Carbon onions: carriers of the 217.5 nm interstellar absorption feature

Fast electron damage mechanism of epoxy resin studied by electron energy loss spectroscopy and electron diffraction

The damage mechanism and exposure tolerance of epoxy resins to fast electrons remain unclear. We quantitatively investigated the effects of electron irradiation on a common epoxy resin by dose-dependent electron energy loss spectroscopy. The results show that sp3 states of nitrogen, oxygen, and their adjacent carbon atoms were converted to sp2 states, forming imine (C=N) and carbonyl (C=O) as the total electron dose increased. The sp3 to sp2 conversion mechanism was proposed. The epoxy resin was very sensitive to fast electrons and the original electronic states were maintained up to a total dose of ∼103e- nm-2 at a low temperature of 103 K. Dose-dependent electron diffraction revealed that the intra- and intermolecular geometries changed below and around the total dose of ∼103e- nm-2.

Nanographenes and Graphene Nanoribbons as Multitalents of Present and Future Materials Science

As cut-outs from a graphene sheet, nanographenes (NGs) and graphene nanoribbons (GNRs) are ideal cases with which to connect the world of molecules with that of bulk carbon materials. While various top-down approaches have been developed to produce such nanostructures in high yields, in the present perspective, precision structural control is emphasized for the length, width, and edge structures of NGs and GNRs achieved by modern solution and on-surface syntheses. Their structural possibilities have been further extended from "flatland" to the three-dimensional world, where chirality and handedness are the jewels in the crown. In addition to properties exhibited at the molecular level, self-assembly and thin-film structures cannot be neglected, which emphasizes the importance of processing techniques. With the rich toolkit of chemistry in hand, NGs and GNRs can be endowed with versatile properties and functions ranging from stimulated emission to spintronics and from bioimaging to energy storage, thus demonstrating their multitalents in present and future materials science.

Temperature-dependent c-axis lattice-spacing reduction and novel structural recrystallization in carbon nano-onions filled with Fe3C/α-Fe nanocrystals

Carbon nano-onions are approximately spherical nanoscale graphitic shells. When filled with ferromagnetic Fe3C/α-Fe nanocrystals, these structures have several important applications, such as point electron-sources, magnetic data recording, energy storage, and others, that exploit the interaction of either or both the shells and the magnetic moments in the filling. Despite these applications receiving much recent attention, little is known about the structural relationship between the carbon shells and the internal nanocrystal. In this work, the graphitic c-axis lattice-spacing in Fe3C/α-Fe-filled multi-shell structures was determined by XRD in the temperature range from 130 K to 298 K. A significant reduction in the c-axis lattice-spacing was observed in the multi-shell structures. A defect-induced magnetic transition was probed and ascribed to the formation of randomly oriented ferromagnetic clusters in the recrystallized disclination-rich regions of the CNOs-shells, in agreement with the percolative theory of ferromagnetism.

Theoretical identification of buckyonion fullerene C20@C60 isomers by XPS and NEXAFS spectroscopy

The C 1s X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of two buckyonion fullerene C₂₀@C₆₀ isomers were theoretically simulated by density functional theory (DFT) method. In this paper, we mainly investigated the relationship between spectroscopy and structure and obtained the spectral dependence on the structures with different symmetries. Our results showed that both XPS and NEXAFS spectra exhibited remarkable dependence on the molecular structures, thus these two spectroscopic techniques could be adopted to identify the two C₂₀@C₆₀ isomers effectively. Additionally, we found that the building block approach could not predict the spectra for C₂₀@C₆₀ isomers due to the strong interaction between the two layer cages. Finally, we studied the decompositions of the total spectra from carbon atoms in different local environments to analyse the origins of the main features.

