Pyrolytic Carbon Films Research Articles

Study of nanometric thin pyrolytic carbon films for explosive electron emission cathode in high-voltage planar diode

We report on an experimental study of explosive electron emission properties of cathode made by nanometric thin pyrolytic carbon (PyC) films (2–150nm) deposited on Cu substrate via methane-based chemical vapor deposition. High current density at level of 300A/cm2 in 5·10−5Pa vacuum has been observed together with very stable explosive emission from the planar cathode. The Raman spectroscopy investigation proves that the PyC films remain the same after seven shots. According to the optical image analysis of the cathode before and after one and seven shots, we conclude that the most unusual and interesting feature of using the PyC films/Cu cathode for explosive emission is that the PyC layer on the top of the copper target prevents its evaporation and oxidation, which leads to higher emission stability compared to conventional graphitic/Cu cathodes, and therefore results in longer working life.

Electrochemical reactivity of pyrolytic carbon film electrodes in organic carbonate electrolytes

The electrochemical reactivity of polyimide-derived pyrolytic carbon film electrodes in a standard organic carbonate lithium-ion battery electrolyte was studied and quantified. An oxidative heat treatment at 900°C under CO2 atmosphere was found to lower the reactivity of disordered carbons towards electrolyte oxidation. Cyclic voltammetry and potentiostatic measurements of the carbon film electrodes demonstrate the beneficial effect of the CO2 heat treatment in the potential range between 4.2 and 4.8V vs. Li/Li+ i.e., at potentials where high-energy Li-ion positive composite electrodes operate.

Mo doped DLC nanocomposite coatings with improved mechanical and blood compatibility properties

Abstract Mo (molybdenum) doped diamond like carbon (Mo-DLC) coatings with improved mechanical and blood compatibility properties were deposited by closed field unbalanced magnetron sputtering. The undoped and Mo-doped DLC coatings were analyzed by various characterization techniques such as Raman spectra, Atomic force microscopy, and temperature-dependent frictional wear testing. The results showed that the Mo-DLC coating with low Mo concentration was a effective protective coating with reduced residual stress and increased cohesive strength, and kept good wear resistance at the ambient temperature of 500 °C. The blood compatibility of Mo-DLC coatings was investigated by platelet adhesion. The results showed that the amount of thrombus on the Mo-DLC nanocomposite coatings was much less than that of thrombus on pyrolytic carbon films. The Mo-DLC nanocomposite coatings would be a new kind of promising materials applied to artificial heart valve and endovascula stent.

Filamentous pyrolytic carbon film and its electroanalytical properties

Electrochemical properties of a filamentous pyrolytic carbon film (F-PCF), which was deposited on graphite substrates by chemical vapor deposition (CVD) method, were investigated as a new class of electrode material for use in electroanalytical applications. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) were employed to analyze the structural and morphological features of the electrode material. Some fundamental electrochemical properties of the film were evaluated by studying such parameters as electron transfer rate, capacitance, and potential window using cyclic voltammetry (CV) method and the results were interpreted in relation to its structural analysis results. The results of these tests on F-PCF were compared parallel to traditional CVD-deposited planar pyrolytic carbon film (PCF) electrode. The results of this study showed that F-PCF may have promising potentials to be applied as a useful electrode material in electroanalytical applications, which need to be studied more extensively in the future.

Electromagnetic Properties of Graphene-like Films in Ka-Band

We studied electromagnetic properties of pyrolytic carbon (PyC) films with thicknesses from 9 nm to 110 nm. The PyC films consisted of randomly oriented and intertwined graphene flakes with a typical size of a few nanometers were synthesized by chemical vapor deposition (CVD) at 1100 °C on a quartz substrate. The reflectance and transmittance of these films in Ka-band, 26–37 GHz, were studied both experimentally and theoretically. The discovered remarkably high absorption loss of up to 50% of incident power, along with chemical stability, makes PyC films attractive for electromagnetic (EM) interference shielding in space and airspace communication systems, as well as in portable electronic devices occupying this frequency slot. Since, in practical applications, the PyC film should be employed for coating of dielectric surfaces, two important issues to be addressed are: (i) which side (front or back) of the substrate should be covered to ensure maximum absorption losses; and (ii) the frequency dependence of absorbance/transmittance/reflectance of binary PyC/quartz structures in the Ka-band.

