Single-crystal ZnSe nanowires are grown on a prepatterned gold catalyst by molecular-beam epitaxy. Optimum selectivity and maximum nanowire densities are obtained for growth temperatures in the range 400-450 degrees C, but gold-assisted growth is demonstrated for temperatures as low as 300 degrees C. This suggests a diffusion process onthrough the catalyst particle in the solid state, in contrast to the commonly assumed liquid, pase growth models. Straight wires, as thin as 10 nm, nucleate together with thicker and saw-like structures. A gold particle is always found at the tip in both cases. (C) 2005 American Institute of Physics.