An official website of the United States government
Abstract Plasmonic nanostructures exhibit intriguing optical properties due to spectrally selective plasmon resonance and thus have broad applications, including biochemical sensing and photoelectric detections. However, excited plasmons are often strongly influenced by the substrates supporting the metallic nanostructures, which not only weakens the intrinsic plasmon coupling effect, but also results in a great reduction of optical near‐field enhancement. Here, a plasmonic nanostructure combining collapsible Au‐nanofingers with selective‐etching that enables Au to be suspended is demonstrated, thus avoiding the undesirable influence of the substrates on the local near‐field distribution and forming symmetric electromagnetic‐field enhancements at both the top and bottom surfaces. The polymer support of the Au‐nanofingers is selectively etched by oxygen plasma, while the Au‐cap retains its original size. After an ultrathin dielectric coating is applied on the Au‐nanofingers, suspended Au‐caps with extremely small dielectric gaps are formed via the collapse of neighboring Au‐nanofingers by exposing them to ethanol. These nanostructures can provide a surface‐enhanced Raman scattering (SERS) enhancement of up to ≈109, which is nearly twice that in the nonsuspended system. As a highly active SERS substrate, the label‐free detection of low‐concentration harmful plastic phthalates in a child's urine without any pretreatment is successfully demonstrated, which suggests that this method is suitable for medical prediagnosis.
more »
« less
Large‐Scale Plasmonic Hybrid Framework with Built‐In Nanohole Array as Multifunctional Optical Sensing Platforms
Abstract Light coupling with patterned subwavelength hole arrays induces enhanced transmission supported by the strong surface plasmon mode. In this work, a nanostructured plasmonic framework with vertically built‐in nanohole arrays at deep‐subwavelength scale (6 nm) is demonstrated using a two‐step fabrication method. The nanohole arrays are formed first by the growth of a high‐quality two‐phase (i.e., Au–TiN) vertically aligned nanocomposite template, followed by selective wet‐etching of the metal (Au). Such a plasmonic nanohole film owns high epitaxial quality with large surface coverage and the structure can be tailored as either fully etched or half‐way etched nanoholes via careful control of the etching process. The chemically inert and plasmonic TiN plays a role in maintaining sharp hole boundary and preventing lattice distortion. Optical properties such as enhanced transmittance and anisotropic dielectric function in the visible regime are demonstrated. Numerical simulation suggests an extended surface plasmon mode and strong field enhancement at the hole edges. Two demonstrations, including the enhanced and modulated photoluminescence by surface coupling with 2D perovskite nanoplates and the refractive index sensing by infiltrating immersion liquids, suggest the great potential of such plasmonic nanohole array for reusable surface plasmon‐enhanced sensing applications.
more »
« less
- Award ID(s):
- 1565822
- PAR ID:
- 10456353
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 16
- Issue:
- 11
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Tunable Fano resonances and plasmon–exciton coupling are demonstrated at room temperature in hybrid systems consisting of single plasmonic nanoparticles deposited on top of the transition metal dichalcogenide monolayers. By using single Au nanotriangles (AuNTs) on monolayer WS2as model systems, Fano resonances are observed from the interference between a discrete exciton band of monolayer WS2and a broadband plasmonic mode of single AuNTs. The Fano lineshape depends on the exciton binding energy and the localized surface plasmon resonance strength, which can be tuned by the dielectric constant of surrounding solvents and AuNT size, respectively. Moreover, a transition from weak to strong plasmon–exciton coupling with Rabi splitting energies of 100–340 meV is observed by rationally changing the surrounding solvents. With their tunable plasmon–exciton interactions, the proposed WS2–AuNT hybrids can open new pathways to develop active nanophotonic devices.more » « less
-
Abstract Great opportunities emerge not only in the generation of anisotropic plasmonic nanostructures but also in controlling their orientation relative to incident light. Herein, a stepwise seeded growth method is reported for the synthesis of rod‐shaped plasmon nanostructures which are vertically self‐aligned with respect to the surface of colloidal substrates. Anisotropic growth of metal nanostructure is achieved by depositing metal seeds onto the surface of colloidal substrates and then selectively passivating the seed surface to induce symmetry breaking in the subsequent seed‐mediated growth process. The versatility of this method is demonstrated by producing nanoparticle dimers and linear trimers of Au, Au–Ag, Au–Pd, and Au–Cu2O. Further, this unique method enables the automatic vertical alignment of the resulting plasmonic nanostructures to the surface of the colloidal substrate, thereby making it possible to design magnetic/plasmonic nanocomposites that allow the dynamic tuning of the plasmon excitation by controlling their orientation using an external magnetic field. The controlled anisotropic growth of colloidal plasmonic nanostructures and their dynamic modulation of plasmon excitation further allow them to be conveniently fixed in a thin polymer film with a well‐controlled orientation to display polarization‐dependent patterns that may find important applications in information encryption.more » « less
-
Oxide-metal-based hybrid materials have gained great research interest in recent years owing to their potential for multifunctionality, property coupling, and tunability. Specifically, oxide-metal hybrid materials in a vertically aligned nanocomposite (VAN) form could produce pronounced anisotropic physical properties, e.g. , hyperbolic optical properties. Herein, self-assembled HfO 2 -Au nanocomposites with ultra-fine vertically aligned Au nanopillars (as fine as 3 nm in diameter) embedded in a HfO 2 matrix were fabricated using a one-step self-assembly process. The film crystallinity and pillar uniformity can be obviously improved by adding an ultra-thin TiN-Au buffer layer during the growth. The HfO 2 -Au hybrid VAN films show an obvious plasmonic resonance at 480 nm, which is much lower than the typical plasmonic resonance wavelength of Au nanostructures, and is attributed to the well-aligned ultra-fine Au nanopillars. Coupled with the broad hyperbolic dispersion ranging from 1050 nm to 1800 nm in wavelength, and unique dielectric HfO 2 , this nanoscale hybrid plasmonic metamaterial presents strong potential for the design of future integrated optical and electronic switching devices.more » « less
-
This study shows that a hybridized plasmonic mode, represented by an additional transmission peak, in a compound structure consisting of a nanorod embedded in a nanohole can be effectively described as a quasi-dipole oscillator. When two nanorods are introduced into a nanohole, these two quasi-dipoles can couple and hybridize, giving rise to two additional transmission peaks in the enhanced optical transmission spectrum. The relative intensities of these peaks can be con-trolled by adjusting the incident polarization, while their separations can be tuned by modifying the length of the nanorods. The concept of quasi-dipoles in compound nanohole structures can be further extended to predict the coupling behavior of even more complex compound configura-tions, such as multiple nanorods within nanoholes, resulting in the generation of multiple hy-bridization states. Consequently, the shape and response of the transmission peaks can be pre-cisely engineered. This strategy could be used to design nanohole-based metasurfaces for applica-tions such as ultra-thin optical filters, waveplates, polarizers, etc.more » « less
