Pyrolytic Carbon Films Research Articles

Electrical impedance sensing of organic pollutants with ultrathin graphitic membranes

In this paper we propose an original approach for the real-time detection of industrial organic pollutants in water. It is based on the monitoring of the time evolution of the electrical impedance of low-cost graphitic nanomembranes. The developed approach exploits the high sensitivity of the impedance of 2D graphene-related materials to the adsorbents. We examined sensitivity of the nanomembranes based on pyrolyzed photoresist, pyrolytic carbon (PyC), and multilayer graphene films. In order to realize a prototype of a sensor capable of monitoring the pollutants in water, the membranes were integrated into an ad hoc printed circuit board. We demonstrated the correlation between the sensitivity of the electric impedance to adsorbents and the structure of the nanomembranes, and revealed that the amorphous PyC, being most homogeneous and adhesive to the SiO2 substrate, is the most promising in terms of integration into industrial pollutants sensors.

Sustainable paper templated ultrathin, light-weight and flexible niobium carbide based films against electromagnetic interference

A novel and sustainable paper template-based method was developed for the fabrication of advanced niobium carbide (NbC)-based free-standing films for electromagnetic interference (EMI) shielding application. Through employing the porous structure of paper template, the simultaneous optimization of thickness, flexibility, density and shielding effectiveness (SE) of NbC-based films was facilely achieved. The pyrolytic carbon (PyC) derived from paper worked as a carbon source for the growth of the NbC phase. A hierarchically porous structure with a porosity of ∼80 vol % was established to optimize the flexibility and density of the resultant films. Adjusted heterogeneous NbC-PyC nano-interfaces were formed by controlling the amount of NbC and the remaining PyC phase in the films, which significantly improved the absorption capability of EM waves. At the highest NbC content, the film possesses shielding effectiveness of 50 and 86 dB when the sample thickness is ∼55 and ∼220 μm, respectively compared to 32 dB of pristine paper-derived PyC film (∼55 μm). These results provide guidance to explore more eco-friendly and commercially effective routes for the recycling of used paper through developing their application in the EM field.

Macro-, Micro- and Nano-Roughness of Carbon-Based Interface with the Living Cells: Towards a Versatile Bio-Sensing Platform.

Integration of living cells with nonbiological surfaces (substrates) of sensors, scaffolds, and implants implies severe restrictions on the interface quality and properties, which broadly cover all elements of the interaction between the living and artificial systems (materials, surface modifications, drug-eluting coatings, etc.). Substrate materials must support cellular viability, preserve sterility, and at the same time allow real-time analysis and control of cellular activity. We have compared new substrates based on graphene and pyrolytic carbon (PyC) for the cultivation of living cells. These are PyC films of nanometer thickness deposited on SiO2 and black silicon and graphene nanowall films composed of graphene flakes oriented perpendicular to the Si substrate. The structure, morphology, and interface properties of these substrates are analyzed in terms of their biocompatibility. The PyC demonstrates interface biocompatibility, promising for controlling cell proliferation and directional intercellular contact formation while as-grown graphene walls possess high hydrophobicity and poor biocompatibility. By performing experiments with C6 glioma cells we discovered that PyC is a cell-friendly coating that can be used without poly-l-lysine or other biopolymers for controlling cell adhesion. Thus, the opportunity to easily control the physical/chemical properties and nanotopography makes the PyC films a perfect candidate for the development of biosensors and 3D bioscaffolds.

Pyrolytic Carbon Films with Tunable Electronic Structure and Surface Functionality: A Planar Stand‐In for Electroanalysis of Energy‐Relevant Reactions

AbstractFundamental charge‐transfer dynamics for technologically relevant carbons, such as disordered “hard” carbons, can be studied by designing planar mimics. We fabricate thin films of “pyrolytic carbon” (pyC) by decomposition of benzene at 1000 °C and examine the physical and electrochemical properties of the native pyC film, as well as variants after heteroatom doping, plasma oxidation, and metal nanoparticle modification. The pyC films are optically reflective at the macroscale, relatively planar (1–3 nm RMS roughness by atomic force microscopy) and disordered (via Raman scattering). Thiophenyl‐doped pyC films (0.6–1.7 atom % sulfur) suitably mimic the disorder, chemical state (X‐ray photoelectron spectroscopy), and work function (Kelvin probe) of a workhorse carbon black, Vulcan XC‐72. Using ferri/ferrocyanide as a redox probe, we find that oxygen functionalities enhance the heterogeneous electron‐transfer rate constant up to 3×, while high levels of sulfur dopants decrease the rate 2×. We also explore thiophenyl‐directed adsorption of Au nanoparticles and show that hydrogen evolution at 0.1 mA cm−2 occurs ∼95 mV more positive at <1 % Au@pyC∼S than at pyC∼S.

