3D Plasmonic Nanostructures Research Articles

Directly patterned substrate-free plasmonic “nanograter” structures with unusual Fano resonances

The application of three-dimensional (3D) plasmonic nanostructures as metamaterials (MMs), nano-antennas, and other devices faces challenges in producing metallic nanostructures with easily definable orientations, sophisticated shapes, and smooth surfaces that are operational in the optical regime and beyond. Here, we demonstrate that complex 3D nanostructures can be readily achieved with focused-ion-beam irradiation-induced folding and examine the optical characteristics of plasmonic ‘‘nanograter’’ structures that are composed of free-standing Au films. These 3D nanostructures exhibit interesting 3D hybridization in current flows and exhibit unusual and well-scalable Fano resonances at wavelengths ranging from 1.6 to 6.4 mm. Upon the introduction of liquids of various refractive indices to the structures, a strong dependence of the Fano resonance is observed, with spectral sensitivities of 1400 nm and 2040 nm per refractive index unit under figures of merit of 35.0 and 12.5, respectively, for low-order and high-order resonance in the near-infraredregion.Thisworkindicatestheexciting,increasingrelevanceofsimilarly constructed3Dfree-standingnanostructuresin the research and development of photonics and MMs. Light: Science & Applications (2015) 4, e308; doi:10.1038/lsa.2015.81; published online 3 July 2015

3D Hybrid Plasmonic Nanomaterials for Highly Efficient Optical Absorbers and Sensors.

3D hybrid plasmonic nanomaterials are composed of 3D-stacked Ag nanowires and nanoparticles separated by a nanoscale-thick alumina interlayer. The 3D hybrid plasmonic nanostructures exhibit strong plasmonic coupling between the ultrahigh populations of plasmonic nanomaterials, overcoming the physical limitation of inefficient plasmonic coupling of the Ag nanowire stacks.

Large-Area, Cost-Effective Nanoplasmonic Structures and Their Applications

Nanoscale functional material design and fabrication are essentially fundamental requirement for basic scientific researches and industrial applications of nano-science and engineering. Innovative, effective, reproducible, large-area uniform, tunable and robust nanostructure/material synthesis are still challenging. On the other hand, nanoscale controls of optical effects are a key element in advanced innovative nanophotonics and biophotonics, especially for biological and environmental molecular detection/imaging. Such optical modulation is also the critical technology in many optical devices such as a solar cell and a light-emitting diode (LED). However, optically tunable nanostructures/nanodevices have shown the big problem in the structural stability, thus resulting in a limited life-time under external loads, and moreover, if robust and tunable optical devices can be completed, the effort involved to precisely control the optical effects with structural strength and the reproducibility is so great that commercial-scale manufacture would never be cost-effective. Here, I would like to introduce the novel nanofabrications which rely on template-based nanolithography and present the surface plasmon (SP) which can effectively control the optical effects in nanostructures by simply modulating geometrical properties such as shape, size, and periodicity. Furthermore, in order to provide label-free and non-destructive molecular detection method, Raman scattering will be combined.Plasmonic nanostructures with a localized surface plasmon resonance (LSPR), which is generated by the coupling of light to the collective oscillation of electrons on the nano-sized metallic surface, have generated considerable interest with the development of nanotechnology due to its ability to enhance the weak physical process such as the absorption of light. By adopting such a plasmonic nanostructure inside/onto/beneath a photoactive layer, a power conversion efficiency of solar cells could be improved because an electromagnetic (EM) field is greatly enhanced by plasmonic “hot spots”. Furthermore, optical biosensors such as surface-enhanced Raman scattering (SERS) could be designed with an ultrahigh sensitivity through a local field enhancement from the “hot spots”. A variety of optoelectronic devices and optical biosensors integrated with plasmonic nanostructures thus have been explosively studied and developed. In this study, we report large-area 3D plasmonic nanostructures though a high-throughput and cost-effective process. The surface morphology and optical properties are characterized by SEM and UV-vis. spectroscopy. Furthermore, their enhancement factor is evaluated by using SERS signals.

Plasmonic optical interference.

Understanding optical interference is of great importance in fundamental and analytical optical design for next-generation personal, industrial, and military applications. So far, various researches have been performed for optical interference phenomena, but there have been no reports on plasmonic optical interference. Here, we report that optical interference could be effectively coupled with surface plasmons, resulting in enhanced optical absorption. We prepared a three-dimensional (3D) plasmonic nanostructure that consists of a plasmonic layer at the top, a nanoporous dielectric layer at the center, and a mirror layer at the bottom. The plasmonic layer mediates strong plasmonic absorption when the constructive interference pattern is matched with the plasmonic component. By tailoring the thickness of the dielectric layer, the strong plasmonic absorption can facilely be controlled and covers the full visible range. The plasmonic interference in the 3D nanostructure thus creates brilliant structural colors. We develop a design equation to determine the thickness of the dielectric layer in a 3D plasmonic nanostructure that could create the maximum absorption at a given wavelength. It is further demonstrated that the 3D plasmonic nanostructure can be realized on a flexible substrate. Our 3D plasmonic nanostructures will have a huge impact on the fields of optoelectronic systems, biochemical optical sensors, and spectral imaging.

