Showing papers by "Anvar A. Zakhidov published in 2003"

Linear and nonlinear wave propagation in negative refraction metamaterials

Abstract: Linear and Nonlinear Wave Propagation in Negative Refraction Meta-Materials V. M. Agranovich 1,2) , Y. R. Shen 3) , R. H. Baughman 1) , A. A. Zakhidov 1) UTD-NanoTech Institute,The University of Texas at Dallas, Richardson TX, 75083-0688 USA Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow obl. 142190, Russia Physics Department, University of California, Berkeley, CA 94720 USA ABSTRACT We discuss linear and nonlinear optical wave propagation in a left-handed medium (LHM) or medium of negative refraction (NRM). We use the approach of characterizing the medium response totally by a generalized electric polarization (with a dielectric r permittivity e ( ω , k ) ) that can be decomposed into a curl and a non-curl part. The description has a one-to-one correspondence with the usual approach characterizing the LHM response with a dielectric permittivity e <0 and a magnetic permeability μ <0. The latter approach is less physically transparent in the optical frequency region because the usual definition of magnetization loses its physical meaning. Linear wave propagation in LHM or NRM is characterized by negative refraction and negative group velocity that could be clearly manifested by ultra-short pulse propagation in such a medium. Nonlinear optical effects in LHM can be predicted from the same calculations adopted for ordinary media using our general approach. I. Introduction. Over 30 years ago, Veselago [1] suggested that electromagnetic wave propagation in an isotropic medium with negative dielectric permittivity, e ( ω ) < 0 and negative magnetic permeability μ ( ω ) < 0 can exhibit very unusual properties. Since in such r r r media, the wave vector k , the electric field E , and the magnetic field H of a wave form a left-handed orthogonal set, in contrast to the right- handed orthogonal set in an ordinary medium, they are sometimes labeled as left-handed meta-materials (LHM), as opposite to the ordinary right-handed media (RHM). Among the many interesting properties of wave propagation in such media are the appearances of a Pointing vector in the direction

Mechanical and electromechanical coupling in carbon nanotube distortions

Abstract: A simple approach is presented for using bond-stretching and bond-bending modes to describe the static deformations of carbon nanotubes and related actuation effects. This approach allows us to analyze various phenomena in a unified way and to clarify their relationships. We discuss gap energy modulation by external strains, dimensional and torsional deformations caused by charge injection, and stretch-induced torsion. We show how symmetry determines the property dependence on the chiral angle of nanotubes. Electrically driven actuator responses related to deformation-induced modulation of electron kinetic energy are particularly interesting and relevant for applications. The strong oscillatory dependence of these responses on the nanotube geometry is explained within an intuitively clear picture of bonding patterns. We show how anisotropic (shear) deformations play an important role in nanotubes, making their responses distinctly different from graphite's.

Photoinduced charge transfer in poly(p-phenylene vinylene) derivatives and carbon nanotube/C60 composites

Abstract: We report on a study of photoexcitation of single wall carbon nanotubes (SWNTs) and C60-doped π-conjugated polymers. We have studied the photoinduced charge transfer (PCT) in two poly(p-phenylene vinylene) (PPV) derivatives (MEH-PPV and PmPV) as pure polymer and when doped with SWNTs or C60. Using photoluminescence (PL) and photoinduced absorption (PA), we found evidence for PCT in the photoexcited PPV derivative composites and no significant interaction in the ground state. Evidences for PCT are supported by a reduction of the PL emission from the polymer in the composite films, an increase of the polarons in the polymer composites and C60− PA bands.

Dynamic light scattering from acoustic modes in single-walled carbon nanotubes

Abstract: We report here the computation and measurement of inelastic light scattering from acoustic vibrational modes in single-walled carbon nanotubes (SWNT's). The measurement was made possible by the preparation of a sample of oriented SWNT's, partially aligned by means of a magnetic field. Long-wavelength confined longitudinal acoustic modes are described by a shell model. Their interaction with light is described by a surface elasto-optic effect. From the dispersion relations of acoustic modes we obtain an estimate of the two-dimensional Young's modulus of the single curved graphenic plane forming the SWNT. The result is consistent with the reported SWNT elastic properties.

Electromagnetic field structure and quenching in one-dimensional photonic crystals

Abstract: The study is devoted to closed and transferred electromagnetic field in one-dimensional both transparent photonic crystals and crystals containing layers which absorb irradiation alternated by transparent layers. General theory of irrdiation closed inside the crystal is developed both in case transparent and adsorbing metallic photonic crystals in wide frequency range. True or absolute photonic gaps existing in the total reflection angle range are analyzed on the base of internal problem's analytical solution for 1D layered superlattices. We have investigated the frequency-angle diagrams for TM and TE photonic spectra trapped inside the whole reflection range for mesoscopic and macroscopic hierarchical 1D photonic crystals of varied topologies, geometry and materials. The effects of double refraction in binary multi-layered system and photon localization in finite periodic layered structures are investigated analytically and numerically. Energy storage and energy decay time in photonic crystals are considered with account for field amplitudes distribution inside the structure and angular band kinetics. The effect of sharp focusing of the butt-end emission for closed electromagnetic waves in 1D photonic crystals is discussed.

