Strong Light-Matter Coupling in Carbon Nanotubes as a Route to Exciton Brightening

We show that strong light-matter coupling can be used to overcome a long standing problem that has prevented efficient optical emission from carbon nanotubes. The luminescence from the nominally bright exciton states of carbon nanotubes is quenched due to the fast nonradiative scattering to the dark exciton state having a lower energy. We present a theoretical analysis to show that by placing carbon nanotubes in an optical microcavity the bright exctonic state may be split into two hybrid exciton-polariton states, while the dark state remains unaltered. For sufficiently strong coupling between the bright exciton and the cavity, we show that the energy of the lower polariton may be pushed below that of the dark exciton. This overturning of the relative energies of the bright and dark excitons prevents the dark exciton from quenching the emission. Our resutls pave the way for a new approach to band-engineering the properties of the nanoscale optoelectronic devices.Comment: 35 pages, 5 figures, 6 pages of supplementary materials, 1 supplementary figur

Ab Initio Study of Absorption Resonance Correlations between Nanotubes and Nanoribbons of Graphene and Hexagonal Boron Nitride

© 2019, Pleiades Publishing, Ltd. Abstract: Density functional theory calculations are performed for the electronic band structures and optical absorption spectra of the zigzag nanoribbons and armchair nanotubes of graphene and hexagonal boron nitride as well as hybrid tubular structures obtained by embedding two dimer lines of B and N atoms into an armchair nanotube. Linear correlation coefficient analysis is carried out to quantitatively investigate relations between energies of absorption resonances in these tube-ribbon pairs. Despite the large disparity in the energy band gaps of some of these structures, our results show a high degree of correlation (r \u3e 0.85 with \u3e95% confidence level) between them

Study of a New Type of Crimped-Shape Nanotubes Cut from Bilayer Graphene with the Moiré Angle Θ = 27.8°

New quasi-one-dimensional hollow nanostructures similar to flattened nanotubes are numerically simu- lated. These nanostructures can be obtained by connecting the edges of nanoribbons cut out of twisted bilayer graphene with the Moiré angle Θ = 27.8°. The resulting nanotubes are non-chiral and contain chains of topo- logical defects at the connected edges. A detailed description of their structure is given, and their energy sta- bility is also demonstrated. The electronic characteristics of such structures and their evolution in the course of deformation are determined using ab initio methods. All nanotubes under study are metallic, except the structure with a width of 14 Å, characterized by the band gap Eg = 0.2 eV. It is shown that the electronic and elastic characteristics of such nanotubes differ significantly from those of nanoribbons forming them and of single-walled carbon nanotube

2N+4-rule and an atlas of bulk optical resonances of zigzag graphene nanoribbons

Development of on-chip integrated carbon-based optoelectronic nanocircuits requires fast and non-invasive structural characterization of their building blocks. Recent advances in synthesis of single wall carbon nanotubes and graphene nanoribbons allow for their use as atomically precise building blocks. However, while cataloged experimental data are available for the structural characterization of carbon nanotubes, such an atlas is absent for graphene nanoribbons. Here we theoretically investigate the optical absorption resonances of armchair carbon nanotubes and zigzag graphene nanoribbons continuously spanning the tube (ribbon) transverse sizes from 0.5(0.4) nm to 8.1(12.8) nm. We show that the linear mapping is guaranteed between the tube and ribbon bulk resonance when the number of atoms in the tube unit cell is 2 N+ 4 , where N is the number of atoms in the ribbon unit cell. Thus, an atlas of carbon nanotubes optical transitions can be mapped to an atlas of zigzag graphene nanoribbons. © 2020, The Author(s)

Tunable Sensing and Transport Properties of Doped Hexagonal Boron Nitride Quantum Dots for Efficient Gas Sensors

The electronic, sensing, and transport properties of doped square hexagonal boron nitride (shBN) quantum dots were investigated using density functional theory calculations. The electronic and magnetic properties were controlled by substitutional doping. For instance, heterodoping with Si and C atoms decreased the energy gap to half its value and converted the insulator shBN quantum dot to a semiconductor. Doping with a single O atom transformed the dot to spin half metal with a tiny spin-up energy gap and a wide spin-down gap. Moreover, doping and vacancies formed low-energy interactive molecular orbitals which were important for boosting sensing properties. The unmodified shBN quantum dot showed moderate physical adsorption of NO2, acetone, CH4, and ethanol. This adsorption was elevated by doping due to interactions between electrons in the low-energy orbitals from the doped-shBN dot and π-bond electrons from the gas. The transport properties also showed a significant change in the current by doping. For instance, the spin-up current was very high compared to the spin-down current in the shBN dots doped with an O atom, confirming the formation of spin half metal. The spin-up/down currents were strongly affected by gas adsorption, which can be used as an indicator of the sensing process