Development of a multi-layer diffusion couple to study fission product transport in β-SiC

A multi-layer diffusion couple was designed to study fission product diffusion behavior while avoiding the pitfalls of direct ion implantation. Thin films of highly anisotropic pyrolytic carbon (PyC) were deposited onto CVD β-SiC substrates. The PyC films were subsequently implanted with 400keV silver, cesium, strontium, europium, or iodine at 22°C to a dose of 1016cm−2, such that the implanted species resided wholly within the PyC layer. The samples were then coated with 50nm of SiC via plasma enhanced CVD (PECVD) to retain the implanted species during post-deposition annealing treatments. The design allows for high spatial resolution tracking of the implanted specie using Rutherford backscattering spectrometry. Annealing at 1100°C for 10h resulted in retention of 100% of implanted cesium, strontium, europium and iodine, and 70% of silver. This diffusion couple design provides the opportunity to determine diffusion coefficients of FPs in PyC and SiC and the role of the PyC/SiC interface in FP transport.

Enhanced microwave shielding effectiveness of ultrathin pyrolytic carbon films

Electromagnetic properties of pyrolytic carbon (PyC) films with thickness from 5 to 241 nm are studied experimentally and numerically at 28 GHz. We observe experimentally that PyC films are capable to absorb up to 50% of microwave power in the Ka-band. By using boundary conditions in the rectangular waveguide, we demonstrate theoretically that 50% of microwave power can be absorbed in a conductive film with thickness much smaller than the skin depth. The results of modelling for PyC films on silica substrate are in excellent coincidence with the experimental data.

Transport and electromagnetic properties of ultrathin pyrolytic carbon films

We experimentally investigated the electrical and electromagnetic (EM) properties of pyrolytic carbon (PyC) ultrathin films synthesized on a quartz substrate by chemical vapor deposition at 1100°C using low pressure CH4∶H2 gas mixture as carbon source. PyC films consist of randomly oriented and intertwined graphene ribbons, which have a typical size of a few nanometers. We discovered that the manufactured PyC films of 35-nm thickness provided remarkably high attenuation caused by absorption of 37% to 24% of incident microwave power. The temperature dependence of PyC’s direct-current (DC) conductivity represents typical behavior for disordered systems. Being semitransparent in visible and infrared spectral range and highly conductive at room temperature, PyC films emerge as a promising material for manufacturing ultrathin microwave (e.g., Ka band) coatings to be used in aerospace applications.

Microwave absorption properties of pyrolytic carbon nanofilm

We analyzed the electromagnetic (EM) shielding effectiveness in the Ka band (26 to 37 GHz) of highly amorphous nanometrically thin pyrolytic carbon (PyC) films with lateral dimensions of 7.2 × 3.4 mm2, which consists of randomly oriented and intertwined graphene flakes with a typical size of a few nanometers. We discovered that the manufactured PyC films, whose thickness is thousand times less than the skin depth of conventional metals, provide a reasonably high EM attenuation. The latter is caused by absorption losses that can be as high as 38% to 20% in the microwave frequency range. Being semi-transparent in visible and infrared spectral ranges and highly conductive at room temperature, PyC films emerge as a promising material for manufacturing ultrathin microwave (e.g., Ka band) filters and shields.

Nitrogen-doped pyrolytic carbon films as highly electrochemically active electrodes

Nitrogen-doped Pyrolytic Carbon (N-PyC) films were employed as an electrode material in electrochemical applications. PyC was grown by via non-catalysed chemical vapour deposition and subsequently functionalised via exposure to ammonia-hydrogen plasma. The electrochemical properties of the N-PyC films were investigated using the ferri/ferro-cyanide and hexaamine ruthenium(III) chloride redox probes. Exceptional electron transfer properties were observed and quantified for the N-PyC compared to the as-grown films. X-ray photoelectron spectroscopy confirmed the presence of nitrogen in edge plane graphitic configurations and the surface of the N-PyC was investigated using scanning electron microscopy and atomic force microscopy. The excellent electrochemical performance of the N-PyC, in addition to its ease of preparation, renders this material ideal for applications in electrochemical sensing.

