Carbon Protective Layer Research Articles

Use of the near vacuum UV spectral range for the analysis of W-based materials for fusion applications using LIBS

The vacuum UV (VUV)-near Infrared (NIR) laser induced breakdown spectroscopy (LIBS) technique was applied to investigate the composition of W-based samples with a protective carbon layer. The sample was analyzed under pressures from 5 to 105 Pa and atmosphere (air, He). The spectra were recorded with three spectrometers at delays from 200 ns to 10 μs at atmospheric pressures and from 100 to 500 ns at low pressures. The electron density was determined from the measured spectra using Stark broadening and the electron temperature from the W I–W III Saha–plot in the VUV–NIR spectral range. The better precision was achieved due to usage W III spectral lines of tungsten. The achieved results are more reliable than results obtained without W III spectral lines. The calibration free LIBS method was then applied to determine the W and C contents of the analyzed sample.

Copper and nickel hexacyanoferrate nanostructures with graphene-coated stainless steel sheets for electrochemical supercapacitors

Copper and nickel hexacyanoferrate (CuHCF and NiHCF) nanostructures featuring three-dimensional open-framework tunnels are prepared using a solution-based coprecipitation process. CuHCF shows superior supercapacitive behavior than the NiHCF, due to the presence of numerous macropores in CuHCF particles for facilitating the transport of electrolyte. Both CuHCF and NiHCF electrodes with stainless steel (SS) substrate tend to lose their electroactivity towards intercalation/deintercalation of hydrated potassium ions owing to the partial corrosion of SS. Formation of a protective and conductive carbon layer in between SS and CuHCF (NiHCF) film is of paramount importance for improving the irreversible loss of electroactivity. Thin and compact graphene (GN) layer without observable holes in its normal plane is the most effective way to suppress the corrosion of SS compared with porous carbon nanotube and activated carbon layers. Specific capacitance of CuHCF electrode with GN layer (CuHCF/GN/SS) reaches 570 F g−1, which is even better than that of CuHCF with Pt substrate (500 F g−1) at 1 A g−1. The CuHCF/GN/SS exhibits high stability with 96% capacitance retention over 1000 cycles, greater than the CuHCF with Pt (75%).

High cyclability of carbon-coated TiO2 nanoparticles as anode for sodium-ion batteries

Owing to the merits of good chemical stability, elemental abundance and nontoxicity, titanium dioxide (TiO2) has drawn increasing attraction for use as anode material in sodium-ion batteries. Nanostructured TiO2 was able to achieve high energy density. However, nanosized TiO2 is typically electrochemical instable, which leads to poor cycling performance. In order to improve the cycling stability, carbon from thermolysis of poly(vinyl pyrrolidone) was coated onto TiO2 nanoparticles. Electronic conductivity and electrochemical stability were enhanced by coating carbon onto TiO2 nanoparticles. The resultant carbon-coated TiO2 nanoparticles exhibited high reversible capacity (242.3mAhg−1), high coulombic efficiency (97.8%), and good capacity retention (87.0%) at 30mAg−1 over 100 cycles. By comparison, untreated TiO2 nanoparticles showed comparable reversible capacity (237.3mAhg−1) and coulombic efficiency (96.2%), but poor capacity retention (53.2%) under the same condition. The rate performance of carbon-coated TiO2 nanoparticles was also displayed as high as 127.6mAhg−1 at a current density of 800mAg−1. The improved cycling performance and rate capability were mostly attributed to protective carbon layer helping stablize solid electrolyte interface formation of TiO2 nanoparticles and improving the electronic conductivity. Therefore, it is demonstrated that carbon-coated TiO2 nanoparticles are promising anode candidate for sodium-ion batteries.

Carbon-protected bimetallic carbide nanoparticles for a highly efficient alkaline hydrogen evolution reaction.