Environmentally stable macroscopic graphene films with specific electrical conductivity exceeding metals

Air stable, lightweight, and electrically conductive carbon-based films are highly desired for flexible electronic devices and products. Graphene film, a macroscopic assembly of individual graphene sheets, holds great potential to replace conventional brittle pyrolytic carbon film due to the excellent electrical transport property and flexibility. However, the electrical conductivity of graphene film is still inferior to metallic conductors, usually unstable in air as doped. We chose metal chloride (MoCl5) as air stable dopant and fabricated doped graphene film with well-controlled intercalation structure. The MoCl5 modified graphene film shows record high electrical conductivity of 1.73 × 107 S m−1, record high mobility of 2190.47 cm2 V−1 s−1, remarkable specific electrical conductivity exceeding benchmark metals (e.g., Au, Ag, Cu), and ultralow temperature coefficient of resistance (1.4 × 10−4 K−1). Importantly, the electrical conductivity and overall structure of MoCl5 intercalated films are exceptional stable in atmospheric environment, enabling wide applications in electronic devices, electromagnetic interference, and energy storage.

Pyrolytic Carbon Films with Tunable Electronic Structure and Surface Functionality: A Planar Stand-in for Electroanalysis of Energy-Relevant Reactions

Nanostructured carbons are critical components within many of the electrodes used for energy-storage and –conversion systems, where they can provide pathways for electron conduction to enable high-rate operation, act as supports for other active materials (e.g., electrocatalytic metals and oxides), and contribute to the mechanical properties of the electrode. Yet often overlooked when selecting a particular carbon is the nature of electronic/chemical/physical interactions at the junction of carbon with nanoscale phases that impart desired storage or electrocatalytic functionality. Our own research with otherwise high-performing carbon-based electrode architectures suggests that sub-optimal interface design ultimately hinders energy and power capability. In order to address fundamental questions regarding interfacial processes, we step back from the complex structure of practical carbon-containing electrodes to a planar electrode configuration designed to mimic those same interfaces. For example, pyrolytic carbon (pyC) films prepared by chemical vapor deposition are planar analogs of the disordered carbon blacks used in many battery and fuel-cell electrodes, and thus serve as an electroanalytical substrate on which we deposit charge-storing metal oxides (e.g., MnO2), electroactive polymers, and metal colloids [1]. We use classical electroanalytical methods to determine fundamental properties such as electron-transfer rate constants and impedance-derived response times, absent the complexities imposed by 3D electrodes. By moving to 2D model surfaces we are also able to interrogate interfacial processes by scanning probe microscopy, including in situ monitoring of conductivity and surface morphology under potential/current control. Lessons learned from these model 2D interfaces are readily applied to the redesign of practical 3D electrode structures to improve next-generation electrochemical capacitors and batteries. [1] J. F. Parker, G. E. Kamm, A. D. McGovern, P. A. DeSario, D. R. Rolison, and J. W. Long, Languir, 33 (2017) 9415–9425.

Nonlinear optical properties of graphene and pyrolytic carbon: A comparative study

We report on [Formula: see text]-scan investigations of the nonlinear optical properties of thin pyrolytic carbon films and two- and three-layer graphene films, utilizing an 800[Formula: see text]nm pulsed laser generating ultrashort 180[Formula: see text]fs pulses. We analyze the sign and magnitude of nonlinear refraction and absorption in these materials, given contradictory results in this respect in the literature. In particular, we find that nonlinear refraction of graphene changes sign with changing light intensity with concomitant subtle changes in nonlinear absorption, a behavior not reported previously that suggests an interplay of several mechanisms that depend on intensity. Pyrolytic carbon films, on the contrary, exhibit positive refraction, whose magnitude (nonlinear refractive index [Formula: see text][Formula: see text]cm2/W) is comparable to that of graphene, and strong negative absorption, i.e., bleaching, contrary to previously reported results. We discuss implications and possible mechanisms of the observed phenomena.

High Temperature SiC Reactor Cleaning Using Chlorine Trifluoride Gas Achieved by Purified Pyrolytic Carbon Coating Film

A reactor cleaning technique for the silicon carbide (SiC) chemical vapor deposition (CVD) method has been developed using chlorine trifluoride (ClF3) gas. The purified pyrolytic carbon film was studied as the improved coating film of the susceptor. At the temperatures up to 570 °C, the purified pyrolytic carbon film could have no serious damage after the exposure to the ClF3 gas, to enable the high temperature and high speed cleaning.

