Compositions and methods for making nanostructures and nanowires on substrates, including but not limited to metal-semiconductor nanostructures and semiconductor nanowires on semiconductor substrates. Particularly described are methods for making cobalt silicide nanostructures on silicon substrates and for making silicon nanowires on silicon substrates using cobalt nanoparticles. Nanogrooves and methods of making nanogrooves. Methods of making silanes.