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Funding Information: The experimental part of the research was supported by the Russian Science Foundation (No. 17-19-01787). Theoretical work was supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST ‘‘MISiS’’. This work was supported by the Ministry of Science and Higher Education of the Russian Federation (project no. FZSR-2020-0007 in the frame-work of the state assignment no. 075-03-2020-097/1). A. P. T. acknowledges the EDUFI Fellowship (No. TM-19-11079) from the Finnish National Agency for Education and the Magnus Ehrnrooth Foundation (the Finnish Society of Sciences and Letters) for personal financial support. H. I., J. K., and K. M. thank the Austrian Science Fund (FWF) for funding under project no. I3181-N36. Publisher Copyright: © 2021 The Royal Society of Chemistry. Copyright: Copyright 2021 Elsevier B.V., All rights reserved. A boost in the development of flexible and wearable electronics facilitates the design of new materials to be applied as transparent conducting films (TCFs). Although single-walled carbon nanotube (SWCNT) films are the most promising candidates for flexible TCFs, they still do not meet optoelectronic requirements demanded for their successful industrial integration. In this study, we proposed and thoroughly investigated a new approach that comprises simultaneous bilateral (outer and inner surface) SWCNT doping after their opening by thermal treatment at 400 °C under an ambient air atmosphere. Doping by a chloroauric acid (HAuCl4) ethanol solution allowed us to achieve the record value of equivalent sheet resistance of 31 ± 4 Ω sq-1 at a transmittance of 90% in the middle of the visible spectrum (550 nm). The strong p-doping was examined by open-circuit potential (OCP) measurements and confirmed by ab initio calculations demonstrating a downshift of the Fermi level of around 1 eV for the case of bilateral doping.

The growing demand for wearable electronics requires flexible and stretchable conductive materials. Among them, carbon nanotubes are recognized for their outstanding mechanical, electrical, optical properties and chemical stability. In this paper, we introduce a novel technique of carbon nanotube fiber fabrication, which we named Wet Pulling. The method allows straightforward fiber production out of carbon nanotube thin films, collected on a filter after the synthesis or deposited onto any substrate. It relies on a combination of film and solvent properties. The wet pulling technique has prominent advantages that make it a promising candidate for both small and large-scale production of CNT fibers with desired properties. The method is also easily adaptive to different kinds of carbon nanotubes and allows rapid fabrication of both active and passive flexible electronic components. A tactile sensor, a pulsometer and an electrical circuit are fabricated for the demonstration of their applicability. We expect this new approach to simplify the production of functional carbon nanotube fibers and to enlarge their usage in diverse applications.

Modern solid-state gas sensors approaching ppb-level limit of detection open new perspectives for process control, environmental monitoring and exhaled breath analysis. Organic field-effect transistors (OFETs) are especially promising for gas sensing due to their outstanding sensitivities, low cost and small power consumption. However, they suffer of poor selectivity, requiring development of cross-selective arrays to distinguish analytes, and environmental instability, especially in humid air. Here we present the first fully integrated OFET-based electronic nose with the whole sensor array located on a single substrate. It features down to 30 ppb limit of detection provided by monolayer thick active layers and operates in air with up to 95% relative humidity. By means of principal component analysis, it is able to discriminate toxic air pollutants and monitor meat product freshness. The approach presented paves the way for developing affordable air sensing networks for the Internet of Things.

We present the state-of-the-art performance of air-coupled thermophones made of thin, freestanding films of randomly oriented single-walled carbon nanotubes (SWCNTs). The work demonstrates both experimentally and theoretically that extremely low heat capacity per unit area of SWCNT films allows centimeter-sized thermophones to achieve record sound pressures (normalized to the input power and geometry) in the frequency range of 1–100 kHz. Our SWCNT films have an aerogel structure. We systematically investigated their thermoacoustic performance as a function of the film thickness and purity. On the theoretical side, we obtained an analytic formula for the sound pressure in the ultrasound region and confirmed it by experiments and numerical simulations.

