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We present an efficient method for easy tuning of optical and electrophysical parameters of macroscopic objects formed from single-wall carbon nanotubes (SWCNTs). We have developed a unique step-by...

Compared to well-studied single-wall carbon nanotubes, narrow graphene nanoribbons (GNRs) are in shadow due to difficulties in their synthesis (necessity of ultra-high vacuum, noble-metal substrate...

Chirality-controlled growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD) is one of the most challenging tasks in carbon nanotube synthesis field. During CVD growth, the catalyst plays crucial roles in governing SWCNT nucleation thermodynamics as well as growth kinetics. However, the performances of catalyst are generally sensitive to the metal loading amount in the catalyst and the reaction conditions, like the partial pressure of carbon source and the reaction time. In this work, we have systematically investigated a robust Co x Mg 1-x O solid solution, which can predominantly yield (6, 5) SWCNTs in a wide range of Co concentration, with a diversity of CO concentrations or a broad-ranging reaction time. Besides, the effect of reaction temperature on SWCNT chirality distribution is demonstrated, the mechanism of which is clarified with the assistance of environmental transmission electron microscopy. Finally, the chirality distribution of SWCNTs grown using CH 4 as the carbon source is presented. The effects of carbon sources are discussed in view of SWCNT growth mode.

Stable dispersions of single-walled carbon nanotubes (SWCNTs) demonstrated great prospects for applications in biomedical engineering, including bioelectronics, nanoparticle-based drug delivery and imaging in vivo. Prolonged stability of individual SWCNTs in suspensions is crucial for these applications. Here we report the method for efficient stabilization of SWCNT dispersions with transfer ribonucleic acid (tRNA). We optimized the SWCNTs/tRNA mass ratio for dispersion of CoMoCAT and HiPCO tubes and studied them by optical absorbance and photoluminescence (PL) spectroscopy. Cryo-TEM and AFM imaging and PL spectroscopy of suspensions prepared even without any ultrasonic treatment confirmed the presence of individual SWCNTs in the dispersions. We propose a straightforward SWCNT/tRNA dipsersion preparation by either mild sonication or even without ultrasonic treatment will boost the biomedical applications due to simplicity of the procedure and minimal damage of tRNA and SWCNTs.

Using automatic structure generation algorithms and large-scale density functional computations we study polyiodide structures encapsulated within a 1 nm diameter single-walled carbon nanotube. The most energetically preferable confined iodine structures are the I3−, I5− and I82− molecular anions and periodic single, double and triple chain systems. The formation energy drops with increasing number of iodine atoms, reaching a minimum for a single iodine chain. Double and triple chains are metastable but have higher formation energies due to spatial confinement within the thin carbon nanotube. The calculated electron transfer from the nanotube to the molecular structures is close to the integer charge values of the molecular anions. The corresponding Fermi energy shift depends on the iodine concentration. For the single, double and triple chains the calculated Fermi shift is ∼0.13, ∼0.23 and ∼0.19 eV below the top of the nanotube valence band, respectively. The computational approaches presented here require minimal a priori knowledge of the system under study, yet are able to predict stable iodine structures observed in experiment.

In this paper we show the advantages of transparent high conductive films based on filled single-wall carbon nanotubes. The nanotubes with internal channels filled with acceptor molecules (copper chloride or iodine) form networks demonstrating significantly improved characteristics. Due to the charge transfer between the nanotubes and filler, the doped-nanotube films exhibit a drop in electrical sheet resistance of an order of magnitude together with a noticeable increase of film transparency in the visible and near-infrared spectral range. The thermoelectric power measurements show a significant improvement of air-stability of the nanotube network in the course of the filling procedure. For the nanotube films with an initial transparency of 87% at 514 nm and electrical sheet resistance of 862 Ohm sq(-1) we observed an improvement of transparency up to 91% and a decrease of sheet resistance down to 98 Ohm sq(-1). The combination of the nanotube synthesis technique and molecules for encapsulation has been optimized for applications in optoelectronics.

