Deposition Of Carbon Layers Research Articles

Surface properties of carbon structures evaporated on polytetrafluoroethylene

Carbon layers were deposited by flash evaporation from carbon fiber on polytetrafluoroethylene (PTFE). The layer thickness, surface roughness, and morphology were determined from atomic force microscopy measurements. The electrokinetic potential of the prepared structures was studied by electrokinetic analysis. Layer wettability was determined by measuring the contact angle and the electrical conductivity by a standard two-point method. The chemical composition of the layers was studied by X-ray photoelectron spectroscopy. It was found that the carbon deposition leads to a decrease of surface roughness of the PTFE and to a significant increase of sample wettability and electrical conductivity. Oxygen-containing groups were detected on deposited carbon layers. Cytocompatibility of the samples was tested using of human diploid fibroblastoids (HDF). In comparison with pristine PTFE the carbon-coated PTFE shows dramatically increased adhesion and proliferation of HDF on the sample surface.

Characterization and Cytocompatibility of Carbon Films

Carbon layers on polyethyleneterephtalate (PET) backing were prepared by 3 different deposition methods as evaporation, sputtering and photo induced chemical vapor deposition. UV-Vis, Raman spectroscopy, Rutherford backscattering techniques, goniometry and electrical resistance measurement were used for the characterization of the layers. Surface morphology of the layers was determined by AFM technique and the thickness was determined by SEM and profilometry. Adhesion and proliferation of 3T3 cells by method in vitro were studied. It was found that the properties of the deposited carbon layer depend on the deposition method. The layers prepared by sputtering are composed from oxidized amorphous carbon in the form of disordered graphite. Contact angle of deposited carbon layers decreases in comparison to pristine PET. The electrical resistance of carbon layer also decreases, a dramatic decrease being observed especially after carbon flash evaporation. The carbon deposition has no significant influence on surface roughness, but the surface morphology is strongly influenced. Adhesion of 3T3 fibroblast didn't show any significant difference between PET, sputtered and CVD layers. Proliferation of 3T3 fibroblast has shows differences due to the surface morphology and also wettability of the surface which is linked to the chemical composition.

Pulsed repetition rate nanosecond laser heating and ablation of the tokamak graphite tile deposited layers

Laser heating and ablation of the plasma-facing surface of a graphite tile from TEXTOR tokamak that was covered by a deposited carbon layer has been studied. Laser heating measurements were performed with a pulsed nanosecond Nd-YAG laser (2nd harmonic, 10 kHz repetition rate, 100 ns pulse duration). Surface temperature measurements were recorded with a home-made pyrometer having a response time of 15 μs ( t 99%). The experimental results are simulated with an analytical model of laser heating of a surface covered by a deposited layer and heated repeatedly by laser pulses. The comparison between experimental and theoretical data of the observed temperature excursions enables us to assess the deposited carbon layer physical parameters (thermal conductivity, porosity, etc.) if the thermal and optical properties of the graphite substrate are known. Laser ablation measurements were performed with two pulsed nanosecond Nd-YAG lasers (20 Hz and 10 kHz repetition rate with 5 ns and 100 ns pulse duration, respectively). For a plasma-facing graphite surface covered by a thick (∼30–50 μm) deposited carbon layer, the ablation threshold is 4.5 ± 1 kJ/m 2 regardless of the pulse duration. The obtained ablation threshold is significantly lower than the one measured for a virgin tokamak graphite sample. The comparison of the experimental results and theoretical data demonstrated that the laser ablation mechanisms for tokamak graphite and thick carbon layers deposited on plasma-facing surface are different.

Characterization of redeposited carbon layers on TEXTOR limiter by Laser Raman spectroscopy

Laser Raman spectroscopy is quite sensitive to detect the changes of graphite structure. In this study, the Laser Raman technique was applied to analyze the deposited carbon layers on TEXTOR test limiters of carbon (C) and tungsten (W) produced by intentional carbon deposition experiments by methane gas puffing. The carbon deposited layers showed the Raman spectra composed of two broad peaks, G-peak and D-peak, centered at around 1580 and 1355 cm −1 respectively. For W limiter, the G-peak position and the integrated intensity of the two peaks well correlate to hydrogen concentrations in the deposited carbon layers and their thicknesses, respectively. Hence Laser Raman spectroscopy is a promising tool for the in situ analysis of carbon redeposit layers on plasma facing W materials and probably on Be materials.

