利用粒子辐照技术实现碳纳米管向金刚石的转变

采用低能氢等离子体和中能C^ 离子束辐照技术相结合的方法,实现了碳纳米管向金刚石纳米晶粒的转变,完成了一个从有序(碳纳米管)到无序(无定形碳纳米线)再到有序(金刚石纳米晶)的转变过程。利用透射电子显微镜(TEM)、选区电子衍射(SAD)和拉曼光谱(Raman)等研究了晶粒的微观结构,并对纳米金刚石晶粒的生成机理进行了初步探讨。     

Low Friction-Coefficient TiBCN Nanocomposite Coatings Prepared by Cathode Arc Plasma Deposition

TiBCN nanocomposite coatings were deposited on cemented carbide and Si（100）by a cathode arc plasma system,in which TiB₂ cathodes were used in mixture gases of N₂ and C₂H₂.X-ray diffraction shows that TiB₂ and Ti₂B₅ peaks enhance at low flow rates of C₂H₂,but they shrink when the flow rate is over 200 seem.An increase of deposition rate was obtained from different TiBCN thicknesses for the same deposition time measured by scanning electron microscopy.Atomic force microscopy shows that the surface roughnesses are ¹0 nm and ²0 nm at C₂H₂ flow rates of 0-100 sccm and of 150-300 sccm,respectively.High resolution transmission electron microscopy and X-ray photoelectron spectroscopy show that the coatings consist of nanocrystal phases Ti₂B₅,TiB₂ and TiN,and amorphous phase carbon and BN.The average crystal sizes embedded in the amorphous matrices are 200 nm and 10 nm at C₂H₂ flow rates of200 sccm and 300 sccm,respectively.In Raman spectra,the D- and G-bands increase with C₂H₂flows at low flow rates,but weaken at high flow rates.The microhardness of the coatings decreases from 28.6 GPa to 20 GPa as the C₂H₂ increases from 0 sccm to 300 sccm,and the ball-on-disk measurement shows a dramatic decrease of the friction coefficient from 0.84 to 0.13.The reason for the reduced hardness and friction coefficient with the change of C₂H₂ flow rates is discussed.     

Conversion of coalbed methane surrogate into hydrogen and graphene sheets using rotating gliding arc plasma

The use of atmospheric rotating gliding arc(RGA) plasma is proposed as a facile, scalable and catalyst-free approach to synthesizing hydrogen(H_2) and graphene sheets from coalbed methane(CBM). CH_4 is used as a CBM surrogate. Based on a previous investigation of discharge properties, product distribution and energy efficiency, the operating parameters such as CH_4 concentration, applied voltage and gas flow rate can effectively affect the CH_4 conversion rate,the selectivity of H_2 and the properties of solid generated carbon. Nevertheless, the basic properties of RGA plasma and its role in CH_4 conversion are scarcely mentioned. In the present work, a 3D RGA model, with a detailed nonequilibrium CH_4/Ar plasma chemistry, is developed to validate the previous experiments on CBM conversion, aiming in particular at the distribution of H_2 and other gas products. Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection, electron migration and electron diffusion, and is prominently determined by the variation of the gas flow rate and applied voltage. Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction, taking into consideration the formation and loss pathways of crucial targeted substances(such as CH_4, C_2H_2, H_2 and H radicals) and corresponding contribution rates. Additionally, the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM) and Raman spectroscopy. The results show that increasing the applied voltage and decreasing CH_4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets, while the size of the graphene sheets is slightly affected by the change in gas flow rate.     

Synthesis of (B-C-N) Nanomaterials by Arc Discharge Using Heterogeneous Anodes

In spite of the current prevalence of the CVD-based processes,the electric arc remains an interesting process for the synthesis of carbon nanoforms,thanks to its versatility,robustness and easiness.It also allows performing in-situ substitution of carbon atoms by hetero-elements in the graphene lattice.Our work aims to establish a correlation between the plasma properties,type and chemical composition (and the substitution rate) of the obtained single-wall carbon nanotubes.The plasma was characterized by optical emission spectroscopy and the products were analyzed by high resolution transmission electron microscopy and core level Electron Energy-Loss Spectroscopy (EELS).Results show that a high boron content leads to a plasma temperature decrease and hinders the formation of nanotubes.This effect can be compensated by increasing the arc current and/or yttrium content.The optimal conditions for the synthesis of boron-and/or nitrogen-substituted nanotubes correspond to a high axial plasma temperature associated to a strong radial gradient.EELS analysis confirmed that the boron incorporates into the graphenic lattice.     