Graphene nanoribbons are attracting much attention as a platform for optoelectronics. Properties of graphene nanoribbons depend on the width, edge type, edge atoms, etc. and can be significantly changed. Inducing magnetism to graphene nanoribbons would open up a new field for applications. In this work we study optical and magnetic properties of graphene nanoribbons with cobalt incorporated atoms that were grown inside single-walled carbon nanotubes from cobalt phthalocyanine molecules.

Long-cavity ytterbium-doped fiber laser operating in the hybrid mode-locked regime was demonstrated. Self-starting and self-similarity of the laser output were achieved. Experiments were performed from the amplifying and frequency doubling of hybrid mode-locked laser radiation.

The suitability of the Ni MgO catalyst as a catalyst in chiral-selective growth of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition has been assessed. It reveals that catalyst calcination temperature plays an important role in affecting the catalyst performances. Using CO as the carbon precursor and a chemical vapor deposition reaction temperature of 600 °C, Ni MgO pre-calcined at 600 °C demonstrates the best performances in catalyzing the growth of SWNTs with predominant (6, 5) species. Systematic characterizations on catalysts calcinated at different temperatures indicate that Ni2+ ions diffuse towards the interior of MgO matrix upon annealing. DFT-based calculations reveal that the binding energy between Ni2+ and adjacent Ni(0) is larger than that between Mg2+ and Ni (0), while Ni2+ situated deep inside MgO has weak interactions with surface Ni atoms. This work highlights the importance of subsurface Ni2+ in anchoring reduced surface Ni atom, which inhibits the aggregation of Ni particles and therefore, facilitates the growth of SWNTs with a narrow chirality distribution.

An MgO supported Co catalyst prepared by atomic layer deposition was applied for the growth of single-walled carbon nanotubes (SWNTs). Different from other catalysts, which generally nucleate SWNTs by base-growth mode, the Co-MgO catalyst uniquely generates SWNTs by tip-growth mode, indicating a weak metal-support interaction. During chemical vapor deposition process, the lift-off of Co nanoparticles from support inhibits the aggregation of Co nanoparticles and favors the synthesis of small-diameter SWNTs with a narrow chirality distribution, even at a high reaction temperature. Particularly, product grown at 800 °C maintains a preferential synthesis of small-diameter (6, 5) SWNTs. The enrichment of (6, 5) SWNT arises from the combination of SWNT-catalyst interface thermodynamics with growth kinetic. The growth dynamics of SWNTs was further investigated by in situ Raman spectroscopy, which revealed that SWNTs with smaller diameters appeared prior to the growth of large-diameter counterparts.

Electrical transport mechanisms of 2D carbon nanotube networks are presently under intensive studies. The related experimental data are ambiguous and controversial. We report on terahertz-infrared spectra of optical conductivity and dielectric permittivity of thin transparent films composed of pristine and CuCl- or iodine-doped single-walled carbon nanotubes (SWCNTs) measured in the frequency range from 7 to 25 000 cm−1 and at temperatures from 5 to 300 K. Controversially to the existing results, we have not observed a clear signature of the so-called terahertz conductivity peak. Instead, a typical metallic-like frequency- and temperature-dependent behavior of the conductivity and permittivity has been discovered. It was attributed to the high quality interconnected SWCNT network providing the almost free pathways for charge carriers. Applying Drude conductivity model, we have determined the temperature and doping dependences of effective parameters of the carriers in the films: plasma frequency, scattering rate, mobility, mean-free path. The obtained results demonstrate a great potential of the material in the field of electromagnetic applications at frequencies up to few terahertz.