Multilayer graphene films grown by molecular beam deposition

Few-layer graphene films are grown using a Molecular Beam Deposition (MBD) technique in ultra-high vacuum by evaporation of atomic carbon and subsequent annealing of the samples at 800–900 °C. The graded thickness layers are grown on strip-shaped oxidized silicon substrates which are covered with 300 nm thick nickel films deposited by e -beam evaporation. The thickness of the deposited carbon layers changes continuously from ∼70 Å to less than 4 Å. The relatively narrow optical phonon bands in Raman spectroscopy reveal that good quality multilayer graphene films form on the Ni surface.

Comparison of 13C2H4 and 13CH4 injection through graphite and tungsten limiters in TEXTOR

Experiments in the plasma-wall interaction facility at TEXTOR have been carried out to compare (i) the local transport of 13CH4 and 13C2H4 injected through a gas aperture implemented in spherical limiters made of polycrystalline tungsten and fine-grain graphite and (ii) the properties of local deposited carbon layers on the polished limiter surface. Each limiter was positioned in the scrape-off layer and exposed to ten identical ohmic deuterium discharges of 4s length—accumulating 40 plasma seconds. The injection rates were normalized to the amount of injected 13C. The analysis is twofold: spectroscopy was applied to follow up in situ the observable hydrocarbon break-up products (C2, CD, C+, and C2+), and post mortem analysis was used to determine the 13C deposition efficiency. The penetration depths of hydrocarbon break-up products in the plasma were determined. Significant CH emission was observed in front of W limiter prior to injection. The 13C deposition efficiency shows a dependence on both the limiter material and on the injected hydrocarbon species.

ERO modelling of local deposition of injected 13C tracer at the outer divertor of JET

The 2004 tracer experiment of JET with the injection of 13CH4 into H-mode plasma at the outer divertor has been modelled with the Monte Carlo impurity transport code ERO. EDGE2D solutions for inter-ELM and ELM-peak phases were used as plasma backgrounds. Local two-dimensional (2D) deposition patterns at the vertical outer divertor target plate were obtained for comparison with post-mortem surface analyses. ERO also provides emission profiles for comparison with radially resolved spectroscopic measurements. Modelling indicates that enhanced re-erosion of deposited carbon layers is essential in explaining the amount of local deposition. Assuming negligible effective sticking of hydrocarbons, the measured local deposition of 20–34% is reproduced if re-erosion of deposits is enhanced by a factor of 2.5–7 compared to graphite erosion. If deposits are treated like the substrate, the modelled deposition is 55%. Deposition measurements at the shadowed area around injectors can be well explained by assuming negligible re-erosion but similar sticking behaviour there as on plasma-wetted surfaces.

Temperature Dependence of Carbon Deposition on Tungsten

Since carbon deposition layers in tokamak devices will contain significant amount of tritium, it is important to study its formation mechanism. In this study, tungsten and molybdenum samples with a temperature gradient were irradiated by a mixed ion beam to precisely study temperature dependence of the deposition characteristics. For molybdenum, the temperature of the boundary between “deposition” and “nodeposition” is higher than W. This results roughly agree with the results by the material mixing model proposed by Kriegeretal [K. Krieger. J. Roth. J. of Nucl. Mater. 290-293 (2003) 107.]. Erosion yield of C deposition layer in our experimental conditions was almost equal or less than the yield by Rothmodel [J. Roth, C. Garcia-Rosales, Nucl. Fusion 36 (1996) 1647] for graphite.

Localized tungsten deposition in divertor region in JT-60U

Tungsten local transport in the diverter region emitted from the outer divertor was studied in JT-60U. Tungsten-coated CFC tiles were installed in the outer divertor position, on which outer strike points did not normally sit. A neutron activation method to measure tungsten surface density was used for the first time. On the outer wing tile, W existed only in the top surface, while on the inner divertor tile W was embedded in the thick carbon deposition layer. Poloidal distribution in the same toroidal section as the tungsten tiles showed dense W deposition near the inner strike points, the dome top and outer wing of the dome. Carbon ions by puffing 13CH4 at the same toroidal position of the W-tiles were also deposited near the inner strike points. Toroidal distribution on the outer wing showed significant localization of W deposition near the W tile array. In addition, toroidal asymmetry of W deposition on the outer wing probably due to the plasma parallel flow was observed.