An implementation of carbon nanotube films in optoelectronic devices is still a challenging task which requires further improvement of their both optical and electrical properties. Here, we report an approach to enhance the transmittance of single-walled carbon nanotube films placed onto polymeric substrates without losses in the film conductivity by a low-power laser treatment. Laser pulses facilitate oxidation of nanotube caps thereby exposing iron catalytic particles due to fast local heating which leads to the oxidation of iron whereas the nanotube structure generally remains intact. Thus, we approached transmittance enhancement mainly across the visible range up to 4% (at 550 nm) associated with equivalent sheet resistance improvement of ca. 21%.

The rapid development of flexible and transparent electronics imposes growing demands on new highly conductive, optically transparent and mechanically robust materials. Single-walled carbon nanotubes (SWCNTs) are a unique material with diverse exceptional properties, which could be utilized in many fields of science and technology. We have synthesized high quality SWCNTs using an aerosol CVD method and examined doping technique to enhance their optoelectronic performance for transparent and conducting applications. We empirically selected the most effective dopant, HAuCl4, dissolved in various solvents (ethanol, acetonitrile, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, and n-methyl-2-pyrrolidone). We optimized the doping conditions and obtained the state-of-the-art sheet resistance value of as low as 40 Ω/□ at the transmittance of 90% at the wavelength of 550 nm.

Soft, flexible, and stretchable electronic devices provide novel integration opportunities for wearable and implantable technologies. Despite the existing efforts to endow electronics with the capability of large deformation, the main technological challenge is still in the absence of suitable materials for the manufacturing of stretchable electronic circuits and devices with active (sensitive) and passive (stable) components. Here, we present a universal material, based on single-walled carbon nanotube (SWCNT) films deposited on a polydimethylsiloxane (PDMS) substrate, which can act as a material being both sensitive and insensitive to strain. The diverse performance of SWCNT/PDMS structures was achieved by two simple dry-transfer fabrication approaches: SWCNT film deposition onto the as-prepared PDMS and on the prestretched PDMS surface. The correlation between applied strain, microstructural evolution, and electro-optical properties is discussed on the basis of both experimental and computational results. The SWCNT/PDMS material with the mechanically tunable performance has a small relative resistance change from 0.05 to 0.07, while being stretched from 10 to 40% (stable electrode applications). A high sensitivity of 20.1 of the SWCNT/PDMS structures at a 100% strain was achieved (strain sensing applications). Our SWCNT/PDMS structures have superior transparency and conductivity compared to the ones reported previously, including the SWCNT/PDMS structures, obtained by wet processes.

We propose a novel, scalable, and simple method for aerosol doping of single-walled carbon nanotube (SWCNT) films. This method is based on aerosolization of a dopant solution (HAuCl4 in ethanol) and time-controlled deposition of uniform aerosol particles on the nanotube film surface. The approach developed allows fine-tuning of the SWCNT work function in the range of 4.45 eV (for pristine nanotubes) to 5.46 eV, controllably varying the sheet resistance of the films from 79 to 3.2 Ω/□ for the SWCNT films with 50% transmittance (at 550 nm). This opens a new avenue for traditional and flexible optoelectronics: both to replace existing indium-tin oxide electrodes and to develop novel applications of the highly conductive transparent films.

Correction for ‘Highly efficient bilateral doping of single-walled carbon nanotubes’ by Anastasia E. Goldt et al., J. Mater. Chem. C, 2021, 9, 4514–4521, DOI: 10.1039/D0TC05996J.

Single-walled carbon nanotube (SWCNT) films are promising building blocks for diversified applications in electronics, photovoltaics, and photonics. However, their electrical and optical engineering is still a challenging task owing to multiple obstacles, including the absence of fast and easy-to-use methods for the determination of SWCNT film properties. Here, we present a rapid, contactless, and universal technique for accurate estimation of both SWCNT film thicknesses and their dielectric functions. The approach combines broadband optical absorbance and highly sensitive spectroscopic ellipsometry measurements. The observed linear dependence of the film thickness on its absorbance at 550nm provides a time-effective and contactless method of thickness assignment, which is of significant importance to the practical implementation of SWCNT films in optoelectronic devices. Additionally, our approach revealed that a simple procedure of film densification allows to controllably alter the dielectric response by atleast 40% and, thus, to add extra fine-tuning capabilities during material property engineering. Therefore, this express technique as a whole offers an advanced metrological tool for current and next-generation SWCNT-based devices.

