Carbon Nanoclusters Research Articles

Electrical conductivity of carbon films obtained by thermal sputtering of type I shungite rocks of various deposits

Amorphous carbon films were deposited by thermal evaporation of bulk samples of different shungites and graphite. Structural properties and the size of carbon nanoclusters in the films were determined from the analysis of their selected area electron diffraction (SAED) patterns and Raman spectra. To analyze the possible distribution of trace elements in the films, element mapping was performed using scanning electron microscopy. The electrical conductivity of the obtained films was measured at temperatures ranging from the liquid nitrogen to room temperature. The measurements showed differences in the type of dependence of electrical conductivity on temperature for different nano-crystalline films from monotonic, typical for semiconductors to complex, V-shaped curve containing sections of the metallic and semiconductor types.

A "turn-on" FRET aptasensor based on the metal-organic framework-derived porous carbon and silver nanoclusters for zearalenone determination

Zearalenone (ZEN) is a fungal secondary metabolite with an estrogen-like structure. Its widespread existence and potential hazards to human and animal health call for alternative rapid determination methods to monitor ZEN in food and the environment. Herein, a robust and enzyme-free "turn-on" aptasensor based on fluorescence resonance energy transfer (FRET) was developed for the sensitive identification of ZEN. Aptamer-modified silver nanoclusters (AgNCs) and porous Fe3O4/carbon octahedra derived from the metal-organic framework (MOF) acted as the FRET energy donor−acceptor pair in fluorescence quenching. DNA-templated AgNCs can be adsorbed onto the surface of porous Fe3O4/carbon octahedra through π-π stacking, which will lead to the FL quenching of AgNCs. However, in the presence of the ZEN, the formation of the ZEN/aptamer complex promoted the release of AgNCs and thereby brought about the recovery of fluorescence, which can be used to indicate the concentration of ZEN. The prepared aptasensor was characterized by various physicochemical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), energy-dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS) and circular dichroism spectroscopy (CD). By combining the excellent quenching properties and easy separation of magnetic porous Fe3O4/carbon octahedra, as well as the appealing photostability and water solubility of AgNCs, the proposed FRET platform demonstrated superior analytical performance with a linear range of 0.01–250 ng mL−1 and a LOD as low as 2 × 10−3 ng mL−1. Most importantly, the practicability and reliability of the FRET-based strategy were confirmed by conducting the determination of ZEN in real samples.

СИСТЕМА АВТОМАТИЗИРОВАННОГО ПРОЕКТИРОВАНИЯ И ПРОТОТИПИРОВАНИЯ УЧАСТКОВ СИНТЕЗА УГЛЕРОДНЫХ НАНОКЛАСТЕРНЫХ СТРУКТУР

The article focuses on using the integrated multi-component computer-aided design and control systems, which changes the product life cycle processes in the high-tech complex chemical and technological systems. In the integrated design of production facilities, special attention is paid to safety, productivity, reliability, ergonomics of the production line and the material and technical environment. The most effective in project management are flexible life cycle models that connect diverse specialists in a single information environment. The relevance of the task of developing and implementing problem-oriented heterogeneous computer-aided design and digital prototyping systems is justified. There is described a method for improving the efficiency of designing production facilities while minimizing the time required preparing a design solution, and the risks of design errors caused by the communication dissonance of diverse specialists. The architecture of the computer-aided design and digital prototyping system with a description of its basic components is presented. The creation of a digital model of the design object is described on the example of the reactor site and the material and technical base of the process of synthesis of carbon nanocluster structures that are in high demand in various industries. The conducted tests and the introduction of the resulting applied software solution into the educational process proved its efficiency in solving problems of integrated computer-aided design and digital modeling not only of objects of the carbon nanoindustry, but also for other industries with a similar material and technical base.

A Study of the Antioxidant, Cytotoxic Activity and Adsorption Properties of Karelian Shungite by Physicochemical Methods.

