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Lithium adsorption on high-surface-area porous carbon (PC) nanomaterials provides superior electrochemical energy storage performance dominated by capacitive behavior. In this study, we demonstrate the influence of structural defects in the graphene lattice on the bonding character of adsorbed lithium. Thermally evaporated lithium was deposited in vacuum on the surface of as-grown graphene-like PC and PC annealed at 400 °C. Changes in the electronic states of carbon were studied experimentally using surface-sensitive X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS data in combination with density functional theory calculations revealed the dative interactions between lithium sp 2 hybridized states and carbon π*-type orbitals. Corrugated defective layers of graphene provide lithium with new bonding configurations, shorter distances, and stronger orbital overlapping, resulting in significant charge transfer between carbon and lithium. PC annealing heals defects, and as a result, the amount of lithium on the surface decreases. This conclusion was supported by electrochemical studies of as-grown and annealed PC in lithium-ion batteries. The former nanomaterial showed higher capacity values at all applied current densities. The results demonstrate that the lithium storage in carbon-based electrodes can be improved by introducing defects into the graphene layers., Competing Interests: The authors declare no conflict of interest.

Molybdenum disulfide (MoS 2 ) is the second two-dimensional material after graphene that received a lot of attention from the research community. Strong S-Mo-S bonds make the sandwich-like layer mechanically and chemically stable, while the abundance of precursors and several developed synthesis methods allow obtaining various MoS 2 architectures, including those in combinations with a carbon component. Doping of MoS 2 with heteroatom substituents can occur by replacing Mo and S with other cations and anions. This creates active sites on the basal plane, which is important for the adsorption of reactive species. Adsorption is a key step in the gas detection and electrochemical energy storage processes discussed in this review. The literature data were analyzed in the light of the influence of a substitutional heteroatom on the interaction of MoS 2 with gas molecules and electrolyte ions. Theory predicts that the binding energy of molecules to a MoS 2 surface increases in the presence of heteroatoms, and experiments showed that such surfaces are more sensitive to certain gases. The best electrochemical performance of MoS 2 -based nanomaterials is usually achieved by including foreign metals. Heteroatoms improve the electrical conductivity of MoS 2 , which is a semiconductor in a thermodynamically stable hexagonal form, increase the distance between layers, and cause lattice deformation and electronic density redistribution. An analysis of literature data showed that co-doping with various elements is most attractive for improving the performance of MoS 2 in sensor and electrochemical applications. This is the first comprehensive review on the influence of foreign elements inserted into MoS 2 lattice on the performance of a nanomaterial in chemiresistive gas sensors, lithium-, sodium-, and potassium-ion batteries, and supercapacitors. The collected data can serve as a guide to determine which elements and combinations of elements can be used to obtain a MoS 2 -based nanomaterial with the properties required for a particular application.

The effect of humidity on the electrical conductivity of single-walled carbon nanotube (SWCNT) films depends on both the conductivity of individual nanotubes and the electrical contacts between them. Here, we study these factors by comparing the sensor response of nanotubes with fluorine- and nitrogen-containing groups attached to the sidewalls. Experiments carried out in a wide range of relative humidity (RH) at room and elevated temperatures showed that the conductivity of non-functionalized SWCNTs and contacts between them decreases upon the adsorption of water molecules. Covalent fluorination reduces the conductivity of SWCNTs and significantly increases the sensitivity of the film to low concentrations of water vapor. The response at high RH decreases due to the large number of water molecules adsorbed on the conductive regions of the nanotubes. As a result of substitutional reactions of fluorinated SWCNTs with dimethylformamide and ethylenediamine, nitrogen-containing groups are added, the amount of which, however, is much less than the amount of fluorine. This modification of the SWCNTs improves intertube contacts in the film and increases the surface area for water adsorption. Our results show that an increase in the number of functional groups on the SWCNT surface enhances the sensitivity of the sensor to low water concentrations and worsens the response at high RH. SWCNTs modified with ethylenediamine have the highest sensitivity over the entire range of RH.

Diamond is an important material for electrical and electronic devices. Because the diamond is in contact with the metal in these applications, it becomes necessary to study the metal-diamond interaction and the structure of the interface, in particular, at elevated temperatures. In this work, we study the interaction of the (100) and (111) surfaces of a synthetic diamond single crystal with spattered titanium and molybdenum films. Atomic force microscopy reveals a uniform coating of titanium and the formation of flattened molybdenum nanoparticles. A thin titanium film is completely oxidized upon contact with air and passes from the oxidized state to the carbide state upon annealing in an ultrahigh vacuum at 800 °C. Molybdenum interacts with the (111) diamond surface already at 500 °C, which leads to the carbidization of its nanoparticles and catalytic graphitization of the diamond surface. This process is much slower on the (100) diamond surface; sp 2 -hybridized carbon is formed on the diamond and the top of molybdenum carbide nanoparticles, only when the annealing temperature is raised to 800 °C. The conductivity of the resulting sample is improved when compared to the Ti-coated diamond substrates and the Mo-coated (111) substrate annealed at 800 °C. The presented results could be useful for the development of graphene-on-diamond electronics.

