Continuous Carbon Film Research Articles

Carbon film-coated 304 stainless steel as PEMFC bipolar plate

Carbon film-coated stainless steel (CFCSS) has been evaluated as a low-cost and small-volume substitute for graphite bipolar plate in polymer electrolyte membrane fuel cell (PEMFC). In the present work, AISI 304 stainless steel (304SS) plate was coated with nickel layer to catalyze carbon deposits at 680°C under C 2H 2/H 2 mixed gas atmosphere. Surface morphologies of carbon deposits exhibited strong dependence on the concentration of carbonaceous gas and a continuous carbon film with compact structure was obtained at 680 °C under C 2H 2/H 2 mixed gas ratio of 0.45. Systematic analyses indicated that the carbon film was composed of a highly ordered graphite layer and a surface layer with disarranged graphite structure. Both corrosion endurance tests and PEMFC operations showed that the carbon film revealed excellent chemical stability similar to high-purity graphite plate, which successfully protected 304SS substrate against the corrosive environment in PEMFC. We therefore predict CFCSS plates may practically replace commercial graphite plates in the application of PEMFC.

Behavior of carbon readsorbed on tungsten during low energy Ar ion irradiation at elevated temperatures

A study of the behavior of carbon sputtered and readsorbed after scattering collisions with particles of surrounding gas on the tungsten surface affected by Ar ion irradiation with the flux equal to 2 × 10 16 cm −2 s −1 extracted from plasma under 300 V negative bias voltage in the temperature range 370–870 K was performed. The dependence of the W sample weight change on the working gas pressure in the range 0.1–10 Pa was registered and the information was deduced about prevailing sputtering-redeposition processes. The depth profiles of carbon at the tungsten surface were measured. We found that carbon distribution profiles in tungsten depend on the C redeposition rate for fixed ion irradiation parameters. Three regimes have been distinguished: (i) at working gas pressure equal to 5 Pa and more, the C redeposition rate prevails the sample surface erosion rate and the W surface is covered by continuous amorphous carbon film (the C film growth regime), (ii) at working gas pressure equal to about 1 Pa, the C redepostion rate is approximately equal to the erosion rate and the W surface is partially covered by redeposited carbon, and (iii) at working gas pressure less than 0.2 Pa, the erosion rate prevails the C redeposition rate (the W surface erosion regime). In the regime of balanced redeposition and erosion deep C penetration depth into nanocrystalline W was registered. It is suggested that under simultaneous C adsorption and ion irradiation at elevated temperature C adatoms are driven from the W surface into grain boundaries and into the bulk by the difference in chemical potentials between the activated W surface and grain boundaries. As the W surface is covered by amorphous C film, the grain boundaries are blocked and the efficiency of carbon transport decreases.

Negative staining across holes: Application to fibril and tubular structures

The negative staining technique, when used with holey carbon support films, presents superior imaging conditions than is the case when samples are adsorbed to continuous carbon films. A demonstration of this negative staining approach is presented, using ammonium molybdate in combination with trehalose, applied to several fibrillar and tubular samples. Fibrils formed from the amyloid-β peptide and the protease inhibitor pepstain A spread very well unsupported across holes and the different polymorphic fibril forms can be readily assessed. However, tubular forms of amyloid-β have a tendency to be flattened, due to surface tension forces prior to and during specimen drying. Sub-fibril assembly forms and D-banded rat tail type 1 collagen fibres are presented. The air-dried collagen images produced are shown to contain almost as much detail as those obtainable by cryo-negative staining. Fragile DNA and DNA-protein nanotubes are also shown to yield superior quality images to those produced on continuous carbon films. The iron-storage protein, frataxin, creates elongated oligomeric assemblies, containing bound ferrihydrite microcrystals. The iron particles within these flexuous oligomers can be defined in the presence of ammonium molybdate, but they are more readily demonstrated if the frataxin is spread across holes in the presence of trehalose alone. The samples used here serve to show the likely benefit obtainable from negative staining across holes for a range of other fibrillar and tubular samples in biology, medicine and nanobiotechnology.