Although carbon nanotubes have already been demonstrated to be a promising material for bolometric photodetectors, enhancing sensitivity while maintaining the speed of operation remains a great challenge. Here, we present a holey carbon nanotube network, designed to improve the temperature coefficient of resistance for highly sensitive ultra-fast broadband bolometers. Treatment of carbon nanotube films with low-frequency oxygen plasma allows fine tuning of the electronic properties of the material. The temperature coefficient of resistance of our films is much greater than the reported values for pristine carbon nanotubes, up to −2.8% K−1 at liquid nitrogen temperature. The bolometer prototypes made from the treated films demonstrate high sensitivity over a wide IR range, a short response time, smooth spectral characteristics and a low noise level.

Electrically conductive hydrogels (ECHs) are attracting much interest in the field of biomaterials science because of their unique properties. However, effective incorporation and dispersion of conductive materials in the matrices of polymeric hydrogels for improved conductivity remains a great challenge. Here, we demonstrate highly transparent, electrically conductive, stretchable tough hydrogels modified by single-walled carbon nanotubes (SWCNTs). Two different approaches for the fabrication of SWCNT/hydrogel structures are examined: a simple SWCNT film transfer onto the as-prepared hydrogel and the film deposition onto the pre-stretched hydrogel. Functionality of our method is confirmed by scanning electron microscopy along with optical and electrical measurements of our structures while subjecting them to different strains. Since the hydrogel-based structures are intrinsically soft, stretchable, wet, and sticky, they conform well to a human skin. We demonstrate applications of our material as skin-like passive electrodes and active finger-mounted joint motion sensors. Our technique shows promise to accelerate the development of biointegrated wearable electronics.

Carbon nanotubes (CNT) are being intensively studied for many applications because of their unique properties, such as high electrical and thermal conductivities, excellent mechanical and chemical stability. One of the areas of CNT application is a bolometric detection of near- and mid-infrared (IR) radiation. The record near-IR bolometric performance of CNT devices is comparable to the performance of the commercial vanadium oxide detectors [1]. However, the low intrinsic absorption of CNT in the mid-IR range limits their applications for the detection in the crucial 3-5 µm and 8-12 µm regions. The phenomenon of surface plasmon excitation has been utilized to improve light harvesting efficiency of solar cells and to increase absorption of monolayer graphene [2]. Plasmons were recently observed on an individual CNT [3], but the excitation of a surface plasmon on the macroscopic CNT films have not been reported yet. In the study, we experimentally demonstrate the 100%-enhanced bolometric response of a single-walled carbon nanotube (SWCNT) film in the vicinity of a mid-IR surface plasmon resonance. As a basis for the sample we use a pristine SWCNT film with the thickness of 400 nm, the width of 3 mm, and the length of 6 mm, suspended between two gold contacts. The femtosecond laser is used to drill 3- µm round holes which are arranged in a 2D square lattice with a period of 10 µm. Only one half of the film (3x3 mm2) is structured, while the second half is left unstructured to perform reference measurements. Reflectance and transmittance spectra of both parts of the film are measured with the Fourier-transform infrared spectrometer in the range 2-100 µm. Surface plasmon manifests itself as a Fano-type resonance in spectra of the structured part of the film at the wavelengths around 15 µm. The absorption of the structured part is enhanced in the same spectral region by 75% as compared with the unstructured part. Spectral dependence of the bolometric voltage sensitivity is measured using the sample as a detector of the spectrometer. It is shown that the voltage response of the structured part is enhanced in the vicinity of the surface-plasmon resonance by 100%. We show that the wavelength of the resonance and its magnitude can be controlled by tailoring the geometry of the sample. Numerical calculations by scattering-matrix method show that the central wavelength of the absorption resonance can be tuned in the range 5-25 µm. The maximum available enhancement of absorption is 240% as compared with the unstructured film. We claim that the proposed method applies to achieve enhanced spectrally selective response for any CNT-based bolometer in both near- and mid-infrared ranges of the spectrum. [1] G. E. Fernandes, J. H. Kim, A. K. Sood, J. Xu, Adv. Funct. Mater. 2013, 23, 4678. [2] N. K. Emani, T.-F. Chung, A. V Kildishev, et al. Nano Lett. 2013, 14, 78. [3] Z. Shi, X. Hong, H. A. Bechtel, et al. Nat. Photonics 2015, 9, 515