Inverse gold photonic crystals and conjugated polymer coated opals for functional materials

Abstract: Inverse gold photonic crystals templated from synthetic opals with a face centered cubic (FCC) crystal lattice were constructed by heat converting gold chloride to metallic gold. Tetrahedral formations constructed of alternating large and small octahedrons oriented in the zinc sulfide structure were created by controlling the infiltration of gold chloride. Silica spheres were coated with polyanilinesulfonic acid, polypyrrole, poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and 5 nm colloidal gold. Ordinary yeast cells were coated with polyanilinesulfonic acid, polypyrrole and 5 nm colloidal gold. Spheres coated with MEH-PPV were dispersed in H2O and coated with polyelectrolytes which recharged and sterically stabilized the colloidal surfaces. The recharged spheres self-assembled by sedimentation with a FCC crystalline lattice possessing 500 μm wide and 1 mm long crystallites. Silica spheres with diameters as large as 1500 μm were self-assembled along the [1 0 0] direction of the FCC crystal lattice. Opals infiltrated with gold and opals constructed from polymer coated spheres were co-infiltrated with polypropylene yielding inverse polypropylene composite photonic crystals.

Nanostructure and EELS characterization of catalyst assisted SiC nanorods generated from single-walled carbon nanotubes

Abstract: Catalyst assisted nanowires synthesis is widely used as building blocks for assembling nanodevices including FETs, p-n diodes, bipolar junction transistors, and complementary inverters, etc [1]. Generally the diameters of catalysts control the size and growth of nanowires. Seeking new catalysts and elucidating the growth mechanisms are crucial to functionalize the nanowires and achieve novel properties. In this paper we present a transmission electron microscopy study of SiC nanorods fabricated by annealing single-walled carbon nanotubes between Si wafers.

Functional Polymeric Photonic Crystals for Infra-Red Bands by Guided Colloidal Assembly Techniques

Abstract: A technique utilizing polyelectrolytes to assist in the self assembly of colloidal silica spheres into ordered crystallites is introduced. Techniques for coating silica spheres with poly(anilinesulfonic) acid, polypyrrole, and poly[2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene] (MEH-PPV) are described with a self assemble method to guide them into face centered cubic (FCC) opals and into thin films with star shaped opalescent patterns. Inverse gold photonic crystals constructed from silica opal templates were constructed by the heat conversion of gold chloride to metallic gold and inverse gold/ polypropylene composite photonic crystals were fabricated. Inverse conjugated polymer/ polypropylene composite photonic crystals were constructed with MEH-PPV, poly(anilinesulfonic) acid and polypyrrole. The photoluminescence from MEH-PPV/ polypropylene photonic crystals was blue shifted compared to a uniform MEH-PPV film. Chalcogenide was infiltrated into 1.5µm opals and inverse chalcogenide photonic crystals were fabricated.

Self-assembly methods for photonic crystals

Abstract: Colloidal silica spheres self-assembled along the [100] direction of the FCC lattice templating the growth of vertical crystallites and large elongated crystallites were obtained by controlling the geometry of sedimenting dispersions.

Quantum model of phonon transport and heat conductivity in carbon nanoclusters and nanotubes

Abstract: A complex approach phonon quantum discrete model (PQDM) was developed to describe dynamics, kinetics and statistics of phonons in carbon nanostructures with zero-chirality of both zig-zag and armchair geometry. The model allows include into the pure phonon problem existing interaction with others subsystems: electrons, photons, impurities and defects. We predict that planar C- structures are geometrically stable and may bridge interelectrode space in strong external electric field. The exact solution of generalized thermal conductivity (TC) equation was obtained for nanotubes. Temperature distribution along the tube was derived analytically. The diagonalization procedure for the case ofstrong ph-ph interaction was proposed. It was shown the quadratic increasing of heat conductivity with the growth of the phonon mean free path (PMFP). Heat capacitance and the entropy of carbon linear tubes were calculated as the function of temperature. Our theoretical approach explains the nature of good TC in carbon and carbon-like materials by existing of the soft vibration branch (low frequency radial breathing mode phonons with high density of states at thermal energies) accompanied by structure hardness (high frequency $\phi$- and z-branches) providing big PMFP. TC coefficient for high conducting channel in surrounding medium was calculated. The mechanism of heat conductivity temperature damping was analyzed. Two competitive tendencies produce TC maximum at intermediate temperatures (100-300)K. It was shown the strongly non-linear increasing of effective heat conductivity with the growth nanotubes concentration. It was shown that insertion of armchair nanotube inside a medium or its coating by polyacetilene molecule considerably changes the structure of radial breathing phonons.