Vacancy-induced interfacial ferromagnetic features in SmFeO3-filled graphitic carbon foam

We report a novel structural and magnetic investigation of carbon foam (CFM) materials filled with SmFeO₃ crystals produced by (1) high temperature fusion between Sm₂O₃- and Fe₃C-filled carbon onions and (2) annealing of iron filled CFM with nanosized Sm₂O₃. Presence of a defect-rich monolayer-like CFM arrangement characterized by sharp interfaces with a SmFeO₃ single-crystal phase is demonstrated through TEM and HRTEM. Further, the presence of intense sp³-rich features with variable carbonate content is evidenced by XPS and Raman spectroscopy. Complementary VSM, SQUID and ESR show also presence of intrinsic magnetization features which appeared to be attributable to the interfacial vacancy-rich regions of the graphitic CFM layers, as confirmed by Raman spectroscopy. Together with these signals, possible ferromagnetic contributions from the SmFeO₃ phase and α-Fe impurities are reported. These observations highlight therefore the presence of switchable interfacial magnetization features at the carbon/SmFeO₃ interface due to the variable concentrations of vacancies at the CFM interface, opening new directions towards applications in magnetic and interfacial-driven ferroelectric devices.

We report a novel structural and magnetic investigation of carbon foam (CFM) filled with SmFeO₃ crystals produced by (1) high temperature fusion between Sm₂O₃ and Fe₃C-filled carbon onions, and (2) annealing of iron filled CFM with nanosized Sm₂O₃.

How much graphene in space?

The possible presence of graphene in the interstellar medium (ISM) is examined by comparing the interstellar extinction curve with the ultraviolet absorption of graphene calculated from its dielectric functions experimentally obtained with the electron energy loss spectroscopy (EELS) method. Based on the absence in the interstellar extinction curve of the [Formula: see text] π-π* electronic interband transition of graphene, we place an upper limit of [Formula: see text] of C/H on the interstellar graphene abundance, exceeding the previous estimate by a factor of [Formula: see text]3 which made use of the dielectric functions measured with the spectroscopic ellipsometry (SE) method. Compared with the SE method which measures graphene in air (and hence its surface is contaminated) in a limited energy range of [Formula: see text]0.7-5 [Formula: see text], the EELS probes a much wider energy range of [Formula: see text]0-50 [Formula: see text] and is free of contamination. The fact that the EELS dielectric functions are substantially smaller than that of SE naturally explains why a higher upper limit on the graphene abundance is derived with EELS. Inspired by the possible detection of C24, a planar graphene sheet, in several Galactic and extragalactic planetary nebulae, we also examine the possible presence of C24 in the diffuse ISM by comparing the model IR emission of C24 with the observed IR emission of the Galactic cirrus and the diffuse ISM towards l = 44°20' and b = -0°20'. An upper limit of [Formula: see text] on C24 is also derived from the absence of the characteristic vibrational bands of C24 at [Formula: see text]6.6, 9.8, and 20 [Formula: see text] in the observed IR emission.

Green Transforming Metallurgical Residue into Alkali-Activated Silicomanganese Slag-Based Cementitious Material as Photocatalyst

Silicomanganese slag is a solid waste in metallurgical industry and can be transformed into an alkali-activated silicomanganese slag-based cementitious-material (ASSC) for the first time. The ASSC shows quite low electro-conductivity and can be raised dramatically by incorporated carbon black (CB) in the matrix of ASSC to create an electro-conductive alkali-activated silicomanganese slag-based cementitious-composite (EASSC), served as a low cost and environmentally-friendly photocatalyst for the removal of dye pollutant in the paper. The interrelationships of mechanical, optical, electroconductive, microstructural, and photocatalytic properties are evaluated. The network of CB plays a critical role in the electron transfers. The electrical conductivity of EASSC doped 4.5% CB drastically increases by 594.2 times compared to that of ASSC. The FESEM, XRD, and XPS results indicated that the EASSC with mean grain size about 50 nm is composed of amorphous calcium silicate hydrate (CSH), alabandite (α-MnS) and CB. The UV–vis DRS and PL exhibit that the absorption edges of electro-conductive alkali-activated silicomanganese slag-based cementitious-composite EASSC samples are gradually blue-shifted and the photoluminescence intensities progressively decrease with increasing CB content. The activities of photocatalytic degradation of basic violet 5BN dye are positive correlated to the electro-conductivities. The separation efficiency of photo-generated electron-hole pairs is enhanced due to the electron transfers from α-MnS to the network of CB. The photocatalytic degradation of dye pollutant belongs to the second order kinetics via a reaction mechanism of superoxide radical (•O₂⁻) intermediate.