Fabrication of continuous mesoporous carbon films with face-centered orthorhombic symmetry through a soft templating pathway

Preparation of well-ordered continuous mesoporous carbon films without the use of an intermediate inorganic template was achieved by spin coating of a thermosetting phenolic resin, resorcinol/phloroglucinol/formaldehyde, and a thermally-decomposable organic template, Pluronic F127 (PEO106–PPO70–PEO106). The carbon films were deposited onto silicon, platinum/silicon, copper, glass, and quartz substrates. Afterwards, decomposition of the organic template and solidification of the carbon precursors are simultaneously performed through a carbonization process. The resulting films referred to as CKU-F69, are (010)-oriented, and possess a face-centered orthorhombic Fmmm symmetry. Film periodicity is maintained even after a 68% uniaxial contraction perpendicular to the substrate brought on by carbonization at 800 °C. This method could facilitate the mass-production and creation of new carbon and carbon–polymer porous films that find broad potential applications in catalysis, separation, hydrogen storage, bioengineering, nanodevices, and nanotemplates.

Silica‐Templated Continuous Mesoporous Carbon Films by a Spin‐Coating Technique

Continuous mesoporous carbon thin films (see Figure) have been synthesized through direct carbonization of sucrose/silica nanocomposite films and subsequent removal of the silica to create a mesoporous carbon network. This method provides a simple and efficient method to synthesize continuous, high surface area and pore volume mesoporous carbon thin films with uniform‐sized and interconnected pore channels.

On the role of carbon in the formation and properties of hot pressed icosahedral Al-Cu-Fe phase

Al-Cu-Fe icosahedral (i) quasicrystal phase exists only within a restricted temperature range between 750 ◦C and 850 ◦C or at a very sharply defined composition around Al62Cu25.5Fe12.5 [1–3]. As a stable i-phase, interests in this system have arised mainly to study its quasiperiodic structure, its bulk and surface properties, and the possibility of growing large single quasicrystals [4–7]. Recently, starting from the Al-Cu-Fe system, work has been performed to study the effects of nonmetallic elemental additions such as oxygen and boron on the structure and stability of the icosahedral phase [8–10]. To the authors’ knowledge, however, no information exists on the effects of metalloid carbon addition on the alloys. In this paper, we present in situ carburization of the i-AlCuFe quasicrystalline phase prepared by the hot-pressing of gas atomized powders at a temperature for which it is thermodynamically stable. The influence of carbon on the formation and mechanical properties of the i-AlCuFe quasicrystalline phase is also studied to contribute to the understanding of the carburization behavior of bulk icosahedral Al-Cu-Fe phase. The starting materials were powders of the composition Al62Cu26Fe12 prepared by gas atomization of the liquid alloy. The majority of the sieved powder particles were less than 38 microns in diameter. The corresponding as-atomized structure consists of primary icosahedral (i) dendrites with small amount of τ phase in the interdendritic region [11]. The bulk quasicrystalline sample, a three-dimensional body 40 × 40 × 8 mm3, was fabricated by hot-pressing the powder particles. The hot-pressing process was performed in two steps. The former was a degassing process at a low temperature of 600 ◦C for 30 min under high-vacuum condition (5 × 10−5 Torr); the latter was a sintering and densification process of the icosahedral phase formed at a high temperature of 800 ◦C for 120 min under a pressure of 35 MPa. In the whole hot-pressing process, a graphite paper of approximately 0.5 mm was used as a separator to protect both graphite mold and graphite punch. In this case, the graphite paper is expected to behave as a carburizer and consequently to induce the contamination of the quasicrystalline forming alloys during hot pressing. The characterization of the hot pressed samples was performed as shown in Fig. 1 on the sample surface and its cross-section, respectively. First, the carbon distribution and microstructure were detected perpendicular to the cross section of sample. Second, a mechanical polishing method was used to remove the surface of the carburized sample layer by layer so as to obtain the depth profiles of the phase constituents and mechanical properties. It should be noted that the measurement of the initial surface started from the freshly abraded surface following the removal of the carbon film. The phase constituents and microstructure were assessed by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The chemical analysis was carried out by X-ray energy dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) for qualitative purposes, respectively. The Vickers microhardness Hv was determined from at least 15 different indentations, and the fracture toughness KIC was evaluated from the crack length initiated at the corners of the Vickers microindentation by using an empirical equation proposed by Niihara et al. [12]. The SEM image and the elemental EDS X-ray scans of the cross-section of the carburized sample are presented in Fig. 2. A continuous carbon film developed during hot-pressing can be seen on the surface of sample in the upper left-hand side image. The film thickness is about 35 μm. In addition, a spare dispersion of Al element in the carbon film was detected, as evidenced by the X-ray mapping of Al (middle left-hand side). This illustrates that the formation of this film results in the selective consumption of aluminum. Beneath the film a multiphase microstructure in the carburized sample can be observed; the multiphase assemblages were later identified further using XRD technique. Owing

