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Register a new userNear-unity quantum yield from carbon nanotube excitons coupled to plasmonic nanocavities
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Single-walled carbon nanotubes (SWCNTs) are promising absorbers and emitters to enable novel photonic and optoelectronic applications but are also known to severely suffer from low optical quantum yields. Here we demonstrate SWCNTs excitons coupled to plasmonic nanocavities reaching deeply into the Purcell regime with FP=234 (average FP=76), near unity quantum yields of 70% (average 41%), and a photon emission rate of 1.7 MHz into the first lens. The measured ultra-narrow exciton linewidth (18 micro eV) implies furthermore generation of indistinguishable single photons from a SWCNT. To demonstrate utility beyond quantum light sources we show that nanocavity-coupled SWCNTs perform as single-molecule thermometers detecting plasmonically induced heat (Delta T=150K) in a unique interplay of excitons, phonons, and plasmons at the nanoscale.
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The efficiencies of photonic devices are primarily governed by radiative quantum efficiency, which is a property given by the light emitting material. Quantitative characterization for carbon nanotubes, however, has been difficult despite being a prominent material for nanoscale photonics. Here we determine the radiative quantum efficiency of bright excitons in carbon nanotubes by modifying the exciton dynamics through cavity quantum electrodynamical effects. Silicon photonic crystal nanobeam cavities are used to induce the Purcell effect on individual carbon nanotubes. Spectral and temporal behavior of the cavity enhancement is characterized by photoluminescence microscopy, and the fraction of the radiative decay process is evaluated. We find that the radiative quantum efficiency is near unity for bright excitons in carbon nanotubes at room temperature.
Single-walled carbon nanotubes are a promising material as quantum light sources at room temperature and as nanoscale light sources for integrated photonic circuits on silicon. Here we show that integration of dopant states in carbon nanotubes and silicon microcavities can provide bright and high-purity single photon emitters on silicon photonics platform at room temperature. We perform photoluminescence spectroscopy and observe enhancement of emission from the dopant states by a factor of $sim$100, and cavity-enhanced radiative decay is confirmed using time-resolved measurements, where $sim$30% decrease of emission lifetime is observed. Statistics of photons emitted from the cavity-coupled dopant states are investigated by photon correlation measurements, and high-purity single photon generation is observed. Excitation power dependence of photon emission statistics shows that the degree of photon antibunching can be kept low even when the excitation power increases, while single photon emission rate can be increased up to $sim 1.7 times 10^7$ Hz.
Recently nanomechanical devices composed of a long stationary inner carbon nanotube and a shorter, slowly-rotating outer tube have been fabricated. In this Letter, we study the possibility of using such devices as adiabatic quantum pumps. Using the Brouwer formula, we employ a Greens function technique to determine the pumped charge from one end of the inner tube to the other, driven by the rotation of a chiral outer nanotube. We show that there is virtually no pumping if the chiral angle of the two nanotubes is the same, but for optimal chiralities the pumped charge can be a significant fraction of a theoretical upper bound.
We present the numerical tool DECaNT (Diffusion of Excitons in Carbon NanoTubes) that simulates exciton transport in thin films of carbon nanotubes. Through a mesh of nanotubes generated using the Bullet Physics C++ library, excitons move according to an ensemble Monte Carlo algorithm, with the scattering rates that account for tube chirality, orientation, and distance. We calculate the diffusion tensor from the position--position correlation functions and analyze its anisotropy and dependence on the film composition, morphology, and defect density.
Graphene and single-wall carbon nanotube (SWCNT) have attracted great attention because of their ultra-high thermal conductivity. However, there are few works exploring the relations of their thermal conductivity quantitatively. The carbon nanocone (CNC) is a graded structure fall in between graphene disk (GD) and SWCNT. We perform non-equilibrium molecular dynamics (NEMD) simulation to study the thermal conductivity of CNC with different apex angles, and then compare them with that of GD and SWCNT. Our results show that, different from the homogeneous thermal conductivity in SWCNT, the CNC also has a natural graded thermal conductivity which is similar to the GD. Unexpectedly, the graded rate keeps almost the same when the apex angle decreases from 180{deg} (GD) to 19{deg}, but then suddenly declines to zero when the apex angle decreases from 19{deg} to 0{deg} (SWCNT). What is more interesting, the graded effect is not diminished when the interatomic force constant is weakened and mean free path is shorten. That is, besides nanoscale, the graded effect can be observed in macroscale graphene or CNC structures.
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