Strong and Broadly Tunable Plasmon Resonances in Thick Films of Aligned Carbon Nanotubes

Abstract

Abstract:Low-dimensional plasmonic materials can function as high quality terahertz and infrared antennas at deep subwavelength scales. Despite these antennas' strong coupling to electromagnetic fields, there is a pressing need to further strengthen their absorption. We address this problem by fabricating thick films of aligned, uniformly sized carbon nanotubes and showing that their plasmon resonances are strong, narrow, and broadly tunable. With thicknesses ranging from 25 to 250 nm, our films exhibit peak attenuation reaching 70%, quality factors reaching 9, and electrostatically tunable peak frequencies by a factor of 2.3×. Excellent nanotube alignment leads to the attenuation being 99% linearly polarized along the nanotube axis. Increasing the film thickness blueshifts the plasmon resonators down to peak wavelengths as low as 1.4 µm, promoting them to a new near-infrared regime in which they can both overlap the S11 nanotube exciton energy and access the technologically important infrared telecom band. Keywords: Carbon nanotube, plasmon, resonator, nanophotonics, infrared, multispectral Main text:The Fabry-Pérot plasmon resonances of carbon nanotubes, longitudinal charge oscillations bound by the nanotube ends [1][2][3][4][5][6] In addition, semiconducting nanotubes can be purified in solution and exhibit a higher photothermoelectric coefficient than either metallic nanotubes or graphene 26 .For this Letter, we assembled thick films of uniform nanotube-plasmon resonators, resulting in strong absorption and narrow ensemble linewidths. The peak attenuation that we observe (up to 70%) is markedly higher than both the ~2% peak attenuation observed in a thin film (t = 6 nm) of nanotube resonators 6 and the ~6% peak attenuation typically seen in graphene nanoribbons 9 . The Q factors are as high as 9, attenuation is 99% linearly polarized, and the plasmon-resonance frequencies are electrostatically tunable by a factor of 2.3×, a higher factor than the 1.4× observed 6 in thin nanotube films. We tune the plasmon resonators through the nanotube's S11 exciton to wavelengths as low as 1.4 µm, half the wavelength of previously fabricated nanotube resonators. Our results show that nanotube-plasmon resonators provide an exciting pathway toward efficient and broadband infrared cameras, compact chemical sensors, and optoelectronics at deep subwavelength scales.To fabricate these films, we made use of a controlled vacuum filtration method 27 to produce thick films of remarkably well-aligned nanotubes (Fig 1(a) and Supporting Information (SI)). We dispersed semiconducting nanotubes in an aqueous solution with the surfactant sodium dodecylbenesulfonate (SDBS), sonicated and centrifuged the solution, and filtered the supernatant through polycarbonate filter membranes at a very low filtration speed (1 ml/hr). The nanotube alignment is templated by grooves in the filter paper, with the overall degree of alignment determined by the competition between van der Waals forces, pressure from vacuum pumping, and electrostatic interact...

Tunable Hyperbolic Metamaterials Based on Self-Assembled Carbon Nanotubes

“…34 Highly ordered and large area SWCNT films have proven to be a unique platform to study nanoscale light-matter interactions, including intersubband plasmons, 33 hybrid phonon-plasmon modes, 30,31 ultrastrong exciton-cavity coupling, 32,34 and polarization-sensitive mid-infrared (MIR) and terahertz emission and detection. 10,29,30 In this study, we focus specifically on the anisotropic bulk optical properties of these films. To probe the hyperbolic nature of our SWCNT system, we investigate both the bulk optical properties of the aligned SWCNT metamaterial, using ellipsometry, and the behavior of hyperbolic plasmon modes (HPMs) confined in nanoribbon resonators patterned from the metamaterial.…”

“…To pattern these films into nanoribbon resonators and directly probe the HPM modes of the SWCNT system, we use electron-beam lithography and reactive ion oxygen etching, with fabrication parameters taken from ref. 30 To characterize the HPM ribbon resonators, we employ micro-Fourier transform infrared (-FTIR) spectroscopy on the arrays, with the incident light polarization parallel to the SWCNT axis.…”

Intrinsically ultrastrong plasmon–exciton interactions in crystallized films of carbon nanotubes

“…Due to coupled antenna effects, increasing the thickness of the nanotube film leads to higher-energy plasmon resonances (22). The plasmon-exciton anticrossing can therefore be reached at smaller wave vectors (i.e., higher L values) ( Fig.…”

“…3B)(20,22), whose extinction is 99% polarized along the nanotube alignment axis (SI Appendix). As with graphene nanoribbon resonators(34), the resonance frequency (ω p ) is approximately proportional to ffiffiffiffi qt p(22), where the wave vector q = π/L, L is the nanoribbon width (i.e., the etched length of the nanotubes), and t is the out-of-plane thickness of the material Crystallized carbon nanotube films. (A-C) Cross-sectional TEM images of the crystallized nanotube films at three magnifications.…”

Finite-thickness effects in plasmonic films with periodic cylindrical anisotropy [Invited]

“…Aligned carbon nanotube films present a typical example of plasmonic films with cylindrical anisotropy. They are in the process of intensive experimental development [23,33,34], with a great potential to become the next generation advanced flexible platform for multifunctional metasurfaces and nonlinear optical devices with adjustable characteristics on de- frequencies as compared to thinner ones of the same length [33,34].…”