Plasmachemische Gasphasenabscheidung und Plasmaätzen bei Atmosphärendruck

Plasma enhanced Chemical Vapour Deposition and plasma etching at atmospheric pressure Plasma processes are applied for a variety of surface modifications. Examples are, e.g. coatings to achieve an improved corrosion and scratch protection, or surface cleaning and texturising. Since these processes, however, usually take place in vacuum, they are unfortunately not applicable for large area industrial use. Plasma enhanced CVD processes at atmospheric pressure enable the deposition of functional coatings on components and semi‐finished parts with in a continuous air‐to‐air process without the use of expensive vacuum systems. By their integration into in‐line production processes the substrate handling and the coating costs are definitely reduced. A thermal plasma source, basing on a linearly extended DC arc discharge at atmospheric pressure, has been tested for the deposition of silicon nitride at substrate temperature of less than 300° in a continuous PECVD process. Furthermore this source has been tested for plasma‐chemical etching and texturising of silicon as well.     

Abscheidung superharter Kohlenstoffschichten mittels Laser‐Arco® auf dem Weg vom Labor in die industrielle Serienfertigung

Superhard carbon film deposition by means of Laser‐Arco® on the way from the Laboratory into the industrial series coating Diamond‐like carbon films (DLC) are more and more applied as wear protection coatings for components and tools due to their unique combination of high hardness, low friction and sticking tendency to metallic counter bodies. Up to now applied DLC films are hydrogen containing (a‐C:H) or metal carbon films (Me‐C:H) deposited by a plasma assisted CVD process from carbon‐hydrogen gas mixtures. Their wide industrial effort results from that the can be deposited with slowly modified coating machines for classical hard coating (e.g. TiN or CrN). A new generation DLC films are the hydrogen‐free ta‐C films (ta‐C = tetrahedral bounded amorphous carbon) with a between two and three‐times higher hardness and with a resulting higher wear resistance under extreme condition than classical DLC films. They have excellent emergency running properties at lubrication break down. Their industrial application is more difficult due to that they cannot deposited with modified coating machines for classical hard and DLC coating and a new technology with corresponding equipment was not available up to now. The laser controlled, pulsed arc deposition technology (Laser‐Arco®) of the Fraunhofer IWS Dresden has this potential. In kind of a Laser‐Arc‐Module‐source the ta‐C film deposition can be integrated in every industrial used deposition machine.     

Transparente und leitfähige Veredelung von Kunststoffoberflächen

Deposition Techniques for Transparent Conducting Thin‐Films on Glass and Polymer Substrates We report on thin films deposited at atmospheric pressures on glass and polymer substrates with various techniques. The introduced thin‐film materials show intrinsic properties being suitable for different applications while maintaining the principle properties of the substrates themselves (e. g. shape. rigidity/flexibility, transparency). With the main focus on optical and electronic applications the properties of the deposited films can be adjusted by the choice of coating material (e. g. metal oxide, CNT), the film's shape (compact, particulate) and the deposition process itself. We compare deposition and properties of different TCO‐materials with CNT‐based thin film techniques and demonstrate approaches for the integration of these processes in production lines.     

CVD ZrO2‐Beschichtung von Fasern bei Normaldruck

Atmospheric pressure CVD of ZrO₂ on fibers Two different Chemical vapor deposition processes on fiberbundles (number of fibers a few thousand, diameter of the single fiber ≈10 µm) with zirconium dioxide at atmospheric pressure have been developed (AiF project 12783N): 1) ZrO₂ thin films on SiTiC fibers were grown by flame‐CVD using zirconium dipivaloylmethanate or acetylacetonate as precursors. The total deposition rate of 3·10^–5 mol·m^–2·s^–1 was achieved in a 4 cm long deposition zone. 2) In a new atmospheric pressure CVD process the deposition took place via hydrolysis of zirconium dipyvaloylmethanate in water vapor. The total deposition rate of 7·10^–6 mol·m^–2·s^–1 has been achieved in a 60 cm long pilot setup. This value allows to deposit continuously a 10 nm thick ZrO₂ films on fibers moving with velocity of 30 m/h. The deposition rate demonstrated in this work is the highest achieved so far for ZrO₂ CVD at atmospheric pressure.     