Carbon nanomaterials (carbon nanotubes (CNTs) and graphene) are promising materials for optoelectronic applications, including flexible transparent and conductive films (TCFs) due to their extraordinary electrical, optical and mechanical properties. However, the performance of CNT- or graphene-only TCFs still needs to be improved. One way to enhance the optoelectrical properties of TCFs is to hybridize CNTs and graphene. This approach leads to creation of a novel material that exhibits better properties than its individual constituents. In this work, the novel hybrid CNT-graphene nanomaterial was fabricated by graphene oxide deposition on top of CNT films. The graphene oxide was then reduced by thermal annealing at ambient atmosphere or in H2 atmosphere. At the final step the CNT-graphene hybrids were chemically doped using gold(III) chloride. As a result, we show that the hybrids demonstrate excellent optoelectrical performance with the sheet resistance as low as 73 Ω/□ at 90% transmittance.

We report an experimental observation of the midinfrared surface plasmon excited in a carbon nanotube plasmonic metasurface. The absorption of a 400-nm-thick single-walled carbon nanotube film perforated with laser-drilled subwavelength holes arranged in a 2D lattice is resonantly enhanced by 75% as compared with the unstructured film. The enhancement of absorption has a resonant behavior associated with the excitation of the surface plasmon and occurs at the wavelengths around 15 μm for the lattice period of 10 μm. The spectral position and the magnitude of the resonance are controlled entirely by the structure geometry and can be tuned in a broad range. We demonstrate that periodic patterning can be applied to tailor the bolometric performance of carbon nanotube thin films. Namely, the voltage response of the metasurface is enhanced by 100% at the wavelength of the plasmon resonance as compared with the unstructured film. We discuss mechanisms of the enhancement and compare experimental results with the finite-difference time-domain and scattering-matrix method simulations.

We report a simple approach to fabricate hybrid solar cells (HSCs) based on a single-walled carbon nanotube (SWCNT) film and thin film hydrogenated amorphous silicon (a-Si:H). Randomly oriented high-quality SWCNTs with conductivity enhanced by means of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate are used as a window layer and a front electrode. A series of HSCs are fabricated in ambient conditions with varying SWCNT film thicknesses. The polymethylmethacrylate layer drop-casted on fabricated HSCs reduces the reflection fourfold and enhances the short-circuit J sc , open-circuit V oc , and efficiency by nearly 10%. A state-of-the-art J-V performance is shown for SWCNT/a-Si HSC with an open-circuit voltage of 900 mV and an efficiency of 3.4% under simulated one-sun AM 1.5 G direct illumination.

We report high-performance, stable, low equivalent series resistance all-nanotube stretchable supercapacitor based on single-walled carbon nanotube film electrodes and a boron nitride nanotube separator. A layer of boron nitride nanotubes, fabricated by airbrushing from isopropanol dispersion, allows avoiding problem of high internal resistance and short-circuiting of supercapacitors. The device, fabricated in a two-electrode test cell configuration, demonstrates electrochemical double layer capacitance mechanism and retains 96% of its initial capacitance after 20 000 electrochemical charging/discharging cycles with the specific capacitance value of 82 F g−1 and low equivalent series resistance of 4.6 Ω. The stretchable supercapacitor prototype withstands at least 1000 cycles of 50% strain with a slight increase in the volumetric capacitance from 0.4 to 0.5 mF cm−3 and volumetric power density from 32 mW cm−3 to 40 mW cm−3 after stretching, which is higher than reported before. Moreover, a low resistance of 250 Ω for the as-fabricated stretchable prototype was obtained, which slightly decreased with the strain applied up to 200 Ω. Simple fabrication process of such devices can be easily extended making the all-nanotube stretchable supercapacitors, presented here, promising elements in future wearable devices.

Broad-band (4–20 000 cm−1) spectra of real and imaginary conductance of a set of high-quality pristine and AuCl3-doped single-walled carbon nanotube (SWCNT) films with different transparency are systematically measured. It is shown that while the high-energy (≥1 eV) response is determined by well-known interband transitions, the lower-energy electrodynamic properties of the films are fully dominated by unbound charge carriers. Their main spectral effect is seen as the free-carrier Drude-type contribution. Partial localization of these carriers leads to a weak plasmon resonance around 100 cm−1. At the lowest frequencies, below 10 cm−1, a gap-like feature is detected whose origin is associated with the energy barrier experienced by the carriers at the intersections between SWCNTs. It is assumed that these three mechanisms are universal and determine the low-frequency terahertz-infrared electrodynamics of SWCNT wafer-scale films.