This study reveals that fossil shungite samples exhibit antioxidant activity, can reduce oxidized components, and bind to free radicals. A sample of Sh20 (size fraction—20 μm) (1.30 mg equivalents of ascorbic acid/g of shungite; 3.46 mg equivalents of trolox/g of shungite; 0.99 mg equivalents of quercetin/g of shungite) had the maximal activity according to the amperometric method. The obtained data indicate that shungite has antioxidant properties, but these are approximately 1000 times less pronounced than those of quercetin. A ShT20 sample (size fraction—20 μm + heat treatment) was found to have the highest antioxidant activity against the 2,2-diphenyl-1-picrylhydrazyl radical and cytotoxicity. Further studies, including the optimization of the antioxidant extraction conditions of shungite, and the analysis of the qualitative and quantitative composition of the obtained extracts, are required for a more accurate interpretation of the results. Shungite can be applied as an alternative to activated carbon in water purification, due to its absorption, catalytic, antioxidant, regenerating, and antibacterial properties, as well as its high environmental safety and relatively low cost. It is possible to identify new structural forms of carbon within, and other valuable properties of, shungite substance, which will make it possible to create effective technologies for the practical use of shungite rocks, particularly in the production of fullerenes and other carbon nanoclusters.

Close‐packed storage of potassium metallic clusters achieved through nanostructure engineering of ultrafine hollow nanoparticles‐based carbon nanoclusters

AbstractUltrafine hollow nanoparticles‐based (7 nm) carbon nanoclusters (HNPCNCs) are developed by a facile and novel method. Benefiting from the ultrafine nanostructure, we have achieved close‐packed storage of K metallic clusters and a close‐packed K metallic clusters with a diameter of 7 nm has been observed for the first time through ex TEM. In K‐ion batteries, HNPCNCs anodes deliver an ultrahigh capacity of 269.8 mA h g−1 at 0.5 A g−1 after 200 cycles, outstanding rate performance of 150.5 mA h g−1 after 5000 cycles at 5 A g−1. Moreover, an excellent electrochemical performance has been obtained by HNPCNCs//potassium Prussian blue potassium‐ion full cells, highlighting the practicability of HNPCNCs. The unprecedented electrochemical performance is attributed to the close‐packed K metallic clusters achieved by unique ultrafine hollow nanoparticles in the carbon nanoclusters.image

A Computer-Aided Design System for Virtual Models for Training in Control of the Synthesis Process of Carbon Nanostructures

A conceptual description of a complex, potentially dangerous process of electric arc synthesis of carbon nanocluster structures is presented. The architecture and basic functional elements of a modular computer system for designing virtual models of a production facility for training operators to control the synthesis of carbon nanocluster structures are presented. A complex task of training to control a chemical-technological process is formulated, which is executed on the basis of the obtained software solution. The stages of the multistage process of designing a virtual model and setting up a computer system for the logistics base of an industrial enterprise are presented as part of testing the reactor island model, Kretschmer’s electric arc, industrial and expert data on the synthesis of fullerene С60.

Functionalized multi-walled carbon nanotubes with strong fluorescence emission

Multi-walled carbon nanotubes (MWCNTs) with strong visible fluorescence were synthesized via oxidation and amination. A large number of oxygen-containing surface functional groups contributing to fluorescence emission have been found, and the novel structure of carbon nanoclusters with the diameter of 20–30 nm are formed at the tips of MWCNTs. The fluorescent MWCNTs exhibit distinct excitation-wavelength dependence and pH response. Furthermore, the temperature sensitivity of fluorescence has been described carefully. The fluorescence intensity first increases and then decreases upon increasing temperature, and the maximum emission is achieved when the functionalized MWCNTs are dried at 150 °C.

Graphite Ion Source Geometry and Ne-Gas Pressure Dependent Growth and Morphology of Carbon Nanoclusters: AFM Analysis

The understanding of the growth and morphological evolution of nanoclusters with process parameters such as ion source geometry, voltage, current, time, and gas pressure are highly important to achieve their desired sizes, morphology, and concentration. Carbon nanoclusters (0-dimensional) were synthesized using the DC glow discharge technique at different process parameters (such as Ne-gas pressures, current, voltage, etc.) using custom fabricated graphite ion sources of cylindrical and U-shaped geometries. The morphology and density of carbon nanoclusters were studied with an atomic force microscope (AFM) to understand their evolution at different process parameters. The study suggests that the U-shaped hollow cathode ion source produces tiny carbon nanoclusters at greater concentration as compared to the cylindrical cathode. Similarly, the density of tiny nanoclusters enhances greatly with the increasing pressures (e.g., 75 mbar). In addition, the AFM morphology of the nanoclusters shows that they are more agglomerated at relatively lower pressure (e.g., 25 mbar). This may be due to the higher fragmentation of carbon soot with the increasing pressure because of more collisions among gas molecules and carbonaceous species. At controlled and optimized Ne-gas pressures and source geometry, carbon nanoclusters of the desired sizes can be fabricated, which may become promising candidates for nanoscale electronics, optoelectronic, and spintronic devices.

