Carbon Clusters Research Articles

Carbon dots derived from cellobiose for temperature and phosalone detection

Cellobiose, the hydrolysis product of cellulose and the dimer of glucose, was employed to synthesize carbon dots (CDs) via a simple hydrothermal method. The inducing of nitrogen can act as a “molecular glue”, more and more carbon clusters were “glued” together, which would push the hydrothermal reaction in the positive direction. Besides, the linear response of the fluorescence of N-CDs to temperature ensured its potential application in temperature sensing. In the temperature range of 10∼80 °C, the fluorescence of as-prepared N-CDs was reversible and recoverable. Moreover, the dual fluorescence centers and dual-absorption bands of the as-prepared N-CDs permitted the novel dual-mode ratiometric assays for phosalone detection. The linear range and limit of detection (LOD) for dual fluorescence center-based ratiometric assay were 0.12∼5.45 μg/mL and 42.90 ng/mL, respectively. While that for the dual absorption-based ratiometric assay were 0.02∼1.40 μg/mL, and 6.67 ng/mL, respectively.

Structural Transformations Induced by Swift Heavy Ions in Polysiloxanes and Polycarbosilanes

Abstract High-resolution electron microscopy in connection with electron energy filtered microscopy is used for evidencing the precipitation of free C clusters in polysiloxanes and polycarbosilanes, responsible for the hardening and luminescence of these classes of inorganic polymers after ion irradiation. While during irradiation with 3 MeV Au ions randomly distributed carbon clusters are formed, in the case of irradiation with 100 MeVAu ions, the carbon clusters are aligned along tubular ion tracks without forming continuous wires. Contrary to observations in some other polymers and semiconductors, no tubular voids or crystallization of amorphous SiC were found. It is concluded that in both cases the carbon precipitation is due to a solid state transformation induced by electronic excitations.

Catalytic properties of cyclo-carbon clusters: An investigation on o[formula omitted] activation and CO oxidation

The carbon allotrope-based catalysts attracted considerable attention for oxidation–reduction reactions due to their low-cost and environmentally friendly properties. Systematic investigations are required to explore the catalytic properties and corresponding mechanisms of the new discovered carbon allotropes such as cyclocarbon clusters (cyclo-Cn). Here, using first-principles calculations, we study the stability and electronic properties of cycloCn. Regarding the spin multiplicity and geometry of cycloCn the electronic properties of n-odd and n-even cycloCn were found to be significantly different. Also, based on the EleyRideal (ER) and LangmuirHinshelwood (LH) mechanisms, we focus on the CO oxidation over sp-hybridized molecular carbon allotropes (cyclo-Cn) including recently synthesized cycloC18 by Kaiser, K. et al. (Science2019 365(6459), 1299–1301). In particular, thirteen cycloCn (with n=12-24) are studied. It was found that these carbon clusters may be useful for CO oxidation. We also elucidate the effects of NaCl(100) substrate on the catalytic performance of two cycloCn (n=17, 18) where we found that their optimized structures and the corresponding energy barriers are not very different than that of isolated molecular allotropes. The results show that cycloCn clusters may be a metal-free catalyst for CO oxidation. However, the stability of the cycloCn is a major concern under the acidic or basic conditions required for oxygen electrocatalysis that other groups must consider for further in situ calculations and characterizations.

Chemical reaction zone measurements in pressed trinitrotoluene (TNT) and comparison with triaminotrinitrobenzene (TATB)

Photonic Doppler velocimetry and digital high-speed shadowgraphy have been used to characterize the chemical reaction zone parameters of pressed trinitrotoluene (TNT) samples with an initial density of 1.568 g cm−3. Comparison of the nanosecond time-resolved particle velocity histories of the free surfaces of detonating charges in air and light vacuum and of the interfaces between TNT detonation products and lithium fluoride or polymethyl methacrylate windows allow one to bracket the von Neumann spike pressure between 24.8 and 28.8 GPa. Our velocity waveforms confirm the two-step reaction pathway already observed in TNT, triaminotrinitrobenzene (TATB), and nitromethane, with a first fast energy release over 80 ns followed by a slower release over 250 additional ns. We consider the end of the first release zone as the locus of the Chapman–Jouguet (CJ) state, and the CJ pressure thus lies between 17.6 and 17.7 GPa. The energy release is not completed in this Jouguet plane but only after about ≈280 ns when the carbon cluster formation process ends. This corresponds to both the end of the slow release part of the interface velocity profiles and to the moment at which the free surface velocity profiles reach their maximum. Our shadowgraphy images confirm that carbon formation occurs very rapidly after the detonation breakout, in good agreement with previous time-resolved small-angle x-ray scattering measurements. The comparison with similar results previously obtained on TATB allows one to further highlight their similarities, which mainly result from their excess carbon production at late times.

