Search

The electronic structure of iodine-doped single-walled carbon nanotubes (9, 0), (11, 0), (13, 0) has been simulated. All calculations have been based on a density functional theory with a planewave basis set and a pseudopotential method. Two linear and nine spiral molecules of iodine were considered. The criteria for stability of these complexes were a binding energy and a pressure in the cell. It has been found, that the linear configuration of iodine with an interatomic distance equal to 2.84 A is the most probable for the thin (with diameter up to 11 A) single-walled carbon nanotubes. Such structure is characterized by the lowest binding energy (0.64190 eV/atom) and cell pressure (2.57 kBar). The band structures of these molecules, both in free space and inside the nanotubes were calculated. It was found, that the semiconducting nanotubes change their conductivity type after iodine doping. Such effect is caused by a charge transfer from the tube to an iodine impurity serving as an efficient acceptor. It should be noted, that all obtained results are in a good agreement with experimental data.

A novel nanomaterial, graphene nanoribbons encapsulated inside single-walled carbon nanotubes (GNR@SWNT), was studied by combined optical methods. This nanomaterial was found to have a bright photo ...

In this work the Raman spectroscopy abilities for diagnostics of carbon onions synthesized from nanodiamonds have been analyzed. Several series of nanodiamonds transformed into onion-like carbon by heating at 1000–1900 K in vacuum were characterized with Raman spectroscopy. A high resolution transmission electron microscopy (HRTEM) was used to estimate the average size of nanodiamonds in the series synthesized by different methods. Each series consisted of a pristine nanodiamond powder and materials appeared after its heat treatment at different temperatures in vacuum. The changes corresponding to the nanodiamond crystal transformation into the onion-like carbon (via the stage of diamond cores enveloped by a few layer graphene) have been revealed in Raman spectra. The basic attention has been paid to behavior of D (disorder-induced), G (graphite) and 2D (two-phonon scattering)-bands in the Raman spectra.

Single-wall carbon nanotubes have attracted recently a great interest in various applications. Existing methods for growing single-wall carbon nanotubes produce samples with a range of geometrical structures and different electronic properties, but many potential applications require nanotube samples with the determined properties and structure. Several techniques have been reported for sorting nanotubes. A density gradient ultracentrifugation allows sorting surfactant-encapsulated mixtures of single-walled nanotubes into their distinct (n m) structural forms or into fractions of metallic and semiconducting nanotubes. Here, we report our chievements in separation of nanotubes with this technique. We obtained a liquid fraction up to 97% enriched in metallic single-wall nanotubes and a fraction enriched in (7, 3) semiconducting nanotubes. The surfactant roles in realizing this separations also is discussed.

The metal oxide nanowires were produced by a resistive heating of various metals under ambient conditions at normal atmospheric pressure. The obtained nanowires of CuO, V2O5, ZnO, Fe2O3 were typically of 1–5 m in length and 10–50 nm in diameter. Field emission properties of the oxidized metal surfaces covered by the nanowires, including current–voltage dependencies and distribution of the emission sites, were measured in a flat diode configuration with the use of a phosphor coated anode. The obtained data on field emission properties were compared with the structural characteristics of the nanowires. The highest efficiency of field emission (with 5 V/m threshold field at 0.01 mA/cm 2 current density) was observed for CuO nanowires. Obtained maximal current density (up to 100 mA/cm 2 for such kind of cathodes is very promising for various

Single-wall carbon nanotubes (SWNTs) are very attractive for fundamental researches and applications due to their unique chemical and physical properties. New application fields are triggered by peculiarities of electronic structure of this material. One of such fields is the single-wall carbon nanotube introduction in modern polymeric materials used for formation of antiballistic fabrics. This application is based on the characteristics determining the unique mechanical properties of nanotubes: a high degree of elasticity, a feather-weight and a high volume energy absorption. These properties already have been used for fabrication of high-strength composite materials for air- and mechanical engineering. In this work a possibility of the nanotube introduction into aramid-based polymeric fibers and approaches for the optical diagnostics of such materials are analyzed.

A diode pumped passively mode-locked YAG:Nd laser operated at wavelength 1.32 μm has been developed using a novel saturable absorber based on single-wall carbon nanotubes incorporated in a polymer matrix. Laser pulses with the output energy up to 70 μJ and the duration of 50 ps have been generated. A stable mode-locking regime has been obtained with the pump frequency up to 1 kHz. The femtosecond time-resolved measurements of the nonlinear absorption coefficient of the nanotube-based saturable absorber have been performed. In the spectral range of 1.2-1.45 μm, the third-order optical susceptibility of the carboxymetylcellulose film with incorporated single-wall HiPCO carbon nanotubes has been found to be as high as 10 -12 esu. The characteristic time of the fast component of the electronic relaxation was estimated as 200 fs.

Single-walled nanotubes have been synthesized by arc discharge technique from C:BN:B 4 C catalytic mixture with an admixture of a typical Ni:Y 2 O 3 catalyst. Nitrogen and helium have been used as ambient gases. The arc current and voltage were varied in the process. The synthesized materials have been characterized by a Raman spectroscopy. The arc current value increase induced a frequency shift of the dominating Raman radial breathing mode toward higher frequencies. This trend was opposite to that observed for the pure carbon nanotubes. A probability of doping and other mechanisms being able to result in such shift are discussed in this article.

