Optically Definable Reaction-Diffusion-Driven Pattern Generation of Ag–Au Nanoparticles on Templated Surfaces

Abstract

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.

Silver–Gold Nanocomposite Substrates for Metal-Enhanced Fluorescence: Ensemble and Single-Molecule Spectroscopic Studies

“…The AgCl that is codeposited on the substrate as a byproduct of the reaction can be removed by washing the nanocomposite samples with concentrated NaCl solution. 19,30 However, no significant differences were observed in our subsequent fluorescence studies using the Ag–Au–NC substrates, with or without the treatment with NaCl.…”

“…The reaction also produces AgCl, which being insoluble in the aqueous solution, crystallizes on the substrate in the form of microparticles. 19,20,30 Moreover, depending on the reaction time and the concentration of HAuCl 4 , a fraction of the unreacted Ag remains on the metal film, leading to the generation of desired Ag–Au–NC substrates. The EDS analysis performed on the as-fabricated substrates (Figure 1C) yields an elemental composition of Au (26%), Ag (64%), and Cl (10% by weight), which is in accordance with the reaction (eq 1).…”

Fluorescence enhancement using silver-gold nanocomposite substrates

“…As will be discussed later, this residual Ag is found to play an important role in the fluorescence enhancement obtained with the fabricated Ag-Au-NC substrates. It is possible to remove the AgCl from the substrates by washing with concentrated NaCl solution [16]. However, no significant differences were observed in our subsequent fluorescence studies using the Ag-Au-NC substrates, with or without the treatment with NaCl.…”

“…1). Since AgCl is insoluble in the aqueous solution, it is co-deposited as microcrystals on the substrate along with the Au nanoparticles [11, 16]. So the percentage of Ag obtained from the EDS analysis is due to the contribution of both AgCl, as well as any residual unreacted Ag that remains from the starting Ag film ( cf .…”

Galvanic reaction based generation of electronically transparent corrugated Ag–Au nanoparticle thin films

“…It may be mentioned here that we had used a similar galvanic replacement reaction between the Ag foil of CDs/ DVDs and HAuCl 4 to generate arrays of nanoparticles (NPs) consisting of Ag and Au, and in addition AgCl microparticles. 18 However, the reaction conditions reported here are different along with the use of CTAB for the formation of the film. In addition, the current method is a new way of generating thin metallic films consisting of Ag and Au NPs and CTAB.…”