Doping of single-walled carbon nanotubes leads to the formation of new energy levels which are able to participate in optical processes. Here, we investigate (6,5)-single walled carbon nanotubes doped in a solution of hydrochloric acid using optical absorption, photoluminescence, and pump-probe transient absorption techniques. We find that, beyond a certain level of doping, the optical spectra of such nanotubes exhibit the spectral features related to two doping-induced levels, which we assign to a localized exciton $$X$$ X and a trion T, appearing in addition to an ordinary exciton $${E}_{1}$$ E 1 . We evaluate the formation and relaxation kinetics of respective states and demonstrate that the kinetics difference between E1 and X energy levels perfectly matches the kinetics of the state T. This original finding evidences the formation of trions through nonradiative relaxation via the $$X$$ X level, rather than via a direct optical excitation from the ground energy state of nanotubes.

Long single-wall carbon nanotubes (SWCNTs) with a controlled conductivity type or chirality are interesting for fundamental study and are promising in many different technological applications, such as nanoelectronics, optoelectronics, and also upon utilizing them as nanoscale reactors to produce nanomaterials. In this study, the long aligned large diameter SWCNTs and the large diameter nanotube dense networks were synthesized via a vapor-phase epitaxial re-growth method. The nanotubes were re-grown on ST (stable temperature)-cut quartz substrates from short SWCNT seeds using the mixture of ethanol and acetylene as a precursor. The efficient nanotube re-growth was achieved using unsorted SWCNTs with diameters of 1.2–2.0 nm and semiconducting SWCNTs, sorted by an aqueous two-phase extraction method, as seeds. According to our study, the re-grown nanotubes in an array have an average length of 5.5 μm, while the individual re-grown nanotubes can reach up to 20–30 μm. The extensive optical study confirms the preservation of SWCNTs diameter during the re-growth and signifies the high quality of produced nanotubes. We demonstrate the SWCNT chirality selective efficiency of the re-growth, which leads to predominance of the metallic nanotubes.

We report the observation of Coulomb blockade in field electron emission (FE) from single-wall carbon nanotubes (SWCNTs), which is manifested as pronounced steps in the FE current-voltage curves and oscillatory variations in the energy distribution of emitted electrons. The appearance of the Coulomb blockade is explained by the formation of nanoscale protrusions at the apexes of SWCNTs due to the electric field-assisted surface diffusion of adsorbates and carbon adatoms. The proposed adsorbate-assisted FE mechanism is substantially different from the well-known resonant tunneling associated with discrete electronic states of adsorbed atoms. The simulations based on the Coulomb blockade theory are in excellent agreement with the experimental results. The SWCNT field emitters controlled by the Coulomb blockade effect are expected to be used to develop on-demand coherent single-electron sources for advanced vacuum nanoelectronic devices., Comment: 19 pages, 8 figures

International audience; MgO supported monometallic Fe (FeMgO) and bimetallic FeMn (FeMnMgO) catalysts were developed for growing carbon nanotubes using CO as carbon source. Characterizations on the FeMgO catalyst revealed that Fe cations were well-dispersed in the porous MgO support, forming a solid solution. Since most Fe cations in the solid solution are difficult to reduce, FeMgO can only catalyze the growth of single-walled carbon nanotubes (SWCNTs) at temperatures of 700 °C and above. While Fe cations in FeMnMgO could be reduced at lower temperatures with the assistance of Mn, catalyzing the subsequent growth of SWCNTs. Compared with most SWCNTs grown on components like Co or Ni at ambient reaction pressure, the Fe-catalyzed SWCNTs demonstrate rather narrow chirality distributions. Particularly, preferential (6, 5) tube growth on FeMnMgO was achieved at 600 °C. The narrow SWCNT chirality distribution could be inherently related to the high carbon solubility of Fe nanoparticles, favoring the nucleation of SWCNTs by a perpendicular mode. The present studies not only offer essential insights into SWCNT growth mechanisms, but can guide the design of novel catalysts for chirality-controlled growth of SWCNTs.