We propose an original technique for the grating metasurfaces fabrication by low-power ultraviolet laser treatment of fluorinated graphene (FG) films with the focus on terahertz applications. The laser treatment reduces dielectric FG to its conductive counterparts, increasing DC conductivity to 170 S·m -1 for treated areas. The electromagnetic response of the grating metasurfaces studied by THz time-domain spectroscopy in the 100 GHz-1 THz frequency range demonstrates enhanced resonant transmittance through metasurfaces. The intensity and position of transmittance peak could be tuned by changing the metasurface geometry, i.e. the period of the structure and width of the reduced and unreduced areas. In particular, the decrease of the reduced FG area width from 400 to 170 μ m leads to the shift of the resonance peak from 0.45 THz to the higher frequencies, 0.85 THz. Theoretical description based on the multipole theory supported by finite element numerical calculations confirms the excitation of the dark state in the metasurface unit cells comprising reduced and unreduced FG areas at resonance frequency determined by the structure geometrical features. Fabricated metasurfaces have been proved to be efficient narrowband polarizers being rotated by 50° about the incident THz field vector., (© 2023 IOP Publishing Ltd.)

Ni supported on N-doped carbon is rarely studied in traditional catalytic reactions. To fill this gap, we compared the structure of 1 and 6 wt% Ni species on porous N-free and N-doped carbon and their efficiency in hydrogen generation from gaseous formic acid. On the N-free carbon support, Ni formed nanoparticles with a mean size of 3.2 nm. N-doped carbon support contained Ni single-atoms stabilized by four pyridinic N atoms (N 4 -site) and sub-nanosized Ni clusters. Density functional theory calculations confirmed the clustering of Ni when the N 4 -sites were fully occupied. Kinetic studies revealed the same specific Ni mass-based reaction rate for single-atoms and clusters. The N-doped catalyst with 6 wt% of Ni showed higher selectivity in hydrogen production and did not lose activity as compared to the N-free 6 wt% Ni catalyst. The presented results can be used to develop stable Ni catalysts supported on N-doped carbon for various reactions.

We report the fabrication of high-performance NO 2 gas sensors based on oxyfluorinated graphene (OFG) layers. At room temperature, the times of adsorption/desorption of NO 2 on/from the surface of thin OFG films are less than 1200 s and can be reduced by increasing the operation temperature. The sensors are capable of detecting NO 2 molecules at sub-ppm level with a sensitivity of 0.15 ppm -1 at 348 K. The temperature dependence of the rate constants shows that the simultaneous presence of a large number of fluorine- and oxygen-containing groups on the graphene surface provides the formation of low-energy sites (Δ H a < 0.1 eV) for NO 2 adsorption. The combination of the high sensitivity of the sensor and a reasonable adsorption/desorption time of the analyte is promising for on-line monitoring.

Single-walled carbon nanotubes (SWCNTs) with their high surface area, electrical conductivity, mechanical strength and elasticity are an ideal component for the development of composite electrode materials for batteries. Red phosphorus has a very high theoretical capacity with respect to lithium, but has poor conductivity and expends considerably as a result of the reaction with lithium ions. In this work, we compare the electrochemical performance of commercial SWCNTs with red phosphorus deposited on the outer surface of nanotubes and/or encapsulated in internal channels of nanotubes in lithium-ion batteries. External phosphorus, condensed from vapors, is easily oxidized upon contact with the environment and only the un-oxidized phosphorus cores participate in electrochemical reactions. The support of the SWCNT network ensures a stable long-term cycling for these phosphorus particles. The tubular space inside the SWCNTs stimulate the formation of chain phosphorus structures. The chains reversibly interact with lithium ions and provide a specific capacity of 1545 mAh·g -1 (calculated on the mass of phosphorus in the sample) at a current density of 0.1 A·g -1 . As compared to the sample containing external phosphorus, SWCNTs with encapsulated phosphorus demonstrate higher reaction rates and a slight loss of initial capacity (~7%) on the 1000th cycle at 5 A·g -1 .

Arrays of aligned carbon nanotubes (CNTs) are anisotropic nanomaterials possessing a high length-to-diameter aspect ratio, channels passing through the array, and mechanical strength along with flexibility. The arrays are produced in one step using aerosol-assisted catalytic chemical vapor deposition (CCVD), where a mixture of carbon and metal sources is fed into the hot zone of the reactor. Metal nanoparticles catalyze the growth of CNTs and, during synthesis, are partially captured into the internal cavity of CNTs. In this work, we considered various stages of multi-walled CNT (MWCNT) growth on silicon substrates from a ferrocene-toluene mixture and estimated the amount of iron in the array. The study showed that although the mixture of precursors supplies evenly to the reactor, the iron content in the upper part of the array is lower and increases toward the substrate. The size of carbon-encapsulated iron-based nanoparticles is 20-30 nm, and, according to X-ray diffraction data, most of them are iron carbide Fe 3 C. The reasons for the gradient distribution of iron nanoparticles in MWCNT arrays were considered, and the possibilities of controlling their distribution were evaluated.

Single-walled carbon nanotubes (SWCNTs) are a perfect host for the formation of one-dimensional phosphorus structures and to obtain hybrid materials with a large P-C ratio. This work presents a procedure for high-yield phosphorus filling of commercial Tuball SWCNTs and efficient removal of phosphorus deposits from the external nanotube surface. We probed white and red phosphorus as precursors, varied the synthesis temperature and the ampoule shape, and tested three solvents for sample purification. High-resolution transmission electron microscopy and Raman spectroscopy indicated crystallization of interior phosphorus in a form resembling fibrous red phosphorus. An aqueous sodium hydroxide solution allowed removing the majority of external phosphorus particles. Thermogravimetric analysis of the product determined ∼23 wt % (∼10 atom %) of phosphorus, and the X-ray photoelectron spectroscopy (XPS) data showed that ca. 80% of it is in the form of elemental phosphorus. Externally purified SWCNTs filled with phosphorus were used to study the interaction between the components. Raman spectroscopy and core-level XPS revealed p-type SWCNT doping. Valence-band XPS data and density functional theory calculations confirmed the transfer of the SWCNT electron density to the encapsulated phosphorus.

