Silicon nanocrystals of a few nanometers in size are of great interest for optoelectronic applications. Here we present a mini-arc plasma method to produce silicon nanocrystals at atmospheric pressure directly from solid silicon precursors. The product silicon nanocrystals are then assembled onto the external surface of carbon nanotubes (CNTs) to form hybrid nanostructures. The absorption properties of both the silicon nanocrystals and the Si-CNT hybrid structures have been characterized. Quantum size effects have been observed for as-produced silicon nanocrystals. The resulting silicon nanocrystals and hybrid nanostructures are promising for optoelectronic applications.