Epitaxial silicon nanowires on Si(111) surface and nonepitaxial silicon nanowires on thermally oxidized silicon substrates have been synthesized using ultrahigh vacuum sputtering. Silicon nanowires with noncylindrical shape and diameter of 200-300 nm were obtained on thermally oxidized Si substrates using Au(15 angstrom)/Si(8 angstrom)/Au(15 angstrom) trilayer as catalysts. Cylindrical silicon nanowires with diameter between 40 and 100 nm and length up to 8 mu m were synthesized using epitaxial growth on Si(111) substrates. Sputter provides an alternative fabrication technique for silicon nanowire synthesis in ultrahigh vacuum environment. (C) 2008 American Vacuum Society.