Nonlinear refraction in semitransparent pyrolytic carbon films

We report on Z–scan measurements of the nonlinear refractive index of semitransparent pyrolytic carbon films. The nonlinear refractive index of the film is as high as 8.23 × 10−9 cm2/W and shows a non–monotonous dependence on the film thickness. We demonstrate that, although the linear absorption coefficient of the pyrolytic carbon films is comparable to that of crystalline graphite, the nonlinear absorption coefficient of the films is much lower than that of graphene.

Direct deposition of semitransparent conducting pyrolytic carbon films

Ultrathin pyrolytic carbon films were synthesized in a single step on dielectric substrates, using a methane-based chemical vapor deposition technique. The developed technique enables the production of wafer scale transparent conductive films suitable for applications in optics and optoelectronics.

Nanocrystalline graphite-like pyrolytic carbon films as electrodes for electrochemical sensing application

Pyrolytic carbon films (PCFs) were deposited on graphite substrates by methane pyrolysis at temperature range of 1000–1100°C. The fundamental electrochemical behaviors in relation to the surface microstructural properties were investigated to ascertain the potential use of these carbon film electrodes for electroanalytical applications. Cyclic voltammetry were performed to examine the residual current and capacitance and the kinetics parameters were obtained in the presence of Fe(CN)63-/4- as a model redox system. Beside, the effects of electrochemical pretreatment were examined using cyclic voltammetry and electrochemical impedance spectroscopy. Fe(CN)63-/4-, Co(phen)33+/2+, Fe3+/2+, and hydroquinone were the redox systems employed to evaluate the electrochemical behavior of the PCF electrodes after pretreatment. Raman spectroscopy, scanning electron microscopy (SEM), and polarized light optical microscopy (PLOM) were carried out to explain the microstructural and morphological properties. Low and stable residual currents toward anodic activation and high electron transfer kinetics specifically after anodic activation were the attractive features of those carbon film electrodes prepared at the higher part of the processing temperature range.

Application of nanocrystalline graphite-like pyrolytic carbon film electrode for voltammetric sensing of lead

A nanocrystalline pyrolytic carbon film was employed as working electrode to detect micromolar-level concentrations of lead by anodic stripping voltammetery as an example of its potential applications in environmental analysis. The response was compared with conventional carbon-based electrodes such as glassy carbon, edge-plane pyrolytic graphite, and basal-plane pyrolytic graphite electrodes. The favorable properties of this carbon coating for Pb detection lie in its high degree of sensitivity, high response stability, low memory effect, and a good repeatability. The applicability of this sensor was tested on spiked tap water and river water samples.

Simultaneous electrochemical sensing of ascorbic acid, dopamine and uric acid at anodized nanocrystalline graphite-like pyrolytic carbon film electrode

Nanocrystalline graphite-like pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used for the simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electrode was studied with respect to changes in electrocatalytic activity caused by a simple and fast electrochemical pretreatment. The anodized electrode exhibited excellent performance compared to many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Differential pulse voltammetry (DPV) was used for the simultaneous determination of ternary mixtures of DA, AA, and UA. Under optimum conditions, the detection limits were 2.9μM for AA, 0.04μM for DA, and 0.03μM for UA with sensitivities of 0.078, 5.345, and 6.192AM−1, respectively. The peak separation was 219mV between AA and DA and 150mV between DA and UA. No electrode fouling was observed and good reproducibility was obtained in all the experiments. The sensor was successfully applied for the assay of DA in an injectable drug and UA in human urine by using standard addition method.