The hydrogen evolution reaction (HER) is one of the two important half reactions in current water-alkali and chlor-alkali electrolyzers. To make this reaction energy-efficient, development of highly active and durable catalytic materials in an alkaline environment is required. Herein we report the synthesis of carbon-coated cobalt-tungsten carbide nanoparticles that have proven to be efficient noble metal-free electrocatalysts for alkaline HER. The catalyst affords a current density of 10 mA cm(-2) at a low overpotential of 73 mV, which is close to that (33 mV) required by Pt/C to obtain the same current density. In addition, this catalyst operates stably at large current densities (>30 mA cm(-1)) for as long as 18 h, and gives nearly 100% Faradaic yield during alkaline HER. The excellent catalytic performance (activity and stability) of this nanocomposite material is attributed to the cooperative effect between nanosized bimetallic carbide and the carbon protection layer outside the metal carbide. The results presented herein offer the exciting possibility of using carbon-armoured metal carbides for an efficient alkaline HER, although pristine metal carbides are not, generally, chemically stable enough under such strong alkaline conditions.

Novel halogen-free flame retardants based on adamantane for polycarbonate

The surface of PC/FR compositions presents a continuous and protective carbon layer with several bubbles and folds.

Recyclable chestnut-like Fe3O4@C@ZnSnO3 core–shell particles for the photocatalytic degradation of 2,5-dichlorophenol

Numerous efforts have been made to integrate nanorods into 3D ordered multifunctional architectures. Herein, we report a rational design and the successful fabrication of a novel chestnut-like Fe3O4@C@ZnSnO3 core–shell hierarchical structure. Reactive Zn and Sn colloids obtained using laser ablation in liquids were used as non-ion precursors to intentionally grow ZnSnO3 nanorods onto the surfaces of core–shell Fe3O4@C particles under solvothermal conditions. The core–shell hierarchical structures were analyzed by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis (EDX), X-ray diffraction, and a superconducting quantum interference device magnetometer (Quantum Design MPMS). The results showed that the Fe3O4@C particles served as nucleation sites for the oriented growth of ZnSnO3 nanorods on the surfaces of the carbon layer. The synthesized core–shell composite exhibited cyclic photocatalytic ability toward the degradation of 2,5-dichlorophenol model molecules because of the compact assembly of the magnetic Fe3O4 core, the active ZnSnO3 photocatalyst, and a protective carbon layer.

Synthesis of hollow TiO2@N-doped carbon with enhanced electrochemical capacitance by an in situ hydrothermal process using hexamethylenetetramine

A unique and novel soft template-based hydrothermal approach was developed for the synthesis of hollow TiO2 and hollow TiO2@N-doped carbon. The synthesis strategy involves the slow hydrolysis of hexamethylenetetramine (HMTA) at 100 °C in the presence of a block copolymer (Pluronic F127) as the surfactant, resorcinol as the polymer precursor and titanium salt as the metal oxide precursor to form a hollow composite nanostructure consisting of TiO2 nanoparticles (NPs) covered with a resorcinol–formaldehyde (RF) polymer shell. Hydrolysis of HMTA provides a gradual and controlled supply of hydroxide ions, formaldehyde and ammonia. The resulting ammonia initiates the polymerization reaction of the generated formaldehyde with resorcinol to produce an RF–polymer framework over the TiO2 NPs thereby generating TiO2@RF polymer particles, which in turn self-assemble to form a hollow TiO2@RF polymer composite nanostructure. Subsequent pyrolysis under an N2 atmosphere produces a hollow TiO2 nanostructure covered with a thin layer of N-doped carbon. The resulting novel nanostructure not only possesses a high surface area of 310 m2 g−1, but also provides a protective N-doped carbon layer. As a result, this hollow TiO2@N-doped carbon material demonstrates high potential as an electrode material for use as an electrochemical capacitor with high specific capacitance and high durability. Interestingly, this work proceeds through a very effective, simple one-pot synthesis route to generate novel hollow TiO2 composite structures, and will enable the synthesis of various active hollow metal oxide@N-doped carbon and/or hollow organic–inorganic hydride nanocomposite materials for many possible applications.

