Abstract
Formation of Au nanoparticles on Si bicrystal has been investigated by transmission electron microscopy. The Au nanoparticles were found to form preferentially at the node points of the dislocation network to relieve the strains induced by the dislocations. Surface strain field of substrate with smaller dislocation spacing provides higher particle distribution density and better size uniformity. After annealing at 150 °C, the Au nanoparticles were found to be confined by the dislocation grids. Upon further annealing at 250 °C, small nanoparticles shrank in favor of the large nanoparticles, with a size larger than the critical size, as a manifestation of the classical Oswald ripening process. The shrinkage of Au nanoparticles exhibited a stepped behavior in that clusters shrank by steps of dislocation grids [Chapter 4]. The movement of nanosized Au clusters on Si bicrystal was found to be critically influenced by strained fields of the buried twist-dislocation network by in situ ultrahigh vacuum transmission electronic microscopy (in situ UHV TEM). Collective movement of Au atoms was observed. Most strikingly, clusters of more than three million atoms move concertedly by one dislocation spacing (7–45 nm) within 1/30 s at a substrate temperature of 250 °C. The “jumping” mechanism is attributed to the viscous flow. The observation shall serve as a good reference to refine the theory to realize the control of self-organized nanoparticles on silicon bicrystals [Chapter 5]. Directed movement of Au–Si alloy droplets towards buried dislocation grids on a Si bicrystal has been observed. It was found that once the underlying dislocation structure was dissolved, the movement of Au–Si droplets was directed to the region with remaining dislocation network. The migration of Au–Si droplets is driven by the energy difference between the strained bicrystal and nonstrained single-crystal silicon. The directed movement by the buried dislocation network is potentially significant in a wide range of technologies [Chapter 6]. Influence of heating temperature on the behavior of Au-Si eutectic alloy droplet on silicon bicrystal has been investigated. It was observed that under high heat temperature the droplet had conspicuous high moving velocity, which enhanced by the lower active energy of eutectic reaction. High velocity of droplet leaded to silicon precipitation without enough time, and left a lot amount of gold silicide behind the droplet [Chapter 7].