Empirical formulation of broadband complex refractive index spectra of single-chirality carbon nanotube assembly

Abstract

Assemblies of single-walled carbon nanotubes with a specific chiral structure are promising future optofunctional materials because of their strong light–matter coupling arising from sharp optical resonances of quasi-one-dimensional excitons. Their strong optical resonances, which lie in the infrared-to-visible wavelength region, can be selected by their chiralities, and this selectivity promises a wide range of applications including photonic and thermo-optic devices. However, the broadband complex optical spectra of single-chirality carbon nanotube assemblies are scarce in the literature, which has prevented researchers and engineers from designing devices using them. Here, we experimentally determine broadband complex refractive index spectra of single-chirality carbon nanotube assemblies. Free-standing carbon nanotube membranes and those placed on sapphire substrates were fabricated via filtration of the nanotube solution prepared by the separation method using gel chromatography. Transmission and reflection spectra were measured in the mid-infrared to visible wavelength region, and the complex refractive indices of nanotube assemblies were determined as a function of photon energy. The real and imaginary parts of the refractive indices of the nanotube membrane with a bulk density of 1 g cm−3 at the first subband exciton resonance were determined to be approximately 2.7–3.6 and 1.3i–2.4i, respectively. We propose an empirical formula that phenomenologically describes the complex refractive index spectra of various single-chirality nanotube membranes, which can facilitate the design of photonic devices using carbon nanotubes as the material.

Statistical Verification of Anomaly in Chiral Angle Distribution of Air-Suspended Carbon Nanotubes

“…In contrast, the large-chiral-angle (21,12) SWCNT has consecutive A-sites forming partially straight open tube edges (adjacent blue and red squares). This is more apparent in the schematic representation of the open tube edges as A-sites and Z-sites in the upper panel of Figure 3d.…”

“…Among carbon nanotubes, single-walled carbon nanotubes (SWCNT) have excellent properties that depend on their chiral structures, which are specified by pairs of a diameter d and chiral angle θ (Figure a) or by chiral indices ( n , m ) (Figure b). Even when SWCNTs have similar diameters and chiral angles, they may be metallic ( n – m = 3 q ; q is an integer) or semiconducting ( n – m ≠ 3 q ) − with different optical transition energies originating from exciton resonances. − The structure-dependent narrow-window exciton resonance provides a promising application as a wavelength-selective near-infrared-to-visible photon emitter. ,− In addition, even the mechanical strength of SWCNTs, whose strength-to-weight ratio is among the highest among known materials, depends on the chiral structures of the SWCNTs. , The preferred structure of SWCNTs depends on the applications; thus, structure-controlled synthesis of SWCNTs has attracted attention in a wide range of scientific fields. − …”

High Quantum Yield Amino Acid Carbon Quantum Dots with Unparalleled Refractive Index

“…37 Their optical proper-ties made them particularly appealing as opto-functional materials, which led to the observation of different physical phenomena, such as RI changes. 38 It was further reported that the RIs of individual carbon materials are affected by photon energy using a nonlinear optical device. 39 It was also reported that CQDs incorporated into polyvinyl alcohol (PVA) nanocomposites show a maximal RI of 1.84.…”

“…Furthermore, nanographene’s plasmon-enhanced optical response over the visible and near-infrared spectrum was shown to provide an ideal platform for the development of electrically tunable nonlinear optical nanodevices . Their optical properties made them particularly appealing as opto-functional materials, which led to the observation of different physical phenomena, such as RI changes . It was further reported that the RIs of individual carbon materials are affected by photon energy using a nonlinear optical device .…”