By using the excellent optical and electrical properties of pristine SWNTs with long bundle lengths, we present single-walled carbon nanotube–silicon (SWNT/Si) solar cells of 11% power conversion efficiency (PCE), prepared without doping. The PCEs of the fabricated solar cells even increased slightly after 10 months of exposure to ambient conditions, without any external protection. The open-circuit voltage of the SWNT/Si solar cells under low light intensities, down to 10 mW cm−2, demonstrated the characteristics of the ideal p–n junction model. The mechanism was discussed, taking into account the effect of varying the interfacial oxide layer thickness between the SWNTs and Si on the solar cell’s performance. The high efficiency and stability demonstrated in this study make SWNT/Si solar cells one of practical choices for next generation energy system.

A mixture of single-walled and double-walled carbon nanotubes (CNTs) was synthesised by an aerosol CVD (floating catalyst) method for fabrication of highly conductive and transparent films. The feedstock solution contained ferrocene as a catalyst particle precursor, toluene and ethylene as carbon sources and thiophene as a promoter was introduced in the reactor in a hydrogen atmosphere and heated up in the temperature range of 1000–1200 °C. The product was collected downstream of the reactor by filtering the flow in the form of thin films with adjustable thicknesses (transmittance) and subsequently transferred on a desirable substrate by a dry transfer technique. This method allowed us to fabricate excellent quality CNT films with a high optoelectronic performance: with a sheet resistance of 86 Ω/sq. at the transmittance of T = 90%. To our best knowledge, for the first time the CNT transparent and conductive thin films were fabricated from direct filtration of gas phase grown CNTs using hydrocarbon as a carbon source.

Carbon NanoBud® transparent conductive films were Roll-to-Roll manufactured by aerosol synthesis and Direct Dry Printing®. For the first time, carbon based conductors are produced at 150 Ω/□ at 95% transmission. Carbon NanoBud® films are ready for scaling to volume manufacturing for high-quality flexible and rigid projected capacitive touch sensors.

Stretchable all-solid supercapacitors based on aerosol synthesized single-walled carbon nanotubes (SWCNTs) have been successfully fabricated and tested. High quality SWCNT films with excellent optoelectrical and mechanical properties were used as the current collectors and active electrodes of the stretchable supercapacitors. A transmittance of up to 75% was achieved for supercapacitors made from the assembly of two PDMS/SWCNT electrodes and a gel electrolyte in between. The transparent supercapacitor has a specific capacitance of 17.5 F g-1 and can be stretched up to 120% with practically no variation in the electrochemical performance after 1000 stretching cycles and 1000 charging-discharging cycles.

We report a hybrid solar cell based on single walled carbon nanotubes (SWNTs) interfaced with amorphous silicon (a-Si). The high quality carbon nanotube network was dry transferred onto intrinsic a-Si forming Schottky junction for metallic SWNT bundles and heterojunctions for semiconducting SWNT bundles. The nanotube chemical doping and a-Si surface treatment minimized the hysteresis effect in current-voltage characteristics allowing an increase in the conversion efficiency to 1.5% under an air mass 1.5 solar spectrum simulator. We demonstrated that the thin SWNT film is able to replace a simultaneously p-doped a-Si layer and transparent conductive electrode in conventional amorphous silicon thin film photovoltaics.

We report a simple and rapid method to prepare multifunctional free-standing single-walled carbon nanotube (SWCNT) films with variable thicknesses ranging from a submonolayer to a few micrometers having outstanding properties for a broad range of exceptionally performing devices. We have fabricated state-of-the-art key components from the same single component multifunctional SWCNT material for several high-impact application areas: high efficiency nanoparticle filters with a figure of merit of 147 Pa(-1), transparent and conductive electrodes with a sheet resistance of 84 Ω/◻ and a transmittance of 90%, electrochemical sensors with extremely low detection limits below 100 nM, and polymer-free saturable absorbers for ultrafast femtosecond lasers. Furthermore, the films are demonstrated as the main components in gas flowmeters, gas heaters, and transparent thermoacoustic loudspeakers.

