Growth of gold nanostructures on a Si wafer by concerted mechanisms of photoreduction and galvanic displacement

The development of a facile growth method of gold nanocrystals with a controlled shape is of crucial importance to expand the potential applications of gold nanoarchitectures which have various unique and useful physicochemical properties. Here, we report the site-preferential formation of gold nanostructures with various shapes on Si substrates. When a Si wafer covered with cetyltrimethylammonium bromide (CTAB, an organic salt) is immersed in Au center dot OH)(4)(-) aqueous solution and immediately photoirradiated, dendritic gold nanostructures grow on the surface of the Si wafer. Interestingly, the gold nanodendrites preferentially grow on scratched portions drawn by using a pen-type diamond glass cutter on the Si wafer. The shape of gold nanocrystals depends on the structure of both quaternary alkylammonium cations and halide anions, which are components of the organic salt film, and gold nanostructures with various shapes are successfully obtained at the scratched portions. It is revealed that concerted mechanisms of photoreduction of Au3+ ions and a new type of galvanic displacement reaction between Si and Au(OH)(4)(-) cause the site-preferential growth of gold nanoarchitectures.