Pulsed-DC Discharge for Plasma CVD of Carbon Thin Films

A pulsed-dc discharge method for plasma chemical vapor deposition (CVD) was developed using a constructed versatile pulsed-dc generator and a vacuum discharge chamber. Argon (Ar) gas discharge experiments were performed under a variety of discharge conditions, and plasma conditions were evaluated using optical emission spectroscopy. The developed system can perform glow discharge by employing nearly rectangular, unipolar, and high-voltage negative pulses with a wide variation of voltage amplitudes and a set discharge current, pulse repetition rate, and duty cycle. Plasma conditions could also be tuned by varying the pulse parameters. A preliminary test of the deposition of diamond-like carbon (DLC) films on silicon (Si) substrates and ultrathin pyrolytic carbon (PyC) films on nanothickness metal-catalyzed glass substrates was performed with acetylene (C 2 H 2 ) by selecting some typical deposition conditions based on the gas discharge experiments. The deposited films were characterized via Raman spectroscopy. The characteristic properties of DLC and PyC films were achieved. The DLC films demonstrated conventional hard insulating properties while the ultrathin PyC films exhibited conductive and semitransparent properties. These results revealed that the developed pulsed-dc discharge system for plasma CVD is applicable for the synthesis of insulating hard as well as soft conducting carbon thin films.

Quick and Practical Cleaning Process for Silicon Carbide Epitaxial Reactor

In order to develop a quick and practical cleaning process for the silicon carbide chemical vapor deposition reactor, the pyrolytic carbon-coated susceptor was used. The 30-μm-thick silicon carbide film was formed on the susceptor; the film was cleaning by chlorine trifluoride gas at 460 °C for 15 min. The remained fluorine was removed by the annealing at 900 °C in ambient hydrogen. The pyrolytic carbon surface did not suffer from any damage, because the pyrolytic carbon film surface morphology after the cleaning process was the same as that before the silicon carbide film deposition.

Tailoring stress in pyrolytic carbon for fabrication of nanomechanical string resonators

In order to achieve high resonance frequencies and quality factors of pyrolytic carbon MEMS string resonators the resonator material needs to have a large tensile stress. In this study, the influence of pyrolysis temperature, dwell time and ramping rate on the residual stress in thin pyrolytic carbon films is investigated with the bending plate method. The results show that the pyrolysis temperature is the most important parameter for tailoring the residual stress, with a transition from tensile stress at temperature below 800ºC to compressive stress at temperatures above 800ºC. Two kinds of photoresist: positive (AZ5214E) and negative (SU-8) and different pyrolysis conditions are used to fabricate pyrolytic carbon string resonators at variable pyrolysis conditions. The best performance is obtained for devices with a length of 400 μm fabricated at a pyrolysis temperature of 700ºC, ramping rate of 30ºC/min and 10 min dwell time corresponding to the conditions for maximum tensile stress in pyrolytic carbon thin films. The optimized pyrolytic carbon string resonators have resonant frequencies above 300 kHz and quality factors (Q) in the order of 104, which is suitable for their application as nanomechanical sensors.

Pyrolytic carbon supported alloying metal dichalcogenides as free-standing electrodes for efficient hydrogen evolution

Electrochemical reduction of water is a renewable way to produce clean hydrogen energy. In order to overcome the high-cost and shortage of noble metals, transition metal compounds involving earth-abundant elements, such as MoS2 and WS2, have been proposed as novel catalysts for hydrogen evolution reaction (HER). Efforts have been made to increase the intrinsic catalytic activity of transition metal dichalcogenides (TMDCs), while alloying same- group elements has not been vastly investigated. Moreover, besides the catalytic activity, the design of free-standing catalytic electrodes is also critical for HER. In this work, we synthesize pyrolytic carbon film with MoxW1-xS2 nanoflakes embedded as a free-standing flexible electrodes for HER catalysis. The pyrolytic carbon acts as conductive and flexible matrix for TMDC alloys with controlled composition, resulting in remarkably enhanced HER activity. The highest HER activity was observed for Mo0.37W0.63S2/C samples with an overpotential of 0.137 V at geometric current densities of jgeo = 10 mA cm−2 and a Tafel slope of 53 mV dec−1. These results now provide low-cost viable alternatives for the design and construction of catalysts based on alloyed TMDCs.

Quick Cleaning Process for Silicon Carbide Chemical Vapor Deposition Reactor

A quick cleaning process was developed for a silicon carbide chemical vapor deposition reactor. For this purpose, the stability of the susceptor coating film made of pyrolytic carbon was evaluated by means of exposing it to 100% chlorine trifluoride gas for 10 min at various temperatures. The original surface morphology of the pyrolytic carbon film was maintained under 480°C. The fluorine atoms incorporated into the pyrolytic carbon film were removed by annealing at 900°C either in ambient hydrogen or in ambient nitrogen. Finally, the 30-μm thick silicon carbide film formed on the pyrolytic carbon was successfully cleaned by the chlorine trifluoride gas either at 400°C for 30 min or at 460°C for 15 min and by additional annealing in ambient nitrogen at 900°C.

