Synergistic Effect of Au Interband Transition on Graphene Oxide/ZnO Heterostructure: Experimental Analysis with FDTD Simulation.

We furnish a comprehensive study on light-induced carrier generation due to the synergistic contribution of Au interband transition and graphene oxide (GO)/ZnO heterostructure. Plasmonic gold nanoparticles (Au_nps) are incorporated as a substructure sandwiched between GO and ZnO, assisting in additional photo-induced charge carrier generation. GO is prepared by a single-step plasma-enhanced chemical vapor deposition process. The GO/ZnO heterostructure having an active working area of 0.25 cm2 is created to unleash the pyroelectric property of ZnO, and subsequently, Au_np is introduced at the interface of GO/ZnO. Here, the interband transition of Au_np and its capability for charge carrier generation combined with the excitonic charge carrier generation of the highly crystalline non-centrosymmetric hexagonal wurtzite ZnO enhances the photoresponse. Furthermore, the interaction of Au_np with ZnO and its spatial electric field intensity distribution is demonstrated by finite difference time domain simulation which indicate toward an efficient carrier generation at the interface of Au_np and ZnO. The fabricated heterostructure has an active working wavelength in the UV-A region with the highest responsivity at 375 nm of the electromagnetic spectrum. The ultrafast response time (∼29 µs) of the device is due to the pyro-phototronic effect of the GO/ZnO heterostructure enhanced by the interband transition of Au. In the comparative study of the Au_np-enriched GO/ZnO heterostructure device with a GO/ZnO device, the former shows better performance. Both the devices work in the self-powered mode as well as the photoconductive mode, but with a higher on-off current ratio in the photoconductive mode. Hence, this work helps in properly understanding photo-induced charge generation in a Au interband transition enriched GO/ZnO heterostructure.

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.