Ab initio study of anisotropic mechanical and electronic properties of strained carbon-nitride nanosheet with interlayer bonding

Due to the noticeable structural similarity and being neighborhood in periodic table of group-IV and-V elemental monolayers, whether the combination of group-IV and-V elements could have stable nanosheet structures with optimistic properties has attracted great research interest. In this work, we performed first-principles simulations to investigate the elastic, vibrational and electronic properties of the carbon nitride (CN) nanosheet in the puckered honeycomb structure with covalent interlayer bonding. It has been demonstrated that the structural stability of CN nanosheet is essentially maintained by the strong interlayer σ bonding between adjacent carbon atoms in the opposite atomic layers. A negative Poisson’s ratio in the out-of-plane direction under biaxial deformation, and the extreme in-plane stiffness of CN nanosheet, only slightly inferior to the monolayer graphene, are revealed. Moreover, the highly anisotropic mechanical and electronic response of CN nanosheet to tensile strain have been explored.     

Surface decoration of carbon nanosheets with amino-functionalized organosilica nanoparticles

Carbonaceous nanosheets decorated with amino-functionalized organosilica nanoparticles have been synthesized by a direct pyrolysis of betaine at 400 °C in air, followed by a simple surface treatment with ([3-(2-aminoethylamino) propyl]trimethoxysilane under reflux conditions. Both pristine and organosilica modified carbon nanosheets (OMCNs), were characterized by Fourier-transform infrared (FTIR), Raman, and electron paramagnetic resonance (EPR) spectroscopies, transmission electron microscopy and thermal analysis methods. The experimental data reveal a dramatic increase in the number of radical centers on the surface of the developed OMCN hybrid. The organosilica nanoparticles, ranging in size between 3 and 15 nm, are spherical and homogenously anchored on the surface of carbon nanosheets. The formation of COSi bridges between carbon sheets and the organosilica nanoparticles has been supported by FTIR and EPR. These nanoparticles are bound to the nanosheet surface together with individual functional organosilane groups at a spacing of about 4 Å distance. The final hybrid is the complex nanosystem composed of 2D carbon nanosheets, spherical organosilica nanoparticles and immobilized amino organosilane molecules.     

One-step synthesis of TiC/multilayer graphene composite by thermal plasma

Graphene hybrid materials have been attracting a great deal of attention due to their superior properties. Nevertheless, problems such as expensive and complicated production processes have limited their application to industrial fields. Here, we introduce a one-step synthesis of titanium carbide (TiC) nanoparticles on multilayer graphene nanosheet (TiC/multilayer graphene) composites using thermal plasma. Although there are three types of titanium alkoxides (titanium ethoxide, titanium isopropoxide and titanium n-butoxide), the TiC/multilayer graphene was synthesized from only titanium isopropoxide. The injection temperature of the precursor was varied to investigate the effects of the precursor concentration in the plasma region. A TiC/multilayer graphene hybrid material with crystalline TiC nanoparticles below 50 nm on graphene nanosheets was observed. The number of graphene nanosheet layers varied from one to over 10 according to the injection temperature. When titanium ethoxide and titanium butoxide were injected, TiC with amorphous carbon and graphite were synthesized. The formation of graphene is considered to be affected by the structure of the carbon chain in the precursors and the concentration in the plasma region.     

γ-graphyne and its boron nitride analogue as nanocarriers for anti-cancer drug delivery

Presently, many studies are directed toward the design of new drug delivery systems. Inspired by a fascinating finding of a new carbon allotrope, namely graphyne (GY), we suggest the pristine and BN analogue of GY (BNY) nanosheets in the drug delivery applications. The purpose of the present study is to investigate the interaction of an anti-cancer drug (hydroxyurea (HU)) with GY and BNY nanosheets by means of the density functional theory (DFT). Results show that the GY nanosheet with B and N atoms could remarkably increase the tendency of nanosheet for adsorption of HU drug. Also, our ultraviolet-visible results show that the electronic spectra of the drug/nanosheet complexes exhibit a red shift toward higher wavelengths (lower energies). It was found that the HU/BNY had high chemical reactivity, which was important for binding of the drug onto the target site. In order to go further and gain insight into the binding features of considered systems with HU drug, the Atoms in Molecules (AIM) analysis was performed. Our results determine the strong interaction features of the HU/BNY bonding. Consequently, the present study demonstrated that the BNY could be used as potential carrier for delivery of HU drug.     