Effects of Confinement on Arborescent Graft Polystyrene Particle Shape

Abstract Arborescent graft polymers are highly branched materials synthesized by grafting multiple generations of macromolecular precursors on a central core [1,2]. They can be synthesized with controllable size and molecular weight depending on the number of generations and the precursor molecular weight. They possess many of the unique structural [3], thermodynamic, and rheological [4] properties of dendrimers but do so on a length scale roughly one order of magnitude higher. This research describes the effect of confinement on the shape of arborescent graft polystyrene (PS). This work used 3rd generation arborescent graft PS synthesized with 5kg/mole linear polystyrene precursor (G3- 5K). The G3-5K PS sample was mixed to a dilution of approximately 0.005 wt% in toluene. A single drop of solution was placed on either a holey-carbon film or an ultrathin continuous carbon film. The solvent was evaporated under ambient conditions. A Philips CM20 FEG TEM/STEM equipped with a Gatan 666 PEELS and a 679 multiscan CCD camera was used to study the structure of these specimens.

Nano-diamond films deposited by direct current glow discharge assisted chemical vapor deposition

Continuous carbon films are deposited by the direct current (DC) glow discharge assisted chemical vapor deposition method using a hydrogen–methane gas mixture. As a result of the DC-glow discharge–surface interaction, the substrate is covered by a film whose properties are strongly affected by the glow discharge and substrate conditions. It was found that under appropriate combination of the experimental parameters, a nano-sized carbon composite film containing a predominating diamond phase can be produced. The properties of the deposited carbon films were studied as a function of experimental conditions by a number of complementary techniques. The composition of the films was assessed by electron spectroscopy and the elastic recoil detection method; the morphology and structure of the films were investigated by high-resolution scanning and transmission electron microscopy (HR TEM and HR SEM). Particular attention was paid to the studies of chemical bonding of the deposited materials. For this purpose, the near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy and electron energy loss spectroscopy (EELS) techniques were used. The average film density was measured by Rutherford backscattering spectrometry. Electron diffraction, NEXAFS and EELS measurements render unambiguous evidence of diamond phase formation by the DC-glow discharge process. The nano-size dimensions of the deposited material were determined from both HR-SEM and -TEM measurements. The critical role of substrate temperature for the formation of nano-diamond particles was established based on the spectroscopic and microscopic results. Hydrogen adsorption/desorption appears to be a critical factor in this process.

Two-dimensional crystallization of proteins on lipid monolayers at the air–water interface and transfer to an electron microscopy grid

The two-dimensional (2-D) crystallization of proteins on lipid monolayers at the air–water interface is a well established method for crystallizing soluble proteins. The transfer of 2-D crystals from the air–water interface to an electron microscopy (EM) grid constitutes a critical and ill-controlled step in the whole procedure, which is likely to be responsible for the high variability of results obtained with this method. In this paper, we address the following questions: (1) does the material observed on EM grids constitute a true representation of the material present at the air–water interface? (2) is there an optimal method of transfer to obtain well-ordered protein 2-D crystals? To answer these questions, we combine data obtained on three different protein systems, annexin V, streptavidin and cholera toxin, using two types of EM grids, coated with either holey carbon films or continuous carbon films. These combined observations help us draw a coherent picture of the state of the interfacial films at the air–water surface and provide new insight into the perturbing influence of the transfer step. The main conclusions are: (1) both annexin V and streptavidin form crystalline monolayers at the air–water interface, which are well preserved when transfer is performed by means of holey carbon films; (2) a major reorganization of the material present at the water surface accompanies transfer with continuous carbon films; the basal monolayer is extensively damaged, transforming into domains and vesicular structures, which do not pre-exist at the water surface; with the three protein systems studied here, these domains are often crystalline; (3) the most striking structural reorganization induced by transfer with continuous carbon films is observed with annexin V, for which the native p6 crystalline assembly is transformed into another crystal form more ordered, with p3 symmetry. It is most probable that these conclusions also apply to other protein 2-D crystals formed by the lipid monolayer method. The recent in situ observation of 2-D crystals of annexin V formed on solid-supported bilayers, by atomic force microscopy, supports our interpretation that monolayers transferred with holey carbon films represent the genuine material pre-exisiting at the air–water interface.

