Optical properties of single-walled 4 A carbon nanotubes

Plasmon-enhanced high order harmonic generation of open-ended finite-sized carbon nanotubes: The effects of incident field's intensity and frequency and the interference between the incident and scattered fields

The nonlinear optical properties of hybrid systems composed of a silver nanosphere and an open-ended finite-sized armchair single-walled carbon nanotube (SWCNT) are systematically investigated by the hybrid time-dependent Hartree-Fock (TDHF)/finite difference time domain (FDTD) approach, which combines the real-time TDHF approach for the molecular electronic dynamics with the classical computational electrodynamics approach, the FDTD, for solving Maxwell's equations. The high order harmonic generation (HHG) spectra of SWCNTs are studied as a function of the intensity (I₀) and frequency (ω₀) of the incident field, and SWCNTs length as well. It is found that the near field generated by a Ag nanoparticle has an overall enhancement to the molecular HHG in all the energy range, and it extends the HHG spectra to high energy. The inhomogeneity of the near field results in the appearance of even-order harmonics, and their corresponding spectral intensities are sensitive to ω₀, therefore the near field's gradient. When ω₀ is far away from the frequency of plasmon resonance of the silver nanosphere (ω_c), the interference between the incident and scattering light beams extends the spectral range and makes the HHG spectra more sensitive to I₀, while at ω₀ = ω_c, the impact of the interference on the spectra is negligible.

Conductive Nanowires Templated by Molecular Brushes

In this paper, we report the fabrication of conductive nanowires using polymer bottle brushes as templates. In our approach, we synthesized poly(2-dimethylamino)ethyl methacrylate methyl iodide quaternary salt brushes by two-step atom transfer radical polymerization, loaded them with palladium salt, and reduced them in order to form metallic nanowires with average lengths and widths of 300 and 20 nm, respectively. The obtained nanowires were deposited between conductive gold pads and were connected to them by sputtering of additional pads to form an electric circuit. We connected the nanowires in an electric circuit and demonstrated that the conductivity of these nanowires is around 100 S·m(-1).

THEORETICAL STUDIES ON THE LASER-DRIVEN MANY-ELECTRON DYNAMICS OF FINITE-SIZE BORON-NITRIDE NANOTUBES

We present a theoretical study on the electronic dynamics of finite-size Boron-Nitride Nanotubes (BNNTs) driven by the linearly polarized (LP) and circularly polarized (CP) intense laser fields. The many-electron dynamics is described by propagating the reduced one-electron density matrix in real-time domain. The high harmonic generation (HHG) spectra and the time evolution of charge density during harmonic generation are demonstrated. Comparison is made with Carbon Nanotubes (CNTs). The selection rules (SRs) for HHG of finite-size nanotubes are established. One of the important consequences of our results is that HHG of finite-size nanotubes are dependent not only on the molecular point-groups but also on the strength of inter chain interactions. The characteristic difference in nonlinear optical properties between finite and infinitely extended zigzag and armchair BNNTs is significant. Another important consequence is that the laser pulse can drive the electrons to move along or normal to tube axis and produce a charge current on the tube wall.

Density matrix based time-dependent density functional theory and the solution of its linear response in real time domain

A density matrix based time-dependent density functional theory is extended in the present work. Chebyshev expansion is introduced to propagate the linear response of the reduced single-electron density matrix upon the application of a time-domain delta-type external potential. The Chebyshev expansion method is more efficient and accurate than the previous fourth-order Runge-Kutta method and removes a numerical divergence problem. The discrete Fourier transformation and filter diagonalization of the first-order dipole moment are implemented to determine the excited state energies. It is found that the filter diagonalization leads to highly accurate values for the excited state energies. Finally, the density matrix based time-dependent density functional is generalized to calculate the energies of singlet-triplet excitations.

Polymer-mediated chain-like self-assembly of functionalized gold nanoparticles

We report an easy solution phase template-based method to assemble mercaptoundecanoic acid-functionalized gold nanoparticles (MUA-GNPs) along poly(ethylene oxide) (PEO) chains. Transmission electron microscopy (TEM) images show one-dimensional and two-dimensional chain-like sequences of GNPs resembling PEO chains. The progress of the assembly was monitored by the evaluation of surface plasmon resonance band of MUA-GNPs with time by UV-vis spectroscopy. The assembly process is a result of hydrogen bonding interaction between the ethereal oxygen of PEO and carboxylic acid group of MUA attached to GNPs surface, which was confirmed through FTIR spectroscopy. The interaction between PEO and MUA-GNPs was further confirmed by thermal analysis using differential scanning calorimetry.

Small Fullerenes with BN Belts: A Density Functional Theory Investigation

Density functional calculations have been carried out on a series of BCN hybrid fullerenes with certain substitution patterns in comparison with their parent compounds Cn (n = 30, 32, 36, 38, 40, 44, 48, 50, 52). The substitutional structures, energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, ionization potentials, electron affinities, as well as molecular electrostatic potentials have been systematically investigated. The following important points of BCN hybrid fullerenes are stressed: The present studied fullerenes, comprising tubular "belt" and polar "cap", could be divided into three types of structure; each has different indexes of tubular structure and terminal caps. The properties of BCN hybrid fullerenes depend on the type of "tubular belt + polar cap" structures, especially, the HOMO and LUMO characters and MEPs of BCN fullerene are strongly governed by their structure types.

Low-lying excited states of light-harvesting system II in purple bacteria

The low-lying excited states of a B850 ring of Rhodospirillum (Rs.) molischianum are determined accurately by a semiempirical INDO/S method. Results obtained are found to fit extremely well with a Frenkel exciton model with long-range dipolar interactions, and the spatial size of the electron-hole pair is confirmed to fall predominantly within one bacteriochlorophyll with a small leakage to its nearest neighbors. More importantly, the nearest neighbor exciton coupling constants are found to be close to those evaluated directly from dimers, and thus, an existing discrepancy between calculated results of dimers and B850 rings has been resolved.

Electronic structures and energetics of [5,5] and [9,0] single-walled carbon nanotubes

Standard enthalpies of formation, ionization potentials, electron affinities, and band gaps of finite-length [5,5] armchair and [9,0] zigzag single-walled carbon nanotubes (SWNTs) capped with C(30) hemispheres obtained by halving the C(60) fullerene have been computed at the B3LYP/6-311G* level of theory. Properties of SWNTs are found to depend strongly on the tube length and, in the case of the [9,0] zigzag species, on the relative orientation of the caps. The metallic character of an uncapped infinite-length [5,5] armchair SWNT manifests itself in the oscillatory dependence of the properties of capped finite-length tubes on their size. An infinite-length [9,0] zigzag SWNT is predicted to be a semiconductor rather than a metal irrespective of the presence of caps. The present results underscore the slow convergence of SWNT properties with respect to the tube length and uncover small but significant radial distortions along the long axes of SWNTs.