Sandwich-structured graphene–NiFe2O4–carbon nanocomposite anodes with exceptional electrochemical performance for Li ion batteries

Graphene–NiFe2O4–carbon nanocomposites with a sandwich structure are synthesized via the hydrothermal growth of NiFe2O4 nanoparticles on graphene sheets, followed by carbon coating. As a promising anode material for Li ion batteries, the nanocomposites deliver exceptional cycle stability of 1195 mA h g−1 after 200 cycles measured at 500 mA g−1. This value is among the highest reported so far for anodes containing similar NiFe2O4 nanoparticles. The synergy arising from the conductive graphene substrate, the well-dispersed, ultrafine NiFe2O4 nanoparticles and the protective carbon layer sustaining the sandwich together is responsible for this trait.

Effect of nanosized carbon black on thermal stability and flame retardancy of polypropylene/carbon nanotubes nanocomposites

Nanosized carbon black (CB) was introduced into polypropylene/carbon nanotubes (PP/CNTs) nanocomposites to investigate the effect of multi‐component nanofillers on the thermal stability and flammability properties of PP. The obtained ternary nanocomposites displayed dramatically improved thermal stability compared with neat PP and PP/CNTs nanocomposites. Moreover, the flame retardancy of resultant nanocomposites was greatly improved with a significant reduction in peak heat release rate and increase of limited oxygen index value, and it was strongly dependent on the content of CB. This enhanced effect was attributed mainly to the formation of good carbon protective layers by CB and CNTs during combustion. Rheological properties further confirmed that CB played an important role on promoting the formation of crosslink network on the base of PP/CNTs system, which were also responsible for the improved thermal stability and flame retardancy of PP. Copyright © 2013 John Wiley & Sons, Ltd.

Fabrication, Characterization, and Printing of Conductive Ink Based on Multi Core–Shell Nanoparticles Synthesized by RAPET

AbstractIn the current research, conductive patterns are deposited on different substrates by direct inkjet printing of conductive inks based on metal@carbon and bimetal@carbon core–shell nanoparticles synthesized by the RAPET (reaction under autogenic pressure at elevated temperatures) technique. Various co‐solvents and additives are examined for production of stable conductive ink. The morphology of the deposited layers is characterized by optical and scanning electron microscopy measurements. The stability of the prepared inks is examined by dynamic light scattering measurements. The electrical resistivity is measured by a four‐point probe system and calculated using the geometric dimensions. The results obtained are very promising and indicate that the conductivity of the deposited layers is close to that of bulk metals and higher than most results published so far. Moreover, the importance and advantages of the protective carbon layer that prevents metal oxidation is demonstrated.

Design, synthesis and the electrochemical performance of MnO2/C@CNT as supercapacitor material

Carbon-coated carbon nanotubes (C@CNT) was designed, synthesized and used as conductive substrate for loading manganese dioxide to prepare MnO2/C@CNT composite. C@CNT with self-sacrificial carbon layer as protection is suitable for loading higher content of MnO2. The morphology and microstructure of the as-prepared MnO2/C@CNT composite with MnO2 loading up to 78wt% were investigated by SEM and TEM. The electrochemical performance of MnO2/C@CNT was evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) method. With the protective carbon layer on the surface of CNTs, MnO2/C@CNT composite presents superior specific capacitance of 227F/g with MnO2 loading up to 78wt% at a current density of 0.2A/g and good cyclic stability with 94% of its maximal specific capacitance maintained after 1000 CV scans.