Carbon nanosheets by microwave plasma enhanced chemical vapor deposition in CH4-Ar system

We employ a new gas mixture of CH₄-Ar to fabricate carbon nanosheets by microwave plasma enhanced chemical vapor deposition at the growth temperature of less than 500 °C. The catalyst-free nanosheets possess flower-like structures with a large amount of sharp edges, which consist of a few layers of graphene sheets according to the observation by transmission electron microscopy. These high-quality carbon nanosheets demonstrated a faster electron transfer between the electrolyte and the nanosheet surface, due to their edge defects and graphene structures.     

Graphene oxide templated alumina nanosheet for the removal of As(V)

The current paper demonstrates a simple preparative method of alumina nanosheet through controlled hydrolysis and condensation on the surface of graphene oxide (GO). Taking into account the moisture sensitivity of the alumina precursor, its hydrolysis was carried out after introduction of interaction between the functional groups of GO and the alumina precursor in a non-aqueous solvent. On pyrolysis of the aluminum oxide-GO composite, a free-standing alumina nanosheet was obtained, which was further confirmed by XRD, TEM, STEM-EDX, FE-SEM, TGA, and N₂ physisorption. Due to a favorable nanosheet structure, the alumina nanosheets showed a better performance in the removal of As (V) when compared to alumina prepared without GO template, even though the latter had a larger surface area than the alumina nanosheet.     

Preparation, electronic structure, and photocatalytic properties of Bi2O2CO3 nanosheet

Bi₂O₂CO₃ nanosheet with a thickness of less than 20 nm was synthesized via hydrothermal and solvothermal process. The properties of the as-prepared nanosheet were characterized by X-ray diffraction, scanning electron microscopy, and diffuse reflectance spectra. The electronic structure was investigated using first-principle calculations. Application of the as-prepared Bi₂O₂CO₃ nanosheet in photocatalysis was also studied.     

Quantum oscillations in a hexagonal boron nitride-supported single crystalline InSb nanosheet

A gated Hall-bar device is made from an epitaxially grown, free-standing InSb nanosheet on a hexagonal boron nitride (hBN) dielectric/graphite gate structure and the electron transport properties in the InSb nanosheet are studied by gate-transfer characteristic and magnetotransport measurements at low temperatures. The measurements show that the carriers in the InSb nanosheet are of electrons and the carrier density in the nanosheet can be highly efficiently tuned by the graphite gate. The mobility of the electrons in the InSb nanosheet is extracted from low-field magneotransport measurements and a value of the mobility exceeding $\sim 1.8\times10^4$ cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$ is found. High-field magentotransport measurements show well-defined Shubnikov-de Haas (SdH) oscillations in the longitudinal resistance of the InSb nanosheet. Temperature-dependent measurements of the SdH oscillations are carried out and key transport parameters, including the electron effective mass $m^{\ast }\sim 0.028 m_{0}$ and the quantum lifetime $\tau \sim 0.046 $ ps, in the InSb nanosheet are extracted. It is for the first time that such experimental measurements have been reported for a free-standing InSb nanosheet and the results obtained indicate that InSb nanosheet/hBN/graphite gate structures can be used to develop advanced quantum devices for novel physics studies and for quantum technology applications.     

基于硬度回归法测定退火碳钢的含碳量

测量了已知退火碳钢的硬度,揭示了含碳量与硬度线性相关的特性.利用最小二乘法进行回归分析,得到硬度与含碳量的线性方程,并以此实现对未知碳钢的估计.另通过金相组织观察法和杠杆定律再次对未知碳钢含碳量进行估计,结果发现与硬度测量法估计的含碳量基本一致.比较两种方法,硬度测量法更客观,更准确.并与标准金相图谱比对,进一步验证了实验结论.     

Synthesis and characterization of carbon nanotubes on carbon microfibers by floating catalyst method

In this paper, carbon nanotubes were synthesized on carbon microfibers by floating catalyst method with the pretreatment of carbon microfibers at the temperature of 1023 K, using C₂H₂ as carbon source and N₂ as carrier gas. The morphology and microstructure of carbon nanotubes were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The composition of carbon nanotubes was determined by energy dispersive X-ray spectroscopy (EDX). The results showed that the surface of treated carbon microfibers was thickly covered by carbon nanotubes with diameters of about 50 nm. EDX image indicated that the composition of carbon nanotubes was carbon. In comparison with the sample grown on untreated carbon microfibers surface, it was found that after carbon microfibers were boiled in the solution of sulfur acid and nitric acid (VH₂SO₄:VHNO₃ = 1:3) and immersed in the solution of iron nitrate and xylene, carbon nanotubes with uniform density can be grown on carbon microfibers surface. Based on the results, we concluded that the pretreatment of carbon microfibers had great effect on the growth of carbon nanotubes by floating catalyst method.     

