查看更多>>摘要：Electric-current-induced structural changes in a suspended multiwall carbon nanotube (MWCNT) were observed through in situ transmission electron microscopy. The bias voltage and electric current were measured simultaneously as the MWCNT was imaged. The passage of excessive current led to breakdown of the surface of the MWCNT and to subsequent layer-by-layer removal of the broken outermost shell via sublimation of carbon atoms. The surface breakdown of the MWCNT was accompanied by a discrete decrease in the current. Under the assumption that the current passes solely through the outermost shell of the MWCNT, we found that the critical current densities at which the breakdown in the renewed outermost shell occurred after the removal of the broken outermost shell were limited to a remarkably narrow range of (2.4 +/- 0.2) x 10(9) A/cm(2), irrespective of the outermost diameter of the MWCNT. The present results provide invaluable information about electron transport phenomena in MWCNTs and about the durability of CNT nanocircuits.
Marandi, AlirezaKolvari, EskandarGilandoust, MaryamZolfigol, Mohammad Ali...
16页
查看更多>>摘要：Anchoring -OSO3H on activated carbon powder presents an innovative approach in the green catalysis field by improving its performance for synthesizing several organic compounds. In this study, we evaluated the efficiency of fabricated activated carbon-OSO3H (AC-OSO3H) catalyst in synthesizing 1H-indazolo[1,2-b]phthalazine-tri-one and quinolines derivatives through a one-pot multicomponent reaction under solvent-free conditions. In this procedure, incorporating the -OSO3H functional group with activated carbon was performed in three steps, including acid-treatment (oxidation), reduction, and sulfonation, respectively. The fabricated AC-OSO3H was characterized by FT-IR, EDS, XRD, and XPS binding studies. XPS studies confirmed the presence of -SO3H groups anchored on activated carbon powder by comparing neat, oxidized, and reduced activated carbon XPS patterns. Therefore, AC-OSO3H powder operates as an effective catalyst for phthalazine and quinoline derivatives synthesis via one-pot multicomponent reactions. Also, the synthesized compounds were characterized by FT-IR, 1H NMR, and 13C NMR techniques. Features that make this approach practical, green, and safe for the environment and humans included shorter reaction time, cost-effectiveness, reusability, easy separation, and higher efficiency than other methods.
Martino, MaurizioVerwilligen, PietCaricato, Anna PaolaCesaria, Maura...
12页
查看更多>>摘要：Diamond-like carbon (DLC) is an attractive inexpensive alternative to diamond. The control of the C (sp(3))/C(sp(2)) ratio, influencing the material properties, is fundamental for its use in dedicated applications like, for example, the fabrication of a particular class of gas detectors for ionizing particles termed Micro-Pattern Gaseous Detectors (MPGDs).& nbsp;A deposition technique enabling control on the amount of C(sp(3)) hybridized bonds, hydrogen content and disorder is pulsed lased deposition (PLD).& nbsp;In this paper, we report on the preparation of hydrogen-free DLC films by nanosecond excimer laser-based ablation of a graphite target correlating the laser fluence with the electrical properties of the DLC films to be used as protective resistive layers in MPGD detectors.& nbsp;Moreover, unprecedented physical insight and discussion are provided about the critical aspects of both occurrence of a V-branched plume and its composition on the spatial distribution of C(sp(3)) bonds and film uniformity. Improvement strategies are demonstrated by comparing and discussing two classes of PLD experiments: ON-axis (coaxial plasma expansion axis and substrate symmetry axis) and OFF-axis (substrate-axis shifted with respect to the plume-axis and rotating substrate). Optimally working OFF-axis configuration conditions are shown to lead to fine tuning of resistivity and uniformity of composition of C(sp(3)) bonding over a few cm(2) extended areas. Sheet resistance (3.1 +/- 0.3) x 10(9) omega/sq., corresponding to C(sp3) bonding concentration of ~& nbsp;86%, is reported in OFF-axis experiments at a fluence of 5.5 J/cm(2) onto kapton substrates which are used for the realization of MPGDs.
Petrov, M. P.Vezo, O. S.Trusov, A. A.Voitylov, A. V....
9页
查看更多>>摘要：In this article certain features of the electro-orientation effect are used to study the kinetics of coagulation in diamond colloidal dispersions. The results of a study of the influence of multivalent ions on the formation of paired aggregates from diamond particles in colloidal systems are presented. A technique was developed for studying the rate of coagulation at the early stages, using the relaxation dependences of electro-optical effects. The effect of aqueous electrolytes on the rate of formation of paired aggregates from diamond particles has been studied. It is shown that the rate of formation of paired aggregates at the isoelectric point is consistent with the theory of rapid coagulation. Based on electro-optical studies of the polarizability anisotropy of individual particles and paired aggregates from them, it was assumed that the polarizability anisotropy of a paired aggregate is lower than the polarizability anisotropy of an individual particle with volume and shape close to that of an aggregate. The rates of coagulation of colloidal systems of diamond and graphite with the same particle number concentration and size are compared. It is shown that at the isoelectric point the coagulation period of graphite colloid is five times shorter than the coagulation period of diamond colloid.
查看更多>>摘要：We observed the effect of high (up to 80 GPa) pressure, catalyst (CS2) and laser irradiation on the process of three-dimensional (3D) polymerization of fullerene C-60 and the mechanical properties of the 3D C(60 )samples. The studies were carried out using resonant Raman spectroscopy and piezospectroscopy, high resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy. We have revealed that the 3D C-60 structure consists of at least two types of clusters formed by covalent bonds with a different set of force constants, while C-60 molecules, as one of the elements of the 3D C-60 structure (clusters), are preserved at least up to a pressure of 80 GPa. The intensity of Raman scattering depends on the wavelength of the exciting radiation (resonance effect) and a set of force constants: the higher their values, the shorter-wavelength exiting radiation is required for Raman scattering observation by such clusters. Clusters with bulk moduli from 454 GPa to 644 GPa are formed depending on methods of C-60 polymerization. According to the set of clusters, 3D C-60 samples with bulk moduli from 506 GPa to 608 GPa were obtained.
