Ab initio simulations of excited carrier dynamics in carbon nanotubes

Combining time-dependent density functional calculations for electrons with molecular dynamics simulations for ions, we investigate the dynamics of excited carriers in a (3,3) carbon nanotube at different temperatures. Following an hv=6.8 eV photoexcitation, the carrier decay is initially dominated by efficient electron-electron scattering. At room temperature, the excitation gap is reduced to nearly half its initial value after ~230 fs, where coupling to phonons starts dominating the decay. We show that the onset point and damping rate in the phonon regime change with initial ion velocities, a manifestation of temperature dependent electron-phonon coupling.Comment: 8 pages, 3 figures, 1 EPAPS supplementary fil

Modifying the interlayer interaction in layered materials with an intense IR laser

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).We propose a transient interlayer compression in two-dimensional compound materials by using an intense IR laser resonant with the out-of-plane optical phonon mode (A2u mode). As a test case, we studied bilayer hexagonal boron nitride (h-BN), which is one of the compound layered materials. Excited state molecular dynamics calculations using time-dependent density functional theory show an 11.3% transient interlayer contraction of h-BN due to an interlayer dipole-dipole attraction of the laser-pumped A2u mode. These results are applicable to other layered compound materials. Such layered materials are a good material for nanospace chemistry, e.g., intercalating molecules and acting with them, and IR irradiation to contract the interlayer distance could provide a new route for chemical reactions under pressure. The duration of the contraction is at least 1 ps in the current simulation, which is observable by high-speed electron-beam diffraction measurements.Y. M. acknowledges the support by MEXT Grants-in-Aid for Scientific Research on Innovative Areas “Science of Atomic Layers” (Projects No. 2506, No. 26107534). H. Z. acknowledges financial support from the National Natural Science Foundation of China (NSFC. Grant No. 11474207). A. R. acknowledges the financial support from the European Research Council Advanced Grant DYNamo (No. ERC-2010- AdG-267374), Spanish Grant (No. FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (No. IT578-13), and European Community FP7 Project CRONOS (Grant No. 280879-2), and COST Actions Grants No. CM1204 (XLIC) and No. MP1306 (EUSpec).Peer Reviewe

Three-dimensional crystalline carbon: Stable polymers of C20 fullerene

We report on a first-principles total-energy calculation that provides the energetics and electronic structure of stable polymerized fullerites consisting of the smallest fullerene C20. We find that the C20 fullerene has periodic three-dimensional covalent networks with orthorhombic and tetragonal symmetries. Both are found to be energetically stable and to be elemental semiconductors with a moderate energy gap of about 1.5 eV. Substantially high peaks of the density of states are found to appear below the top of the valence band, suggesting that these materials under hole-doped conditions are candidates for superconductors

Spectroscopic characterization of Stone-Wales defects in nanotubes

We combined resonant photoabsorption and vibration spectroscopy with scanning tunneling microscopy (STM) to unambiguously identify the presence of Stone-Wales (SW) defects in carbon and boron nitride nanotubes. Based on extensive time-dependent ab initio density functional calculations, we propose to resonantly photoexcite SW defects in the infrared and ultraviolet regime as a means of their identification. Onset of nonradiative decay to a local defect vibration with a frequency of 1962 cm-1 serves as a fingerprint of such defects in carbon nanotubes. The bias dependence of the STM images shows distinct features associated with the presence of SW defects.Y.M. was supported by NAREGI Nanoscience Project, Ministry of Education, Culture, Sports, Science and Technology, Japan. A.R. acknowledges support from the EC grants (HPRN-CT-2000-00128 and HPRN-CT-2000-00167) and Spain MCyT. M.Y. and D.T. acknowledge partial support by NSF-NIRT grant DMR- 0103587.Peer reviewe