Metallic Carbon Nanotube Nanocavities as Ultracompact and Low-loss Fabry-Perot Plasmonic Resonators

High-quality nanocavities through multimodal confinement of hyperbolic polaritons in hexagonal boron nitride

Compressing light into nanocavities substantially enhances light-matter interactions, which has been a major driver for nanostructured materials research. However, extreme confinement generally comes at the cost of absorption and low resonator quality factors. Here we suggest an alternative optical multimodal confinement mechanism, unlocking the potential of hyperbolic phonon polaritons in isotopically pure hexagonal boron nitride. We produce deep-subwavelength cavities and demonstrate several orders of magnitude improvement in confinement, with estimated Purcell factors exceeding 108 and quality factors in the 50-480 range, values approaching the intrinsic quality factor of hexagonal boron nitride polaritons. Intriguingly, the quality factors we obtain exceed the maximum predicted by impedance-mismatch considerations, indicating that confinement is boosted by higher-order modes. We expect that our multimodal approach to nanoscale polariton manipulation will have far-reaching implications for ultrastrong light-matter interactions, mid-infrared nonlinear optics and nanoscale sensors.

Guided spiraling phonon polaritons in rolled one-dimensional MoO3 nanotubes

Polaritons in reduced-dimensional materials, such as nanowire, nanoribbon and rolled nanotube, usually provide novel avenues for manipulating electromagnetic fields at the nanoscale. Here, we theoretically propose and study hyperbolic phonon polaritons (HPhPs) with rolled one-dimensional molybdenum trioxide (MoO3) nanotube structure. We find that the HPhPs in rolled MoO3 nanotubes exhibit low propagation losses and tunable electromagnetic confinement along the rolled direction. By rolling the twisted bilayer MoO3, we successfully achieve a canalized phonon polaritons mode in the rolled nanotube, enabling their propagation in a spiraling manner along the nanotube. Our findings demonstrate the considerable potential of the rolled MoO3 nanotubes as promising platforms for various applications in light manipulation and nanophotonics circuits, including negative refraction, waveguiding and routing at the ultimate scale.

Impact of point vacancy defects on vibrational behaviour of three-walled carbon nanotubes

CONTEXT

Through experimental observations and reports, various challenges have been identified in carbon nanotubes (CNT), including Stone Wales (SW) flaws and position flaws. Among these imperfections, point vacancies are the most prevalent in the CNT lattice. However, there is currently no established method for detecting these issues, and the influence of these flaws on the vibrational properties of three-walled carbon nanotubes (TWCNTs) remains uncertain. This research paper introduces a novel approach that utilizes vibrational analysis to detect flaws in TWCNTs. By conducting the first investigation into the impact of point vacancies on the vibrational modal frequencies of TWCNTs, our study bridges these knowledge gaps.

METHODS

This study examines the impact of defect quantity on various types of TWCNTs and investigates the vibrational properties of TWCNTs with point vacancies using a molecular structural mechanics technique. A total of 432 TWCNT models were simulated using molecular structural mechanics (MSM), and their modes were identified through finite element (FE) analysis. The fundamental vibration's natural frequency in TWCNTs with defects was then determined. The findings indicate that the depth of the mode shape is influenced by the TWCNTs' diameter, the extent of point vacancy defects, and the boundary condition. It was observed that as the number of vacancy defects increases from 0 to 4%, the natural frequency decreases. The study also establishes the order of TWCNTs with the highest natural vibrational frequency at 0%-point vacancy and [Formula: see text] a given attached mass, which follows the sequence of chiral, armchair, and zigzag TWCNTs.

Broadband plasmonic indium arsenide photonic antennas

An on-chip integrated mid-infrared Fabry-Perot (F-P) polariton resonator exhibits excellent biosensing, thermal emission, and quantum laser utility potential. However, the narrow optical response range and absence of optoelectronic tunability have hindered the development of a F-P phonon polariton resonator. The discovery of surface plasmons in semiconductor nanowires provides a novel route to F-P polariton resonator devices with a broadband optical response and multi-field tunability. Due to their high electron mobility and crystalline quality, InAs twinning superlattice (TSL) nanowires have become a promising candidate in plasmonic electronics. We systemically studied the F-P plasmonic resonance of individual InAs TSL nanowires with a scattering-type near-field optical microscope. Using a metallic AFM tip to excite surface plasmons, we can observe odd-order and even-order modes of F-P polariton resonance, breaking the symmetric selection rules. Through nano Fourier transform infrared spectroscopy, we found that InAs nanowires' F-P polariton resonances appear in a broadband frequency range (650-1100 cm^-1) and calculated that the corresponding Q factor is 5-10. This semiconductor F-P polariton resonator with inherent electrical tunability will be essential in integrated nanophotonic circuits.