Controllable Formation of Niobium Nitride/Nitrogen‐Doped Graphene Nanocomposites as Anode Materials for Lithium‐Ion Capacitors

Niobium nitride/nitrogen‐doped graphene nanosheet hybrid materials are prepared by a simple hydrothermal method combined with ammonia annealing and their electrochemical performance is reported. It is found by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the as‐obtained niobium nitride nanoparticles are about 10–15 nm in size and homogeneously anchored on graphene. A non‐aqueous lithium‐ion capacitor is fabricated with an optimized mass loading of activated carbon cathode and the niobium nitride/nitrogen‐doped graphene nanosheet anode, which delivers high energy densities of 122.7–98.4 W h kg^?1 at power densities of 100–2000 W kg^?1, respectively. The capacity retention is 81.7% after 1000 cycles at a current density of 500 mA g^?1. The high energy and power of this hybrid capacitor bridges the gap between conventional high specific energy lithium‐ion batteries and high specific power electrochemical capacitors, which holds great potential applications in energy storage for hybrid electric vehicles.     

A double quantum dot defined by top gates in a single crystalline InSb nanosheet

We report on the transport study of a double quantum dot (DQD) device made from a freestanding, single crystalline InSb nanosheet. The freestanding nanosheet is grown by molecular beam epitaxy and the DQD is defined by the top gate technique. Through the transport measurements, we demonstrate how a single quantum dot (QD) and a DQD can be defined in an InSb nanosheet by tuning voltages applied to the top gates. We also measure the charge stability diagrams of the DQD and show that the charge states and the inter-dot coupling between the two individual QDs in the DQD can be efficiently regulated by the top gates. Numerical simulations for the potential profile and charge density distribution in the DQD have been performed and the results support the experimental findings and provide a better understanding of fabrication and transport characteristics of the DQD in the InSb nanosheet. The achieved DQD in the two-dimensional InSb nanosheet possesses pronounced benefits in lateral scaling and can thus serve as a new building block for the developments of quantum computation and quantum simulation technologies.     

High-field electron emission of carbon nanotubes grown on carbon fibers

Carbon nanotubes with uniform density were synthesized on carbon fiber substrate by the floating catalyst method. The morphology and microstructure were characterized by scanning electron microscopy and Raman spectroscopy. The results of field emission showed that the emission current density of carbon nanotubes/carbon fibers was 10 μA/cm² and 1 mA/cm² at the field of 1.25 and 2.25 V/μm, respectively, and the emission current density could be 10 and 81.2 mA/cm² with the field of 4.5 and 7 V/μm, respectively. Using uniform and sparse density distribution of carbon nanotubes on carbon fiber substrate, the tip predominance of carbon nanotubes can be exerted, and simultaneously the effect of screening between adjacent carbon nanotubes on field emission performance can also be effectively decreased. Therefore, the carbon nanotubes/carbon fibers composite should be a good candidate for a cold cathode material.     

Dimensional changes of carbon fiber fabrics reinforced phenolic resin-based carbon/carbon composites during pyrolysis

The dimensional changes of two-dimensional phenolic resin-based carbon/carbon composites during pyrolysis were investigated. The carbon/carbon composites were obtained by pyrolyzing the carbon fiber/phenolic resin composites that were fabricated using a vacuum bag hot pressing technique. Length, width and thickness of the rectangular composite samples were measured carefully before and after pyrolysis. The effects of heat treatment temperature and fiber pre-heat treatment on the dimensional changes of carbon/carbon composites were investigated. The measurement results indicated that different behavior in dimensional changes could be obtained for carbon/carbon composites with different fiber–matrix bonding in the interface.     

Effects of carbon content on the electrochemical properties of spherical pyrrhotine/carbon nanocomposites

Spherical pyrrhotine/carbon nanocomposites with different carbon contents were synthesized by a solvothermal method followed by heat treatment. The carbon content of the nanocomposites was controlled by changing the amount of the carbon precursor. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); the influence of carbon layer thickness on the electrochemical performance was analyzed by charge/discharge cycling and X-ray photoelectron spectroscopy (XPS). Results show that the moderate carbon layer displays a positive effect in improving reversible capacity and the rate capability. The optimal carbon content in the pyrrhotine/carbon nanocomposites was about 15 wt.%, which can retain a high reversible capacity of 689.5 mAh/g even after 50 cycles at 0.1 C and an excellent rate capability of 393.4 mAh/g at 5 C. The synthesized nanocomposites show a promising potential as a novel anode material for lithium-ion batteries.     

