusion dynamics of 2D nanoclusters.
• Compare nanoscale diffusion behavior with macroscale theoretical predictions.
• Analyze the influence of cluster size and shape on diffusion coefficients.

Main Methods:

• Modeling of nanoclusters on metal(100) surfaces.
• Analysis of diffusion coefficients (D_N) as a function of cluster size (N).
• Examination of nucleation-mediated and nucleation-free diffusion pathways.

Main Results:

• "Perfect" cluster sizes (N_p = L², L(L+1)) exhibit slow, nucleation-mediated diffusion with weak size scaling (β < 1).
• Sizes N_p+1 and N_p+2 show fast, nucleation-free diffusion with strong size scaling (β ≈ 2.5).
• Diffusion coefficients oscillate significantly with cluster size, diverging from monotonic macroscale predictions until N = O(10³).

Conclusions:

• Nanoscale diffusion exhibits unprecedented diversity, strongly size-dependent and oscillating.
• Observed behaviors challenge simple continuum models for small systems.
• Macroscale behavior emerges only for significantly larger cluster sizes (N = O(10³)).