Multiwalled carbon nanotubes (MWCNTs) were successfully incorporated inside silica aerogel matrix. Solid composite materials were investigated by high-resolution transmission microscopy, scanning electron microscopy, optical spectroscopy. MWCNTs in the form of small bundles and individual tubes get locked inside the aerogel between its pores resulting in the local solution-free environment for nanotubes. Optical transmission of the composite material can be modified by the amount of the added MWCNTs. Nonlinear optical properties were studied by a Z-scan technique. Composite materials demonstrate saturable absorption for femtosecond laser pulses at 515 nm wavelength that are attributed to the properties of embedded nanotubes. Silica aerogels possess significantly better thermal stability compared to polymer matrices, hosts that are frequently used for saturable absorption applications of carbon nanotubes. Solid and lightweight silica aerogels with embedded nanotubes can be used as optical elements for various photonic devices. Photo of silica aerogel with embedded MWCNTs. Normalized Z-scan transmittance of silica aerogel with nanotubes for two different on-focus intensities.

Metallic and semiconducting fractions of single-walled carbon nanotubes (SWCNTs) sorted by an aqueous two-phase extraction technique and integrated into thin films were used to produce CuCl@SWCNT hybrid material via a gas phase filling the nanotubes with CuCl. As a result of doping, the SWCNTs in the hybrid material possess a higher optical transparency than the pristine ones. The hybrid material properties strongly depend on the metallic/semiconducting tube ratio in a pristine material. In this work, with UV-vis-NIR optical absorption and Raman techniques we show that upon filling with CuCl the solely metallic nanotubes provide much higher doping efficiency than the solely semiconducting SWCNTs. The CuCl@SWCNT hybrid material based on sorted nanotubes is more competitive as a transparent conductive material for the future photovoltaics. A schematic view of electron transfer between CuCl@s-SWCNT and CuCl@m-SWCNT within a bundle of CuCl@SWCNT.

We have investigated the laser radiation parameters of the hybrid mode-locked holmium-doped fiber laser. To realize this regime we have combined nonlinear polarization evolution (NPE) and carbon nanotubes (CNT) as an additional nonlinear saturable absorber.

Demand for efficient terahertz radiation detectors resulted in intensive study of the carbon nanostructures as possible solution for that problem. In this work we investigate the response to sub-terahertz radiation of graphene field effect transistors of two configurations. The devices of the first type are based on single layer CVD graphene with asymmetric source and drain (vanadium and gold) contacts and operate as lateral Schottky diodes (LSD). The devices of the second type are made in so-called Dyakonov-Shur configuration in which the radiation is coupled through a spiral antenna to source and top electrodes. We show that at 300 K the LSD detector exhibit the room-temperature responsivity from R = 15 V/W at f= 129 GHz to R = 3 V/W at f = 450 GHz. The DS detector responsivity is markedly lower (2 V/W) and practically frequency independent in the investigated range. We find that at low temperatures (77K) the graphene lateral Schottky diodes responsivity rises with the increasing frequency of the incident sub-THz radiation. We interpret this result as a manifestation of a plasmonic effect in the devices with the relatively long plasmonic wavelengths. The obtained data allows for determination of the most promising directions of development of the technology of nanocarbon structures for the detection of THz radiation.

Molecule encapsulation inside the single-walled carbon nanotube (SWCNT) core has been demonstrated to be a successful route for the modification of nanotube properties. SWCNT diameter-dependent filling results in band gap modification together with the enhancement of photoluminescence quantum yield. However, the interaction between the inner structure and the outer shell is complex. It depends on the orientation of the molecules inside, the geometry of the host nanotube and on several other mechanisms determining the resulting properties of the hybrid nanosystem. In this work we study the influence of encapsulated graphene nanoribbons on the optical properties of the host single-walled carbon nanotubes. The interplay of strain and dielectric screening caused by the internal environment of the nanotube affects its band gap. The photoluminescence of the filled nanotubes becomes enhanced when the graphene nanoribbons are polymerized inside the SWCNTs at low temperatures. We show a gradual photoluminescence quenching together with a selective signal enhancement for exact nanotube geometries, specifically (14,6) and (13,8) species. A precise adjustment of the optical properties and an enhancement of the photoluminescence quantum yield upon filling for nanotubes with specific diameters were assigned to optimal organization of the inner structures.