Direct Visualization of Ultrastrong Coupling between Luttinger-Liquid Plasmons and Phonon Polaritons

Ultrastrong coupling of light and matter creates new opportunities to modify chemical reactions or develop novel nanoscale devices. One-dimensional Luttinger-liquid plasmons in metallic carbon nanotubes are long-lived excitations with extreme electromagnetic field confinement. They are promising candidates to realize strong or even ultrastrong coupling at infrared frequencies. We applied near-field polariton interferometry to examine the interaction between propagating Luttinger-liquid plasmons in individual carbon nanotubes and surface phonon polaritons of silica and hexagonal boron nitride. We extracted the dispersion relation of the hybrid Luttinger-liquid plasmon-phonon polaritons (LPPhPs) and explained the observed phenomena by the coupled harmonic oscillator model. The dispersion shows pronounced mode splitting, and the obtained value for the normalized coupling strength shows we reached the ultrastrong coupling regime with both native silica and hBN phonons. Our findings predict future applications to exploit the extraordinary properties of carbon nanotube plasmons, ranging from nanoscale plasmonic circuits to ultrasensitive molecular sensing.

Fabry-Pérot Phonon Polaritons in Boron Nitride Nanotube Resonators

Phonon polaritons (PhPs) offer extreme confinement of optical fields and strong dispersion in the mid-infrared spectral region. To study the propagation and interference of PhPs in a 1-D system, we employ scattering scanning near-field optical microscopy (s-SNOM), analytical, and computational techniques to describe the resonance behavior observed in boron nitride nanotubes (BNNTs). In BNNTs of a sufficiently small length, the reflected standing waves from both terminals strongly interfere with one another, leading to large constructive enhancement at select wavelengths through the Fabry-Pérot interference. This 1-D nanoresonant behavior illustrates methods to increase and localize field strength at positions on a BNNT nanotube.

Gate-tunable plasmons in mixed-dimensional van der Waals heterostructures

Surface plasmons, collective electromagnetic excitations coupled to conduction electron oscillations, enable the manipulation of light-matter interactions at the nanoscale. Plasmon dispersion of metallic structures depends sensitively on their dimensionality and has been intensively studied for fundamental physics as well as applied technologies. Here, we report possible evidence for gate-tunable hybrid plasmons from the dimensionally mixed coupling between one-dimensional (1D) carbon nanotubes and two-dimensional (2D) graphene. In contrast to the carrier density-independent 1D Luttinger liquid plasmons in bare metallic carbon nanotubes, plasmon wavelengths in the 1D-2D heterostructure are modulated by 75% via electrostatic gating while retaining the high figures of merit of 1D plasmons. We propose a theoretical model to describe the electromagnetic interaction between plasmons in nanotubes and graphene, suggesting plasmon hybridization as a possible origin for the observed large plasmon modulation. The mixed-dimensional plasmonic heterostructures may enable diverse designs of tunable plasmonic nanodevices.

Nanoscale Patterning of Carbon Nanotubes: Techniques, Applications, and Future

Carbon nanotube (CNT) devices and electronics are achieving maturity and directly competing or surpassing devices that use conventional materials. CNTs have demonstrated ballistic conduction, minimal scaling effects, high current capacity, low power requirements, and excellent optical/photonic properties; making them the ideal candidate for a new material to replace conventional materials in next-generation electronic and photonic systems. CNTs also demonstrate high stability and flexibility, allowing them to be used in flexible, printable, and/or biocompatible electronics. However, a major challenge to fully commercialize these devices is the scalable placement of CNTs into desired micro/nanopatterns and architectures to translate the superior properties of CNTs into macroscale devices. Precise and high throughput patterning becomes increasingly difficult at nanoscale resolution, but it is essential to fully realize the benefits of CNTs. The relatively long, high aspect ratio structures of CNTs must be preserved to maintain their functionalities, consequently making them more difficult to pattern than conventional materials like metals and polymers. This review comprehensively explores the recent development of innovative CNT patterning techniques with nanoscale lateral resolution. Each technique is critically analyzed and applications for the nanoscale-resolution approaches are demonstrated. Promising techniques and the challenges ahead for future devices and applications are discussed.