The present invention provides nanowires which are substantially straight and substantially free of nanoparticles and methods for making the same The nanowires can be made by seeded approaches, wherein nanocrystals bound to a substrate are used to promote growth of the nanowire. Nanocrystals in solution may also be used to make the nanowires of the present invention. Supercritical fluid reaction conditions can be used in a continuous or semi-batch process.