碳纳米管的放射性材料填充

开口纯化后的碳纳米管(CNTs)用放射性(^125I)NaI和(^110Ag^m)AgNO3溶液进行了浸泡、洗涤和洗脱研究，用高分辨透射电镜(HREM)和X射线散射能谱(EDS)对CNTs的填充情况进行了表征；使用放射性同位素示踪技术确定了CNTs内部样品的填充量。结果显示用本工作所采用的简单水溶液浸泡技术能将水溶性无机盐材料填充到CNTs中空结构内。实验表明，放射性核素示踪技术能有效地应用于CNTs的填充、释放等行为的研究。     

Amyloid fibril-supported Pd nanoparticles as electrocatalyst for hydrogen peroxide reduction

Palladium nanoparticles(Pd NPs) were fabricated by using insulin amyloid fibrils(INSAFs) as biotemplates.Atomic force microscopy measurements showed that ultrasmall Pd NPs were well adsorbed and dispersed on surfaces of INSAFs. X-ray photoelectron spectroscopy confirmed the partial reduction of Pd ion into metallic Pd(0) probably due to the presence of Cys groups on surface of the insulin fibrils. The electrochemical performance of Pd/INSAFs to reduction of H_2O_2 was further evaluated by cyclic voltammetry. The remarkably high electrocatalytic activity, low detection limitation and excellent stability make the Pd/INSAFs a promising bio-nanoelectrocatalyst.     

Structural change of carbon nanotubes produced by Si ion beam irradiation

Multi-walled carbon nanotubes (MWCNTs) were irradiated by 40 keV Si ion beam with different doses. The structural change of the MWCNTs was revealed by transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The structural characterization after irradiation shows that the formation of amorphous carbon nanowires proceeds through two periods, carbon nanotube – semi-solid amorphous carbon nanowire with hollow structure – solid amorphous carbon nanowire. Based on the interaction between energetic particles and carbon nanotubes, the structural transformation process and corresponding mechanisms are discussed. A model is presented to illustrate the structural change of carbon nanotubes with increased irradiation dose.     

Changes in metal nanoparticle shape and size induced by swift heavy-ion irradiation

Changes in the shape and size of Co, Pt and Au nanoparticles induced by swift heavy-ion irradiation (SHII) have been characterized using a combination of transmission electron microscopy, small-angle X-ray scattering and X-ray absorption near-edge structure. Elemental nanoparticles of diameters 2-15 nm were first formed in amorphous SiO₂ by ion implantation and thermal annealing and then irradiated at room temperature with 27-185 MeV Au ions as a function of fluence. Spherical nanoparticles below a minimum diameter (4-7 nm) remained spherical under SHII but progressively decreased in size as a result of dissolution into the SiO₂ matrix. Spherical nanoparticles above the minimum diameter threshold were transformed to elongated rods aligned with the ion beamdirection. The nanorod width saturated at an electronic energy deposition dependent value, progressively increasing from 4-6 to 7-10 nm (at 5-18 keV/nm, respectively) while the nanorod length exhibited a broad distribution consistent with that of the unirradiated spherical nanoparticles. The threshold diameter for spherical nanoparticle elongation was comparable to the saturation value of nanorod width. We correlate this saturation value with the diameter of the molten track induced in amorphous SiO₂ by SHII. In summary, changes in nanoparticle shape and size are governed to a large extent by the ion irradiation parameters.     

Synthesis of Carbon Nanotubes by MWPCVD at Low Temperature

Growth of carbon nanotubes(CNTs) at low temperature is very important to the applications of nanotubes.In this paper,under the catalytic effect of cobalt nanoparticles supported by SiO2,CNTs were synthesized by microwave plasma chemical vapor deposition(MWPCVD) below 500℃.It demonstrates that MWPCVD can be a very efficient process for the synthesis of CNTs at low temperature.     

A molecular dynamics study of the clustering of implanted potassium in multiwalled carbon nanotubes

We have studied the low energy irradiation of carbon nanotubes (CNT) with K ions using classical molecular dynamics simulations with analytical potentials. The studied CNTs had diameters of about 0.5–1.2 nm and single or multiple walls. The average penetration depth and probabilities to introduce an impurity atom into CNT were studied with simulations on irradiating the CNT with single K ion. The number of potassium clusters, their average sizes and the damage produced into the CNT due to the irradiation were studied using multiple K ion irradiations. We found that the K ions are mobile in CNTs right after the implantation event and that they cluster together. For CNTs with 1–3 coaxial tubes, the highest ratio of K atoms in clusters per total number of K ions was obtained by using an irradiation energy of about 100 eV. Also the least damage per K ion was found to be produced into the CNT with this energy when those energies high enough for the ion to penetrate the outermost wall of the CNT were considered.     

