Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDirect Experimental Evidence of Exciton-Phonon Bound States in Carbon Nanotubes
150
0
0.0
(
0
)
Added by
Fl\\'avio Plentz Dr.
Publication date
2005
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We present direct experimental observation of exciton-phonon bound states in the photoluminescence excitation spectra of isolated single walled carbon nanotubes in aqueous suspension. The photoluminescence excitation spectra from several distinct single-walled carbon nanotubes show the presence of at least one sideband related to the tangential modes, lying {200 meV} above the main absorption/emission peak. Both the energy position and line shapes of the sidebands are in excellent agreement with recent calculations [PRL {bf 94},027402 (2005)] that predict the existence of exciton-phonon bound states, a sizable spectral weight transfer to these exciton-phonon complexes and that the amount of this transfer depends on the specific nanotube structure and diameter. The observation of these novel exciton-phonon complexes is a strong indication that the optical properties of carbon nanotubes have an excitonic nature and also of the central role played by phonons in describing the excitation and recombination mechanisms in carbon nanotubes.
rate research
Read More
Single-walled carbon nanotubes (SWCNTs) are quasi-one-dimensional systems with poor Coulomb screening and enhanced electron-phonon interaction, and are good candidates for excitons and exciton-phonon couplings in metallic state. Here we report back scattering reflection experiments on individual metallic SWCNTs. An exciton-phonon sideband separated by 0.19 eV from the first optical transition peak is observed in a metallic SWCNT of chiral index (13,10), which provides clear evidences of excitons in metallic SWCNTs. A static dielectric constant of 10 is estimated from the reflectance spectrum.
A coherent two-phonon bound state has been impulsively generated in ZnTe(110) via second-order Raman scattering in the time domain for the first time. The two-phonon bound state, composed of two anticorrelated in wave vector acoustic phonons, exhibits full {Gamma}1 symmetry and has energy higher than the corresponding 2TA(X) overtone. By suppressing two-phonon fluctuations with a double-pulse excitation, the coexistence of coherently excited bound and unbound two-phonon states has been demonstrated.
Light emission from carbon nanotubes is expected to be dominated by excitonic recombination. Here we calculate the properties of excitons in nanotubes embedded in a dielectric, for a wide range of tube radii and dielectric environments. We find that simple scaling relationships give a good description of the binding energy, exciton size, and oscillator strength.
We calculate the radiative lifetime and energy bandstructure of excitons in semiconducting carbon nanotubes, within a tight-binding approach. In the limit of rapid interband thermalization, the radiative decay rate is maximized at intermediate temperatures, decreasing at low temperature because the lowest-energy excitons are optically forbidden. The intrinsic phonons cannot scatter excitons between optically active and forbidden bands, so sample-dependent extrinsic effects that break the symmetries can play a central role. We calculate the diameter-dependent energy splittings between singlet and triplet excitons of different symmetries, and the resulting dependence of radiative lifetime on temperature and tube diameter.
We calculate the electron-phonon scattering and binding in semiconducting carbon nanotubes, within a tight binding model. The mobility is derived using a multi-band Boltzmann treatment. At high fields, the dominant scattering is inter-band scattering by LO phonons corresponding to the corners K of the graphene Brillouin zone. The drift velocity saturates at approximately half the graphene Fermi velocity. The calculated mobility as a function of temperature, electric field, and nanotube chirality are well reproduced by a simple interpolation formula. Polaronic binding give a band-gap renormalization of ~70 meV, an order of magnitude larger than expected. Coherence lengths can be quite long but are strongly energy dependent.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