Simultaneous electrochemical determination of dopamine and paracetamol based on thin pyrolytic carbon films

This paper describes the determination of dopamine and paracetamol using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The selective, stable and reproducible simultaneous measurement of the two compounds is achieved using thin pyrolytic carbon (PyC) films as working electrodes. These are created via a reliable, non-catalytic chemical vapour deposition (CVD) process, and the electron transfer characteristics of the films are optimised using a simple oxygen plasma treatment. This new class of carbon electrode can detect dopamine in the range 18 to 270 μM, with a 2.3 μM limit of detection (LoD), while simultaneously sensing paracetamol in the range 15 to 225 μM (LoD 1.4 μM). A 225 mV separation between the two competing signals is realised. The accuracy of the sensor is demonstrated using human serum and commercially available pharmaceutical products. This is the first report of the application of PyC to this problem, and the performance is shown to be competitive with the leading carbon electrodes available today, particularly edge-plane pyrolytic graphite (EPPG). This work will serve as an important benchmark in the development of inexpensive, disposable, high-performance nano-structured electrodes for sensors, fuel cells and energy conversion.

Effect of temperature on the structure and electrochemical performance of LiFePO4-based composite prepared by microwave chemical vapor deposition

LiFePO4-based composite cathode materials have been synthesized by a rapid microwave chemical vapor deposition method within 10min at temperatures as low as 550°C. The samples prepared at different temperatures have been characterized by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy and electrochemical measurements in lithium cells. Results show that the composite prepared at 650°C exhibits the best electrochemical properties, with the discharge capacity as high as 122.7mAhg−1 at 5C and the charge transfer resistance as low as 80Ω. This can mainly be attributed to the formation of a three-dimensional conductive network provided by vapor-grown carbon fiber, pyrolytic carbon film and graphite. The synthesis and processing approach presented here offer a simple and high-efficiency method to obtain high-performance LiFePO4 cathode materials.

Synthesis and analysis of thin conducting pyrolytic carbon films

We report on an adjustable process for chemical vapour deposition of thin films of pyrolytic carbon on inert substrates using an acetylene feedstock. Through modification of the reaction parameters control over film thickness and roughness is attained. These conducting films can be deposited in a conformal fashion, with thicknesses as low as 5 nm and a surface roughness of less than 1 nm. The highly reliable, cost effective and scalable synthesis may have a range of applications in information and communications technology and other areas. Raman and X-ray photoelectron spectroscopies, as well as high resolution transmission electron microscopy are used to investigate the composition and crystallinity of these films. The suitability of these films as electrodes in transparent conductors is assessed through a combination of absorbance and sheet resistance measurements. The films have a resistivity of ∼2 × 10 −5 Ωm but absorb strongly in the visible range. The electrochemical properties of the films are investigated and are seen to undergo a marked improvement following exposure to O 2 or N 2 plasmas, making them of interest as electrochemical electrodes.

Application of nanocrystalline graphite-like pyrolytic carbon film electrode for determination of thiols

The quantification of some biologically important amino acids, namely cysteine, homocysteine, and N-acetylcysteine, was reported using pyrolytic carbon film (PCF) electrodes. Optimum responses were observed for the carbon films fabricated at a deposition temperature of 1100 °C (PCF1100) by chemical vapor deposition (CVD). Electro-oxidation of these sulfur-containing compounds at the PCF1100 showed well-defined signals and no electrode fouling was observed during a set of experiments. The PCF1100 electrode exhibited good resistance against interference by ascorbic acid with distinct separation from cysteine in voltammetric signals. The performance of this electrode was comparable to and in some cases even better than those observed at other unmodified carbon-based electrodes and many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Moreover, the electrode was successfully applied for the determination of cysteine in a tissue growth medium and the results proved that the sensitivity is not affected by presence of a large variety of potential interferences in this medium.

Nanocrystalline graphite-like pyrolytic carbon film electrode for electrochemical sensing of hydrazine

Pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used as an electrochemical sensor for the detection of hydrazine. The electrode response was found to be electrocatalytic producing a reduction in the overpotential compared to other unmodified carbon-based electrodes such as glassy carbon (GC), basal-plane pyrolytic graphite (BPPG), and edge-plane pyrolytic graphite (EPPG) electrodes. The overall number of electrons involved in the electro-oxidation of hydrazine, the number of electrons involved in the rate-determining step, and diffusion coefficient of hydrazine at PCF electrode were estimated using cyclic voltammetry and chronoamperometry. The performance of PCF electrode was comparable to and in some cases even better than many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Moreover, the sensor exhibited fast response time (within 2 s), high response stability, and reproducibility. All the results indicated this sensor is suitable for hydrazine analysis.