Carbon nanobuds (CNBs) represent an emerging nanostructure, in which fullerene molecules are covalently bonded to the outer surface of single-walled carbon nanotubes (SWNTs). The Raman spectra of CNBs were systematically investigated and compared to those of SWNTs. The spectra were recorded using a 514 nm laser and evaluating the temperature-dependent Raman frequency shift in CNBs in the range 27−475 °C. The temperature coefficient of the G-mode frequency of the CNBs was much larger than that of the SWNTs. Consequently, the CNBs have lower thermal stability, which is attributed to the fact that the fullerenes are covalently bonded to the sidewall of SWNTs. At the same time, we observed that the radical breathing modes (RBMs) of CNBs downshift ∼2−6 cm−1 compared to the RBMs of SWNTs, and this shift can be attributed to the smaller van der Waals (VDWs) interactions between the CNBs. Using a 750 nm laser, a broad G− band, which is an intrinsic character of metallic properties, was clearly observed. This characteristic feature provides evidence that the nanobuds of some nanotubes remain metallic.

The single-walled carbon nanotubes (SWCNTs) were synthesized by the carbon monoxide disproportionation reaction on Fe catalyst particles formed by ferrocene vapor decomposition in a laminar flow aerosol (floating catalyst) reactor. On the basis of in situ sampling of the product collected at different locations in the reactor, kinetics of the SWCNT growth and catalyst particle crystallinity were studied. Catalyst particles captured before SWCNT nucleation as well as inactive particles were determined to have cementite (Fe3C) phase, while particles with γ- and α-Fe phases were found to be embedded in the SCWNTs. The growth rate in the temperature range from 804 to 915 °C was respectively varied from 0.67 to 2.7 μm/s. The growth rate constant can be described by an Arrhenius dependence with an activation energy of Ea = 1.39 eV, which was attributed to the carbon diffusion in solid iron particles. CNT growth termination was explained by solid–liquid phase transition in the catalyst particles. A high temperature gradient in the reactor was found to not have any effect on the diameter during the SWCNT growth and as a result on the chirality of the growing SWCNTs.

We studied a NanoBud structure in a local‐scale using high resolution transmission electron microscopy (HRTEM), scanning tunnelling microscopy (STM) and Raman spectroscopy. The HRTEM images show fullerenes on the outer surface of a single‐walled carbon nanotube (SWCNT) and the bonding between the fullerenes and SWCNT were examined by STM measurement, in which the fullerene attachment was stable against high bias imaging. We were also able to perform Raman measurement on a NanoBud structure. Characteristic features of the individual SWCNT, assigned as (16,11), and fullerenes were observed in the vibrational spectrum. The G band and the radial breathing mode (RBM) of SWCNTs as well as an additional feature at 1460 cm–1 were clearly presented simultaneously, which indicate the NanoBud structure.

We present a novel dry and room-temperature method for the deposition of random carbon nanotube networks (CNTNs) onto various substrates. This method is based on natural charging of carbon nanotube (CNT) bundles in the gas-phase and their efficient deposition directly downstream of the synthesis reactor by means of an electric field. The density of the deposited CNTNs was controllably adjusted by varying the deposition time and the electric field strength. Application of this deposition technique for the fabrication of single-walled CNTN-based field-effect transistors (FETS), where a random CNTN serves as a transport channel, is presented.

We developed a simple and direct thermo-compression method for integrating single-walled carbon nanotube (SWCNT) mats of adjustable thicknesses, transparency and conductivity into polymer films. Produced SWCNT/polyethylene composite films have exhibited good optical transparency and conductivity as well as high mechanical flexibility. It was found that the electrical conductivity of the SWCNT mats could be significantly improved by ethanol densification. SWCNT/polyethylene thin films demonstrated excellent cold electron field emission properties.