Chemical vapour deposition of coatings

Chemical Vapour Deposition (CVD) of films and coatings involve the chemical reactions of gaseous reactants on or near the vicinity of a heated substrate surface. This atomistic deposition method can provide highly pure materials with structural control at atomic or nanometer scale level. Moreover, it can produce single layer, multilayer, composite, nanostructured, and functionally graded coating materials with well controlled dimension and unique structure at low processing temperatures. Furthermore, the unique feature of CVD over other deposition techniques such as the non-line-of-sight-deposition capability has allowed the coating of complex shape engineering components and the fabrication of nano-devices, carbon-carbon (C-C) composites, ceramic matrix composite (CMCs), free standing shape components. The versatility of CVD had led to rapid growth and it has become one of the main processing methods for the deposition of thin films and coatings for a wide range of applications, including semiconductors (e.g. Si, Ge, Si_1-xGe_x, III-V, II-VI) for microelectronics, optoelectronics, energy conversion devices; dielectrics (e.g. SiO₂, AlN, Si₃N₄) for microelectronics; refractory ceramic materials (e.g. SiC, TiN, TiB₂, Al₂O₃, BN, MoSi₂, ZrO₂) used for hard coatings, protection against corrosion, oxidation or as diffusion barriers; metallic films (e.g. W, Mo, Al, Au, Cu, Pt) for microelectronics and for protective coatings; fibre production (e.g. B and SiC monofilament fibres) and fibre coating. This contribution aims to provide a brief overview of CVD of films and coatings. The fundamental aspects of CVD including process principle, deposition mechanism, reaction chemistry, thermodynamics, kinetics and transport phenomena will be presented. In addition, the practical aspects of CVD such as the CVD system and apparatus used, CVD process parameters, process control techniques, range of films synthesized, characterisation and co-relationships of structures and properties will be presented. The advantages and limitations of CVD will be discussed, and its applications will be briefly reviewed. The article will also review the development of CVD technologies based on different heating methods, and the type of precursor used which has led to different variants of CVD methods including thermally activated CVD, plasma enhanced CVD, photo-assisted CVD, atomic layer epitaxy process, metalorganic assisted CVD. There are also variants such as fluidised-bed CVD developed for coating powders; electrochemical vapour deposition for depositing dense films onto porous substrates; chemical vapour infiltration for the fabrication of C-C composites and CMCs through the deposition and densification of ceramic layers onto porous fibre preforms. The emerging cost-effective CVD-based techniques such as electrostatic-aerosol assisted CVD and flame assisted CVD will be highlighted. The scientific and technological significance of these different variants of CVD will be discussed and compared with other vapour processing techniques such as Physical Vapour Deposition.     

Hierarchical composites of carbon nanotubes on carbon fiber: Influence of growth condition on fiber tensile properties

Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) provides a means to tailor the thermal, electrical and mechanical properties of the fiber–resin interface of a composite. However, many CNT growth processes require pretreatment of the fiber, deposition of an intermediate layer, or harsh growth conditions which can degrade tensile properties and limit the conduction between the fiber and the nanotubes. In this study, high density multi-wall carbon nanotubes were grown directly on two different polyacrylonitrile (PAN)-based carbon fibers (T650 and IM-7) using thermal Chemical Vapor Deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of the resultant hybrid fibers were shown to depend on the carbon fiber used, the presence of a sizing (coating), the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. The CNT density and alignment morphology was varied with growth temperature and precursor flow rate. Overall, it was concluded that a hybrid fiber with a well-adhered array of dense MWCNTs could be grown on the unsized T650 fiber with no significant degradation in tensile properties.     

Thin coatings on carbon fibers as diffusion barriers and wetting agents in Al composites

This paper describes the preparation of CVD coatings (Ta, TiC, TiN, TiNC and SiC) on carbon fibers and the effect of the deposition parameters on the mechanical properties of the fibers. Ta does not influence the fiber strength, whereas for the other coating materials the deposition conditions must be optimized in order to retain the original fiber properties.In view of the application of such coated carbon fibers in composites, their wetting behavior with liquid aluminum as well as the behavior of the coatings as diffusion barriers were studied. The coatings are instantly wetted only at temperatures so high that a partial penetration of aluminum through the thin coatings and hence a reaction at the surface of the carbon fiber leading to the formation of aluminum carbide become inevitable. The fiber strength of high performance fibers is then considerably impaired although low strength fibers are hardly affected.Wetting by liquid aluminum below 800°C can be achieved by using additional thin nickel layers. In this way the infiltration of coated carbon fiber bundles can be realized and theoretical fiber strength yields in accordance with the rule of mixtures can be obtained. This improved wetting behavior was found not to depend on the type of coating.The barrier effect of the coatings allows heat treatments at up to 600°C for short times with high fiber strength yields. Heat treatments of the order of 100 h, however, gradually decrease the composite strength. In order to retain high fiber strength during long heat treatments at high temperatures, a minimum coating thickness of some microns is needed. The preparation of such thicker coatings is discussed in detail. With such a procedure, one can obtain reinforcing elements comparable with commercially available boron or silicon carbide monofilaments.     

