Optical properties of carbon nanotubes under external electric fields

Abstract

We study the optical properties of carbon nanotubes within the single-band tight-binding approximation. The great number of one-dimensional-like subbands of the nanotubes lead to typical van Hove singularities on the local density of states. When a tube is under the influence of a laser beam, optical transitions are allowed between Van Hove singularities and they can be observed experimentally in absorption spectra. External magnetic and electric fields modify the energy spectrum of carbon nanotubes inducing changes on the optical phenomena at low frequencies. Results for the inter-band absorption coefficient are shown for nanotubes under an additional external electrostatic potential for parallel light polarization. This is an important problem to understand since low energy laser beams are being used to identify the chirality and diameter of the tubes and their electronic character.

Optoelectronic Switching of a Carbon Nanotube Chiral Junction Imaged with Nanometer Spatial Resolution

“…In contrast, the bandgap reduction of the semiconducting part of the junction in Figure is from 0.86 to 0.18 eV when the laser is on. A realistic Stark coefficient of 1.5 eV/(V/nm) 2 for the S 11 state based on the theoretical literature ,, cannot account for the full shift by only the tip electric field. Instead we invoke laser excitation as an additional source of bandgap shift.…”

“…Computational studies have predicted that fields on the order of V/nm can induce Stark effects that strongly perturb the electronic structure of semiconducting and metallic carbon nanotubes. 11,17 Such calculations also show how electronic structure varies across a semi-conductingÀmetallic junction. 5 We showed that we can tune the bandgaps of the two halves of a single semiconducting-metallic CNT junction with an applied electric field.…”

“…Stark effect-tuning of CNT bandgaps in the presence of strong static and optical electric fields, but away from junctions, has been studied extensively. − To a first approximation, tight binding models describe the band edges as van Hove singularities, although more sophisticated models − and experiments − highlight the electron–hole bound character of the optically brightest excited states, with exciton dimeters of 1.5–1.8 nm calculated and measured. The conclusion from various levels of theory is that static and optical fields on the order of several V/nm can cause semiconducting tubes to acquire metallic character (close the bandgap), and vice versa for metallic tubes. − …”

Imaging of Carbon Nanotube Electronic States Polarized by the Field of an Excited Quantum Dot

“…To capture the effect of a QD neighboring the CNT, the onsite energy of each carbon atom in the tight-binding unit cell was modified by the electric potential of the QD at each carbon position . The excited QD was approximated as a point dipole of magnitude μ.…”

Carboxylated Carbon Nanotubes under External Electrical Field: An Ab Initio Investigation

“…The field is applied perpendicularly to the tube axis, and the intensities are within the range of 10 -2 -10 -1 V/Å, as used in previous calculations. [16][17][18][19][20][21][22][23] The applied field is always parallel to the COOH radical, as shown in Figure 1.…”