Search

Funding Information: A.G.N and A.E.G thank the Council on grants of the President of the Russian Federation grant number НШ-1330.2022.1.3 and Russian Science Foundation (Project no. 22-13-00436). The theoretical calculations (L.Y.A.) were supported by Russian Science Foundation (Project identifier 21-79-10411). E.D.O. is grateful to RSF (project no. 21-72-20050) for support of photoluminescence investigations. Publisher Copyright: © 2022 Kalachikova et al.; licensee Beilstein-Institut. License and terms: see end of document. We propose a novel approach to disperse and extract small-diameter single-walled carbon nanotubes (SWCNTs) using an aqueous solution of riboflavin and Sephacryl gel. The extraction of small-diameter semiconducting SWCNTs was observed, regardless of the initial diameter distribution of the SWCNTs. Dispersion of SWCNTs occurs due to the adsorption of π-conjugated isoalloxazine moieties on the surface of small-diameter nanotubes and interactions between hydroxy groups of ribityl chains with water. During the SWCNT extraction, specific adsorption of riboflavin to SWCNTs leads to the minimization of interactions between the SWCNTs and gel media. Our experimental findings are supported by ab initio calculations demonstrating the impact of the riboflavin wrapping pattern around the SWCNTs on their interaction with the allyl dextran gel.

Rapid and accurate detection of cancer and neurological diseases is a major issue that has received great attention recently to enable early therapy treatment. In this report, we utilize an atmospheric pressure microplasma system to convert a natural bioresource chitosan into nitrogen-doped graphene quantum dots (NGQDs) for photoluminescence (PL) based selective detection of cancer and neurotransmitter biomarkers. By adjusting the pH conditions during the detection, multiple biomolecules including uric acid (UA), folic acid (FA), epinephrine (EP), and dopamine (DA) can be simultaneously detected with high selectivity and sensitivity using a single material only. Linear relationships between the biomarker concentration and the PL intensity ratio are obtained starting from 0.8 to 100 μM with low limits of detection (LoDs) of 123.1, 157.9, 80.5, and 91.3 nM for UA, EP, FA, and DA, respectively. Our work provides an insight into the multiple biomarker detection using a single material only, which is beneficial for the early detection and diagnosis of cancer and neurological diseases, as well as the development of new drugs.

The influence of saturable absorber parameters on the operation regimes of a dumbbell-shaped thulium fibre laser is studied. As saturable absorbers, polymer films with nanotubes characterised by different transmission coefficients in the saturated and unsaturated states are used. The operation of lasers with absorbers of different configurations used to obtain stable Q-switching and mode-locking regimes in the spectral range 1930 – 1960 nm is demonstrated. The average output power in the single-pulse mode-locking regime is 3.5 mW at a pulse repetition rate of 8.4 MHz and a pulse duration of 1.08 ps.

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...

Molybdenum- and tungsten-disulfide films are synthesized by chemical-vapor deposition. The set of optimal synthesis parameters (temperature, time, and amount and ratio of precursors) is established at which MoS2 domains with maximum lateral sizes of up to 250 μm on sapphire and MoS2 and WS2 domains up to 80 μm in size on SiO2 can be grown. Domain intergrowth leads to the formation of homogeneous single-layer MoS2 films. The Raman spectra of the synthesized films contain two characteristic peaks corresponding to the atomic vibrations in MoS2 and WS2. Photoluminescence of the single-layer and bilayer MoS2 films with a maximum intensity of 670 ± 2 nm and of the single-layer WS2 films with a maximum intensity of 630 ± 2 nm is detected. The photoluminescence spectral maps (the dependences of the photoluminescence intensity on the luminescence and excitation-light wavelengths) are measured. According to the measured data, the photoluminescence excitation spectrum of MoS2 has a maximum at 350 ± 5 nm and the photoluminescence excitation spectrum of WS2 has a maximum at 330 ± 5 nm. The I–V characteristics of the synthesized films are photosensitive in the visible spectral range.