Projection structure of the cytochrome bo ubiquinol oxidase from Escherichia coli at 6 A resolution.

The haem-copper cytochrome oxidases are terminal catalysts of the respiratory chains in aerobic organisms. These integral membrane protein complexes catalyse the reduction of molecular oxygen to water and utilize the free energy of this reaction to generate a transmembrane proton gradient. Quinol oxidase complexes such as the Escherichia coli cytochrome bo belong to this superfamily. To elucidate the similarities as well as differences between ubiquinol and cytochrome c oxidases, we have analysed two-dimensional crystals of cytochrome bo by cryo-electron microscopy. The crystals diffract beyond 5 A. A projection map was calculated to a resolution of 6 A. All four subunits can be identified and single alpha-helices are resolved within the density for the protein complex. The comparison with the three-dimensional structure of cytochrome c oxidase shows the clear structural similarity within the common functional core surrounding the metal-binding sites in subunit I. It also indicates subtle differences which are due to the distinct subunit composition. This study can be extended to a three-dimensional structure analysis of the quinol oxidase complex by electron image processing of tilted crystals.

Electron energy loss spectroscopy: Application to synthetic organic polymers

AbstractElectron energy loss spectroscopy has been examined as a possible tool for measuring the atomic composition of polymers on a local scale in the transmission electron microscope. Thin films of nylon 6,6 and single crystal lamellae of poly(chlorotrifluorethylene) were investigated as model systems. Spectra were obtained using an 100 kV electron beam. Results for nylon 6,6 gave fairly good quantitative agreement between the measured relative atomic contents of carbon, nitrogen, and oxygen (77, 9, and 14%, ± 5%, respectively) and the calculated values (75, 12.5, and 12.5%, respectively). Spectra obtained for poly(chlorotrifluoroethylene) single crystals revealed significant mass loss of chlorine as a function of electron dose. The amount of chlorine decayed exponentially with a characteristic dose D* of 96 C/m2. Supporting the poly(chlorotrifluoroethylene) crystals on a continuous carbon film, a holey carbon film, or sandwiched between two carbon films did not effect the mass loss decay constant significantly but did effect the amount of chlorine remaining in the irradiated area at large electron doses. The poly(chlorotrifluorethylene) crystals sandwiched between two carbon films retained more chlorine at large doses, possibly due to the carbon film on both sides of the crystals, inhibiting surface diffusion of the chlorine. Analysis of the spectrum from a portion of a trilayer PCTFE crystal suspended over a hole in the support film gave the relative contents of C, Cl, and F (extrapolated to zero dose) as being 38, 15, and 47%, respectively. The calculated values are 33, 17, and 50%, respectively.

Immobility of reduced carbon along grain boundaries in dunite

Carbon‐14 radiotracer experiments at 10 kbar (1 GPa) and 1000°‐1200°C reveal that, due to low diffusivity or low solubility (or both), carbon is immobile in the grain boundary regions of natural dunite. Within the resolution of the beta‐track mapping technique, grain boundary diffusion of carbon from a pure graphite source is not detectable in experiments of up to 10 days duration at 1200°C, even though measurable volume diffusion profiles are generated at these conditions (D ∼ 3‐4 × 10−10 cm²/s, in agreement with previous estimates). The documented immobility of carbon in dunite grain boundaries precludes development of a continuous carbon film by diffusion from an initially localized source. If such a film is the cause of the mantle high‐conductivity layer, it probably originated by a process involving fluid (CO/CO2) infiltration and subsequent reduction.