Carbon-Layer-Protected Cuprous Oxide Nanowire Arrays for Efficient Water Reduction

In this work, we propose a solution-based carbon precursor coating and subsequent carbonization strategy to form a thin protective carbon layer on unstable semiconductor nanostructures as a solution to the commonly occurring photocorrosion problem of many semiconductors. A proof-of-concept is provided by using glucose as the carbon precursor to form a protective carbon coating onto cuprous oxide (Cu₂O) nanowire arrays which were synthesized from copper mesh. The carbon-layer-protected Cu₂O nanowire arrays exhibited remarkably improved photostability as well as considerably enhanced photocurrent density. The Cu₂O nanowire arrays coated with a carbon layer of 20 nm thickness were found to give an optimal water splitting performance, producing a photocurrent density of -3.95 mA cm⁻² and an optimal photocathode efficiency of 0.56% under illumination of AM 1.5G (100 mW cm⁻²). This is the highest value ever reported for a Cu₂O-based electrode coated with a metal/co-catalyst-free protective layer. The photostability, measured as the percentage of the photocurrent density at the end of 20 min measurement period relative to that at the beginning of the measurement, improved from 12.6% on the bare, nonprotected Cu₂O nanowire arrays to 80.7% on the continuous carbon coating protected ones, more than a 6-fold increase. We believe that the facile strategy presented in this work is a general approach that can address the stability issue of many nonstable photoelectrodes and thus has the potential to make a meaningful contribution in the general field of energy conversion.

Characterization of nanoscaled solder material

AbstractThe properties of nanoscaled layers of pure tin have been studied. The layers were produced by sputtering in different thicknesses between 10 and 100 nm. The surface topography and the influence of process parameters on the sputtering rate were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods. To avoid oxidation carbon and silicon nitride protective layers were sputtered in the same process chamber. The function of this coating was investigated by X‐ray diffraction (XRD). The crystallographic structure of tin layer under silicon nitride was measured directly after sputtering, melting and cooling processes. The crystalline tin film after cooling down and the absence of tin oxide peaks were used as indicators for impermeability of oxygen. For investigation of phase change the method of chip differential calorimetry (DSC) was used. The samples were prepared as standalone samples for reuse of DSC‐chips and also sputtered directly on the DSC chip for single use. The prepared samples with one tin layer and multilayer of tin scaled down to 10 nm were investigated with this method.

Electron beam induced carbon deposition using hydrocarbon contamination for XTEM analysis

The optimal parameters of electron beam induced carbon deposition (EBICD) using hydrocarbon contamination were studied as a function of electron beam energy and scanning time to avoid the mixing or damage layer formation at the interface of the electron beam assisted Pt protection layer and the sample surface by dual beam focused ion beam (DB FIB) for cross sectional transmission electron microscopy (XTEM) analysis. The optimal condition of EBICD was determined. The thickness of EBICD layer increases with electron beam scanning time and amount of hydrocarbon contamination on the sample surface. EBICD using hydrocarbon contamination successfully provides a carbon protection layer for XTEM analysis.

Experimental study of the stability and reflective properties of depleted uranium thin films at a wavelength of 4.5 nm

A technology of depleted uranium thin films, which can be used as high-reflectivity X-ray mirrors at a wavelength of 4.5 nm, is presented. The coefficient of X-ray reflection by these mirrors varies from 90 to 10% at grazing angles between 1° and 10°. The stability of the reflection coefficients for 200-A-thick depleted uranium films covered by a protective carbon layer 100 and 200 A in thickness and for 200-A-thick uranium-nickel films with a nickel content of 9 and 23 wt % is studied. A high-reflectivity mirror is fabricated with the goal of increasing the X-ray radiation intensity in RKK-1-100 X-ray calibration equipment. Advice on fabrication of X-ray mirrors based on depleted uranium films is given.

Quantitative Analysis of Surface Functional Groups on the Amorphous Carbon in Magnetic Media with XPS Preceded by Chemical Derivatization

Abstract In thin film magnetic recording media, the carbon protective layer and the outermost lubricant layer have a significant influence on the tribological properties. It is thought that the functional groups on the surface of the carbon influence the adsorption of the lubricant. The present study describes the identification and quantification of the functional groups on the surface of magnetic thin film media based on an X-ray photoelectron spectroscopy (XPS) preceded by chemical derivatization. The number of functional groups on the surface of the carbon protective layer was obtained from the ratio of the fluorine and carbon in the XPS spectrum. Gas-phase chemical modification was found to be preferable as a pretreatment for surface analysis, and the number of carbonyl, hydroxy, and carboxylic acid groups were directly determined. The number of hydroxy group was higher immediately after deposition, and the carbonyl group, of which the concentration rapidly increased with exposure time to air, became the most abundant. Both groups improved the affinity of the lubricant and will probably lead to a better lubricity.

