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Nanoimprint Lithography Facilitated Plasmonic-Photonic Coupling for Enhanced Photoconductivity and Photocatalysis
2021, Gupta, Vaibhav, Sarkar, Swagato, Aftenieva, Olha, Tsuda, Takuya, Kumar, Labeesh, Schletz, Daniel, Schultz, Johannes, Kiriy, Anton, Fery, Andreas, Vogel, Nicolas, König, Tobias A.F.
Imprint lithography has emerged as a reliable, reproducible, and rapid method for patterning colloidal nanostructures. As a promising alternative to top-down lithographic approaches, the fabrication of nanodevices has thus become effective and straightforward. In this study, a fusion of interference lithography (IL) and nanosphere imprint lithography on various target substrates ranging from carbon film on transmission electron microscope grid to inorganic and dopable polymer semiconductor is reported. 1D plasmonic photonic crystals are printed with 75% yield on the centimeter scale using colloidal ink and an IL-produced polydimethylsiloxane stamp. Atomically smooth facet, single-crystalline, and monodisperse colloidal building blocks of gold (Au) nanoparticles are used to print 1D plasmonic grating on top of a titanium dioxide (TiO2) slab waveguide, producing waveguide-plasmon polariton modes with superior 10 nm spectral line-width. Plasmon-induced hot electrons are confirmed via two-terminal current measurements with increased photoresponsivity under guiding conditions. The fabricated hybrid structure with Au/TiO2 heterojunction enhances photocatalytic processes like degradation of methyl orange (MO) dye molecules using the generated hot electrons. This simple colloidal printing technique demonstrated on silicon, glass, Au film, and naphthalenediimide polymer thus marks an important milestone for large-scale implementation in optoelectronic devices. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
Mechanotunable Plasmonic Properties of Colloidal Assemblies
2020, Brasse, Yannic, Gupta, Vaibhav, Schollbach, H.C. Tomohiro, Karg, Matthias, König, Tobias A.F., Fery, Andreas
Noble metal nanoparticles can absorb incident light very efficiently due to their ability to support localized surface plasmon resonances (LSPRs), collective oscillations of the free electron cloud. LSPRs lead to strong, nanoscale confinement of electromagnetic energy which facilitates applications in many fields including sensing, photonics, or catalysis. In these applications, damping of the LSPR caused by inter- and intraband transitions is a limiting factor due to the associated energy losses and line broadening. The losses and broad linewidth can be mitigated by arranging the particles into periodic lattices. Recent advances in particle synthesis, (self-)assembly, and fabrication techniques allow for the realization of collective coupling effects building on various particle sizes, geometries, and compositions. Beyond assemblies on static substrates, by assembling or printing on mechanically deformable surfaces a modulation of the lattice periodicity is possible. This enables significant alteration and tuning of the optical properties. This progress report focuses on this novel approach for tunable spectroscopic properties with a particular focus on low-cost and large-area fabrication techniques for functional plasmonic lattices. The report concludes with a discussion of the perspectives for expanding the mechanotunable colloidal concept to responsive structures and flexible devices. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Mechanotunable Surface Lattice Resonances in the Visible Optical Range by Soft Lithography Templates and Directed Self-Assembly
2019, Gupta, Vaibhav, Probst, Patrick T., Goßler, Fabian R., Steiner, Anja Maria, Schubert, Jonas, Brasse, Yannic, König, Tobias A.F., Fery, Andreas
We demonstrate a novel colloidal self-assembly approach toward obtaining mechanically tunable, cost-efficient, and low-loss plasmonic nanostructures that show pronounced optical anisotropy upon mechanical deformation. Soft lithography and template-assisted colloidal self-assembly are used to fabricate a stretchable periodic square lattice of gold nanoparticles on macroscopic areas. We stress the impact of particle size distribution on the resulting optical properties. To this end, lattices of narrowly distributed particles (∼2% standard deviation in diameter) are compared with those composed of polydisperse ones (∼14% standard deviation). The enhanced particle quality sharpens the collective surface lattice resonances by 40% to achieve a full width at half-maximum as low as 16 nm. This high optical quality approaches the theoretical limit for this system, as revealed by electromagnetic simulations. One hundred stretching cycles demonstrate a reversible transformation from a square to a rectangular lattice, accompanied by polarization-dependent optical properties. On the basis of these findings we envisage the potential applications as strain sensors and mechanically tunable filters. © 2019 American Chemical Society.
Casting of Gold Nanoparticles with High Aspect Ratios inside DNA Molds
2020, Ye, Jingjing, Weichelt, Richard, Kemper, Ulrich, Gupta, Vaibhav, König, Tobias A.F., Eychmüller, Alexander, Seidel, Ralf
DNA nanostructures provide a powerful platform for the programmable assembly of nanomaterials. Here this approach is extended to synthesize rod-like gold nanoparticles in a full DNA controlled manner. The approach is based on DNA molds containing elongated cavities. Gold is deposited inside the molds using a seeded-growth procedure. By carefully exploring the growth parameters it is shown that gold nanostructures with aspect ratios of up to 7 can be grown from single seeds. The highly anisotropic growth is in this case controlled only by the rather soft and porous DNA walls. The optimized seeded growth procedure provides a robust and simple routine to achieve continuous gold nanostructures using DNA templating.
Hybridized Guided-Mode Resonances via Colloidal Plasmonic Self-Assembled Grating
2019, Sarkar, Swagato, Gupta, Vaibhav, Kumar, Mohit, Schubert, Jonas, Probst, Patrick T., Joseph, Joby, König, Tobias A.F.
For many photonic applications, it is important to confine light of a specific wavelength at a certain volume of interest at low losses. So far, it is only possible to use the polarized light perpendicular to the solid grid lines to excite waveguide-plasmon polaritons in a waveguide-supported hybrid structure. In our work, we use a plasmonic grating fabricated by colloidal self-assembly and an ultrathin injection layer to guide the resonant modes selectively. We use gold nanoparticles self-assembled in a linear template on a titanium dioxide (TiO 2 ) layer to study the dispersion relation with conventional ultraviolet-visible-near-infrared spectroscopic methods. Supported with finite-difference in time-domain simulations, we identify the optical band gaps as hybridized modes: plasmonic and photonic resonances. Compared to metallic grids, the observation range of hybridized guided modes can now be extended to modes along the nanoparticle chain lines. With future applications in energy conversion and optical filters employing these cost-efficient and upscalable directed self-assembly methods, we discuss also the application in refractive index sensing of the particle-based hybridized guided modes. Copyright © 2019 American Chemical Society.