Nanocarbon-Modified Metal Porous Cathodes with High Durability for Application in Microwave Devices

The paper presents the calculations of the physical and energy parameters of nanocarbon structures with the components of a metal-porous cathode active substance. Obtained results match experimental data. It has been experimentally determined that the active substance modified by the sulfoadduct of carbon nanoclusters has an evaporation rate 1.5 times lower than the typical one. Tests of nanocarbon-modified cathodes as part of a travelling wave tube for space applications have shown them to have a durability of 1 740 800 h at a 0.645-A/cm2 current density on collector.

Characterization of the impact of nanoparticles on micro strain in 2D graphene synthesized by arc discharge plasma

In this study, we report the impact of side growth of nanoparticles on crystalline graphene nanostructure by facile and stable arc discharge plasma method. The plasma generated between two highly purity graphite electrodes, not only exfoliate graphene layers on cathode surface, but also produces micro and nanoparticles. The characterization of microstructures produced on the graphene layers deposited under different background environments and pressures by arc discharge plasma is presented. The morphologies of graphene sheets, comprising eight to twelve layers, were confirmed using transmission electron microscopy (TEM). Furthermore, the increment of background pressure from 10−2 to 102 mbar has found to increase numbers of graphene layers resulting in a reduction in I2D/IG ratio. Tuning the background environment and pressure led to different levels of carbon nanoclusters embedment on the surface of graphene layer under the air and H2 environments. This embedment demonstrates the rise of microstrain in the form of tensile stress on graphene indicated by Williamson-Hall plot calculated at 1232 × 10−3 and 151 × 10−3 respectively under H2 and air. The redshift and splitting of G and 2D bands in Raman spectra also support the rise of strain in graphene layers. Overall, embedment of nanoparticles might be accounted by the increase in stress on graphene layers that manipulate the electronic interaction between layers, suggesting it a promising candidate for nanoelectronic and nanophotonic device applications based on graphene.

Irreversible high pressure phase transformation of onion-like carbon due to shell confinement

Onion-like carbon (OLC) was investigated at high pressure (up to 48 GPa) in a shear diamond anvil cell (SDAC) equipped with in-situ Raman spectroscopy control. The OLC was obtained from natural gas by a highly productive and efficient partial oxidation method. Vast bulk modulus B0 = 486 ± 15 GPa and outstanding stability under high pressure were registered in the experiment. A phase transition was observed at 20 GPa under conditions of shear deformation. The transition is characterized by an appearance of a new Raman band at 1560 cm−1 accompanied with disappearance of G band of OLC. We attribute these features to sp2-sp3 transition in the carbon nanoclusters. It was found however that the concentric multi-shell onion-like structure remains intact after pressure release, which may witness that the outer shell of the OLC serves as a confinement and prevents structural collapse. X-ray photoelectron spectroscopy revealed however that the phase transition was not completely reversible because the OLC after pressure release showed the presence of sp3-hybridized carbon in significant amounts.

Molecular dynamics simulation of graphene sinking during chemical vapor deposition growth on semi-molten Cu substrate

Copper foil is the most promising catalyst for the synthesis of large-area, high-quality monolayer graphene. Experimentally, it has been found that the Cu substrate is semi-molten at graphene growth temperatures. In this study, based on a self-developed C–Cu empirical potential and density functional theory (DFT) methods, we performed systematic molecular dynamics simulations to explore the stability of graphene nanostructures, i.e., carbon nanoclusters and graphene nanoribbons, on semi-molten Cu substrates. Many atomic details observed in the classical MD simulations agree well with those seen in DFT-MD simulations, confirming the high accuracy of the C–Cu potential. Depending on the size of the graphene island, two different sunken-modes are observed: (i) graphene island sinks into the first layer of the metal substrate and (ii) many metal atoms surround the graphene island. Further study reveals that the sinking graphene leads to the unidirectional alignment and seamless stitching of the graphene islands, which explains the growth of large single-crystal graphene on Cu foil. This study deepens our physical insights into the CVD growth of graphene on semi-molten Cu substrate with multiple experimental mysteries well explained and provides theoretic references for the controlled synthesis of large-area single-crystalline monolayer graphene.