Correlation between structural properties and electrical conductivity of porous carbon derived from hemp bast fiber

A comprehensive study of the correlation between the structural and morphological parameters and the frequency-temperature dependences of the conductivity of porous carbon materials obtained by carbonization of hemp fibers has been carried out. The effect of treatment with nitric acid and additional annealing on the transport of charge carriers in carbon materials carbonized in the temperature range of 500–1000 °C has been established. Porous carbon materials have been described as a heterophase system, in which highly conductive graphitized particles are separated by low conductivity amorphous carbon, from the standpoint of the effect of carbonization temperature and changes in the morphology of materials due to acid treatment and annealing on the formation of conduction channels with the simultaneous implementation of fluctuation-assisted tunneling between graphitic clusters separated by low conductive barriers and the formation of conduction channels as a result of contact of individual graphitized carbon clusters. A model has been constructed that relates the results of measuring the specific surface area and pore size distribution, changes in the size of graphite crystallites, and changes in conductivity with temperature. The possibility of applying the theory of percolation conductivity to describe the charge transport has been analyzed and the percolation threshold has been established.

MeV Cluster Ion Beam–Material Interaction

This paper treats the characteristic topics of MeV/atom cluster ion beams produced using tandem accelerators both in the production stage and in the penetration stage from the viewpoint of fundamental processes. The former is related to atomic collisions in that production and decay of a cluster ion Cn+ (n=1−4) colliding with a charge-changing rare gas underlined through the electron-loss process. Regarding the latter, relatively small carbon clusters Cn+ (n=2−10) are treated. The reduction effect of the average charge of cluster ions in a material is first presented. Next, the electronic stopping power and the energy loss, the polarization force, and the coulomb explosion under cluster-ion impact are described in the dielectric function form. Alignment and structure effects are stressed. As a large and highly symmetric cluster, the electronic stopping power and the average charge are shown for a C60 cluster ion moving inside a solid. Throughout the paper, it is emphasized that the vicinage effect originating from correlation on spatial structure and orientation of constituent ions plays the key role. Moreover, results obtained in cluster production and penetration phenomena are mostly different from multiplication of those under single-ion impact.

Thermodynamics of carbon point defects in hexagonal boron nitride

We present a first-principles computational study of the thermodynamics of carbon defects in hexagonal boron nitride (hBN). The defects considered are carbon monomers, dimers, trimers, and larger carbon clusters, as well as complexes of carbon with vacancies, antisites, and substitutional oxygen. Our calculations show that monomers ($\text{C}_{\text{B}}$, $\text{C}_{\text{B}}$), dimers, trimers, and $\text{C}_{\text{N}}\text{O}_{\text{N}}$ pairs are the most prevalent species under most growth conditions. Compared to these defects, larger carbon clusters, as well as complexes of carbon with vacancies and antisites, occur at much smaller concentrations. Our results are discussed in view of the relevance of carbon defects in single-photon emission in hBN.

Accelerating the prediction of large carbon clusters via structure search: Evaluation of machine-learning and classical potentials

From as small as single carbon dimers up to giant fullerenes or amorphous nanometer-sized particles, the large family of carbon nanoclusters holds a complex structural variability that increases with cluster size. Capturing this variability and predicting stable allotropes remains a challenging modelling task, crucial to advance technological applications of these materials. While small cluster sizes are traditionally investigated with first-principles methods, a comprehensive study spanning larger sizes calls for a computationally efficient alternative. Here, we combine the stochastic ab initio random structure search algorithm (AIRSS) with geometry optimisations based on interatomic potentials to systematically predict the structure of carbon clusters spanning a wide range of sizes. We first test the transferability and predictive capability of seven widely used carbon potentials, including classical and machine-learning potentials. Results are compared against an analogous cluster dataset generated via AIRSS combined with density functional theory optimizations. The best performing potential, GAP-20, is then employed to predict larger clusters in the nanometer scale, overcoming the computational limits of first-principles approaches. Our complete cluster dataset describes the evolution of topological properties with cluster size, capturing the complex variability of the carbon cluster family. As such, the dataset includes ordered and disordered structures, reproducing well-known clusters, like fullerenes, and predicting novel isomers.