Decomposition of ferrocene vapor in CO and N2 atmospheres in the temperature range from 800 to 1150 °C leading to the formation of single-walled carbon nanotubes (CNTs) and maghemite (γ-Fe2O3) particles, respectively, was investigated by means of a differential mobility analyzer (DMA) and Fourier transform infrared spectroscopy, transmission electron microscopy, and laser desorption ionization time-of-flight spectrometry. This allowed us to produce aggregated iron oxide particles with mobility diameters of 20−60 nm and bundles of single-walled CNTs with mobility diameters of 60−100 nm. The DMA measurements of iron oxide particles revealed an equal negative and positive natural single charging with similar bimodal size distributions. Increasing the temperature resulted in the increase of the total particle concentration and a slight decrease in the fraction of charged particles from 30% to 20%. It was found that CNTs form spontaneously charged (92−99%) bundles carrying up to five elementary electrical charges. The concentration ratio between positively and negatively charged CNTs decreased from 6 to 1, increasing the temperature in the system from 800 to 1150 °C. The charging phenomenon can be explained by electron and ion emission owing to the surface minimization processes in both particles and CNTs, resulting in high-energy release.

Two different floating catalyst synthesis methods were used to investigate the effect of CO2 and H2O vapor on the growth of single‐walled carbon nanotubes (CNTs). As a carbon source and catalyst material, carbon monoxide and iron nanoparticles were used. The catalyst particles were prepared by evaporation from a resistively heated iron wire (hot wire generator) and by thermal decomposition of ferrocene vapor. The essential role of CO2 and H2O in the CNT formation was demonstrated. The addition of small amounts of CO2 and H2O vapor in the reactor resulted in an increase in CNT length. Also, the CO2 introduction was found to decrease the minimum temperature of the CNT synthesis from 890 °C to below 600 °C.

A spontaneous gas-phase charging phenomenon of single-walled carbon nanotube (CNT) bundles synthesized with an aerosol (floating catalyst) method has been discovered. CNT bundles were naturally both positively and negatively charged with up to four elementary charges, whereas individual nanotubes remained electrically neutral. On the basis of the observed self-charging of CNTs, a novel method for the gas-phase separation of individual CNTs from bundles and their subsequent deposition on any substrate at ambient temperature was developed.

This work for the first time reports the results on study of a polymer-free carbon nanotube (CNT) films used as a saturable absorber in an all-fibre laser. It is demonstrated that free-standing single-walled CNT films fabricated by an aerosol method are able to ensure generation of transform-limited pulses in an Er all-fibre ring laser with duration of several picoseconds and high quality of mode locking. The optimal average output power levels are identified, amounting to 0.4-0.5 mW depending on the linear transmission of the studied samples (60% or 80%). Application of polymer-free CNT films solves problems related to degradation of conventional polymer matrices of CNT-based saturable absorbers and paves the way to longer-lasting and more reliable saturable absorbers compatible with all-fibre laser configurations.

Single-walled carbon nanotube network field effect transistors were fabricated and studied as humidity sensors. Sensing responses were altered by changing the gate voltage. At the open channel state (negative gate voltage), humidity pulse resulted in the decrease of the source-drain current, and,vice versa, the increase in the source-drain current was observed at the positive gate voltage. This effect was explained by the electron-donating nature of water molecules. The operation speed and signal intensity was found to be dependent on the gate voltage polarity. The positive or negative change in current with humidity pulse at zero-gate voltage was found to depend on the previous state of the gate electrode (positive or negative voltage, respectively). Those characteristics were explained by the charge traps in the gate dielectric altering the effective gate voltage, which influenced the operation of field effect transistor.

The formation of a novel hybrid material, NanoBuds, single-walled carbon nanotubes (CNTs) with covalently attached fullerenes was investigated in a ferrocene–carbon monoxide system. Fullerenes and CNTs were simultaneously formed by carbon monoxide disproportionation on the surface of iron particles in the presence of etching agents such as H2O and CO2. On the basis of parametric investigations and in situ sampling of the product from different locations in the reactor the mechanisms for NanoBud formation are discussed.

Both fullerenes and single-walled carbon nanotubes (SWNTs) exhibit many advantageous properties. Despite the similarities between these two forms of carbon, there have been very few attempts to physically merge them. We have discovered a novel hybrid material that combines fullerenes and SWNTs into a single structure in which the fullerenes are covalently bonded to the outer surface of the SWNTs. These fullerene-functionalized SWNTs, which we have termed NanoBuds, were selectively synthesized in two different one-step continuous methods, during which fullerenes were formed on iron-catalyst particles together with SWNTs during CO disproportionation. The field-emission characteristics of NanoBuds suggest that they may possess advantageous properties compared with single-walled nanotubes or fullerenes alone, or in their non-bonded configurations.