We identify the "missing" 1D-phosphorus allotrope, red phosphorus chains, formed in the interior of tip-opened single-walled carbon nanotubes (SWCNTs). Via a comprehensive experimental and theoretical study we show that in intermediate diameter cavities (1.6-2.9 nm), phosphorus vapor condenses into linear P8]P2 chains and fibrous red-phosphorus type cross-linked double-chains. Thermogravimetric and X-ray photoelectron spectroscopy analysis estimates ∼7 atom % of elemental phosphorus in the sample, while high-resolution energy dispersive X-ray spectroscopy mapping reveals that phosphorus fills the SWCNTs. High-resolution transmission electron microscopy (HRTEM) shows long chains inside the nanotubes with varying arrangement and packing density. A detailed match is obtained between density functional theory (DFT) simulations, HRTEM, and low-frequency Raman spectroscopy. Notably, a signature spectroscopic signal for phosphorus chain cross-linking is identified. When coupled with reinterpretation of literature data and wide-ranging DFT calculations, these results reveal a comprehensive picture of the diameter dependence of confined 1D-phosphorus allotropes.

Fluorinated graphitic layers with good mechanical and chemical stability, polar C-F bonds, and tunable bandgap are attractive for a variety of applications. In this work, we investigated the photolysis of fluorinated graphites with interlayer embedded acetonitrile, which is the simplest representative of the acetonitrile-containing photosensitizing family. The samples were continuously illuminated in situ with high-brightness non-monochromatized synchrotron radiation. Changes in the compositions of the samples were monitored using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NEXAFS N K-edge spectra showed that acetonitrile dissociates to form HCN and N 2 molecules after exposure to the white beam for 2 s, and the latter molecules completely disappear after exposure for 200 s. The original composition of fluorinated matrices CF 0.3 and CF 0.5 is changed to CF 0.10 and GF 0.17 , respectively. The highly fluorinated layers lose fluorine atoms together with carbon neighbors, creating atomic vacancies. The edges of vacancies are terminated with the nitrogen atoms and form pyridinic and pyrrolic units. Our in situ studies show that the photolysis products of acetonitrile depend on the photon irradiation duration and composition of the initial CF x matrix. The obtained results evaluate the radiation damage of the acetonitrile-intercalated fluorinated graphites and the opportunities to synthesize nitrogen-doped graphene materials.

Herein, ZIF-8 pre-grown on carbon cloth (CC) leads to preferential and homogenizing Zn deposition to accelerate Zn-ion diffusion. CC with uniform Zn deposits induced from ZIF-8 promotes rapid Zn plating, resulting in balanced kinetics between electrodes. The as-assembled ZICs show a high specific capacitance of 302 F g -1 at 0.5 A g -1 , an outstanding rate performance of 188 F g -1 at 20 A g -1 and 100% capacitance retention after 10000 cycles.

The patterning of arrays of aligned multi-walled carbon nanotubes (MWCNTs) allows creating metastructures for terahertz (THz) applications. Here, the strips and columns from MWCNTs vertically grown on silicon substrates are prepared using CO 2 laser treatment. The tops of the patterned arrays are flat when the laser power is between 15 and 22 W, and craters appear there with increasing power. Laser treatment does not destroy the alignment of MWCNTs while removing their poorly ordered external layers. The products of oxidative destruction of these layers deposit on the surfaces of newly produced arrays. The oxygen groups resulting from the CO 2 laser treatment improve the wettability of nanotube arrays with an epoxy resin. We show that the patterned MWCNT arrays absorb the THz radiation more strongly than the as-synthesized arrays. Moreover, the pattern influences the frequency behavior of the absorbance.

The interlayer space of 2D materials can be a slit reactor where transformations not typical for the gas phase occur. We report redox reactions involving acetonitrile and nitrogen oxide guests in galleries of fluorinated graphite. Fluorinated graphite intercalation compounds with acetonitrile are treated with dinitrogen tetraoxide and the synthesis products are studied by a set of experimental methods. Data analysis reveals that N2O4 dissociates in fluorinated graphite matrices to form nitrogen-containing species NO3, NO2, NO, and N2. The interaction of NO3 with acetonitrile yields HNO3, which predominates as a guest in the synthesis products independently of the fluorination degree of the matrix. This reaction is accompanied by the removal of fluorine atoms weakly bonded to the graphite layers, leading to partial defluorination of the matrices. Our work demonstrates the possibility of using fluorinated graphite as a test nanoreactor whose dimension can be controlled by fluorination of the layers.

Robust electrode materials without the addition of binders allow increasing efficiency of electrical storage devices. We demonstrate the fabrication of binder-free electrodes from modified single-walled carbon nanotubes (SWCNTs) for electrochemical double-layer capacitors (EDLCs). Modification of SWCNTs included a sonication in 1,2-dichlorobenzene and/or fluorination with gaseous BrF 3 at room temperature. The sonication caused the shortening of SWCNTs and the splitting of their bundles. As a result, the film prepared from such SWCNTs had a higher density and attached a larger amount of fluorine as compared to the film from non-sonicated SWCNTs. In EDLCs with 1M H 2 SO 4 electrolyte, the fluorinated films were gradually defluorinated, which lead to an increase of the specific capacitance by 2.5-4 times in comparison with the initial values. Although the highest gravimetric capacitance (29 F g -1 at 100 mV s -1 ) was observed for the binder-free film from non-modified SWCNT, the fluorinated film from the sonicated SWCNTs had an enhanced volumetric capacitance (44 F cm -3 at 100 mV s -1 ). Initial SWCNT films and defluorinated films showed stable work in EDLCs during several thousand cycles.

