External Strain Enabled Post-Modification of Nanomembrane-Based Optical Microtube Cavities

Optical microtube cavities formed by self-rolling of pre-strained nanomembranes feature unique optical resonance properties for both fundamental and applied research. A post-fabrication treatment of the microcavities made of rolled-up nanomembranes is attractive in order to better manipulate and control the optical modes therein. Here, we report a new approach of modifying the resonant modes by applying external strain using a stretchable polymer substrate. The properties of both azimuthal and higher order axial modes are systematically investigated by varying external strain along the tube axial direction. The post-treatment process leads to a spectral redshift and improvement of quality factors, which is attributed to a modification of tube shape and interlayer compactness. For tubes with axial confinement, the measurements suggest that both the eigenenergies and mode spatial distributions of optical axial modes get significantly modified after applying the external strain. Our numerical calculation results show good agreement with the experimental results. This work reports a simple and robust strain-based modification scheme for manipulating the resonant mode energies, mode spacing, and mode field distributions

Exploring Rolled-up Au–Ag Bimetallic Microtubes for Surface-Enhanced Raman Scattering Sensor

A technique to design and fabricate Au–Ag bimetal microtubes for the investigation of curvature-dependent localized surface plasmon modes is demonstrated. Highly surface-enhanced Raman scattering (SERS) is observed that illustrates the distribution of localized surface plasmon modes leading to an enhanced electromagnetic field. A finite-difference time-domain method is also employed to simulate the electromagnetic field properties on the metal surface. The enhanced SERS performance of such noble bimetal microtubes could spur further interest in the integration of highly sensitive biosensors for rapid, nondestructive, and quantitative bioanalysis, particularly in microfluidics

Silver Nanocap Enabled Conversion and Tuning of Hybrid Photon–Plasmon Modes in Microtubular Cavities

Hybrid photon–plasmon modes are promising for the study of enhanced light–matter interactions due to the formation of a unique plasmon-type evanescent field. Here, we demonstrate the tunability of photon–plasmon coupling enabled by a metal nanocap on a microtubular cavity. An angle-dependent tuning of the photon–plasmon hybridization is revealed, where the dominant polarization is transverse-magnetic (TM) polarized at the middle-top of the nanocap and gradually converts to be transverse-electric (TE) polarized at the sidewall of the microtube cavity. The intensity ratio of strongly hybridized TM and TE modes is extremely sensitive to nanoperturbations at the metal nanocap, thus providing a novel scheme for surface sensing. Theoretical calculations show that the sensitive intensity ratio change originates from the distinct tuning effect on the TM- and TE-polarized hybrid modes, which is particularly significant in thin-walled microtubular cavities. Our work reports photon–plasmon modes tuned by a metal nanostructure, which are promising for the fundamental studies of enhanced light–matter interactions and relevant applications

<i>In Situ</i> Generation of Plasmonic Nanoparticles for Manipulating Photon–Plasmon Coupling in Microtube Cavities

<i>In situ</i> generation of silver nanoparticles for selective coupling between localized plasmonic resonances and whispering-gallery modes (WGMs) is investigated by spatially resolved laser dewetting on microtube cavities. The size and morphology of the silver nanoparticles are changed by adjusting the laser power and irradiation time, which in turn effectively tune the photon–plasmon coupling strength. Depending on the relative position of the plasmonic nanoparticles spot and resonant field distribution of WGMs, selective coupling between the localized surface plasmon resonances (LSPRs) and WGMs is experimentally demonstrated. Moreover, by creating multiple plasmonic-nanoparticle spots on the microtube cavity, the field distribution of optical axial modes is freely tuned due to multicoupling between LSPRs and WGMs. The multicoupling mechanism is theoretically investigated by a modified quasipotential model based on perturbation theory. This work provides an <i>in situ</i> fabrication of plasmonic nanoparticles on three-dimensional microtube cavities for manipulating photon-plasmon coupling which is of interest for optical tuning abilities and enhanced light-matter interactions

Controlled Patterning of Plasmonic Dimers by Using an Ultrathin Nanoporous Alumina Membrane as a Shadow Mask

We report on design and fabrication of patterned plasmonic dimer arrays by using an ultrathin anodic aluminum oxide (AAO) membrane as a shadow mask. This strategy allows for controllable fabrication of plasmonic dimers where the location, size, and orientation of each particle in the dimer pairs can be independently tuned. Particularly, plasmonic dimers with ultrasmall nanogaps down to the sub-10 nm scale as well as a large dimer density up to 1.0 × 10¹⁰ cm^–2 are fabricated over a centimeter-sized area. The plasmonic dimers exhibit significant surface-enhanced Raman scattering (SERS) enhancement with a polarization-dependent behavior, which is well interpreted by finite-difference time-domain (FDTD) simulations. Our results reveal a facile approach for controllable fabrication of large-area dimer arrays, which is of fundamental interest for plasmon-based applications in surface-enhanced spectroscopy, biochemical sensing, and optoelectronics

High-Quality In-Plane Aligned CsPbX₃ Perovskite Nanowire Lasers with Composition-Dependent Strong Exciton–Photon Coupling

Cesium lead halide perovskite nanowires have emerged as promising low-dimensional semiconductor structures for integrated photonic applications. Understanding light–matter interactions in a nanowire cavity is of both fundamental and practical interest in designing low-power-consumption nanoscale light sources. In this work, high-quality in-plane aligned halide perovskite CsPbX₃ (X = Cl, Br, I) nanowires are synthesized by a vapor growth method on an annealed M-plane sapphire substrate. Large-area nanowire laser arrays have been achieved based on the as-grown aligned CsPbX₃ nanowires at room temperature with quite low pumping thresholds, very high quality factors, and a high degree of linear polarization. More importantly, it is found that exciton–polaritons are formed in the nanowires under the excitation of a pulsed laser, indicating a strong exciton–photon coupling in the optical microcavities made of cesium lead halide perovskites. The coupling strength in these CsPbX₃ nanowires is dependent on the atomic composition, where the obtained room-temperature Rabi splitting energy is ∼210 ± 13, 146 ± 9, and 103 ± 5 meV for the CsPbCl₃, CsPbBr₃, and CsPbI₃ nanowires, respectively. This work provides fundamental insights for the practical applications of all-inorganic perovskite CsPbX₃ nanowires in designing light-emitting devices and integrated nanophotonic systems