Molecular tuning of sulfur doped quinoline oligomer derived soft carbon for superior potassium storage

Soft carbon has been considered as one of the most promising high-performance potassium-ion battery anodes owing to the advantages of high carbon crystallinity and conductivity. Nevertheless, the lack of microstructure tunning strategy for soft carbon generally leads to low interlayer spacing and limited active sites, which results in relatively low storage capacity and sluggish kinetics. Herein, sulfur doped quinoline oligomer derived soft carbon nanosheets (SNC) have been successfully fabricated with expanded interlayer spacing, modest defects, and relatively ordered carbon clusters. These favorable characteristics can not only contribute to a high potassium storage capacity, but also shorten the diffusion spacing for both electrons and ions. Hence, SNC displays an extremely high capacity (456 mA h g−1 at 0.05 A g−1) and long cyclability (189 mA h g−1 at 2.0 A g−1 after 1000 cycles), superior to most of recently reported carbon anodes. Kinetic analyses demonstrate that sulfur doped quinoline oligomer derived soft carbon can significantly boost the potassium diffusion. Additionally, the enlarged interlayer spacing and modest defect sites benefitted from high sulfur doping could further enhance potassium storage properties. This study provides a facile molecular tuning and large-scale production strategy for soft carbon anodes with high capacity and long life.

One-Step In Situ Patternable Reduction of a Ag-rGO Hybrid Using Temporally Shaped Femtosecond Pulses.

In recent years, metallic nanoparticle (NP)–two-dimensional material hybrids have been widely used for photocatalysis and photoreduction. Here, we introduce a femtosecond laser reduction approach that relies on the repetitive ablation of recast layers by usi–ng temporally shaped pulses to achieve the fast fabrication of metallic NP–two-dimensional material hybrids. We selectively deposited silver-reduced graphene oxide (Ag–rGO) hybrids on different substrates under various fabrication conditions. The deposition of the hybrids was attributed to the redistribution of the cooling ejected plume after multiple radiation pulses and the exchange of carriers with ejected plume ions containing activated species such as small carbon clusters and H2O. The proposed one-step in situ fabrication method is a competitive fabrication process that eliminates the additive separation process and exhibits morphological controllability. The Ag–rGO hybrids demonstrate considerable potential for chemomolecular and biomolecular detection because the surface-enhanced Raman scattering signal of the enhancement factor reached 4.04 × 108.

Evolution of C-rich SiOC ceramics

Abstract Carbon-rich Si –O–C polymer-derived ceramics (PDCs) were investigated by various spectroscopic techniques, in order to characterize the evolution of their predominantly amorphous microstructure upon thermal treatment up to 1450 °C. Particular attention was addressed to modifications of the excess free carbon phase present in these materials. Surprisingly, the carbon clusters exhibited high stability above the pyrolysis temperature. Despite the high volume fraction of carbon, only a very limited carbothermal reduction process was detected. This study is divided into two parts: Part I deals with characterization tools that reveal a rather low lateral resolution and are hence termed here as integral spectroscopic techniques, i. e., solid-state NMR and Raman spectroscopy. In contrast, Part II illustrates the experimental results obtained from the very same materials characterized by spectroscopic and imaging techniques with high lateral resolution, i. e., electron energy-loss spectroscopy (EELS), high-resolution transmission electron microscopy (HRTEM), and energy-filtered TEM. In addition to materials characterization, emphasize of both papers is also to compare the information gained by either integral or local spectroscopy techniques and to highlight the strengths and weaknesses of either approach.