The graphene flakes were prepared by a micromechanical cleavage of a highly oriented pyrolytic graphite (HOPG) and were deposited on silicon substrates covered with thin films of SiO 2 , ZnS or ZrO 2 of different thickness. A good adhesion and good contrast have been achieved. The films have been studied with the Raman scattering technique. In this work we present a modeling of the light beam passage through a three layer system "graphene-thin film-silicon" and a calculation of the graphene vision contrast dependence on the incident light wavelength. A refractive index and a thickness of the covering thin film were also varied in this work. As a conclusion a material being transparent in a visible spectral range with the refractive index ranging from 2 to 2.2 should be chosen for the best graphene layer contrast.

The aim of this work was to investigate the excimer laser action (λ = 248, T = 20 ns) on the ultrananocrystalline diamond films grown by CVD technique with different nitrogen gas phase content (0% and 30%). The origin of the films ablation was found to be strongly dependent on laser fluence. A high radiation intensity induces the surface graphitization of the film and a consequent ablation with the rate over 10 nm/pulse. Contrariwise at the fluence below the certain threshold the ablation rate was found to be extremely low (∼10 -2 nm/pulse) and not constant across the thickness in case of the nitrogen doped ultrananocrystalline diamond film. Though the low-rate etching is not accompanied by graphitization a certain structure modification has been detected by a Raman spectroscopy.

The electron and phonon properties of single-wall nanotubes synthesized from C:BN mixtures by arc-discharge technique have been analyzed. The BN content was varied from 0 to 50 weight%. The direct measurements of the absorption spectra of hetero-tubes obtained were performed for the suspensions of individual single-wall nanotubes in 1%-SDBS/D2O solution. The main optical absorption bands E sem 11 , E sem 22 , E met 11 ... were shifted toward the "blue" part of the spectrum while the BN content was increased in the initial mixture used for synthesis. Under all BN contents (0-50%) the typical features of carbon single-wall nanotubes were observed in the Raman spectra of heterotubes grown. No significant changes in G-mode (at 1592 cm -1 ) have been detected. In a low-frequency range a position of the dominating Raman breathing mode showed a "blue shift" while the BN content in the initial mixture increased. This was interpreted as an evidence of the bandgap increase in C:BN heterotubes. The "blue" shift of the optical absorption bands (about 140 nm) has been ascribed to the effect of incorporation of B and N atoms or BN clusters into the graphitic lattice of the nanotube wall. This led to the bandgap enlarge.

In this paper we present the results of the first-principles electronic structure computations of the two-dimensional GaSe tetralayers and the bulk material. The calculations were performed within the density functional theory with a plane wave basis set. The comparison of the obtained band structures shows an expected splitting of the energy bands in a multi-layer GaSe, which causes the change of the bandgap width. Thus, a narrowing of the bandgap for the bigger number of tetralayers has been demonstrated. These results can provide an important information for understanding the optical properties of GaSe quantum dots which are known to be synthesized in form of thin disks.

A. M. Prokhorov General Physics Institute, RAS, 38 Vavilov Street, 119991, Moscow, RussiaAn original method for forming a layered thermodynamically incompatible systems with the alternat-ing layers of a polyvinyl chloride (PVC) and a water-soluble polymer carboxymethylcellulose (CMC)with dispersed therein the single-wall carbon nanotubes (SWNTs) has been developed. Such struc-tures can be used to create a moisture- and heat-resistant nonlinear-optical elements. Analyses ofthe optical properties of nanocomposites obtained by the optical absorption and the Raman scat-tering techniques con“rm the presence in the nanocomposite individual (not coalescent in bundles)SWCNTs.

In this paper we represent the results of ab-initio computer modeling of electronic dispersion surfaces in graphite with a variable number of layers (from 1 up to 6). The density functional theory with a pseudo-potential method has been used for the calculations. Modeling has shown a splitting of the dispersion surfaces corresponding to π-electrons while the number of layers increases. An acceptable coincidence has been obtained between the results of modeling and the experimental data, observed earlier. One of the applications of this modeling is an interpretation of the resonant Raman spectra of graphite clusters with a small number of graphene sheets.

A great breakthrough in separation of single-wall carbon nanotubes (SWNTs) by a density gradient ultracentrifugation during last years has allowed to obtain fractions of separated metal or semiconductor SWNTs. Another important property of this separation method is the possibility to obtain fractions with the desired positions of absorption peaks. For such fractions a quantum efficiency is significantly increased in case of using them as a non-linear optical material for formation of ultrafast beam modulators. Arc SWNTs demonstrate a saturable absorption in a wide spectral range (from 1.3 μm up to 1.95 μm). The density gradient ultracentrifugation allows to obtain the fractions with a narrow nanotube diameter distribution. This also increases the efficiency of SWNT-based saturable absorbers. In this work the density gradient ultracentrifugation technique has been used and optimized for SWNT separation. The aqueous suspensions of arc nanotubes have been treated. Different combinations and concentrations of surfactants (sodium dodecyl sulphate (SDS) and sodium cholate (SC)) were used for the gradient and the sample layer formation. A gradual shift of the absorption peaks over the layers has been obtained. This shift is very important because it opens a way to adjust the absorption peak position to the exact laser wavelength. The fractions with a prevalence of metallic SWNTs (up to 97%) have been obtained.