Application of Nanocrystalline Graphite‐like Pyrolytic Carbon Film Electrode in the Electroanalytical Determination of Famotidine

AbstractDirect electro‐oxidation of famotidine at different graphitic carbon‐based electrode materials was evaluated. These materials included conventional electrodes of edge‐plane pyrolytic graphite, basal‐plane pyrolytic graphite, carbon paste, and glassy carbon as well as nano‐structured carbon‐based materials such as pyrolytic carbon film, carbon nanotube, and nano‐graphene. Raman spectroscopy and scanning electron microscopy were employed to analyze their structural and morphological features. It was found that the pyrolytic carbon film electrode, after a simple and fast anodic activation, shows superior electroanalytical performance. The method was successfully applied for the electroanalytical determination of famotidine in tablet dosage forms and urine samples.

Electrically pumped microdisk lasers with semitransparent conducting pyrolytic carbon film

Electrically driven microdisk lasers with top contacts made of a semitransparent conducting pyrolytic carbon film are developed. Electrical properties of the pyrolytic carbon contact to a p-type doped GaAs epitaxial layer are studied. Room temperature electroluminescence spectra from an array of the microdisk lasers and a single 27 μm in diameter microdisk laser are demonstrated.

Ultrathin pyrolytic carbon films on a magnetic substrate

We report the growth of ultrathin pyrolytic carbon (PyC) films on nickel substrate by using chemical vapor deposition at 1000 °C under methane ambience. We find that the ultra-fast cooling is crucial for PyC film uniformity by controlling the segregation of carbon on nickel. We characterize the in-plane crystal size of the PyC film by using Raman spectroscopy. The Raman peaks at ∼1354 and ∼1584 cm−1 wavenumbers are used to extract the D and G bands. The corresponding peak intensities are then used in an excitation energy dependent equation to calculate the in-plane crystal size. Using Raman area mapping, the mean value of in-plane crystal size over an area of 100 μm × 100 μm is about 22.9 nm with a standard deviation of about 2.4 nm.

A robust approach to the design of an electromagnetic shield based on pyrolitic carbon

A robust approach to the design of an electromagnetic shield based on ultra-thin pyrolytic carbon (PyC, 5 ÷ 110 nm) films is proposed. Finite Element Method (FEM) simulations and Monte Carlo based tolerance analysis are used to show that even a deviation of 15 ÷ 20% from the nominal values of the most important design parameters of the PyC film, i.e. its thickness and sheet resistance, does not significantly affect the wanted level of electromagnetic interference shielding efficiency (EMI SE). The ranges of the SE show that EMI shield based on PyC film is characterized by a robust behavior with respect to the variation of such parameters due to the production processes. Therefore, since the PyC can be produced on a scalable basis, is chemically inert, significantly transparent in the visible range and can be deposited onto both metal and dielectric substrates, including flexible polymers, it may be appropriate for the highly demanding technological needs associated to the graphene revolution and can be developed from laboratory to mass production applications.

STRUCTURE AND PROPERTIES OF SOOT IN HYDROCARBON FLAMES

The “active sites” were identified in the ensemble of soot particles, the place of their location, the nature of their structure. The mechanism of the formation and physico-chemical properties of the pyrolytic carbon film were studied in hydrocarbon flames. Integrated technique, including infrared spectral analysis, sampling of the condensed combustion products, studying of the surface topography of the soot particles, finding values of the optical constants, revealing irregularities in the brightness of the flame, identify irregularities in the brightness of the flame can be applied in the research of mechanisms of soot formation in heterogeneous condensed media.

Optical Properties of Pyrolytic Carbon Films Versus Graphite and Graphene.

We report a comparative study of optical properties of 5–20 nm thick pyrolytic carbon (PyC) films, graphite, and graphene. The complex dielectric permittivity of PyC is obtained by measuring polarization-sensitive reflectance and transmittance spectra of the PyC films deposited on silica substrate. The Lorentz-Drude model describes well the general features of the optical properties of PyC from 360 to 1100 nm. By comparing the obtained results with literature data for graphene and highly ordered pyrolytic graphite, we found that in the visible spectral range, the effective dielectric permittivity of the ultrathin PyC films are comparable with those of graphite and graphene.

Electrochemical determination of guaifenesin in a pharmaceutical formulation and human urine based on an anodized nanocrystalline graphite-like pyrolytic carbon film electrode

A simple and sensitive electrochemical method was developed for the determination of guaifenesin based on a pyrolytic carbon film (PCF) electrode.