Carbon nanohorns (CNHs) are attractive for various applications, where a high specific surface area and long dispersion stability in water are important. In the present work, we study these parameters of CNHs prepared by arc evaporation of graphite depending on the conditions of the synthesis and subsequent oxidation in air. It is shown that the addition of toluene in the reactor during the arcing allows obtaining CNHs functionalized with -CH x groups. Heating of CNHs in air at 400 °C leads to substitution of -CH x groups for oxygen-containing groups. Moreover, the CNH endcaps are opened at 500 °C, and as a result, the specific surface area of CNHs increases 4 times. Aqueous suspensions with a concentration of oxidized CNHs of 100 µg/mL are stable for 8 months.

In this paper we present a successful approach for the generation of partially fluorinated graphene structures. A computationally simple model optimized on a large density functional theory dataset quickly and precisely predicts experimentally observed structures. From the analysis of the structural diversity of fluorinated graphene in a wide range of synthesis temperatures, the general structural patterns are identified and the conditions for their achievement are determined. In addition, to facilitate further studies of fluorinated graphene, we present a ready-to-use GenCF code that implements the described structure generator.

Highly porous nitrogen-doped carbon nanomaterials have distinct advantages in energy storage and conversion technologies. In the present work, hydrothermal treatments in water or ammonia solution were used for modification of mesoporous nitrogen-doped graphitic carbon, synthesized by deposition of acetonitrile vapors on the pyrolysis products of calcium tartrate. Morphology, composition, and textural characteristics of the original and activated materials were studied by transmission electron microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared spectroscopy, and nitrogen gas adsorption method. Both treatments resulted in a slight increase in specific surface area and volume of micropores and small mesopores due to the etching of carbon surface. Compared to the solely aqueous medium, activation with ammonia led to stronger destruction of the graphitic shells, the formation of larger micropores (1.4 nm vs 0.6 nm), a higher concentration of carbonyl groups, and the addition of nitrogen-containing groups. The tests of nitrogen-doped carbon materials as electrodes in 1M H 2 SO 4 electrolyte and sodium-ion batteries showed improvement of electrochemical performance after hydrothermal treatments especially when ammonia was used. The activation method developed in this work is hopeful to open up a new route of designing porous nitrogen-doped carbon materials for electrochemical applications., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Vertically aligned carbon nanotube (CNT) arrays show potential for the development of planar low-voltage emission cathodes. The characteristics of cathodes can be improved by modifying their surface, e.g., by hydrogen plasma treatment, as was performed in this work. The surface of multi-walled CNT arrays grown on silicon substrates from toluene and ferrocene using catalytic chemical vapor deposition was treated in a high-pressure (~10 4 Pa) microwave reactor. The structure, composition, and current-voltage characteristics of the arrays were studied before and after hydrogen plasma treatment at various power values and durations. CNT tips were destroyed and catalytic iron was released from the CNT channels. The etching rate was influenced by iron particles that formed on the array surface. The lower emission threshold in the plasma-treated arrays than in the initial sample is explained by the amplification factor of the local electric field increasing due to graphene structures of unfolded nanotube layers that formed at the CNT tips.

The electrical conductivity of graphene materials is strongly sensitive to the surface adsorbates, which makes them an excellent platform for the development of gas sensor devices. Functionalization of the surface of graphene opens up the possibility of adjusting the sensor to a target molecule. Here, we investigated the sensor properties of fluorinated graphene films towards exposure to low concentrations of nitrogen dioxide NO 2 . The films were produced by liquid-phase exfoliation of fluorinated graphite samples with a composition of CF 0.08 , CF 0.23 , and CF 0.33. Fluorination of graphite using a BrF 3 /Br 2 mixture at room temperature resulted in the covalent attachment of fluorine to basal carbon atoms, which was confirmed by X-ray photoelectron and Raman spectroscopies. Depending on the fluorination degree, the graphite powders had a different dispersion ability in toluene, which affected an average lateral size and thickness of the flakes. The films obtained from fluorinated graphite CF 0.33 showed the highest relative response ca. 43% towards 100 ppm NO 2 and the best recovery ca. 37% at room temperature.

Filling of single-walled carbon nanotubes (SWCNTs) and extraction of the encapsulated species from their cavities are perspective treatments for tuning the functional properties of SWCNT-based materials. Here, we have investigated sulfur-modified SWCNTs synthesized by the ampoule method. The morphology and chemical states of carbon and sulfur were analyzed by transmission electron microscopy, Raman scattering, thermogravimetric analysis, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopies. Successful encapsulation of sulfur inside SWCNTs cavities was demonstrated. The peculiarities of interactions of SWCNTs with encapsulated and external sulfur species were analyzed in details. In particular, the donor-acceptor interaction between encapsulated sulfur and host SWCNT is experimentally demonstrated. The sulfur-filled SWCNTs were continuously irradiated in situ with polychromatic photon beam of high intensity. Comparison of X-ray spectra of the samples before and after the treatment revealed sulfur transport from the interior to the surface of SWCNTs bundles, in particular extraction of sulfur from the SWCNT cavity. These results show that the moderate heating of filled nanotubes could be used to de-encapsulate the guest species tuning the local composition, and hence, the functional properties of SWCNT-based materials.