查看更多>>摘要：The composite material of metal sulfide and dielectric material has always been regarded as a research hotspot in the field of electromagnetic wave absorption. In this work, the cobalt sulfide (CoS) particles were successfully grown on the modified graphite nanosheets (GNs) by the two-step hydrothermal method to obtain excellent CoS/GNs EM wave absorption materials. SEM images show that after adding GNs, the morphology of CoS particles will change from micron-scale regular spheres to irregular nano-fragments which attached to the surface of GNs. The reason is that the binding sites on the surface of GNs will limit the growth of CoS particles. Fortunately, the introduction of GNs not only adjusted the impedance matching performance of CoS, but also perfectly combined the dielectric loss and magnetic loss mechanisms. EM analysis showed that the minimum reflection loss (RLmin) of CoS/GNs materials is -52 dB at an ultra-thin thickness of 1.1 mm, and the effective absorption bandwidth (EAB) is 3.7 GHz (14.3 GHz-18 GHz). Therefore, this ultra-thin nanocomposite material is expected to have broad market application prospects.
查看更多>>摘要：Excellent performance of porous carbon adsorbents on wastewater treatment is always stimulating continuous researches to acquire better porous carbon materials by renewable, low-cost and more effective routes. Here, we choose sustainable sorghum distillers' grains (SDGs) as carbon source and utilize a pre-burning treatment plus KOH activation procedure to prepare porous carbon. The pre-burning treatment is demonstrated effective on boosting pores formation and increasing surface area of the prepared porous carbon. The maximum BrunauerEmmett-Teller (BET) surface area of 1965 m(2) g(-1) can be achieved. The adsorption capacity of the prepared porous carbon for methylene blue (MB) is evaluated and a maximum adsorption capacity of 2276.3 mg g(-1) is acquired (increasing by 47% than that of one without pre-burning). The XPS and FTIR evaluations reveal that the pre-burning can also raise surficial oxygen-contained groups, which as active sites boost the MB adsorption.
查看更多>>摘要：This present work investigated the capability of the spark plasma sintering (SPS) method to synthesize h-BN powders from urea and acid boric mixture without any extra additives. Accordingly, the 1:1 M ratio of the starting materials was mixed through a simple method at the aqueous solution and then dried at a hot plate (80 degrees C) while it was stirred. Subsequently, the mixture was directly inserted to a graphite mold and the sintering process was performed with the constant pressure of 10 MPa and the initial vacuum condition of 19 Pa, as well as the maximum temperature of 1950 degrees C. Then, the obtained powders were ground and the graphite foils as the separators were removed from the sample. The prepared thin layer of the specimen was milled by the agate mortar. The characterization of the obtained powders was done without any post treatment. The XRD patterns demonstrated only h-BN peaks, as the applied high sintering temperature removed any impurities at this system according to the vacuum condition. The FESEM images of the synthesized powders demonstrated the formation of flower-like h-BN powders. Moreover, the HRTEM images of the prepared powders showed the formation of a highly crystalline h-BN.
查看更多>>摘要：The development of copper-based composite materials is increasingly requiring both high electrical conductivity and better mechanical properties. In this paper, a novel copper-based composite was prepared by combining carbonized polymer dot (CPD) with flake copper powder (BMCu) and Al2O3 with molecular-level copper powder (MLCu). The composite obtained good mechanical properties with the yield strength of 157.00 MPa and the tensile strength of 366.14 MPa, which are increased by 17.4% and 25.1% compared with those of pure copper matrix (133.76 MPa and 292.72 MPa). The hardness of the composite is 124.7 HV, 27.4% higher than that of pure copper (97.9 HV), and the conductivity is 93.15% IACS. Besides, the strengthening mechanism of tensile property is also discussed, and the improvement of composite strength is mainly due to the dislocation strengthening. This study provides a new idea for the preparation of copper-based composite materials with high electrical conductivity and mechanical properties.
Cuenca, Jerome A.Mandal, SoumenThomas, Evan L. H.Williams, Oliver A....
11页
查看更多>>摘要：A microwave plasma model of a chemical vapour deposition (CVD) reactor is presented for understanding spatial heteroepitaxial growth of polycrystalline diamond on Si. This work is based on the TM0((n > 1)) clamshell style reactor (Seki Diamond/ASTEX SDS 6K, Carat CTS6U, ARDIS-100 style) whereby a simplified H-2 plasma model is used to show the radial variation in growth rate over small samples with different sample holders. The model uses several steps: an electromagnetic (EM) eigenfrequency solution, a frequency-transient EM/plasma fluid solution and a transient heat transfer solution at low and high microwave power densities. Experimental growths provide model validation with characterisation using Raman spectroscopy and scanning electron microscopy. This work demonstrates that shallow holders result in non-uniform diamond films, with a radial variation akin to the electron density, atomic H density and temperature distribution at the wafer surface. For the same process conditions, greater homogeneity is observed for taller holders, however, if the height is too extreme, the diamond quality reduces. From a modelling perspective, EM solutions are limited but useful for examining electric field focusing at the sample edges, resulting in accelerated diamond growth. For better accuracy, plasma fluid and heat transfer solutions are imperative for modelling spatial growth variation.
NSTL
Elsevier