Effect of carbon nanotubes on the interfacial shear strength of T650 carbon fiber in an epoxy matrix

The interfacial shear strength of carbon nanotube coated carbon fibers in epoxy was studied using the single-fiber composite fragmentation test. The carbon fibers were coated with carbon nanotubes (CNT) on the fiber surface using thermal chemical vapor deposition (CVD). The CVD process was adjusted to produce two CNT morphologies for the study: radially aligned and randomly oriented. The purpose of the CNT coating was to potentially produce a multifunctional structural composite. Results of the single-fiber fragmentation tests indicate an improvement in interfacial shear strength with the addition of a nanotube coating. This improvement can most likely be attributed to an increase in the interphase yield strength as well as an improvement in interfacial adhesion due to the presence of the nanotubes.     

Simulation of SiC Deposition in a Fiber Coating CVD Reactor

A simulation was carried out to study the Chemical Vapor Deposition (CVD) of SiC on a thin cylindrical substrate in a hot wall reactor. The results of this simulation are expected to apply to the process of fiber coating for interface control in fiber reinforced composites. The reactant in this study is methyltrichlorosilane (CH₃SiCl₃) in a background of hydrogen. The simulation was carried out using a commercial code (FLUENT). The simulation results compared well with experimental data from a hot wall reactor. It was determined that the temperature profiles tend to be uniform in the radial direction, and the deposition process is dominated by reaction kinetics.     

Structure-property relations for silicon nitride matrix composites reinforced with pyrolytic carbon pre-coated Hi-Nicalon fibers

Si₃N₄ matrix composites reinforced with pyrolytic carbon pre-coated Hi-Nicalon (SiC) fibers, were studied using tensile testing and transmission electron microscopy. Three types of samples were evaluated all with a nominal coating thickness of 200 nm. The composites were densified by hot pressing at 1550 °C (type I and II) and at 1600 °C (type III). The fibers were coated with pyrolytic carbon via CVD with identical (sample I) and opposite (samples II and III) directions of the gas flow and of the fiber movement through the reactor. Tensile testing indicated for the three sample types respectively: brittle behaviour with huge pull out of the fibers, pseudo-plastic behaviour and brittle behaviour with little pull out. TEM indicated for the three sample types debonding typically at the fiber/coating interface, at the coating/matrix interface and in the coating, respectively. The relation between processing, structure, particularly of the coating and its interfaces with the matrix and the fibers and mechanical properties is addressed.     

Highly Adsorptive,MOF‐Functionalized Nonwoven Fiber Mats for Hazardous Gas Capture Enabled by Atomic Layer Deposition

While metal‐organic frameworks (MOFs) show great potential for gas adsorption and storage, their powder form limits deployment opportunities. Integration of MOFs on polymeric fibrous scaffolds will enable new applications in gas adsorption, membrane separation, catalysis, and toxic gas sensing. Here, we demonstrate a new synthesis route for growing MOFs on fibrous materials that achieves high MOF loadings, large surface areas and high adsorptive capacities. We find that a nanoscale coating of Al₂O₃ formed by atomic layer deposition (ALD) on the surface of nonwoven fiber mats facilitates nucleation of MOFs on the fibers throughout the mat. Functionality of MOFs is fully maintained after integration, and MOF crystals are well attached to the fibers. Breakthrough tests for HKUST‐1 MOFs [Cu₃(BTC)₂] on ALD‐coated polypropylene fibers reveal NH₃ dynamic loadings up to 5.93 ± 0.20 mol/kg_(MOF+fiber). Most importantly, this synthetic approach is generally applicable to a wide range of polymer fibers (e.g., PP, PET, cotton) and MOFs (e.g., HKUST‐1, MOF‐74, and UiO‐66).     

