Growth and motion of liquid alloy droplets of Au on Ge(1Â 1Â 0)

The growth of low-dimensional nanostructures of Au on Ge(1 1 0) and their temperature-induced motion were observed with Low Energy Electron Microscopy (LEEM). Ge(1 1 0) was dosed with 0.5-4 ML of Au and heated to 850°C. Above 500°C, liquid AuGe eutectic alloy islands grew on the surface. Islands were 0.3-3.0 µm in width, 1-10 µm in length, and elongated in the [11¯0] direction. Above 600°C, islands began moving with speeds of 0.1-1.0 µm/s, absorbing smaller stationary islands upon collision and increasing in size to more than 100 µm in width. A temperature gradient of ∼0.017°C/µm across the sample results in a gradient in the Ge concentration across the islands, inducing their movement in the direction of increasing temperature. Optical microscopy confirmed that the large islands moved from the cooler edges of the sample towards its hotter center. The mechanism for motion of the droplets is discussed, and the island velocities fit well to a model for diffusion-driven motion of the liquid droplet. When the temperature was subsequently lowered, islands became supersaturated with Ge, which crystallized on the island edges.