Here a simple and reproducible method for obtaining terahertz metasurfaces formed from multiwall carbon nanotubes (MWCNTs) is presented. The metasurfaces were obtained from a vertically aligned array of MWCNTs using a laser engraving technique followed by polymer covering. The structures under study demonstrate frequency-selective reflection in terahertz range following the Huygens-Fresnel formalism. For a normal incidence of the electromagnetic wave, the model for numerical calculation of backscattering from the metasurfaces was proposed. Lightweight and compact MWCNT-based metasurfaces are capable to replace conventional pyramidal absorbers and could serve as a versatile platform for scalable cost-efficient production of ultra-light electromagnetic components for THz applications.

Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO 2 /Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n -type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data.

Diamond films are advanced engineering materials for various industrial applications requiring a coating material with extremely high thermal conductivity and low electrical conductivity. An approach for the synthesis of diamond films via high-speed jet deposition of thermally activated gas has been applied. In this method, spatially separated high-speed flows of methane and hydrogen were thermally activated, and methyl and hydrogen radicals were deposited on heated molybdenum substrates. The morphology and structure of three diamond films were studied, which were synthesized at a heating power of 900, 1700, or 1800 W, methane flow rate of 10 or 30 sccm, hydrogen flow rate of 1500 or 3500 sccm, and duration of the synthesis from 1.5 to 3 h.The morphology and electronic state of the carbon on the surface and in the bulk of the obtained films were analyzed by scanning electron microscopy, Raman scattering, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopies. The diamond micro-crystals with a thick oxidized amorphous sp 2 -carbon coating were grown at a heating power of 900 W and a hydrogen flow rate of 1500 sccm. The quality of the crystals was improved, and the growth rate of the diamond film was increased seven times when the heating power was 1700-1800 W and the methane and hydrogen flow rates were 30 and 3500 sccm, respectively. Defective octahedral diamond crystals of 30 μm in size with a thin sp 2 -carbon surface layer were synthesized on a Mo substrate heated at 1273 K for 1.5 h. When the synthesis duration was doubled, and the substrate temperature was decreased to 1073 K, the denser film with rhombic-dodecahedron diamond crystals was grown. In this case, the thinnest hydrogenated sp 2 -carbon coating was detected on the surface of the diamond crystals.

Despite decades of study the precise behavior of bromine in graphitic carbons remains unclear. In this report, using Raman spectroscopy, we reveal two types of bromine structure in graphitic carbon materials. Between fluorinated graphene layers with a composition close to C2F, Br2 molecules are intercalated in a form similar to liquid bromine. Bromination of pristine and low-fluorinated graphitic carbons behaves very differently with distinct Br-related Raman spectra. With the guidance of density functional theory (DFT) calculations, all Raman features are assigned to normal vibration modes of specific bromine species over graphene and fluorinated graphene. When intercalated between extended non-fluorinated sp2-hybridized carbon regions, physisorbed Br2 molecules move freely across the non-functionalized region toward the CF border. Multiple Br2 molecules then combine spontaneously into Br3-based chains, whose coupling activates otherwise Raman inactive modes. Significant charge transfer to bromine species occurs in this case. DFT calculated frequencies match precisely the experimental Br-related Raman bands observed in the intercalation carbon compounds. The fluorine-catalyzed bromine chain-formation process shown here is general and should also operate with edges and other defect species.

We systematically studied the electromagnetic properties of carbon nanohorns (CNHs) and polystyrene composites filled with CNHs in static regime, low frequency and microwave regions. CNHs were synthesized using the direct current arc-discharge method using solid graphite rods and graphite rods filled by melamine mixed with graphite powder. Transmission electron microscopy and thermo-gravimetric analysis showed that CNH agglomerates are the main product, while the addition of melamine promotes the formation of graphite balls. Graphitic contamination causes the internal leakage of inter-agglomerate capacity, lowering the permittivity and enhancing the conductivity of composites. The permittivity of CNH/polystyrene composites increases with the filler fraction, and near the dielectric threshold electromagnetic characteristics of the composites exhibit critical behaviour. Our results suggest that CNHs with relatively high values of permittivity and contact resistance could be used as high- k materials.

We investigated the insertion-extraction behaviors of Li and Na ions in graphitic materials using solid-state NMR. A unique advantage of high-degree 13 C-isotope enrichment of graphitic material allowed sensitive and metastable graphite intercalation compounds to be measured in a short time. Ex situ 13 C magic-angle spinning NMR spectra of 13 C fine-grained graphite are presented as a function of state-of-charge. The observations are discussed with respect to graphite intercalation phenomena, which include the effects of charge transfer and the demagnetizing field. Dramatic narrowing of the 13 C NMR signal in metal-intercalated graphite evidences quasi-complete charge transfer occurring between lithium and graphite host material and resulting in reducing the macroscopic field effects. Upon Na insertion, incomplete charge transfer is observed and explained by inaccessibility of graphitic interlayer space for Na ions in our study. In addition, critical issues of reversibility of Li- and Na-ion electrochemical cells and solid electrolyte interphase formation are considered on the atomic scale. The knowledge gained in the present work can be applied to advanced high-power-density electrode materials for safe and fast-charging metal-ion batteries or for novel spintronic concepts with controlled spin-polarized charge carrier injection and transport combined with the possibility to manipulate magnetic anisotropy.