Nitrogen-doped CVD diamond: Nitrogen concentration, color and internal stress

Single crystal CVD diamond has been grown on (100)-oriented CVD diamond seed in six layers to a total thickness of 4.3 mm, each layer being grown in gas with increasing concentration of nitrogen. The nitrogen doping efficiency, distribution of color and internal stress have been studied by SIMS, optical absorption, Raman spectroscopy and birefringence imaging. It is shown that nitrogen doping is very non-uniform. This non-uniformity is explained by the terraced growth of CVD diamond. The color of the nitrogen-doped diamond is grayish-brown with color intensity gradually increasing with nitrogen concentration. The absorption spectra are analyzed in terms of two continua representing brown and gray color components. The brown absorption continuum exponentially rises towards short wavelength. Its intensity correlates with the concentration of nitrogen C-defects. Small vacancy clusters are discussed as the defects responsible for the brown absorption continuum. The gray absorption continuum has weak and almost linear spectral dependence through the near infrared and visible spectral range. It is ascribed to carbon nanoclusters which may form in plasma and get trapped into growing diamond. It is suggested that Mie light scattering on the carbon nanoclusters substantially contributes to the gray absorption continuum and determines its weak spectral dependence. A Raman line at a wavenumber of 1550 cm−1 is described as a characteristic feature of the carbon nanoclusters. The striation pattern of brown/gray color follows the pattern of anomalous birefringence suggesting that the vacancy clusters and carbon inclusions are the main cause of internal stress in CVD diamond. A conclusion is made that high perfection of seed surface at microscale is not a required condition for growth of low-stress, low-inclusion single crystal CVD diamond. Crystallographic order at macroscale is more important requirement for the seed surface.

The influence of NH3 flow rate on the microstructure and oxidation properties of a-Si-C-N:H films prepared by PECVD technology

Hydrogenated amorphous silicon carbon nitride (a-Si-C-N:H) films embedded with carbon nanoclusters were deposited by plasma enhanced chemical vapour deposition (PECVD) method. The microstructure and oxidation properties of the films were mainly analysed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectroscopy (XPS), Raman and high-resolution transmission electron microscopy (HRTEM). The influence of the NH3 flow rate on the film oxidation properties in air at room temperature has been investigated. The results showed that the carbon atoms tend to bond with each other during the film deposition and then form carbon nanoclusters. In addition, with increasing NH3 flow rate, the results also indicated that more N and C atoms bonded with Si atoms would be replaced by O atoms, and the N atoms mainly bonded with C atoms and the O atoms mainly bonded with Si atoms. Furthermore, the films became more and more dense, but the film oxidation was more and more serious. The oxidation of the film was mainly attributed to the production of the related silicon dangling bonds and the formation of the smaller carbon nanoclusters.

A theoretical indicator of transition-metal nanoclusters applied in the carbon nanotube nucleation process: a DFT study.

Knowledge about the appropriate indicators to point out the best components in a catalytic process is a basic prerequisite for obtaining insights into optimized reactions as, for example, in the chemical vapour deposition method, which enables the growth of carbon nanotubes. In this work, we report a density functional theory study of 13-atom transition-metal nanoclusters interacting with (5,0) zigzag and (3,3) armchair carbon nanotube fragments, considering all transition-metal species from the periodic table as possible candidates for the chemical vapour deposition method. The icosahedral configuration was found to be a good model to simulate the seed of nucleation in the case of the short carbon nanotube fragments that are initially formed during the growth process. From full geometric optimizations, without any constraints, we found that the energetic and structural nanocluster properties change as a function of the occupation of the bonding and anti-bonding d-states. The center of gravity of the occupied d-states for nanoclusters is found to be a good indicator to reveal the best candidates for the interaction with the carbon nanotubes, namely, Sc-Cu, Y-Nb, Pd, Lu, Hf, and Pt. The interaction between all transition-metal nanoclusters with both armchair and zigzag segments is favorable in terms of the adhesion energy, where the adhesion is larger for systems with smaller occupation of the d-states. The bond strength is more pronounced for systems with zigzag fragments than those with armchair fragments, which is confirmed by the smaller average bond length between the metal atoms of the nanocluster and the C atoms of the zigzag segment. Our prediction about the best 13-atom transition-metal candidates is reinforced by the linear relationship between the adhesion energy and the center of gravity of the occupied d-states. Thus, the adhesion energy presents increased intensity for the interaction between carbon nanotube fragments and nanoclusters in relation to the smaller occupation of the d-states. Consequently, our model is able to provide a good descriptor for indicating the best 13-atom transition-metal candidates in the chemical vapour deposition process.