Direct CVD Graphene Growth on Semiconductors and Dielectrics for Transfer‐Free Device Fabrication

Graphene is the most broadly discussed and studied two‐dimensional material because of its preeminent physical, mechanical, optical, and thermal properties. Until now, metal‐catalyzed chemical vapor deposition (CVD) has been widely employed for the scalable production of high‐quality graphene. However, in order to incorporate the graphene into electronic devices, a transfer process from metal substrates to targeted substrates is inevitable. This process usually results in contamination, wrinkling, and breakage of graphene samples ‐ undesirable in graphene‐based technology and not compatible with industrial production. Therefore, direct graphene growth on desired semiconductor and dielectric substrates is considered as an effective alternative. Over the past years, there have been intensive investigations to realize direct graphene growth using CVD methods without the catalytic role of metals. Owing to the low catalytic activity of non‐metal substrates for carbon precursor decomposition and graphene growth, several strategies have been designed to facilitate and engineer graphene fabrication on semiconductors and insulators. Here, those developed strategies for direct CVD graphene growth on semiconductors and dielectrics for transfer‐free fabrication of electronic devices are reviewed. By employing these methods, various graphene‐related structures can be directly prepared on desired substrates and exhibit excellent performance, providing versatile routes for varied graphene‐based materials fabrication.     

Towards the large-scale synthesis of carbon nanotubes in fluidised beds

Carbon nanotubes (CNTs) are a form of crystalline carbon with extraordinary properties, making them valuable in a broad range of applications. However, the lack of suitable large-scale manufacturing techniques, which we define as being of the order 10000 tonnes per annum, continues to inhibit their widespread use. Of the three established synthesis methods for CNTs: (i) chemical vapour deposition (CVD), (ii) laser ablation, and (iii) arc discharge, CVD techniques show the greatest promise for economically viable, large-scale synthesis. In particular, the fluidised bed CVD (FBCVD) technique, where the CVD reaction occurs within a fluidised bed of catalyst particles, has the potential to produce high quality CNTs, inexpensively, in large quantities. In this work we report on the development of a catalytic chemical vapour deposition process, using batch fluidised bed reactors, for the synthesis of straight and spiral carbon nanotubes at pilot scale (up to 1 kg/hr). We believe this to be the first report of the synthesis of spiral carbon nanotubes using fluidised bed CCVD. Iron, nickel and cobalt transition metal catalysts supported on non-porous alumina substrates were fluidised in a mixture of nitrogen, hydrogen and ethylene at temperatures between 550 and 800 degrees C for between 15 and 90 minutes. Nanotube yield was inferred from thermogravimetric analysis and the quality and size of the CNTs from transmission electron microscopy. Conflicting information in the literature about the influence of synthesis parameters on CNT properties suggests that further investigation is necessary to understand the synthesis process at a fundamental level, i.e., independent of reactor design and operation.     

EVALUATION OF SIC MATRIX COMPOSITES FOR HIGH TEMPERATURE APPLICATIONS

SiC matrix composite components have been fabricated by infiltrating and overcoating fiber preforms of graphite, alumina, and SiC via chemical vapor deposition (CVD). The degree of CVD densification could be controlled to yield vacuum tight components as well as porous open mesh structures where only the fiber was coated. These components have been fabricated in a wide variety of shapes including baskets, tubes and corrugated panels. The CVD process has been successfully scaled up to produce panels 80 cm by 80 cm. The morphology, chemistry, and geometry of the fiber was found to have a significant effect on the deposition process. Thus, process conditions had to be modified based on the fiber being infiltrated. These components were subjected to 1400 C temperature treatments including operation in gas-fired furnaces. After 2000 hours of testing in a gas-fired furnace at 1300 C, the SiC composite tubes have remained intact and un cracked. This suggests that the monolithic SiC coating is the controlling material and not the fibers. Hence, in light-load applications these structures still have useful lifetimes.     

Elektrospray‐Ionisation (ESI)

EElectrospray‐ionization (ESI) – pinhole‐free electrophoretic deposition of ultra thin polymer layers Electrospray ionization (ESI) of polymer solutions is used in mass spectroscopy to analyze the molar mass of macromolecules. The singularized polymer molecules are transferred into the mass spectrometer after separating through a special mechanism under high voltage and normal pressure conditions. This process can be adapted for plane deposition of single polymer molecules. Structure, composition and molar mass distribution of polymers are retained. Layers of polar or ionic polymers can be deposited in a thickness of monolayers up to hundreds of nanometers. It is interesting to mention that the ESI‐process belongs to the electrophoretic techniques. Therefore, deposition of pinhole‐free layers on electrical conductive substrates is not only possible on the nozzle facing side of the substrate but although on the back side. This behavior was used to enwrap closely packed carbon fiber bundles with adhesive polymer layers.     