On the morphological, structural and electrochemical properties of entangled Cu-filled carbon nano-onions

We demonstrate an advanced CVS approach in which the synthesis of Cu-filled carbon nano-onions (CNOs) is achieved by direct sublimation and pyrolysis of a not previously used precursor, namely chloro(1,5-cyclooctadiene)copper(i) dimer.

Ferromagnetically filled carbon nano-onions: the key role of sulfur in dimensional, structural and electric control

A key challenge in the fabrication of ferromagnetically filled carbon nano-onions (CNOs) is the control of their thickness, dimensions and electric properties. Up to now literature works have mainly focused on the encapsulation of different types of ferromagnetic materials including α-Fe, Fe3C, Co, FeCo, FePd3 and others within CNOs. However, no report has yet shown a suitable method for controlling both the number of shells, diameter and electric properties of the produced CNOs. Here, we demonstrate an advanced chemical vapour deposition approach in which the use of small quantities of sulfur during the pyrolysis of ferrocene allows for the control of (i) the diameter of the CNOs, (ii) the number of shells and (iii) the electric properties. We demonstrate the morphological, structural, electric and magnetic properties of these new types of CNOs by using SEM, XRD, TEM, HRTEM, EIS and VSM techniques.

Fast low-temperature plasma reduction of monolayer graphene oxide at atmospheric pressure

We report on an ultrafast plasma-based graphene oxide reduction method superior to conventional vacuum thermal annealing and/or chemical reduction. The method is based on the effect of non-equilibrium atmospheric-pressure plasma generated by the diffuse coplanar surface barrier discharge in proximity of the graphene oxide layer. As the reduction time is in the order of seconds, the presented method is applicable to the large-scale production of reduced graphene oxide layers. The short reduction times are achieved by the high-volume power density of plasma, which is of the order of 100 W cm^-3. Monolayers of graphene oxide on silicon substrate were prepared by a modified Langmuir-Schaefer method and the efficient and rapid reduction by methane and/or hydrogen plasma was demonstrated. The best results were obtained for the graphene oxide reduction in hydrogen plasma, as verified by x-ray photoelectron spectroscopy and Raman spectroscopy.

Electronic structure of multi-walled carbon fullerenes

Despite an enormous amount of research on carbon based nanostructures, relatively little is known about the electronic structure of multi-walled carbon fullerenes, also known as carbon onions. In part, this is due to the very high computational expense involved in estimating electronic structure of large molecules. At the same time, experimentally, the exact crystal structure of the carbon onion is usually unknown, and therefore one relies on qualitative arguments only. In this work we present the results of a computational study on a series of multi-walled fullerenes and compare their electronic structures to experimental data. Experimentally, the carbon onions were fabricated using ultrasonic agitation of isopropanol alcohol and deposited onto the surface of highly ordered pyrolytic graphite using a drop cast method. Scanning tunneling microscopy images indicate that the carbon onions produced using this technique are ellipsoidal with dimensions on the order of 10 nm. The majority of differential tunneling spectra acquired on individual carbon onions are similar to that of graphite with the addition of molecular-like peaks, indicating that these particles span the transition between molecules and bulk crystals. A smaller, yet sizable number exhibited a semiconducting gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels. These results are compared with the electronic structure of different carbon onion configurations calculated using first-principles. Similar to the experimental results, the majority of these configurations are metallic with a minority behaving as semiconductors. Analysis of the configurations investigated here reveals that each carbon onion exhibiting an energy band gap consisted only of non-metallic fullerene layers, indicating that the interlayer interaction is not significant enough to affect the total density of states in these structures.