AFM and STM investigation of carbon nanotubes produced by high energy ion irradiation of graphite

Carbon nanotubes (CNT) were produced by high energy, heavy ion irradiation (215 MeV Ne, 246 MeV Kr, 156 MeV Xe) of graphite. On samples irradiated with Kr and Xe ions large craters were found by atomic force microscopy, these are attributed to sputtering. Frequently one or several CNTs emerge from the craters. Some of the observed CNTs showed a regular vibration pattern. No other carbon based materials, like amorphous carbon or fullerenes were evidenced. Focused ion beam cuts were used to compare CNTs with surface folds on graphite.     

Ion sputtered surfaces as templates for carbon nanotubes alignment and deformation

Starting from their discovery in 1991, carbon nanotubes have attracted a great attention, thanks to their peculiar mechanical, electrical and elastic properties that could be used to realize new devices in many different fields.

For nanotechnology applications it is very important to be able to control not only shape and position but also alignment and orientation of carbon nanotubes, both during the growth and after it.

Here we present preliminary results obtained by depositing carbon nanotubes (CNT) solutions on ion sputtered quartz substrates. Atomic force microscopy (AFM) images allow to study both CNTs positioning on the “ripples” generated by Ar⁺ sputtering on the SiO₂ surface and their radial deformation induced by the “rough” surface.

Work is now in progress to optimize the sputtering parameters and solution treatment (purification and functionalization) in order to get single CNTs regularly arranged on a patterned surface.     

Plasma assisted synthesis of hollow nanofibers using electrospun sacrificial templates

In this work, we describe the synthesis of nanostructured polymeric materials of controlled tubular geometries using oxygen plasma and polysiloxane-grafting onto electrospun fiber sacrificial templates. The fibers were characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to determine the extent of grafting, graft chemistry and the influence of plasma treatment. Scanning electron microscopy (SEM) was used to determine the morphology and size of the electrospun fibers and nanotubes. The average diameter of the electrospun fibers employed ranged between 300 nm and 1500 nm. The micrographs revealed differences that are dependent on the type of grafting chemistry as well as plasma treatment times. The template synthesis of polysiloxane nanotubes using polyester track-etched membranes also shows that the technique is applicable to different substrates.     

磁性富羧基碳复合材料的制备及对Pb(Ⅱ)、Ni(Ⅱ)、Hg(Ⅱ)和U(Ⅵ)的吸附

采用溶剂热法制备了富羧基碳,随后通过化学共沉淀法合成了磁性富羧基碳复合材料。利用透射电子显微镜(TEM)、红外光谱分析(FTIR)、X射线衍射(XRD)、振动样品磁强计(VSM)、热重差热分析(TGA)、zeta电位分析及比表面积(BET)等手段对磁性富羧基碳的形貌、组成、结构、磁性以及表面电荷特性等进行了表征,并考察了富羧基碳和磁性富羧基碳对Pb(Ⅱ)、Ni(Ⅱ)、Hg(Ⅱ)和U(Ⅵ)的吸附性能。结果表明:富羧基碳经磁性改性后表面负载了铁氧化物纳米颗粒,比表面积由29.2m2/g提高到45.4m2/g,热稳定性提高,由磁滞回线可知,磁性富羧基碳的饱和磁化强度为30.68A.m2/kg。Pb(Ⅱ)、Ni(Ⅱ)、Hg(Ⅱ)和U(Ⅵ)在磁性富羧基碳上的平衡吸附容量分别为477.50、23.50、260.20、54.86mg/g,低于富羧基碳,吸附等温线符合Langmuir等温模型。从磁性富羧基碳对Pb(Ⅱ)、Ni(Ⅱ)、Hg(Ⅱ)和U(Ⅵ)均具有较高的吸附容量和不同吸附剂对U(Ⅵ)吸附容量的比较可以看出,该吸附剂是重金属污水和放射性废液处理领域中极具发展前景的吸附材料。     

Synthesis of Ag-decorated vertical graphene nanosheets and their electrocatalytic efficiencies

Herein we report the successful preparation of silver (Ag)-decorated vertically oriented graphene sheets (Ag/VGs) via helicon wave plasma chemical vapor deposition (HWP-CVD) and radiofrequency plasma magnetron sputtering (RF-PMS). VGs were synthesized in a mixture of argon and methane (Ar/CH4) by HWP-CVD and then the Ag nanoparticles on the prepared VGs were modified using the RF-PMS system for different sputtering times and RF power levels. The morphology and structure of the Ag nanoparticles were characterized by scanning electron microscopy and the results revealed that Ag nanoparticles were evenly dispersed on the mesoporous wall of the VGs. X-ray diffraction results showed that the diameter of the Ag particles increased with the increase in Ag loading, and the average size was between 10.49 nm and 25.9 nm, consistent with the transmission electron microscopy results. Ag/VGs were investigated as effective electrocatalysts for use in an alkaline aqueous system. Due to the uniquely ordered and interconnected wall structure of VGs, the area of active sites increased with the Ag loading, giving the Ag/VGs a good performance in the oxygen evolution reaction. The double-layer capacitance (Cdl) of the Ag/VGs under different Ag loadings were studied, and the results showed that the highest Ag content gave the best Cdl (1.04 mF cm−2). Our results show that Ag/VGs are likely to be credible electrocatalytic materials.     