Investigation of carbon/lithium interfaces is of great importance for elaboration of energy storage devices. Here, the effect of vacuum thermal deposition of lithium on single-walled carbon nanotubes (SWCNTs) is investigated by in situ X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy. From the XPS data, the composition of lithiated sample is LiC24. That corresponds to the presence of two types of carbon atoms on the SWCNT surface, namely, those located closely and far away from the adsorbed lithium. Quantum-chemical modeling of XPS valence-band spectra and calculation of atomic charges and molecular electrostatic potential map found that the former type of carbon atoms is in strong positive electric field created by lithium, whereas the Li-free SWCNT areas are charged negatively. An alternation of areas of positive potential and negative potential on the surface of partially lithiated SWCNTs can significantly affect processes in an electrochemical cell.

Interface interactions in multicomponent nanoparticles can affect electromagnetic properties of an absorbing system. In this work, we investigate the electromagnetic response of multi-walled carbon nanotubes (MWCNTs) filled with iron-containing nanoparticles (ICNs) in the terahertz frequency range. MWCNTs with different iron content have been synthesized by aerosol-assisted catalytic chemical vapour deposition method from toluene containing a certain quantity of ferrocene used as a catalyst. According to the x-ray diffraction analysis, encapsulated ICNs were mainly in the form of iron carbide. Thin composite films were prepared from the iron-filled MWCNTs and polymethylmethacrylate (PMMA) by casting and stretching methods. The composites showed an enhanced permittivity and anisotropy in the transmittance spectra when iron content increased. This behaviour was related to the mechanism based on electrical conductivity and polarization of ICNs and ICN/MWCNT interfaces. Since terahertz field penetrates inside MWCNTs, the filling of their cavities can be a way of varying the electromagnetic properties of MWCNT-containing composites.

Holes with an average size of 2-5 nm have been created in graphene layers by heating of graphite oxide (GO) in concentrated sulfuric acid followed by annealing in an argon flow. The hot mineral acid acts simultaneously as a defunctionalizing and etching agent, removing a part of oxygen-containing groups and lattice carbon atoms from the layers. Annealing of the holey reduced GO at 800 °C-1000 °C causes a decrease of the content of residual oxygen and the interlayer spacing thus producing thin compact stacks from holey graphene layers. Electrochemical tests of the obtained materials in half-cells showed that the removal of oxygen and creation of basal holes lowers the capacity loss in the first cycle and facilitates intercalation-deintercalation of lithium ions. This was attributed to minimization of electrolyte decomposition reactions, easier desolvation of lithium ions near the hole boundaries and appearance of multiple entrances for the naked ions into graphene stacks.

Novel nitrogen-doped carbon hybrid materials consisting of multiwalled nanotubes and porous graphitic layers have been produced by chemical vapor deposition over magnesium-oxide-supported metal catalysts. CN x nanotubes were grown on Co/Mo, Ni/Mo, or Fe/Mo alloy nanoparticles, and MgO grains served as a template for the porous carbon. The simultaneous formation of morphologically different carbon structures was due to the slow activation of catalysts for the nanotube growth in a carbon-containing gas environment. An analysis of the obtained products by means of transmission electron microscopy, thermogravimetry and X-ray photoelectron spectroscopy methods revealed that the catalyst's composition influences the nanotube/porous carbon ratio and concentration of incorporated nitrogen. The hybrid materials were tested as electrodes in a 1M H 2 SO 4 electrolyte and the best performance was found for a nitrogen-enriched material produced using the Fe/Mo catalyst. From the electrochemical impedance spectroscopy data, it was concluded that the nitrogen doping reduces the resistance at the carbon surface/electrolyte interface and the nanotubes permeating the porous carbon provide fast charge transport in the cell.

Tabby is a pattern of short irregular stripes, usually related to domestic cats. We have produced Tabby patterns on graphene by attaching fluorine atoms running as monoatomic chains in crystallographic directions. Separated by non-fluorinated sp 2 carbon ribbons, sp 3 -hybridized carbon atoms bonded to zigzag fluorine chains produce sp 2 -sp 3 interfaces and spin-polarized edge states localized on both sides of the chains. We have compared two kinds of fluorinated graphite samples C 2 F x , with x near to 1 and x substantially below 1. The magnetic susceptibility of C 2 F x (x < 1) shows a broad maximum and a thermally activated spin gap behaviour that can be understood in a two-leg spin ladder model with ferromagnetic legs and antiferromagnetic rungs; the spin gap constitutes about 450 K. Besides, stable room-temperature ferromagnetism is observed in C 2 F x (x < 1) samples: the crossover to a three-dimensional magnetic behaviour is due to the onset of interlayer interactions. Similarly prepared C 2 F x (x ≈ 1) samples demonstrate features of two-dimensional magnetism without signs of high-temperature magnetic ordering, but with transition to a superparamagnetic state below 40 K instead. The magnetism of the Tabby graphene is stable until 520 K, which is the temperature of the structural reconstruction of fluorinated graphite.