In this work we report on modification of electrical and optical properties of extended thin films of single-wall carbon nanotubes induced by iodination from gaseous phase. High resolution transmission electron microscopy and Raman data have revealed formation of different types of polyiodide species or one-dimensional iodine crystals (depending on pristine nanotube geometry) inside nanotubes. UV–vis–NIR optical absorption spectra of iodinated nanotubes demonstrated a clear suppression of the optical absorption band corresponding to the first electron transition for semiconducting nanotubes (with the factor determined by the nanotube geometry). It was interpreted as a result of charge transfer from nanotubes to polyiodide species formed inside them. Because of this effect the Fermi level shifted down into the valence band, and the nanotube conductivity type was changed. For filled nanotube films the metallic type of temperature-dependent electrical resistance behavior was observed at elevated temperatures. A reduction of the electrical resistance of pristine films by an order of magnitude (from 1550 Ohm/sq to 270 Ohm/sq; from 865 Ohm/sq to 150 Ohm/sq; from 700 Ohm/sq to 70 Ohm/sq at 300 K) has been observed. The obtained sheet resistances are comparable with those for the most popular today material for transparent conductive electrodes – indium tin oxide.

Synchronized proton acceleration by ultraintense slow light (SASL) in low-density targets has been studied in application to fabricated carbon nanotube films. Proton acceleration from low-density plasma films irradiated by a linearly polarized femtosecond laser pulse of ultrarelativistic intensity was considered as result of both target surface natural contamination by hydrocarbons and artificial volumetric doping of low-density carbon nanotube films. The 3D particle-in-cell simulations confirm the SASL concept [A. V. Brantov et al., Synchronized Ion Acceleration by Ultraintense Slow Light, Phys. Rev. Lett. 116, 085004 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.085004] for proton acceleration by a femtosecond petawatt-class laser pulse from realistic low-density targets with a hydrogen impurity, quantify the characteristics of the accelerated protons, and demonstrate a significant increase of their energy compared with the proton energy generated from contaminated ultrathin solid dense foils.

Curved graphene fragments can be considered as building blocks of carbon nanotubes. Thus, the size of graphene fragments may be considered as one of the most important characteristics of their structural disorder. In this paper, we have performed a comparative Raman study of CVD multi-walled carbon nanotubes (MWCNTs) and graphene flakes deposited on MWCNTs. Raman data have been considered in combination with HRTEM characterization of nanotubes. The basic attention has been paid to the behavior of D (disorder-induced), G (tangential mode), and 2D (two-phonon scattering) bands in Raman spectra in order to use them for MWCNT characterization. A ratio of intensities of 2D and D bands (I2D/ID) demonstrates almost a linear dependence on the mean diameter of MWCNTs produced with two different types of catalysts (see abstract figure). It should be mentioned that each type of catalyst provides the linear dependence with its own specific slope. The graphene fragments have been proposed to form a mosaic structure of nanotube walls. I2D/ID ratio depends on the amount of graphene flakes deposited on nanotube surface via ethylene decomposition. A dependence of intensity ratio I2D/ID on the diameter of nanotubes produced with different types of catalysts.

Single-walled carbon nanotubes (SWCNTs) have unique electronic and optical properties, which are attractive in various applications. These properties can be further improved by functionalization. In this work, it is shown that filling nanotubes with CuCl leads to improvement of their electro-conductive and optical transmission properties up to outstanding level. The improvement is due to the significant p-type doping of the functionalized nanotubes. That leads to a huge increase in nanotubes charge carrier density and the considerable decrease of the nanotubes absorption via Pauli blocking. The functionalization was realized via a gas-phase filling of SWCNTs with CuCl. We demonstrate the effect of huge doping on optical properties of nanotubes with different average diameters. The observed sufficient stability of the CuCl@SWCNT composite is proved to be due to the formation of quasi-one-dimensional (1D) CuCl crystal inside nanotubes. AC-HRTEM image of 1D CuCl crystal formed inside SWCNT.

