General features of the energetics and electronic states carbon nanotubes, containing pentagon-heptagon pair (5/7) topological defects in hexagonal network zigzag configuration, are investigated within simple tight-binding models. This 5/7 defect on nanotube structure is not only responsible for a change diameter, but also governs behavior around Fermi level. Furthermore, nanotubes having different helicities properties can be connected using such pair. Various configurations including one,...

Sonic crystals consisting of three-dimensional arrays units which exhibit localized resonances have been discovered recently. Here, it is shown that their two-dimensional counterparts behave in a similar manner. Particularly, observed the transmittance spectra show very asymmetric peaks are explained as Fano-like interference phenomenon. A finite difference time domain method employed to perform comprehensive study resonance line shape function mass density structural units. Also, simple...

Using well-defined samples of SnO and ${\mathrm{SnO}}_{2}$, we have focused our attention on the way two tin oxides could be distinguished using x-ray-photoemission spectroscopy (XPS). Polycrystalline SnO, oxidized in air to give sputtered by argon-ion bombardment single-crystalline ${\mathrm{SnO}}_{2}$ been examined XPS order study formal valencies these partly ionic compounds. On basis a 3d-level line-shape analysis, show that sizable chemical shift 0.7\ifmmode\pm\else\textpm\fi{}0.05 eV...

We report on the first measurements by high-resolution electron-energy-loss spectroscopy of elementary excitations ${\mathrm{C}}_{60}$ thin films deposited Si(100). By varying primary electron energy, spectrum extending from far ir to vuv has been investigated. Many spectral features are comparable earlier observations photon, photoelectron, and neutron spectroscopies. New molecular revealed including lowest electronic excitation at 1.5 eV collective 6.3 28 eV.

The growth of micron-size carbon fibres from thermal decomposition hydrocarbons catalyzed by a metal has been widely studied. Coil-shaped often grow among straight or twisted filaments. Their internal structure not studied in detail as yet. In the present work, cracking acetylene on Co nanoparticles dispersed porous silica produced relatively well graphitized hollow nanotubules, including filaments and regular helices. small diameter coiled tubules absence an amorphous coating allowed...

Mechanically exfoliated graphene layers deposited on ${\text{SiO}}_{2}$ substrate were irradiated with ${\text{Ar}}^{+}$ ions in order to experimentally study the effect of atomic scale defects and disorder low-energy electronic structure graphene. The samples investigated by scanning tunneling microscopy spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification on-site potential, also induce hopping amplitudes....

The Born effective charge tensors of barium titanate have been calculated for each its four phases. Large charges Ti and O, also predicted by shell-model calculations made plausible a simplified model, reflect the partly covalent character chemical bond. A band-by-band decomposition confirms that orbital hybridization is not restricted to O atoms but involves Ba, which appears more than generally assumed. Our reveal strong dependence on atomic positions contrasting with relative...

Scanning tunneling microscopy (STM) is one of the most appropriate techniques to investigate atomic structure carbon nanomaterials. However, experimental identification topological and nontopological modifications hexagonal network $s{p}^{2}$ nanostructures remains a great challenge. The goal present theoretical work predict typical electronic features few defects that are likely occur in nanostructures, such as vacancy, divacancy, adatom, Stone-Wales defect. induced by those properties...

The dielectric theory of electron-energy-loss spectroscopy (EELS) in the reflection geometry is reformulated so as to allow for an arbitrary compositional variation target material direction perpendicular its surface. A new, general expression energy-loss spectrum obtained terms exact ``effective function.'' It shown that effective function, valid at long wavelength, can be by solving a Riccati differential equation, only information required being otherwise profile, normal z, constant...

Thanks to its high electrical conductivity, a graphene plane presents good shielding efficiency against GHz electromagnetic radiations. Several planes separated by thin polymer spacers add their conductivities arithmetically, because each of them conserves the intrinsic properties isolated graphene. Maximum absorption radiations for frequency around 30 is achieved with six planes, which optimum number. This remarkable result demonstrated experimentally from measurements performed in Ka band...

The scientific literature on grain boundaries (GBs) in graphene was reviewed. review focuses mainly the experimental findings grown by chemical vapor deposition (CVD) under a very wide range of conditions (temperature, pressure hydrogen/hydrocarbon ratio, gas flow velocity and substrates). Differences were found GBs depending origin graphene: micro-mechanically cleaved (produced using graphite originating from high-temperature, high-pressure synthesis), rows non-hexagonal rings separating...

Fresnel equations predict that an ultrathin free standing conductive film, thousands times thinner than skin depth, is capable to absorb up 50% of incident electromagnetic radiations. In the microwave range, same holds true for a graphene sheet. We demonstrate theoretically and prove experimentally absorptance can be enhanced considerably by depositing on dielectric substrate. On experimental side, we obtain 80% 65% at 30 GHz 1 THz, respectively. Theory predicts higher achieved with suitable...

Abstract Hexagonal‐shaped nanoplates (HNPs) of MoS 2 on vertically aligned carbon nanotubes (CNTs) over a patterned area (a circular 1 cm diameter) are produced by chemical vapor deposition technique. With an optimized initial Mo film thickness, uniform coverage HNPs with thickness around 20 nm is achieved. The results confirm that the CNT template plays important role in growth. Each HNP consists abundant exposed edges, interesting for sensing and catalysis applications. High crystallinity...

The atomic structure of a carbon nanotube can be described by its chiral angle and diameter specified pair lattice indices $(n,m).$ electronic mechanical properties are critically dependent on these indices. Scanning tunneling microscopy (STM) is useful tool to investigate nanotubes since the as well individual molecules determined. This paper presents discussion technique obtain $(n,m)$ from STM images in combination with current-voltage tunnel spectra. Image contrast, distortion effects,...

The $\ensuremath{\sigma}+\ensuremath{\pi}$ electron densities of states chiral carbon nanotubes are computed with a tight-binding Hamiltonian. Our calculations show that the electronic structures symmetry similar to zigzag and armchair ones. implications these results on characterization single-wall nanotube ropes using resonant Raman experiments discussed.

The electronic properties of carbon nanotubes having polygonized cross sections instead purely circular ones, such as recently observed using transmission electron microscopy, are investigated with plane-wave ab initio pseudopotential local-density-functional calculations and simple tight-binding models. Strong ${\ensuremath{\sigma}}^{*}\ensuremath{-}{\ensuremath{\pi}}^{*}$ hybridization effects occur in zigzag due to the high curvature located near edges polygonal cross-section prism. These...

The propagation of acoustic waves in a two-dimensional composite medium constituted square array parallel copper cylinders air is investigated both theoretically and experimentally. band structure calculated with the plane wave expansion (PWE) method by imposing condition elastic rigidity to solid inclusions. PWE results are then compared transmission coefficients computed finite difference time domain (FDTD) for thickness samples. In low frequency regime, calculations agree FDTD indicating...