Improved corrosion resistance of spin-valve film

We investigated the corrosion behavior and magnetoresistance of spin-valve film in order to improve the corrosion resistance of the spin-valve head for a tape recording system. The conventional spin-valve head (sub./Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta) with no diamond-like carbon (DLC) protective layer showed poor corrosion resistance. This is because the CoFe for ferromagnetic layer and Cu for spacer in the spin-valve film exhibited poor corrosion resistance. The corrosion resistance of the CoFe film and Cu film improved with the addition of Ni and Au, respectively. The spin-valve film (sub./Ta/NiFe/CoNiFe/CuAu/CoNiFe/PtMn/Ta) showed higher pitting potential than the conventional spin-valve film by +0.45 V. This presents a significant improvement over the conventional spin-valve film. We also investigated the effect of the composition of ferromagnetic layer and spacer on the magnetoresistance of the spin-valve film. The magnetoresistance of the spin-valve film by substitution of CoNiFe for CoFe in ferromagnetic layer decreased slightly. The magnetoresistance of the spin-valve film decreased as the addition of Au of the spacer increased. The diffusion at CoNiFe/CuAu interface has not been observed in annealing process. The quantitative relation between corrosion resistance and magnetoresistance of spin-valve film, and its ferromagnetic layer and spacer's compositions have been clarified. The output voltage at 50 Oe of the corrosion-resistant spin-valve head with CoNiFe ferromagnetic layer and CuAu spacer was about 50% of that of the conventional spin-valve head.

Development of Ultrasonic Sensors for Operation in a Heavy Liquid Metal

This paper is devoted to the development of high temperature, gamma, and neutron radiation resistant ultrasonic sensors that must operate continuously in a liquid Pb/Bi alloy up to a temperature of 450 degC. The main problems are acoustic coupling of a piezoelectric element to a protector and wetting of the sensor by a heavy liquid metal. The piezoelement was attached to the sensor body by a gold to gold diffusion bonding process, monitored ultrasonically. Long-lasting wetting of the active surface of the sensors was achieved by coating the front face with a protective diamond-like carbon (DLC) layer. Due to the high radiation, only a limited number of materials could be used in the sensor design. The best performance was obtained using bismuth titanate piezoelectric elements, which showed no noticeable changes of pulse responses and transfer coefficients during irradiation and high-temperature tests. The housing of the sensors is made of stainless steel AISI 316 and is laser welded, and a high-temperature otimes 1-mm 15-m-long mineral cable is used. The ultrasonic velocity in the liquid Pb/Bi in the temperature range 160 degC-460 degC was measured using developed sensors, and the signal losses at various distances up to 0.8 m were evaluated

The influence of ion beam bombardment on the stress of carbon layers prepared by RF magnetron sputtering

Si stencil masks covered with protective carbon layer were tested for their resistance against ion bombardment. The protective layers have been created by RF carbon sputter-deposition. The openings in the structures were etched by reactive ion etching process after carbon deposition. The virgin as well as structured membranes were irradiated by low-energy He+ and Ar+ ions. We measured ion bombardment induced thickness- and stress-changes of the prepared samples.

Drastic enhancement of nanoelectromechanical-system fabrication yield using electron-beam deposition

The most common fabrication processes of nanoelectromechanical structures usually start with a silicon-on-insulator chip and incorporate several lithography and etch steps. The wet etch step, which involves hydrofluoric acid, is generally the most critical of these processing steps. In this letter, we present an enhancement of the wet etch step which relies on electron-beam deposition. The technique of electron-beam deposition utilizes a protective carbon layer which is applied by a scanning electron microscope. It allows us to resolve typical problems associated with the wet etch step and drastically increases the yield.