Activity origin of boron doped carbon cluster for thermal catalytic oxidation: Coupling effects of dopants and edges

Catalytic oxidation plays important roles in energy conversion and environment protection. Boron-doped crystalline carbocatalyst has been demonstrated effective; however, the application potential of boron-doped amorphous carbocatalyst remains to be explored. For amorphous carbon material, finite-sized carbon clusters are the basic structural units, which exhibit unique activity due to edge and size effect. Herein, using sulfur dioxide (SO2) and carbon monoxide (CO) oxidation as probe thermal-catalysis reactions, we found the distribution and reactivity of active sites in boron-doped carbon clusters are simultaneously determined by dopants and edges. According to comparisons of oxygen (O2) chemisorption energy at different sites of symmetric and non-symmetric carbon cluster, the most active site is found to be the edge carbon atom with high electron donation ability, which can be accurately identified by electrophilic Fukui function. More importantly, the reactivity of boron-doped cluster is simultaneously influenced by doping configuration and the type of edge, based on which -O-B-O- configuration embedded into K-region edge (isolated carbon–carbon double bonds that do not belong to Clar sextet) is predicted to exhibit the highest reactivity among various boron doping configurations. This work clarifies unique activity origin of heteroatom-doped amorphous carbon materials, providing new insights into designing high-performance carbocatalysts.

Virtual vibrational spectrometer for sp2 carbon clusters and dimers of fullerene C60

A virtual vibrational spectrometer HF Spectrodyn, based on efficient software exploring unrestricted Hartree–Fock approximation, was used to perform computational spectrometry of C60, C66 and C70 carbon clusters as well as C60 dimers. All the species are presented as digital twins, the structure and properties of which were discussed. The obtained IR absorption and Raman scattering spectra are analyzed to point out strengths, limitations and ongoing developments of the virtual spectrometry.

Tunable electrical properties of C60·m-xylene and the formation of semiconducting ordered amorphous carbon clusters under pressure

Tunable electrical properties of C60·m-xylene and the formation of semiconducting ordered amorphous carbon clusters under pressure

Structure and Magnetism of Few-Layer Nanographene Clusters in Carbon Microspheres

The solid-phase pyrolysis method was used to synthesize carbon microspheres, consisting of clusters of few-layer nanographene and amorphous carbon. Powders of metal-free phthalocyanine and polyethylene served as precursors of the synthesized carbon microspheres. The pyrolysis products of metal-free phthalocyanine samples SPc(700) and SPc(900) contained 4 and 1 atom % nitrogen, respectively, replacing carbon in the graphene lattice in pyrrolic and pyridinic coordination. There are no impurity nitrogen atoms in the products of the pyrolysis of polyethylene. The SPc(700) sample showed strong paramagnetism with a concentration of paramagnetic centers of ∼5 × 1019 spin g–1 and a temperature-independent diamagnetism susceptibility of χDia = −1 × 10–6 emu g–1 Oe–1. In a temperature range of 5–300 K, ferromagnetism was also revealed with a temperature dependence similar to that of ferromagnetic cluster spin glasses, with maximum saturation magnetization, MSFM = 3 × 10–2 emu g–1, and coercive force, Hc = 400 Oe, at Tsg = 25 K. It was shown that the ferromagnetism in the SPc(700) sample is due to π(p)-electrons of zigzag-type edge states as well as nitrogen impurity atoms. The experimental results are interpreted based on the temperature dependence of the spin correlation length. It was revealed that the temperature dependence of the integral of the magnetic resonance absorption intensity closely resembles the temperature behavior of the saturation magnetization of the ferromagnetic component.

Characterization of age hardening mechanism of low-temperature aged low-carbon steel by transmission electron microscopy

Low-temperature aging treatment at 323 K results in the dramatical increase in hardness in low-carbon ferritic steels quenched from 983 K, possibly caused by carbon clusters and/or fine ε-carbides. In this study, transmission electron microscopy (TEM) analysis was carried out to characterize the change of the microstructure during the low-temperature aging treatment. Until the early stage of the peak hardness, the carbon clusters were formed homogeneously with zig-zag structures. At the latter stage of the peak hardness, it was found that the ε-carbides were partially precipitated within the carbon clusters, which suggested that the carbon clusters might have acted as the precursors of ε-carbides. In-situ tensile TEM observations showed that dislocation motions were free-glide type, and carbon clusters and fine-carbides interacted with dislocations via cutting-type. Dislocation interaction force was also evaluated, which suggested that the lattice misfit played as important role of the interaction mechanism.