Molecular magnetism and specifically magnetic molecules have recently gained plenty of attention as key elements for quantum technologies, information processing, and spintronics. Transition to the nanoscale and implementation of ordered structures with defined parameters is crucial for advanced applications. Single-walled carbon nanotubes (SWCNTs) provide natural one-dimensional confinement that can be implemented for encapsulation, nanosynthesis, and polymerization of molecules into nanoribbons. Recently, the formation of atomically precise graphene nanoribbons inside SWCNTs has been reported. However, there have been only a limited amount of approaches to form ordered magnetic structures inside the nanotube channels and the creation of magnetic nanoribbons is still lacking. In this work we synthesize and reveal the properties of cobalt-phthalocyanine based nanoribbons (CoPcNRs) encapsulated in SWCNTs. Raman spectroscopy, transmission electron microscopy, absorption spectroscopy, and density functional theory calculations allowed us to confirm the encapsulation and to reveal the specific fingerprints of CoPcNRs. The magnetic properties were studied by transverse magnetooptical Kerr effect measurements, which indicated a strong difference in comparison with the pristine unfilled SWCNTs due to the impact of Co incorporated atoms. We anticipate that this approach of polymerization of encapsulated magnetic molecules inside SWCNTs will result in a diverse class of protected low-dimensional ordered magnetic materials for various applications.

The narrow graphene nanoribbons (GNRs) are carbon based nanomaterials with interesting optical and electronic properties. We studied the photoluminescence properties of narrow graphene nanoribbons synthesized via the chemical vapor deposition method based on the bottom-up approach. The structure and quality of the synthesized GNR films were confirmed by measuring the Raman fingerprints of the 7-armchair graphene nanoribbons. The produced 7-armchair GNRs have a wide optical bandgap with an excitonic photoluminescence peak maximum at 608 nm (2.04 eV). At the same time, the 7-armchair GNR suspension has a bright photoluminescence in the infrared spectrum range with a peak maximum at 910 nm (1.36 eV). The relative intensity of this peak increases upon adding the p-type dopant to the GNR solution. The energy 1.36 eV of this luminescent transition is in good agreement with the theoretically predicted energy of the lowest bright trion state in the freestanding 7-armchair graphene nanoribbons. The demonstrated results can be beneficial for further study of narrow GNRs, especially in optics, and can be useful in applications of GNRs.

Efficient devices for control properties of electromagnetic waves are essential for the development of terahertz (THz) technologies. But despite the great progress achieved in a study of graphene, the influence of the number of graphene layers on its properties in the THz frequency range has not yet been sufficiently studied. In this work, we experimentally studied properties of multilayer graphene (MLG) films in the frequency range 0.2–0.8 THz, at a room temperature, and a relative humidity of 40%. Using our custom-made THz time-domain spectroscopic polarimetry system, we obtained spectra of the complex relative permittivity and the electrical conductance of the chemical vapor deposition graphene with ∼14, ∼40, and ∼76 layers of graphene on glass substrates. It is shown that the conductance increases nonlinearly with an increase in the graphene layer number and reaches, for ∼76 layers, 0.06 S for the real, and 0.03 S for the imaginary part, respectively.

We experimentally studied the room-temperature polarization-resolved electrical conductance of multilayer graphene-based films using a home-made terahertz time-domain spectroscopic polarimetry system. The conductance increases nonlinearly with an increase in the graphene layer number and reaches, for ~76 layers, 0.06 S for the real, and 0.03 S for the imaginary part, respectively.

We have optimised a hybrid mode-locked holmium-doped fibre laser and a holmium-doped fibre amplifier for obtaining stable pulses as short as possible. Temporal and spectral characteristics of pulsed light have been measured as functions of pump power. Lasing has been achieved in the wavelength range 2066 – 2068 nm, with a full width at half maximum of the emission spectrum from 3 to 4 nm. The pulse duration does not exceed 1 ps and the pulse energy ranges from 0.2 to 0.5 nJ. To raise the pulse energy, holmium-doped fibre amplifiers based on two types of active fibre have been used. We have demonstrated a decrease in the width of the central part of the pulse autocorrelation function and considerable broadening of the spectrum of the pulses. The maximum average power at the amplifier output exceeds 200 mW.

Graphene film formation by carbon deposition from gaseous phase on nickel substrates is investigated using scanning tunnel microscope (STM) unit embedded into reactor of the chemical vapor deposition (CVD) system. The microscope was designed to provide STM measurements at the same 1 μm × 1 μm region on the sample surface before and just after CVD synthesis without taking the sample out of the reactor. The peculiarities of graphene deposits formation on polycrystalline nickel substrates are revealed using developed CVD-STM system. The topology features are analyzed in combination with Raman spectroscopy data. One of particular features revealed in this study is nanobubbles formation and collapse on graphene film surface. We are discussing possible mechanisms of this phenomenon.

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.