Single-walled carbon nanotubes can serve as a template for formation of various structures inside. Depending on conditions, the nanotube filling with coronene molecules may lead to creation of coronene stacks, graphene nanoribbons, or inner tubes. In this work, the formation of coronene stacks inside single-walled carbon nanotubes was studied using photoluminescence (PL) spectroscopy. We demonstrate the difference in the excitation PL maps between the spectral features of coronene stacks inside the nanotubes and products formed outside the nanotube interior. The optical investigation was supported by calculations of adsorption energy of coronene molecules inside and outside nanotubes. The theoretical calculations predict the most energetically favorable configurations of coronene molecules with respect to the diameter of the outer nanotubes. Orientation of coronene stacks depends on the nanotube diameter. Models of ten coronene molecules placed inside (10,10) and (11,11) nanotubes (upper and lower image part, respectively).

Aqueous suspensions of nanotubes, as well as the structure and optical properties of their aggregates (bundles), are studied by spectroscopy and high-resolution electron microscopy. The structure of nanoparticles is controlled by varying the ultrasonication time during preparation of suspensions. It is found that the defectiveness of nanotubes increases with decreasing bundle size. A correlation is shown to take place between the suspension preparation regime, the structure of nanoparticles, and the relaxation of the photoexcitation energy of their electronic shells. It is found that the efficiency of photoexcitation energy conversion into heat increases with increasing degree of aggregation of nanotubes into bundles.

Low-temperature chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs) was achieved on two different types of CoxMg1−xO catalysts prepared by different techniques: atomic layer deposition (ALD) and impregnation. The chirality distribution of SWNTs grown on the ALD-prepared CoxMg1−xO catalyst is wider than that of SWNTs grown on the impregnation-prepared CoxMg1−xO catalyst. The different chirality distributions of SWNTs are related to their different growth modes. The ALD-prepared CoxMg1−xO catalyzes the growth of SWNTs by “tip growth” mode, as revealed by in situ environmental transmission electron microscopy studies. In contrast, SWNTs grow on the impregnation-prepared CoxMg1−xO by “base growth” mode. “Base growth” is attributed to strong metal–support interactions between the epitaxially formed Co nanoparticles and the underlying MgO support, accounting for the synthesis of SWNTs with high chiral-selectivity. In addition, impregnation-prepared CoxMg1−xO catalysts calcinated at different temperatures were systematically studied and their catalytic performances in synthesizing carbon nanotubes were elucidated. This work illustrates the influence of metal–support interactions and catalyst reducibility on the chirality-distribution of the synthesized SWNTs.

The dispersions of semiconducting (sc-) and metallic (m-) SWCNTs with purity more than 98 and 86%, correspondingly, were obtained by using the aqueous two-phase extraction method. The unseparated (un-) SWCNTs contained ~3/4 of semiconducting and ~1/4 of metallic nanotubes. Thin films based on unseparated, semiconducting and metallic SWCNTs were prepared by vacuum filtration method. An Atomic Force Microscopy (AFM) and a Transmission Electronic Microscopy (TEM) were used to investigate the thin film microstructure. The thin SWCNT film transmittance was measured in the wavelength range of 300–1500 nm. Thermoelectric properties were carried out in the temperature range up to 200 °C. The largest Seebeck coefficient was observed for thin films based on semiconducting SWCNTs. The maximum value was 98 μV/K under the temperature of 170 °C. The lowest resistivity was 7.5·10−4·Ohm·cm at room temperature for thin un-SWCNT films. The power factor for m-SWCNT and un-SWCNT films was 47 and 213 μW m−1 K−2, correspondingly, at room temperature and 74 and 54 μW m−1 K−2 at 200 °C, respectively. For a thin sc-SWCNT film the maximum power factor was 2.8 μW m−1 K−2 at 160 °C. The un-SWCNT film thermal conductivity coefficient was 5.63 and 3.64 W m−1 K−1 and a thermoelectric figure of merit was 0.011 and 0.016 at temperatures of 23 and 50 °C, respectively.