Nanocaging Silicon Nanoparticles into a Porous Carbon Framework toward Enhanced Lithium-Ion Storage

Silicon (Si) shows overwhelming promise as the high-capacity anode material of Li-ion batteries with high energy density. However, Si-based anodes are subjected to a limited electrochemical cycling lifetime due to their large volume change. Herein, a honeycomb-like biomass-derived carbon nanosheet framework is reported to encapsulate Si nanoparticles via a facile molten salt templating method. The carbon framework provides sufficient void space for effectively accommodating the large volume expansion of Si upon Li⁺ insertion. Moreover, the interconnected carbon skeletons afford fast electron/ion transport pathways for improving the reaction kinetics. Consequently, the porous Si/carbon composite could exhibit a high and stable Li storage capacity of 1022 mAh g⁻¹ at 0.2 A g⁻¹ over 100 cycles along with superior rate capability (555 mAh g⁻¹ at 5 A g⁻¹). This study demonstrates an effective structural design strategy for Si-based anodes toward stable lithium energy storage.     

Preparation of carbon nanosheets deposited on carbon nanotubes by microwave plasma-enhanced chemical vapor deposition method

Carbon nanosheets were synthesized by microwave plasma-enhanced chemical vapor deposition method on carbon nanotubes substrate which was treated by hydrogen plasma. The results showed that the diameters of carbon nanotubes first got thick and then “petal-like” carbon nanosheets were grown on the outer wall of carbon nanotubes. The diameters of carbon nanotubes without and with carbon nanosheets were 100-150 and 300-500 nm, respectively. Raman spectrum indicated the graphite structure of carbon nanotubes/carbon nanosheets. The hydrogen plasma treatment and reaction time greatly affected the growth and density of carbon nanosheets. Based on above results, carbon nanosheets/carbon nanotubes probably have important applications as cold cathode materials and electrode materials.     

Comparison of carbon fiber and cesium iodide-coated carbon fibercathodes

Presents results of an experimental comparison of a bare carbon fiber cathode and the same cathode when coated with cesium iodide salt (CsI). An annular cathode was constructed by arranging carbon fibers in an annular tuft pattern. The cathode was then operated as a bare carbon fiber cathode and in a configuration with a CsI coating. The cathode was tested at electric field strengths ranging from 50 kV/cm to 265 kV/cm at anode-cathode (A-K) gaps of 3.175 cm. The applied voltage had a 1-μs duration and the modulator was operated at up to 1 Hz repetition rate. The system had a low base pressure (<1.0×10^-7 torr). The article reports on results concerning the conditioning of the cathodes, the shot-to-shot reproducibility of the cathodes and the pressure evolution of the diode under 1 Hz operation. We also report on the impedance evolution of each of the diodes     

Microstructure and wear property of carbon nanotube carburizing carbon steel by laser surface remelting

Carbon nanotube was used to carburize the surface of medium carbon steel and mild steel, respectively, by means of laser surface remelting. The slurry of carbon nanotube of ethanol was coated on the surface of the materials prior to laser irradiation. Microstructures, microhardness and wear property of the surface layers treated by different laser performance parameters were studied. Graphite coating was also used for carburizing. The results showed that both carbon nanotube and graphite were dissolved in the surface molten layer, leading a carburized hardening layer on the surface of the substrate. However, different microstructures formed in the carburizing layers, depending mainly on the type of carburization materials, carbon nanotube or graphite. The carbon nanotube hardening layer exhibits a little higher hardness than the graphite hardening layer. The carburized layer greatly increases the wear resistance of the base material.     

Formation of bamboo-shaped carbon nanotubes on carbon black in a fluidized bed

For the first time, bamboo-shaped multiwalled carbon nanotubes, having diameter of the order of 50 nm, have been grown on carbon black in a fluidized bed in bulk amount. The activation energy for the synthesis of the product was found out to be around 33 kJ/mol in the temperature range of 700−900 °C. The carbon nanotubes were separated from the carbon black by preferential oxidation of the later, the temperature of which was determined by thermogravimetry. The transmission electron microscopy revealed different features of the nanotubes such as “Y” junction, bend, and catalyst filling inside the nanotubes. Small angle neutron scattering was performed on the nanotubes synthesized at different temperatures. The data were fitted into a suitable model in order to find out the average diameter, which decreases with increase in synthesis temperature. The Monte Carlo simulation predicts the same behavior. Based on the above observations, a possible growth mechanism has been predicted. The oscillation in carbon saturation value inside the catalyst in the fluidized bed has been indicated as the responsible factor for the bamboo-shaped structure.