Characterization of carbon nanolayers flash evaporated on PET and PTFE

Carbon nanolayers were prepared by flash evaporation of carbon filaments onto polyethyleneterephthalate and polytetrafluoroethylene substrates. The chemical composition of the deposited layers was determined using Raman, XPS, RBS and ERDA. Also the concentration of free radicals in the deposited layer was determined by EPR method. The thickness of the deposited carbon layer as a function of the deposition distance was determined by a scratch technique and AFM. Surface morphology of the samples was examined by AFM and nanointendation was used to determine microhardness and elasticity modulus and to perform scratch tests. The thickness of the deposited carbon layer decreases with increasing distance between the substrate and the filament. In addition to the dominant amorphous carbon fraction (a-C), various oxidized structures and hydrogen admixture in the deposited material were observed. The deposition of carbon leads to a significant decline of surface electrical resistance in comparison with pristine polymer, the change being a function of the deposition distance. The deposited carbon layer has semicrystalline character and it exhibits higher microhardness and elastic modulus than pristine polymer.

Retention and depth profile of hydrogen isotopes in gaps of the first wall in JT-60U

Hydrogen (H) and deuterium (D) retention in gap side surfaces of the first wall tiles exposed to DD and HH discharges in JT-60U were examined. On the sides of outboard tile, the H and D retention and the deposited amount of boron increased with the gap width. On the sides of inboard tile, thick carbon deposition layer (∼10 μm) was observed. The deposited layers retained rather large amount of hydrogen with ∼0.15 in (H + D)/C atomic ratio compared to that found in the deposited layers on the divertor tiles, most likely due to the lower temperature. The H + D retention on the sides analyzed here was comparable to that of the plasma facing surface.

Effects of tungsten surface conditions on carbon deposition

New results are shown on carbon deposition and mixed layer formation on tungsten surfaces in TEXTOR test limiter experiments by varying surface conditions such as surface roughness ( R a: 10 nm–1 μm), temperature (300–900 °C), and initial surface carbon concentration (0–60%). It is found that surface roughness significantly affected C deposition for both W and graphite substrates such as increase in the C deposition and extension of the C deposition area. Not only the surface roughness parameter R a but also detailed surface morphology closely relate to C deposition on tungsten. Carbon deposition hardly occurred at least above ∼520 °C on tungsten under TEXTOR edge plasma conditions. Carbon behavior on tungsten at 770–930 °C depends on the incident carbon ion energy. Although tungsten and carbon mixing layers affected C deposition, their effect is less than the roughness effect.

Characterization of EUV induced carbon films using laser-generated surface acoustic waves

The deposition of carbon layers on the surfaces of optics exposed to extreme ultraviolet (EUV) radiation has been observed in EUV lithography. It has become of critical importance to detect the presence of the carbon layer in the order of nanometer thickness due to carbon's extremely strong absorption of EUV radiation. Furthermore, the development of efficient cleaning strategies requires that the nature of these carbon layers is well understood. Here, we present experimental results on the detection and characterization of carbon layers, grown on Mo/Si EUV reflecting optics, by laser-generated surface acoustic waves (LG-SAW). It was found that SAW pulses with a frequency bandwidth of more than 220 MHz can be generated and detected for multilayer mirrors and LG-SAW is sensitive enough to detect EUV induced carbon layers less than 5 nm thick. It was inferred from the low Young's modulus (< 100 GPa) that the carbon layer induced by EUV illumination in these vacuum conditions is mechanically soft and polymeric in nature with a high percentage of hydrogen.

Amorphous carbon coated stainless separator for PEFCs

An SUS316L stainless steel separator was coated with amorphous carbon by using an electron cyclotron resonance (ECR) plasma sputtering technique, and used in a polymer electrolyte fuel cell (PEFC). Characteristics of this carbon film were investigated with Raman spectroscopy and XPS. Quantitative depth profiles and chemical depth profiles of the deposited carbon layer were measured with GD-OES and XPS, respectively. The contact resistivity between a carbon paper and the carbon coated SUS316L steel was also measured. The performance of PEFC single cells assembled with carbon coated SUS316L separators, uncoated SUS316L separators, and conventional carbon separators were compared. The results revealed that an assembled PEFC having carbon coated SUS316L separators provided better performance than one having uncoated SUS316L, and the PEFC showed comparable performance to one having conventional carbon separators.

Laser ablation for analysis of nanoscale layers

Deposition of carbon layer, tungsten and carbon migration, as well as retention, co-deposition and diffusion of hydrogen isotopes are the major concerns in fusion devices. We propose laser ablation spectroscopy as an effective method of rapid qualitative and quantitative surface mapping. An average growth of the deposited carbon layer in divertor region of a tokamak is about 0.2 nm/s. Depending on the number of discharges, the thickness of a layer can reach 200–400 nm. The information about the layer must be gained within this range of thickness. Obtained results show that proposed method can be used for analysis of layers in the range of thickness of several hundreds of nanometres.

