3 research outputs found
Coherent Phonons in Carbon Nanotubes and Graphene
We review recent studies of coherent phonons (CPs) corresponding to the
radial breathing mode (RBM) and G-mode in single-wall carbon nanotubes (SWCNTs)
and graphene. Because of the bandgap-diameter relationship, RBM-CPs cause
bandgap oscillations in SWCNTs, modulating interband transitions at terahertz
frequencies. Interband resonances enhance CP signals, allowing for chirality
determination. Using pulse shaping, one can selectively excite
speci!c-chirality SWCNTs within an ensemble. G-mode CPs exhibit
temperature-dependent dephasing via interaction with RBM phonons. Our
microscopic theory derives a driven oscillator equation with a
density-dependent driving term, which correctly predicts CP trends within and
between (2n+m) families. We also find that the diameter can initially increase
or decrease. Finally, we theoretically study the radial breathing like mode in
graphene nanoribbons. For excitation near the absorption edge, the driving term
is much larger for zigzag nanoribbons. We also explain how the armchair
nanoribbon width changes in response to laser excitation.Comment: 48 pages, 41 figure
Thermoelectric properties of two-dimensional hydrogenated borophene: A first-principles study
We theoretically study electronic and thermoelectric properties of two-dimensional hydrogenated borophene (”boro-phane”). We show that, according to the first-principles calculation, hydrogenated borophene is semimetallic, with two bands meeting at a single point at the Fermi level. The thermoelectric properties evaluated by using the Boltzmann equation with a constant relaxation time approximation (CRTA). At room temperature, we obtain large power factor for electron doping regime. Therefore, appropriate doping to this material can enhance its thermoelectric efficiency
Ab-initio calculation of muon spin polarization function to study lithium-ion diffusion in LiTi2O4 battery material
We report the study of lithium-ion diffusion in LiTi2O4 battery material by the analysis of muon spin polarization function at the muon site by DFT calculation. The important parameters which explain the lithium-ion diffusion will be derived from the function, including the field fluctuation rate and the local field distribution. The calculated results are shown in good agreement with the previously measured field distribution and the field fluctuation rate in LiTi2O4 at the ground state temperature. This method, therefore, may apply to the study of other battery materials