Cross-sectional analysis of lithium ion electrodes using spatial autocorrelation techniques.

Join counting, a standard technique in spatial autocorrelation analysis, has been used to quantify the clustering of carbon, fluorine and sodium in cross-sectioned anode and cathode samples. The sample preparation and EDS mapping steps are sufficiently fast for every coating from two Design of Experiment (DoE) test matrices to be characterised. The results show two types of heterogeneity in material distribution; gradients across the coating from the current collector to the surface, and clustering. In the cathode samples, the carbon is more clustered than the fluorine, implying that the conductive carbon component is less well distributed than the binder. The results are correlated with input parameters systematically varied in the DoE e.g. coating blade gap, coating speed, and other output parameters e.g. coat weight, and electrochemical resistance.

Theoretical study of linear and non-linear optical properties of small CaCn (n = 2–7) clusters

The linear and NLO properties of small calcium doped carbon cluster CaCn (n = 2–7) were investigated in the framework of time-dependent density functional theory (TD-DFT) with CAM-B3LYP/6-311+G(d). The absorption wavelength (λ), oscillatory strength (f), transition energy (Eex), and nature of transitions of major excitations have been calculated. It was shown that the most intense peak was fall in the UV region of the spectrum. The most intense peaks among all studied clusters for CaC6was found at 230 nm with oscillatory strength of 0.261, and excitation was due to H-2 → L, H-1 → L + 1, H → L + 13 transition. We observe a few peaks with weaker peaks in the visible region for CaC2, CaC5, and CaC7at560 nm, 525 nm, and 467, respectively. The average polarizability α and first hyperpolarizability βtot have been calculated and found that the polarizability of studied clusters increases with the number of carbon atoms in the cluster. Hyperpolarizability of CaC2 and CaC5 was calculated as 2874.7 a.u. and 1329.9 a.u. Indicating strong NLO prospects among all studied clusters. The optical response of studied clusters suggests that these materials can be considered as auspicious for optoelectronic devices.

Магнетизм нанопористого углерода с кластерами марганца

Theoretical calculations of the electron density (taking into account the spin) of a model 16-atom carbon cluster with a manganese atom in a micropore showed that it is energetically favorable for manganese atoms to localize inside the pore and form metal nanoclusters in the carbon micropore. The magnetic moment of an ensemble of atoms surrounding a micropore with one manganese atom in it turned out to be quite large. An experimental method was proposed for introducing manganese clusters into bulk samples of nanoporous carbon with different porous structures, and the effect of these adsorbates on the magnetic properties of the samples was studied. In parallel, X-ray diffraction studies of the samples were carried out. It has been shown that Mn clusters near the surface are rather rapidly oxidized in air, as a result of which peaks associated with oxides predominate in the X-ray diffraction patterns. However, small Mn clusters have also been found. Measurements of the dependence of the magnetization of the samples on the applied field at T=295K showed the presence of nonlinearity and hysteresis characteristic of superparamagnetism or ferromagnetism.

Magnetism of nanoporus carbon with manganese clusters

Theoretical calculations of the electron density (taking into account the spin) of a model 16-atom carbon cluster with a manganese atom in a micropore showed that it is energetically favorable for manganese atoms to localize inside the pore and form metal nanoclusters in the carbon micropore. The magnetic moment of an ensemble of atoms surrounding a micropore with one manganese atom in it turned out to be quite large. An experimental method was proposed for introducing manganese clusters into bulk samples of nanoporous carbon with different porous structures, and the effect of these adsorbates on the magnetic properties of the samples was studied. In parallel, X-ray diffraction studies of the samples were carried out. It has been shown that Mn clusters near the surface are rather rapidly oxidized in air, as a result of which peaks associated with oxides predominate in the X-ray diffraction patterns. However, small Mn clusters have also been found. Measurements of the dependence of the magnetization of the samples on the applied field at T=295 K showed the presence of nonlinearity and hysteresis characteristic of superparamagnetism or ferromagnetism. Keywords: micropores, manganese, spin density, magnetization.