Deuterium inventory in plasma facing materials by means of NRA: A microbeam probe approach

Particle retention in tokamak walls is a key issue for long time discharges in future thermonuclear fusion reactors. Plasma wall interactions drive the fuel retention through two major mechanisms: co-deposition with carbon produced by wall erosion and particle retention in wall materials. In this study, we report results obtained from the tokamak Tore Supra, from which two types of samples were analyzed by means of micro-NRA: (i) small pieces of deposited carbon layers were collected after cumulative discharges and deuterium contents were measured; (ii) carbon fiber composite (CFC) samples, immersed in the plasma during an experimental campaign were also analyzed. 3D deuterium elemental mapping demonstrated that deuterium can be trapped at depths much higher than usual implantation depths and deep local retention sites have been evidenced and localized.This study demonstrates that μNRA can be used for assessment of deuterium post-mortem inventory in tokamaks, both by measuring uniformly distributed deuterium in small fragments of deposited carbon layers and by locally describing deuterium 2D and 3D distributions in complex structures.

Erosion Behavior of Carbon Deposition Layers Formed by Hydrogen Plasma Sputtering

The erosion of carbon deposition layers by oxygen exposure and the desorpstion of hydrogen retained in the layers were investigated experimentally. Carbon deposition layers were formed by a sputtering method using hydrogen RF plasma. The layers were exposed to an argon gas with oxygen of 1013 Pa in the temperature range of 200-400 °C. The erosion reaction progressed quickly within 10 minutes and then decelerated rapidly. The measurement of the outlet concentration revealed that most of the layer was eroded not as carbon monoxide and carbon dioxide but as soot. Additionally, it was estimated that the soot was released from the carbon deposition layer with a large amount of hydrogen.

Transition from tungsten erosion to carbon layer deposition with simultaneous bombardment of tungsten by helium and carbon

Simultaneous bombardment of tungsten layers with helium and carbon ions leads to both erosion of tungsten and implantation of carbon. The underlying processes have been investigated numerically and experimentally as a function of the carbon fraction in the incident ion flux for ion energies in the kilo electron volt range. Tungsten layers were deposited on polished single-crystal silicon substrate by magnetron sputter deposition to eliminate the influence of surface roughness on the experimental results. The fluence-dependent dynamics of the surface composition was measured in situ by ion beam analysis. The given projectile-target system is subject only to kinematic processes, and is therefore particularly suitable for benchmarking of purely kinematic simulations based on the binary-collision approximation, as implemented in the TRIDYN code. TRIDYN calculations match the experimental results very well, which demonstrates the validity of the kinematic description. In particular, the simulations allow us to predict the change of surface composition by bombardment with gaseous and nonvolatile ions, as well as the transition point from W erosion to C deposition as function of the carbon fraction in the incident ion flux.

Super-Hard Carbon Layers Produced on the Al2O3/Al2O3+x%SiC (whiskers) Ceramic Cutting Edges

The aim of the present study was to examine how the cutting properties of tool blades are affected by super-hard ceramic (carbon) coatings produced by the RF PECVD method. The cutting plates were made of the gradient-type Al2O3/Al2O3 + x%SiCwhiskers composites. The highest density, the greatest bending strength and the highest stress intensity factor were obtained with the layered Al2O3/Al2O3 + x%SiCwhiskers composite. The phase composition of the coatings was examined and the deposited carbon layers were identified to be nanocrystalline diamond (NCD) contaminated with super-finegrained graphite. The thickness, roughness, adhesion to the substrate, friction coefficient and hardness of the coatings were examined. The results evidently show that, when tested in cutting hard aluminium alloys, the carbon coatings deposited on the Al2O3/Al2O3 + x%SiCwhiskers cutting plates by RF PECVD have advantageous cutting properties. The service life of the coated plates compared to that of uncoated plates increased by 65% with the NCD coatings.

Biomechanical and material characteristics of plate stabilisers

The aim of the work was determination of biomechanical and material characteristics of plate stabilisers intended for elastic osteosynthesis. Several types of plate stabilisers applied in the most common fractures were analysed. The stabilisers were made of stainless steel. The implant's surface was modified by means of various methods. Furthermore, resistance to the most common types of corrosion was also tested. In order to determine the biomechanical characteristics of the analysed plate stabilisers, both the finite element method and the experimental verification of the obtained results were applied. The next stage of the work was the surface modification realised by means of grinding, electropolishing, passivation and carbon layer deposition. Then, the modified surfaces were tested for various types of corrosion, occurring in the human body environment. The obtained results indicate that both the applied methods of fixation and the suggested surface modifications can be applied in clinical practice. [Received 10 November 2005, Accepted 27 January 2006]