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The pitch height–dependent optical extinction spectra and the electric field enhancement of helical and multiring nanostructures are studied by the discrete dipole approximation method. For light incident along the axis of the helix, with the increase of the pitch height, the plasmon peak wavelengths redshift monotonically and the electric coupling between two adjacent pitches weakens. The plasmon peak can also be tuned by changing the polarization of the incident light, particularly by circularly polarized light. In most cases, the maximum electric field is distributed near the surface of the helix. As a comparison, since multiring structures do not have helicity, the extinction spectra are polarization independent and the maximum electrical fields always distribute on the top ring. These results show that the optical properties of helical structures are different when irradiated by left or right circular polarized light. Understanding and manipulating pitch height allow one to tune the plasmon peak and rearrange the electric field enhancement distribution of helical nanostructures. [ABSTRACT FROM AUTHOR]

We use the discrete dipole approximation method to investigate the length-dependent optical extinction spectra and the E-field enhancement of Ag nanorods with different topologic shapes, such as cylindrical, needlelike, periodic, L, and Y shapes. Comparing to nanorods with a simple shape (cylinder and needle), irregular nanorods show many distinct plasmon resonances over a large spectral range. The main plasmon peaks are redshifted with the increase of the lengths and enhanced E-field distribution at those wavelengths depends strongly on the shapes of the nanorods. More hot spots are observed for the nanorods with more defects (i.e., periodic, L, and Y shapes) and the maximum E fields are in the same order of magnitude for cylindrical nanorods and depends on the polarization and propagation directions of the excitation light. The polarization dependent extinction spectra of nanorods with different shapes have also been calculated and are shown to be dependent on the symmetry of the nanorod structure. With specific incident direction, by changing the incident polarization angle, the maximum E field of L- and Y-shaped nanorods can vary in location and magnitude. These results show that defects or imperfections in Ag nanorod structures could drastically change the optical properties, generate extra hot spots for surface enhanced spectroscopy, and have different enhanced field distribution for future plasmonic applications. [ABSTRACT FROM AUTHOR]

Geting bituminous coal was sequentially and exhaustively extracted with petroleum ester, carbon disulfide, methanol, acetone, and isometric carbon disulfide/acetone mixed solvent at room temperature to afford extracts 1–5 (E1-E5). All the extracts were analyzed with a gas chromatography/mass spectrometer. As main components, a series of condensed arenes with 4–6 rings were detected in E2, but only extremely small amounts of the condensed arenes were detected in other extracts. The authors' experiment provides an effective approach for enriching condensed arenes from coals, especially from bituminous coals, such as GBC. [ABSTRACT FROM PUBLISHER]

The structural and optical properties of WO3 nanorods prepared by oblique angle depositions were studied and compared with WO3 thin films. The x-ray diffraction analysis revealed that both the thin films and nanorods annealed at temperatures of 400 and 500 °C had an orthorhombic structure, while only the thin films showed a monoclinic phase when annealed at 300 °C. The band gap energies of the thin films and nanorods all decreased with increasing annealing temperature. The polarized optical absorbance spectra of the as-deposited nanorod samples initially showed anisotropy, but after annealing at temperatures above 400 °C, they became isotropic. This is believed to result from the changes in morphology, crystal structure, and orientation of the nanorod arrays after annealing. [ABSTRACT FROM AUTHOR]

Magnesium hydroxide [Mg(OH)2] thin layers were formed by a chemical reaction between Mg nanoblades and water. Infrared (IR) spectroscopy showed a OH bond-stretching vibrational mode at 3699 cm-1. The assignment was verified by reactions with heavy water, producing OD bonds with the expected isotopic frequency shift. An asymmetric Fano line shape was observed for the OH layer on metallic Mg, while a symmetric Lorentzian (or Bright–Wigner) profile was observed for the OH layer on insulating MgH2. The results indicate that the OH layer on the Mg nanoblades is so thin that the vibrational mode couples to the free-electron continuum of Mg metal. [ABSTRACT FROM AUTHOR]

The polarized absorbance spectra of Ag nanorod array substrates with different lengths prepared by oblique angle deposition were studied in detail. An anomalous anisotropic absorbance was obtained which follows the relation α(θ)=-ln[A(1+B sin2 θ)]β, where θ is the polarization angle with respect to p-polarization direction. The exponent β(<0.5) is wavelength independent. This result cannot be interpreted by the conventional anisotropic effective medium theory, and the possible origin is the inhomogeneous size and orientation distributions that cause the variations in transmission and polarization. [ABSTRACT FROM AUTHOR]

The optical extinction spectra of four topologically different Ag nanorod structures, needle, periodic, L, and Y shapes, have been calculated by the discrete dipole approximation. Both the needle and periodic shaped nanorods can be used to effectively tune plasmon resonant peaks, while the L- and Y-shaped nanorods influence the shape of the extinction spectra. This study shows that the topologic defects of nanorods have significant effects on the optical properties, and provides an alternative way to tune the plasmonic characteristics of metallic nanorods. [ABSTRACT FROM AUTHOR]