Enhanced removal of X-ray-induced carbon contamination using radio-frequency Ar/H_2 plasma

Removal of X-ray-induced carbon contamination on beamline optics was studied using radio-frequency plasma with an argon/hydrogen(Ar/H_2) mixture. Experiments demonstrated that the carbon removal rate with Ar/H_2 plasma was higher than that with pure hydrogen or argon. The possible mechanism for this enhanced removal was discussed. The key working parameters for Ar/H_2 plasma removal were determined, including the optimal vacuum pressure, gas mixing ratio, and source power. The optimal process was performed on a carbon-coated multilayer, and the reflectivity was recovered.     

Preparation of Iron Nanoparticles from Iron Pentacarbonyl Using an Atmospheric Microwave Plasma

A novel method is introduced for preparing iron nanoparticles from iron pentacarbonyl using an atmospheric microwave plasma. The prepared iron nanoparticles were characterized by transmission electron microscopy and X-ray diffraction. The results show that the size of the particles can be controlled by adjusting the microwave power and the flow rate of the carrier gas.The magnetic properties of the synthesized iron particles were studied and a saturation magnetization of ～95 emu/g was obtained. The convenient preparation process and considerable production rate were also found to be satisfactory for industrial applications.     

Effect of metal ion location in reaction medium on formation process and structure of PtCu–CuO nanoparticles supported on carbon and γ-Fe2O3

The process of nanoparticle formation by radiochemical synthesis in a heterogeneous system has been investigated considering the effects of the metal ion location in the reaction medium. PtCu nanoparticles supported on carbon and γ-Fe₂O₃ were synthesized using a high-energy electron beam. The metal ions in the precursor were categorized as those dissolved in solution, adsorbed on support, and precipitated. The ratio of metal ions in the solution was varied prior to the electron beam irradiation and its effects on the synthesized particle structures were examined. The nanoparticles were characterized by inductively coupled plasma-atomic emission spectrometry, transmission electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy. A PtCu alloy and CuO were immobilized on the support in all the samples. The PtCu alloy nanoparticle composition depended on the Cu ion content in the solution. The nanoparticle formation mechanism could be explained using the obtained results. Metal ions present in the solution resulted in formation of the alloy. The adsorbed ions also contributed to the alloy formation by desorbing from the support when irradiated. On the other hand, alloy formation with Pt from the precipitated Cu ions was found to be difficult.     

Effects of Surface Pretreatment on Nucleation and Growth of Ultra-Nanocrystalline Diamond Films

The effects of different surface pretreatment methods on the nucleation and growth of ultra-nanocrystalline diamond(UNCD) films grown from focused microwave Ar/CH_4/H_2(argonrich) plasma were systematically studied.The surface roughness,nucleation density,microstructure,and crystallinity of the obtained UNCD films were characterized by atomic force microscope(AFM),scanning electron microscopy(SEM),X-ray diffraction(XRD),and Raman spectroscopy.The results indicate that the nucleation enhancement was found to be sensitive to the different surface pretreatment methods,and a higher initial nucleation density leads to highly smooth UNCD films.When the silicon substrate was pretreated by a two-step method,i.e.,plasma treatment followed by ultrasonic vibration with diamond nanopowder,the grain size of the UNCD films was greatly decreased:about 7.5 nm can be achieved.In addition,the grain size of UNCD films depends on the substrate pretreatment methods and roughness,which indicates that the surface of substrate profile has a "genetic characteristic".     

Microstructure changes and properties of TiC-coated carbon fiber-reinforced carbon composites

In the present paper, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to study distortion of TiC crystals after thermal cycles in plasma environment. Scanning electron microscopy (SEM) was used to observe morphology changes and penetrating cracks in TiC/C coatings. To avoid the cracks and enhance properties of coated carbon fiber-reinforced carbon (C/C) composites, TiC/C composites were prepared as buffer layer to relieve thermal stresses. Thermal cycles indicated that the buffer layer could effectively improve thermal shock resistance of pure TiC coated C/C composites. To study the reason, transmission electron microscopy (TEM) results suggested that TiC particles were uniformly imbedded in pyrocarbon in the buffer layer, which was advantageous to relieve mismatch of coefficient of thermal expansion (CTE) between pure TiC and C/C. Moreover, thermal conductivity tests showed that the buffer layer was in favor of transferring heat loading.