Reversible nanodiamond-carbon onion phase transformations

Because of their considerable science and technical interest, nanodiamonds (3-5 nm) are often used as a model to study the phase transformation between graphite and diamond. Here we demonstrated that a reversible nanodiamond-carbon onion phase transformation can become true when laser irradiates colloidal suspensions of nanodiamonds at the ambient temperature and pressure. Nanodiamonds are first transformed to carbon onions driven by the laser-induced high temperature in which an intermediary bucky diamond phase is observed. Sequentially, carbon onions are transformed back to nanodiamonds driven by the laser-induced high temperature and high pressure from carbon onions as nanoscaled temperature and pressure cell upon the laser irradiation process in liquid. Similarly, the same bucky diamond phase serving as an intermediate phase is found during the carbon onion-to-nanodiamond transition. To have a clear insight into the unique phase transformation the thermodynamic approaches on the nanoscale were proposed to elucidate the reversible phase transformation of nanodiamond-to-carbon onion-to-nanodiamond via an intermediary bucky diamond phase upon the laser irradiation in liquid. This reversible transition reveals a series of phase transformations between diamond and carbon allotropes, such as carbon onion and bucky diamond, having a general insight into the basic physics involved in these phase transformations. These results give a clue to the root of meteoritic nanodiamonds that are commonly found in primitive meteorites but their origin is puzzling and offers one suitable approach for breaking controllable pathways between diamond and carbon allotropes.

Structural, electronic and energetic properties of giant icosahedral fullerenes up to C6000: insights from an ab initio hybrid DFT study

An accurate and detailed electronic structure study of giant carbon fullerenes, benefitting from improved symmetry exploitation in the CRYSTAL14 code.

Nonequilibrium route to nanodiamond with astrophysical implications

Nanometer-sized diamond grains are commonly found in primitive chondritic meteorites, but their origin is puzzling. Using evidence from atomistic simulation, we establish a mechanism by which nanodiamonds form abundantly in space in a two-stage process involving condensation of vapor to form carbon onions followed by transformation to nanodiamond in an energetic impact. This nonequilibrium process is consistent with common environments in space and invokes the fewest assumptions of any proposed model. Accordingly, our model can explain nanodiamond formation in both presolar and solar environments. The model provides an attractive framework for understanding noble gas incorporation and explains all key features of meteoritic nanodiamond, including size, shape, and polytype. By understanding the creation of nanodiamonds, new opportunities arise for their exploitation as a powerful astrophysical probe.

Resonant excitation of precursor molecules in improving the particle crystallinity, growth rate and optical limiting performance of carbon nano-onions

A catalyst-free and highly efficient synthetic method for growing carbon nano-onions (CNOs) in open air has been developed through the laser resonant excitation of a precursor molecule, ethylene, in a combustion process. Highly concentric CNO particles with improved crystallinity were obtained at a laser wavelength of 10.532 µm through the resonant excitation of the CH(2) wagging mode of the ethylene molecules. A higher growth rate up to 2.1 g h( - 1) was obtained, compared with that without a laser (1.3 g h( - 1)). Formation of the CNOs with ordered graphitic shells is ascribed to the decomposition of polycyclic aromatic hydrocarbons (PAHs) into C(2) species. The optical limiting performances of the CNOs grown by the combustion processes were investigated. CNOs grown at 10.532 µm laser excitation demonstrated improved optical limiting properties due to the improved crystallinity.