Металлопористые катоды, модифицированные наноуглеродом, с высокой долговечностью для применения в приборах СВЧ

The results of calculations of the physical and energy parameters of nanocarbon structures with components of the active substance of the dispenser cathode, which are in good agreement with experience, are presented. It was experimentally determined that the active substance modified by the sulfoadduct of carbon nanoclusters has an evaporation rate of 1.5 times lower than the typical one. Tests of cathodes modified by nanocarbon as part of space-based TWTs showed a durability of 1740800 hours with a current density of 0.645 A / cm2.

Ultrafast Melting of Metal–Organic Frameworks for Advanced Nanophotonics

AbstractThe conversion of metal–organic frameworks (MOFs) into derivatives with a well‐defined shape and composition is considered a reliable way to produce efficient catalysts and energy capacitors at the nanometer scale. Yet, approaches based on conventional melting of MOFs provide the derivatives such as amorphous carbon, metal oxides, or metallic nanoclusters with an appropriate morphology. Here ultrafast melting of MOFs is utilized by femtosecond laser pulses to produce a new generation of derivatives with complex morphology and enhanced nonlinear optical response. It is revealed that such a nonequilibrium process allows conversion of interpenetrated 3D MOFs comprising flexible ligands into well‐organized spheres with a metal oxide dendrite core and amorphous organic shell. The ability to produce such derivatives with a complex morphology is directly dependent on the electronic structure, crystal density, ligand flexibility, and morphology of initial MOFs. An enhanced second harmonic generation and three‐photon luminescence are also demonstrated due to the resonant interaction of 100–1000 nm spherical derivatives with light. The results obtained are in the favor of new approaches for melting special types of MOFs for nonlinear nanophotonics.

High-temperature microstructural evolution of SiCN fibers derived from polycarbosilane with different C/N ratios

Research into the high-temperature microstructural evolution of SiCN ceramic fibers is important for the aerospace application of advanced ceramic matrix composites in harsh environments. In this work, we studied the microstructural evolution of SiCN fibers with different C/N ratios that derived from polycarbosilane fibers at the annealing temperature range of 1400∼1600 °C. These results showed that the phase separation of SiCxNy phase and the two-dimension grain growth process of free carbon nanoclusters could be processed at the researched temperature range. As the annealing temperature increased to 1600 °C, the crystallization of amorphous SiC and Si3N4 could be detected. SEM and Raman analysis showed that the decomposition and carbothermal reduction of the Si3N4 phase at high temperatures played primary roles in contributing to the fiber strength degradation. Thus, a higher C/N ratio, which is beneficial for inhibiting the decomposition of amorphous Si3N4, helps SiCN fibers retain high tensile strength at high temperatures.

Pulsed and Static Field Emission VAC of Carbon Nanocluster Structures: Experiment and Its Interpretation

The field emission properties of carbon nanocluster structures and films based on them have been considered. Experimental data, including VAC, at static and pulse modes have been presented. The analysis of size effects, effect of field penetration, and hysteresis effect has been performed. The theoretical explanations of them have been given.

Study of surface topography and emission properties of thin Mo and Zr films

Thin films of Mo and Zr were deposited on Si wafers by the magnetron sputtering process with controlled parameters. Correlation between their field-emission properties and surface morphology was investigated. The study results were found to be in good agreement with previous data acquired for carbon nanocluster films, which witnesses that morphology can have greater effect on field emission capability of thin films than their chemical composition and work function.