Chiral Plasmonic Nanostructures on Achiral Nanopillars

Chirality of plasmonic films can be strongly enhanced by three-dimensional (3D) out-of-plane geometries. The complexity of lithographic methods currently used to produce such structures and other methods utilizing chiral templates impose limitations on spectral windows of chiroptical effects, the size of substrates, and hence, further research on chiral plasmonics. Here we demonstrate 3D chiral plasmonic nanostructures (CPNs) with high optical activity in the visible spectral range based on initially achiral nanopillars from ZnO. We made asymmetric gold nanoshells on the nanopillars by vacuum evaporation at different inclination and rotation angles to achieve controlled symmetry breaking and obtained both left- and right-rotating isomers. The attribution of chiral optical effects to monolithic enantiomers made in this process was confirmed by theoretical calculations based on their geometry established from scanning electron microscope (SEM) images. The chirality of the nanoshells is retained upon the release from the substrate into a stable dispersion. Deviation of the incident angle of light from normal results in increase of polarization rotation and chiral g-factor as high as -0.3. This general approach for preparation of abiological nanoscale chiral materials can be extended to other out-of plane 3D nanostructures. The large area films made on achiral nanopillars are convenient for sensors, optical devices, and catalysis.

3D Hollow Nanostructures as Building Blocks for Multifunctional Plasmonics

We present an advanced and robust technology to realize 3D hollow plasmonic nanostructures which are tunable in size, shape, and layout. The presented architectures offer new and unconventional properties such as the realization of 3D plasmonic hollow nanocavities with high electric field confinement and enhancement, finely structured extinction profiles, and broad band optical absorption. The 3D nature of the devices can overcome intrinsic difficulties related to conventional architectures in a wide range of multidisciplinary applications.

A Three-Dimensional Plasmonic Nanostructure with Extraordinary Optical Transmission

We report a 3D plasmonic nanostructure having an extraordinary optical transmission due to localized surface plasmon (LSP) coupling between nanoholes and nanodisks. The nanostructure contains a free-standing gold nanohole array (NHA) film above a cavity and an array of nanodisks at the bottom of the cavity that is aligned with the NHA. For the device, the LSP-mediated resonance position was dependent on the hole and nanodisk diameter as well as the separation distance. Also, the effect of LSP coupling between each hole and corresponding nanodisk became negligible for cavities deeper than 200 nm as observed as a disappearance of the LSP resonance. The greatest LSP resonance transmission and the highest electric field intensity were observed for the structure with the shallowest cavity. In addition, the structure had high surface plasmon resonance sensitivity and may have potential for surface-enhanced Raman spectroscopy and optical trapping applications.

Direct assembly of three-dimensional mesh plasmonic rolls

A direct-assembly method to construct three-dimensional (3D) plasmonic nanostructures yields porous plasmonic rolls through the strain-induced self-rolling up of two-dimensional metallic nanopore films. This route is scalable to different hole sizes and film thicknesses, and applicable to a variety of materials, providing general routes towards a diverse family of 3D metamaterials with nano-engineerable optical properties. These plasmonic rolls can be dynamically driven by light irradiation, rolling or unrolling with increasing or decreasing light intensity. Such dynamically controllable 3D plasmonic nanostructures offer opportunities both for sensing and feedback in active nano-actuators.

Rolling Up Gold Nanoparticle-Dressed DNA Origami into Three-Dimensional Plasmonic Chiral Nanostructures

Construction of three-dimensional (3D) plasmonic architectures using structural DNA nanotechnology is an emerging multidisciplinary area of research. This technology excels in controlling spatial addressability at sub-10 nm resolution, which has thus far been beyond the reach of traditional top-down techniques. In this paper, we demonstrate the realization of 3D plasmonic chiral nanostructures through programmable transformation of gold nanoparticle (AuNP)-dressed DNA origami. AuNPs were assembled along two linear chains on a two-dimensional rectangular DNA origami sheet with well-controlled positions and particle spacing. By rational rolling of the 2D origami template, the AuNPs can be automatically arranged in a helical geometry, suggesting the possibility of achieving engineerable chiral nanomaterials in the visible range.