Nanodiamonds do not provide unique evidence for a Younger Dryas impact

Microstructural, δ(13)C isotope and C/N ratio investigations were conducted on excavated material from the black Younger Dryas boundary in Lommel, Belgium, aiming for a characterisation of the carbon content and structures. Cubic diamond nanoparticles are found in large numbers. The larger ones with diameters around or above 10 nm often exhibit single or multiple twins. The smaller ones around 5 nm in diameter are mostly defect-free. Also larger flake-like particles, around 100 nm in lateral dimension, with a cubic diamond structure are observed as well as large carbon onion structures. The combination of these characteristics does not yield unique evidence for an exogenic impact related to the investigated layer.

Processing and characterization of ultrathin carbon coatings on glass

Ultrathin carbon layers, on the order of 3-6 nm in thickness, were formed on glass substrates by spin coating and pyrolysis of polymer precursors. The organic precursors used were poly(furfuryl alcohol), coal tar pitch, and a photoresist. The carbon coatings were characterized by ellipsometry, optical profilometry, water contact angle, confocal Raman spectroscopy, UV-vis spectroscopy, and atomic force microscopy. We also report the transparency, hydrophobicity, friction, weathering resistance, and electrical conductivity of the carbon-coated glass. The results reveal that up to 97% transparent, ultrathin carbon films could be formed on glass substrates with a root-mean-square roughness of less than approximately 0.3 nm. This carbon layer modified the otherwise hydrophilic surface of the glass to yield a water contact angle of 85 degrees . The coatings were also found to provide a water barrier against weathering under hot and humid conditions. A 4.5-nm-thick carbon film on glass had a sheet resistance of 55.6 kOmega m and a conductivity of 40 S/cm.

Preparation and Functionalization of Multilayer Fullerenes (Carbon Nano-Onions)

Carbon nano-onions (CNOs) represent a still largely unexplored carbon allotrope. Promising properties of these unique carbon structures are driving the research efforts in this area, but many technical problems remain in their preparation, derivatization, separation and characterization. In this article, we report the preparation, partial purification, and multiple functionalization and solubilization of CNOs. With only one priorly published short communication describing CNO functionalization, the present work is the most comprehensive description of CNO functionalization and characterization to date.

Theoretical support for buckyonions as carriers of the UV interstellar extinction feature

Theoretically simulated UV-visible photoabsorption spectra of the buckyonions are compared with the most recent and complete experimental data. The very good agreement found provides support for our theoretical model of the buckyonions and allows for a detailed analysis of the correspondence between these spectra and the UV interstellar extinction feature. The excellent agreement found between the theoretical and observational features and the consistency of the former with the observational data constraints gives very strong support for the buckyonion origin of the UV interstellar spectrum.

Formation and transformation of carbon nanoparticles under electron irradiation

This article reviews the phenomena occurring during irradiation of graphitic nanoparticles with high-energy electrons. A brief introduction to the physics of the interaction between energetic electrons and solids is given with particular emphasis on graphitic materials. Irradiation effects are discussed, starting from microscopic mechanisms that lead to structural alterations of the graphite lattice. It is shown how random displacements of the atoms and their subsequent rearrangements eventually lead to topological changes of the nanoparticles. Examples are the formation of carbon onions, morphological changes of carbon nanotubes, or the coalescence of fullerenes or nanotubes under electron irradiation. Irradiation-induced phase transformations in nanoparticles are discussed, e.g. the transformation of graphite to diamond, novel metal-carbon phases in nanocomposite materials or modified phase equilibria in metal crystals encapsulated in graphitic shells.

A theoretical model of the photoabsorption spectra of carbon buckyonions

A theoretical model has been developed to predict the photoabsorption spectra of spherical carbon buckyonions in the region dominated by the pi-plasmon feature. This model makes use of the microscopic electronic structure of the system, which is provided by an effective Huckel one-electron model. The important screening effects are treated within the random phase approximation, whose form is an extension to the dynamic case of the one derived in a previous work for the static polarizabilities of these species. A systematic analysis as a function of the buckyonion size is performed. We compare the spectra obtained in this way with those derived from a different representation of the electron motion, namely a two-dimensional spherical electron gas, and from a classical dielectric model.