Turbomolecular pumps designed for plasma processes industry. Turbomolekularpumpen speziell für die Plasmaindustrie

Plasma processes are a very popular method to produce high‐grade quality thin films on many different substrates. There are a large variety of different coating systems. Such systems go from small‐scale machines (i.e. Optical coating systems for ophthalmic lenses and filters), through mid‐size machines (such as systems for deposition on flexible substrates used in the food, electronics and packaging industry or systems used for producing optical and magnetic data storage media), up to large‐area systems (i.e. used for architectural glass coating or in the flat panel display industry). Even if all of these systems look very different, there are few common specific points that characterize most of these applications. The plasma is normally based on Argon, Oxygen, Nitrogen (and more recently Krypton) mixtures in the mid 10^–3 mbar range. The base pressure is generally over the mid 10^–7 mbar range. The deposition rate is very high and so the demand for gas throughput is high as well. (i.e. a glass coater can ionize more than 2000 sccm of Argon per cathode segment). There is a high probability of debris and particle generation within the process; roughing and venting cycles are fast and sometimes uncontrolled (they can be described as air‐in rushes in some cases). Uptime and reliability are not an option, but a must in industrial production environments. It is therefore difficult to believe that turbo molecular pumps originally designed to reach the 10^–10 mbar range with a high number of pumping stages and very tight clearances, are capable to work reliability in this demanding environment. We are keener to think that if we want a reliable and performing pumping solution the design of the turbomolecular pump must be specific and dedicated to the application. Ideally this development process is done side by side with the ultimate equipment users, matching at best process requirements and turbomolecular pump design know‐how. As Varian Vacuum Technologies, we have followed that process and this article is sharing the results.     

Abscheidung optisch,elektrisch und akustisch wirksamer Schichten mit dem Doppel‐Ring‐Magnetron

Numerous applications in optics, electronics and sensor technology require thin dielectric films. Conventionally they are deposited by evaporation, activated evaporation, rf‐sputtering or CVD‐techniques. This paper describes the deposition of such films using reactive Pulse Magnetron Sputtering. This technology not only enables a tenfold deposition rate compared to the conventional techniques but also offers new possibilities for influencing film growth. For example it is possible to alter film composition during deposition and hence to deposit complete optical systems without interruption of the plasma process. Furthermore the energetic bombardment of the growing film can be controlled in a wide range by the pulse mode and the pulse parameters. This can be used to either deposit very dense films by strong energetic bombardment or to deposit films at low thermal load onto temperature sensitive substrates. Examples of film deposition for laser optics, electrical insulation applications and surface acoustic wave devices show how these new technological possibilities advantageously can be used for creating innovative layer systems. Film deposition is carried out in stationary mode using a Double Ring Magnetron. This type of magnetron ensures film thickness uniformity better than ± 1 % on 8” substrates by the superposition of the thickness distributions of two concentric discharges.     

Chemical vapor deposition of titanium nitride on carbon fibres as a protective layer in metal matrix composites

The significance of carbon fibres for reinforcing metals has increased in the last years, because of their excellent mechanical properties. However, to avoid the weakening reaction during MMC fabrication between the fibre and the liquid metal, a protective coating has to be applied. Continuous carbon fibre roving with 6000 filaments were coated with TiN by thermal induced chemical vapour deposition (CVD) using a gas mixture of TiCl₄, N₂ and H₂ as a precursor. The deposition process in the reactor was simulated by a modified Phoenics-CVD software program using a 2D-axisymmetric model. Carbon fibres reinforced magnesium matrix composites are fabricated by a pressure infiltration casting process. The mechanical properties of the MMCs can be used to demonstrate the efficacy of the coated fibre approach. The rule of mixture is realized to 98% for the coated fibre, and only 48% for the uncoated system. The infiltration pressure during the processing of composites was lowered from 10 to 1 MPa for the TiN coated system.     

Air-assisted growth of ultra-long carbon nanotube bundles

We report an air-assisted chemical vapor deposition (CVD) method for the synthesis of super-long carbon nanotube (CNT) bundles. By mixing a small amount of air in the vapor phase catalyst CVD process, the catalyst lifetime can be dramatically increased, and extremely long dense and aligned CNT bundles up to 1.5?cm can be achieved. Electron microscopy characterization shows that the injection of air does not damage the CNT structures. Further, we have estimated that individual ultra-long CNTs can carry moderate current densities ～10(5)?A?cm(-2), indicating their possible use in nanoelectronic devices.