We report nonlinear optical properties of hybrid systems that contain single-walled carbon nanotubes and Coproporphyrin dye suspensions. The studies were performed in Vis-NIR spectral range. Our results depict both bleaching and limiting properties. A phenomenon of optical power limiting synergism is demonstrated.

We report an all-fibre ultrashort pulse erbium-doped ring laser passively mode-locked by single-wall carbon nanotubes dispersed in carboxymethylcellulose-based polymer films. Owing to intracavity dispersion management and controlled absorption in the polymer films, the laser is capable of generating both femto- and picosecond pulses of various shapes in the spectral range 1.53 – 1.56 μm. We have demonstrated and investigated the generation of almost transform- limited, inversely modified solitons at a high normal cavity dispersion.

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 ...

A series of MgO-supported FeCu catalysts with different metal concentrations has been studied for synthesizing single-walled carbon nanotubes (SWCNTs). Spectroscopic characterization results have revealed that the concentrations of Fe and Cu are crucial for the purity of the produced SWCNTs, but have little effect on the SWCNT chirality distributions. The synergistic mechanisms of Fe and Cu in the catalysts were discussed and used for interpreting the growth results. Guided by the roles of Cu, an MgO-supported CoCu catalyst was also developed for low temperature growth of small diameter SWCNTs. All the results indicate that the Cu phase inhibits the sintering of the reduced metal particles and the active Fe or Co nanoparticles determine the chirality distribution of the SWCNTs.

The electrical resistance of pristine and acceptor-doped single-wall carbon nanotubes assembled into transparent films was measured in the temperature range of 5 to 300 K. The doping was accomplished by filling the nanotubes with iodine or CuCl from the gas phase. After doping the films resistance appeared to drop down by one order of magnitude, to change the nonmonotonic temperature behavior, and to reduce the crossover temperature. The experimental data have been perfectly fitted in frames of the known heterogeneous model with two contributions: from the nanotube bundles (with quasi-one-dimensional conductivity) and from the interbundle electron tunneling. The doping was observed to decrease the magnitudes of both contributions. In this paper we have revealed the main reason of changes in the nanotube part. It is considered to be connected with the involvement of low-energy phonons, which start to participate in the intravalley scattering due to the shift of the Fermi level after doping. The values of the Fermi level shift into the valence band are estimated to be equal to -0.6 eV in the case of iodine doping and -0.9 eV in the case of CuCl doping. These values are in qualitative agreement with the optical absorption data.

The filling of single-walled carbon nanotube films with 1-adamantanemethanol and 1-bromoadamantane molecules was carried out by a gas-phase procedure. Optical absorption and Raman spectroscopies revealed the effects of charge transfer for samples treated with 1-bromoadamantane. Using density functional simulations we show that the charge transfer takes place when bromine is detached from the carbon cage and accepts electrons as free-standing atoms or as polybromide structures. Transmission electron microscope images confirm the presence of individual bromine atoms inside carbon nanotubes, treated with 1-bromoadamantane molecules. The observed charge transfer is, therefore, a marker of the dehalogenization reaction, a critical step in the synthesis process of narrow 1D sp3 nanostructures.

This work gives data on the stability of dispersions of single wall carbon nanotubes stabilized by sodium dodecylbenzenesulfonate in binary polar solvents “water + antifreeze” (glycerol, polyethyleneglycole) with eutectic compositions. The absorption spectra of the suspensions demonstrate no changes during 1-year storage with temperature spanning from −40 to +40 °C. The systems provide relevant optical power limiting properties, the one with glycerol showing good resistance to optical bleaching effects. We also demonstrate that aqueous dispersions of nanotubes exhibit considerable enhancement of optical limiting parameters alongside an increase of the bundled material populace.

