Fabrication of large-scale ultra-smooth metal surfaces by a replica technique

This paper describes the growth and characterization of large-scale ultra-smooth metal surfaces produced by an adapted replica technique. Making use of this method, either amorphous or crystalline masters of different materials with ultra-flat surfaces, e.g. mica, glass or polymer coatings on silicon, were coated by a physical vapor deposition (PVD) process with a thin precious-metal layer. On the top of this layer a thick Ni surface was grown by electroplating. Both the precious-metal layer and the nickel reinforcement can be stripped off from the master, and the free metal surface that is made to appear can be used as a substrate for the self-assembly of molecules, mostly via chemisorption of thiol-functionalized moieties. The use of either gold or silver layers led to films exhibiting different morphologies and roughnesses, which are all strongly influenced by the structure of the master's surface and by the conditions during the PVD-coating procedure. Utilizing mica as a master it was possible to grow Ag and Au surfaces made of ultra-smooth well-defined [111]-oriented crystals. A root mean square roughness down to 0.2 nm was measured over micrometer-sized areas by scanning tunneling microscopy. Very flat An and Ag films have been also produced using the amorphous masters.