Single-walled carbon nanotubes (SWCNTs) possessing a confined inner space protected by chemically resistant shells are promising for delivery, storage, and desorption of various compounds, as well as carrying out specific reactions. Here, we show that SWCNTs interact with molten mercury dichloride (HgCl 2 ) and guide its transformation into dimercury dichloride (Hg 2 Cl 2 ) in the cavity. The chemical state of host SWCNTs remains almost unchanged except for a small p-doping from the guest Hg 2 Cl 2 nanocrystals. The density functional theory calculations reveal that the encapsulated HgCl 2 molecules become negatively charged and start interacting via chlorine bridges when local concentration increases. This reduces the bonding strength in HgCl 2 , which facilitates removal of chlorine, finally leading to formation of Hg 2 Cl 2 species. The present work demonstrates that SWCNTs not only serve as a template for growing nanocrystals but also behave as an electron-transfer catalyst in the spatially confined redox reaction by donation of electron density for temporary use by the guests.

Double-walled carbon nanotubes (DWCNTs) are fluorinated using (1) fluorine F 2 at 200 °C, (2) gaseous BrF 3 at room temperature, and (3) CF 4 radio-frequency plasma functionalization. These have been comparatively studied using transmission electron microscopy and infrared, Raman, X-ray photoelectron, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A formation of covalent C-F bonds and a considerable reduction in the intensity of radial breathing modes from the outer shells of DWCNTs are observed for all samples. Differences in the electronic state of fluorine and the C-F vibrations for three kinds of the fluorinated DWCNTs are attributed to distinct local surroundings of the attached fluorine atoms. Possible fluorine patterns realized through a certain fluorination technique are revealed from comparison of experimental NEXAFS F K-edge spectra with quantum-chemical calculations of various models. It is proposed that fluorination with F 2 and BrF 3 produces small fully fluorinated areas and short fluorinated chains, respectively, while the treatment with CF 4 plasma results in various attached species, including single or paired fluorine atoms and -CF 3 groups. The results demonstrate a possibility of different patterning of carbon surfaces through choosing the fluorination method.

Formic acid derived from biomass is known to be used for hydrogen production over Pd catalysts. The effects of preparation variables, structure of the carbon support, surface functional composition on the state of Pd, and catalytic properties of the samples in the vapor-phase decomposition of formic acid were studied. In all catalysts derived from Pd acetate, metal particles visible by conventional TEM had similar sizes, but the adsorption capacity towards CO responded strongly to N-doping of the carbon surface. Moreover, a decrease in the CO/Pd values was accompanied by a significant increase in the reaction rate. Taking account of X-ray photoelectron spectroscopy (XPS) and atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF/STEM) data, the trends observed were assigned to a larger fraction of single electron-deficient Pd atoms in the N-doped samples, which do not adsorb CO but interact with formic acid to produce hydrogen. This was confirmed by extended DFT studies. The obtained results are valuable for the development of Pd catalysts on carbon supports for different processes., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nitrogen-containing multi-wall carbon nanotubes (N-MWCNTs) were synthesized using aerosol assisted chemical vapor deposition (CVD) techniques in conjunction with benzylamine:ferrocene or acetonitrile:ferrocene mixtures. Different amounts of toluene were added to these mixtures in order to change the N/C ratio of the feedstock. X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy detected pyridinic, pyrrolic, graphitic, and molecular nitrogen forms in the N-MWCNT samples. Analysis of the spectral data indicated that whilst the nature of the nitrogen-containing precursor has little effect on the concentrations of the different forms of nitrogen in N-MWCNTs, the N/C ratio in the feedstock appeared to be the determining factor. When the N/C ratio was lower than ca. 0.01, all four forms existed in equal concentrations, for N/C ratios above 0.01, graphitic and molecular nitrogen were dominant. Furthermore, higher concentrations of pyridinic nitrogen in the outer shells and N2 molecules in the core of the as-produced N-MWCNTs suggest that the precursors were decomposed into individual atoms, which interacted with the catalyst surface to form CN and NH species or in fact diffused through the bulk of the catalyst particles. These findings are important for a better understanding of possible growth mechanisms for heteroatom-containing carbon nanotubes (CNTs) and therefore paving the way for controlling the spatial distribution of foreign elements in the CNTs using CVD processes.

Development of graphene spintronic devices relies on transforming it into a material with a spin order. Attempts to make graphene magnetic by introducing zigzag edge states have failed due to energetically unstable structure of torn zigzag edges. Here, we report on the formation of nanoridges, i.e., stable crystallographically oriented fluorine monoatomic chains, and provide experimental evidence for strongly coupled magnetic states at the graphene-fluorographene interfaces. From the first principle calculations, the spins at the localized edge states are ferromagnetically ordered within each of the zigzag interface whereas the spin interaction across a nanoridge is antiferromagnetic. Magnetic susceptibility data agree with this physical picture and exhibit behaviour typical of quantum spin-ladder system with ferromagnetic legs and antiferromagnetic rungs. The exchange coupling constant along the rungs is measured to be 450 K. The coupling is strong enough to consider graphene with fluorine nanoridges as a candidate for a room temperature spintronics material.

Amorphous, low-porosity carbon spheres on the order of a few micrometers in size were prepared by carbonization of squalane (C30H62) in supercritical CO2 at 823 K. The spheres were characterized and used as catalysts' supports for Pd. Near-edge X-ray absorption fine structure studies of the spheres revealed sp(2) and sp(3) hybridized carbon. To activate carbons for interaction with a metal precursor, often oxidative treatment of a support is needed. We showed that boiling of the obtained spheres in 28 wt % HNO3 did not affect the shape and bulk structure of the spheres, but led to creation of a considerable amount of surface oxygen-containing functional groups and increase of the content of sp(2) hybridized carbon on the surface. This carbon was seen by scanning transmission electron microscopy in the form of waving graphene flakes. The H/C atomic ratio in the spheres was relatively high (0.4) and did not change with the HNO3 treatment. Palladium was deposited by impregnation with Pd acetate followed by reduction in H2. This gave uniform Pd clusters with a size of 2-4 nm. The Pd supported on the original C spheres showed 2-3 times higher catalytic activity in vapor phase formic acid decomposition and higher selectivity for H2 formation (98-99%) than those for the catalyst based on the HNO3 treated spheres. Using of such low-porosity spheres as a catalyst support should prevent mass transfer limitations for fast catalytic reactions.

