Optically definable reaction-diffusion-driven pattern generation of Ag-Au nanoparticles on templated surfaces.

We introduce a new lithographic method for the generation of 2D patterns of composite nanoparticles (NPs) of Ag and Au by taking recourse to combine top-down and bottom-up approaches. Micrometer-scale and submicrometer-scale patterned Ag foils of commercially available compact disks (CDs) and digital versatile disks (DVDs), respectively, were used as templates. The galvanic replacement reaction of Ag by HAuCl(4) in the presence of the dye coatings on the foils led to the formation of patterned NP composites of Ag and Au, in addition to the formation of AgCl. The resultant structures appeared in the form of cross patterns of particles with micrometer and submicrometer dimensions. The AgCl crystals thus formed could be removed by using either a saturated NaCl solution or aqueous ammonia. In addition, AgCl could be converted to Ag by electrochemical reduction, thus generating Ag-coated Au NPs. Interestingly, the digital writing on CDs led to the formation of tertiary imprints on the patterns, based on the original writing patterns. This provided an additional handle in generating hierarchical patterns using light in combination with a chemical reaction diffusion process and the nearly parallel line patterns originally present in commercial CDs. The reactions could be carried out in aqueous solution, and the method does not require any additional curing. Also, the density of patterned particles is scalable on the basis of the choice of the original line patterns as present in CDs and DVDs.