Well-aligned boron nanowire arrays were grown vertically on silicon substrates over areas up to several tens of square centimeters using radio-frequency magnetron sputtering of highly pure boron. During growth and self-assembly of boron nanowire arrays, no template or catalyst was needed. The morphology, structure, and composition of the self-organized boron nanowires were characterized in detail using scanning electron microscopy, transmission electron microscopy, and electron energy-loss spectroscopy. Our results might provide insight into the controllable formation of a wide variety of ordered nanostructures with advanced properties. (C) 2002 American Institute of Physics.