We have investigated growth of nanocarbon materials from Au nanoparticle catalysts. Site- and size-controlled Au nanoparticles are formed using atomic steps of a Si surface as templates. Au nanoparticles act as catalysts for chemical-vapor-deposition growth of single-walled carbon nanotubes or carbon nanowires (CNW), depending on the particle size. CNW growth is consistent with the well-known VLS (Vapor-Liquid-Solid) mechanism for semiconductor nanowires, demonstrating that nanocarbon materials grow from liquid Au-C eutectic alloy nanoparticles.