We developed a novel robust technique to produce high-quality dispersions of debundled SWCNTs in aqueous solutions. Direct injection of SWCNTs treated with supercritical nitrogen into the aqueous surfactant solution facilitates the dispersion process without the need of extensive ultrasonication. According to photoluminescence and absorbance measurements, the mild ultrasonic treatment of such dispersions resulted in a higher yield of individual SWCNTs, compared to pristine tubes and tubes collected after the supercritical treatment in the form of powder.

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.

We report a new solid-state waveguide laser generating picosecond pulses with a GHz repetition rate, based on the use of graphene as a saturable absorber. Lasing at the main transverse mode is provided by the geometry of a cylindrical waveguide formed in the active crystal volume by the method of direct writing with a femtosecond laser beam. Fine tuning of the intracavity interferometer formed between the active medium and output mirror makes it possible to control the spectral-temporal parameters of output radiation and to smoothly tune the repetition rate of pulses having a duration of less than 20 ps. In particular, the possibility of dual-wavelength generation in the regime of continuous passive mode locking using a single saturable absorber based on graphene is demonstrated. By amplifying laser output radiation in the ytterbium fibre amplifier, an average output power of 530 mW is obtained.

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.

Theoretical studies of graphene began long before the first real samples were obtained (Wallace, 1947). Calculations performed in the 1930s and 1940s showed that a free two-dimensional film must be thermodynamically unstable. For this reason monolayer structures were obtained only on the surface of bulk materials. The first steps to make single carbon layers were made in the 1960s and 1970s using the reduction of graphite oxide from colloidal solutions (Boehm et al., 1962a, b) and the method of chemical vapor deposition (CVD) of hydrocarbons on metal substrates (Eizenberg and Blakely, 1979) or on their carbides (Aizawa et al., 1990). It has been shown that a high-temperature treatment of silicon carbide with evaporation of silicon leads to the formation of carbon film, that is, the so-called epitaxial growth is realized (van Bommel et al., 1975; Forbeaux et al., 1998). However, in all the works listed above, carbon films with a thickness of at least 20–30 layers were obtained, which were not inherently graphene. A detailed review of early experiments on the preparation of thin graphite layers was given in Jang and Zhamu (2008).

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.

Chemical vapor deposition synthesis of graphene on copper foil from methane is the most promising technology for industrial production. However, an important problem of the formation of the second and subsequent graphene layers during synthesis arises due to the strong roughness of the initial copper foil. Here we demonstrate the various approaches to prepare a smooth copper surface before graphene synthesis to reduce the formation of multi-layer graphene islands. Six methods of surface processing of copper foils are studied, and the decrease of the roughness from 250 to as low as 80 nm is achieved. The correlation between roughness and the formation of multi-layer graphene is demonstrated. Under optimized conditions of surface treatment, the content of the multi-layer graphene islands drops from 9% to 2.1%. The quality and the number of layers of synthesized graphene are analyzed by Raman spectroscopy, scanning electron microscopy, and measurements of charge mobility.

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.

Plasmonic interferometry is a rapidly growing area of research with a huge potential for applications in the terahertz frequency range. In this Letter, we explore a plasmonic interferometer based on graphene field effect transistor connected to specially designed antennas. As a key result, we observe helicity- and phase-sensitive conversion of circularly polarized radiation into dc photovoltage caused by the plasmon-interference mechanism: two plasma waves, excited at the source and drain part of the transistor, interfere inside the channel. The helicity-sensitive phase shift between these waves is achieved by using an asymmetric antenna configuration. The dc signal changes sign with inversion of the helicity. A suggested plasmonic interferometer is capable of measuring the phase difference between two arbitrary phase-shifted optical signals. The observed effect opens a wide avenue for phase-sensitive probing of plasma wave excitations in two-dimensional materials.

The patterning and transfer of a two-dimensional graphene film without damaging its original structure is an urgent and difficult task. For this purpose, we propose the use of the blister-based laser-induced forward transfer (BB-LIFT), which has proven itself in the transfer of such delicate materials. The ease of implementation of laser techniques reduces the number of intermediate manipulations with a graphene film, increasing its safety. The work demonstrates the promise of BB-LIFT of single-layer graphene from a metal surface to a SiO2/Si substrate. The effect of the parameters of this method on the structure of transferred graphene islands is investigated. The relevance of reducing the distance between irradiating and receiving substrates for the transfer of free-lying graphene is demonstrated. The reasons for the damage to the integrity of the carbon film observed in the experiments are discussed. The preservation of the original crystal structure of transferred graphene is confirmed by Raman spectroscopy.