Detonation nanodiamonds (NDs) were deposited on the surface of aligned carbon nanotubes (CNTs) by immersing a CNT array in an aqueous suspension of NDs in dimethylsulfoxide (DMSO). The structure and electronic state of the obtained CNT-ND hybrid material were studied using optical and electron microscopy and Infrared, Raman, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy. A non-covalent interaction between NDs and CNT and preservation of vertical orientation of CNTs in the hybrid were revealed. We showed that current-voltage characteristics of the CNT-ND cathode are changed depending on the applied field; below ~3 V/µm they are similar to those of the initial CNT array and at the higher field they are close to the ND behavior. Involvement of the NDs in field emission process resulted in blue luminescence of the hybrid surface at an electric field higher than 3.5 V/µm. Photoluminescence measurements showed that the NDs emit blue-green light, while blue luminescence prevails in the CNT-ND hybrid. The quenching of green luminescence was attributed to a partial removal of oxygen-containing groups from the ND surface as the result of the hybrid synthesis.

Graphene is a remarkable material with the best surface to volume ratio as a result of its 2D nature, which implies that every atom can be considered as a surface one. These features make graphene attractive for use as a sensing material; however, the limiting factor is the chemical inertness of pristine graphene. Here we propose a method to create reactive centers by removal of fluorine atoms from the outer surface of fluorinated graphene while preserving the backside fluorination. Such partially recovered graphene layers were produced by the action of hydrazine-hydrate vapor on initially non-conducting fluorinated graphite. The reduction degree of the material and its electrical response revealed upon ammonia exposure were controlled by measuring the surface conductivity. We showed experimentally that the sensing properties depend on the reduction degree and found the correlation of the adsorption energy of ammonia with the number of residual fluorine atoms by the use of quantum-chemical calculations.

Generally speaking, excellent electrochemical performance of metal oxide/graphene nanosheets (GNSs) composite is attributed to the interfacial interaction (or "synergistic effect") between constituents. However, there are no any direct observations on how the electronic structure is changed and how the properties of Li-ion storage are affected by adjusting the interfacial interaction, despite of limited investigations on the possible nature of binding between GNSs and metal oxide. In this paper, CuO nanosheets/GNSs composites with a little Cu2O (ca. 4 wt %) were utilized as an interesting model to illustrate directly the changes of interfacial nature as well as its deep influence on the electronic structure and Li-ion storage performance of composite. The interfacial adjustment was successfully fulfilled by removal of Cu2O in the composite by NH3·H2O. Formation of Cu-O-C bonds on interfaces both between CuO and GNSs, and Cu2O and GNSs in the original CuO/GNSs composites was detected. The small interfacial alteration by removal of the little Cu2O results in the obvious changes in electronic structure, such as weakening of covalent Cu-O-C interfacial interaction and recovery of π bonds in graphene, and simultaneously leads to variations in electrochemical performance of composites, including a 21% increase of reversible capacity, degradation of cyclic stability and rate-performance, and obvious increase of charge-transfer resistance, which can be called a "butterfly effect" in graphene-based metal oxide composites. These interesting phenomena could be helpful to design not only the high-performance graphene/metal oxide anode materials but also various advanced graphene-based composites used in the other fields such as sensors, catalysis, fuel cells, solar cells, etc.

Highly oriented pyrolytic graphite characterized by a low misorientation of crystallites is fluorinated using a gaseous mixture of BrF(3) with Br(2) at room temperature. The golden-colored product, easily delaminating into micrometer-size transparent flakes, is an intercalation compound where Br(2) molecules are hosted between fluorinated graphene layers of approximate C(2)F composition. To unravel the chemical bonding in semifluorinated graphite, we apply angle-resolved near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and quantum-chemical modeling. The strong angular dependence of the CK and FK edge NEXAFS spectra on the incident radiation indicates that room-temperature-produced graphite fluoride is a highly anisotropic material, where half of the carbon atoms are covalently bonded with fluorine, while the rest of the carbon atoms preserve π electrons. Comparison of the experimental CK edge spectrum with theoretical spectra plotted for C(2)F models reveals that fluorine atoms are more likely to form chains. This conclusion agrees with the atomic force microscopy observation of a chain-like pattern on the surface of graphite fluoride layers.

Ab initio calculations of dielectric function and electron energy loss (EEL) function of periodically rippled armchair-edged graphene were performed in the framework of the random-phase approximation. The bending of graphene was found to remove restrictions on the electron transitions being forbidden in the flat graphene for certain light polarization. As a result, new peaks appear in the optical absorption spectrum and EEL spectrum of rippled graphene. Energy position, intensity, and width of the peaks are sensitive to the height of out-of-plane graphene bending that can be used in construction of graphene-based materials with variable transparency window.

A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported. Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives. Fluorographene is a high-quality insulator (resistivity >10(12) Ω) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting a Young's modulus of 100 N m(-1) and sustaining strains of 15%. Fluorographene is inert and stable up to 400 °C even in air, similar to Teflon.