Single-wall carbon nanotubes with polyiodide chains inside are interesting from two points of view. According to predictions, first, the iodine structure type inside the nanotube is determined by the nanotube geometry. Second, after iodination all nanotubes become metallic. In this work, we made an attempt to check both predictions. To study the diameter-dependent properties we have taken for a gas-phase iodination the pristine single-wall carbon nanotubes grown by three different techniques providing a different average diameter: a chemical vapor deposition with a Co/Mo catalyst (CoMoCat) with a diameter range (0.6–1.3) nm, a high-pressure CO decomposition (HiPCO) – a diameter range (0.8–1.5) nm, and an aerosol technique with Fe catalyst – a diameter range (1.3–2.0) nm. The Raman spectra have shown a complication of the polyiodide chain structure while the nanotube diameter increased. The optical spectroscopy data (a suppression of E11 band in the UV–Vis–NIR absorption spectrum) have confirmed the theoretical prediction about transformation of all nanotubes into metallic phase after doping.

Chiralities of single-walled carbon nanotubes grown on an atomic layer deposition prepared bimetallic FeCu/MgO catalyst were evaluated quantitatively using nanobeam electron diffraction. The results reveal that the growth yields nearly 90% semiconducting tubes, 45% of which are of the (6,5) type. The growth mechanisms as well as the roles of different components in the catalyst were studied in situ using environmental transmission electron microscopy and infrared spectroscopy. On the basis of the understanding of carbon nanotube growth mechanisms, an MgO-supported FeCu catalyst was prepared by impregnation, showing similar catalytic performance as the atomic layer deposition-prepared catalyst, yielding single-walled carbon nanotubes with a similar narrow chirality distribution.

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.

For preparation of water-resistant and thermally stable nonlinear optical elements containing single-wall carbon nanotubes, an original method for the formation of layered structures based on alternating layers of poly(vinyl chloride) and a water-soluble polymer (carboxymethyl cellulose) with dispersed singlewall carbon nanotubes is proposed. An analysis of the optical properties of the resulting composites by means of optical-absorption spectroscopy and Raman scattering makes it possible to confirm that the nanocomposites contain individual (not united in bundles) single-wall carbon nanotubes.

Single-walled carbon nanotubes (SWCNTs) were successfully grown on calcined stainless steel wires at 700 °C using CO as the carbon source. By contrast, the raw stainless steel wires produced only necklace-like multi-walled carbon nanotubes. Photoluminescence spectroscopy studies showed that SWCNTs grown from calcined stainless steel have a narrow diameter distribution and a high chiral selectivity of (6,5) nanotubes. The pre-growth heat treatment of the stainless steel leads to formation of iron and chromium oxides. The reduction of iron oxide results in formation of Fe nanoparticles which, anchored by chromium oxide, account for the chiral-selective growth of SWCNTs.

Polarization Rotation Locked Vector Solitons (PRLVSs) are experimentally observed for the first time in a fiber ring laser passively mode-locked by a single-wall carbon nanotube (SWCNT) saturable absorber. Period-doubling of these solitons at certain birefringence values has also been observed. We show that fine adjustment to the intracavity birefringence can swing the PRLVSs from period-doubled to period-one state without simultaneous reduction in the pump strength. The timing jitter for both states has also been measured experimentally and discussed analytically using the theoretical framework provided by the Haus model.

We characterize the saturable absorption of the second (E22) electronic transition of a sample of single-walled carbon nanotubes and use it to mode-lock an ytterbium fiber ring laser. The modulation depth of ~ 15% was found to be similar to the corresponding E11 transition (~ 13%), but the saturation intensity (~ 220 MW cm-2) about an order of magnitude larger (~ 10 MW cm-2). We achieved a 15 MHz mode-locked pulse train with an output pulse duration of 6.5 ps. For comparison we also demonstrate stable mode-locking on the E11 transition, of the same nanotubes, with an erbium fiber ring laser, producing 1.1 ps pulses. Using the E22 transition should enable the use of carbon nanotube saturable absorbers at shorter wavelengths than currently possible with the E11 transition, which are limited by the smallest achievable nanotube dimensions.