Thin layers of gallium selenide (GaSe) have been fabricated on Si:SiO2 substrates by micromechanical exfoliation. Size-induced effects in GaSe thin layers of various thickness have been revealed. The photoluminescence maximum associated with direct free exciton transition shifts to higher energies with reduction of GaSe crystal thickness. When going from the bulk GaSe crystal down to 6 tetralayers, the bandgap value increases from 2 eV (620 nm) to 2.17 eV (571 nm). No photoluminescence signal has been detected for GaSe layers thinner than 6 TL. At the same time, the Raman spectra of thin GaSe flakes demonstrate the features corresponding to Ga2Se3, Ga2O3 and other compounds. The appearance of these lines is attributed to thermal and photo-induced oxidation of GaSe layers. For the thin flakes, a remarkable modification of the photoluminescence spectra shape takes place. Presumably, it is a consequence of the electronic structure evolution, as the top of the valence band has undergone changes and has flattened for 8 TL.

Magneto-transport properties were studied on thin films of a 3D topological insulator (TI) Bi 2 Se 3 grown on graphene (Gr) by physical vapor deposition . It was shown that the main contribution to the conductance is from the bulk states, whereas magnetoresistance is determined by both surface and bulk channels. The input of the charge transport over the surface states in the Si/SiO 2/Gr/Bi 2 Se 3 structure reveals itself in the weak antilocalization effect. The transition from a weak antilocalization to a weak localization is observed with decreasing the film thickness. The band bending on both interfaces makes it possible to explain the contribution to a weak antilocalization from different surfaces at different TI film thicknesses.

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.

We report on the detection of sub-terahertz radiation using single layer graphene and graphene-nanoribbon FETs with asymmetric contacts (one is the Schottky contact and one – the Ohmic contact). We found that cutting graphene into ribbons a hundred nanometers wide leads to a decrease of the response to sub-THz radiation. We show that suppression of the response in the graphene nanoribbons devices can be explained by unusual properties of the Schottky barrier on graphene-vanadium interface.

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.

A single-wavelength compact diode-pumped solid-state laser based on a single-mode waveguide with a diameter of 20 µm and graphene saturable absorber is presented in this work. The total reflection coefficient of the intracavity interferometer has a significant effect on the level of intracavity losses. By accurate controlling the intracavity losses a stable continuous wave passive mode-locking at wavelength of 1064 nm with a pulse repetition rate of 9.5 GHz was obtained.

We studied the optical comb peculiarities of the ultra-short dispersion-managed soliton generation in an erbium-doped all-fiber ring laser hybrid mode-locked with carbon:boron nitride single-walled nanotubes in the co-action with a nonlinear polarization evolution. A stable low-intensity-noise optical comb was obtained with a narrow single comb linewidth of 18.1 kHz based on dechirped 90-fs pulses with a repetition rate of 42.22 MHz, a spectral pulse width of 56 nm, and an average output power of 16.7 mW corresponding to 4.4-kW maximum peak power and 0.4-nJ pulse energy.

Structural and optical properties of films and particles prepared from partially fluorinated graphene suspensions were examined. Photoluminescence (PL) coming from partially fluorinated graphene suspensions (quantum dots with fluorinated edges) and films prepared from such suspensions was observed. The necessary conditions for excitation of photoluminescence and PL emission spectra consisting of one to three PL features with energies 2.65, 2.81, and 2.97 eV have been identified. The PL emission spectra were compared with the spectrum of the size quantization levels in partially fluorinated graphene and few-layer graphene films. The spectrum of levels was revealed from the charge deep-level transient spectroscopy measurements taken during studying the electron capture and the emission processes in such films. The PL emission spectra were interpreted with the assumption that fluorination of graphene suspensions leads to formation of quantum dots within graphene. A qualitative model was proposed to explain the observed correlation between the PL emission spectrum and the energy spectrum of graphene quantum dots embedded in a fluorinated graphene matrix.

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.

Ultrafast fiber sources operating in the spectral range of 2–3 μm have attracted attention due to a number of possible applications, e.g. for perspective communications, gas sensing, nonlinear frequency conversion, and medicine. Holmium-doped fibers (HDF) are commonly used as a gain medium for 2 μm lasers due to their broad gain spectrum, extending from 2 to 2.2 μm.

Electrochemical deposition of cobalt nanoparticles was used to modify carrier transport properties of single-layered CVD graphene at the SiO2-on-Si substrate. The structure of graphene with cobalt nanoparticles was analyzed by Raman spectroscopy and scanning electron microscopy. The effect of the deposited cobalt nanoparticles on the sheet resistance of graphene was studied in the temperature range of 4–300[Formula: see text]K.