The development of epitaxy of nanoclusters on lattice-mismatched substrates: Ag on H-Si(1 1 1) surfaces

This study examines the development of epitaxy of nanometer-sized clusters on highly mismatched crystalline substrates. As-grown Ag clusters on hydrogen-terminated Si(1 1 1) surfaces are characterized by high-resolution electron imaging and diffraction. The results show that Ag clusters grow along [1 1 1] normal to the substrate. Small clusters are randomly oriented in the azimuthal direction with a distribution of ∼9°. At the critical size of ∼12 nm in average diameter, Ag clusters become epitaxially oriented with [110]Ag∥[110]Si. At this orientation, the Ag cluster has a buried interface of a 4 × 4 coincidence lattice with Si, and clusters are strained with ε = -0.32%. The epitaxy coincides with the transition from the initial droplet growth to the fractal coalescence of small Ag clusters, which suggests that epitaxy is formed during coalescence. The late development of epitaxy is qualitatively interpreted based on an extended rigid interface model.