Hochleistungsplasmen zur Synthese diamantähnlicher Kohlenstoffschichten

HPPMS high‐performance plasmas for the deposition of diamond‐like carbon coatings Diamond‐like carbon (DLC) coatings Diamond‐like carbon (DLC) coatings can be used in many different applications, due to their adjustable properties like hardness as wear reduction. Regarding to the synthesis of these coatings, research is upon the High Power Pulsed/Impulse Magnetron Sputtering (HPPMS/HiPIMS), which in contrast to conventional processes like the Pulsed Laser Deposition (PLD) provides smooth coatings and therefore less postprocessing. Previous to the coating deposition in‐situ plasma analysis can be utilized to identify the process parameters. The aim relevantof this work was to identify process parameters which enable to generate a high amount and energy of carbon ions, which are required to synthesize hard DLC coatings. Regarding to the carbon ionization the promising process parameters mixture and pressure of the process gas as well as the HPPMS pulse parameters were varied. Finally, process parameters for the DLC coating deposition could be derived from these investigations.     

Analysis of Carbon Materials by X‐ray Photoelectron Spectroscopy and X‐ray Absorption Spectroscopy

Since hard coating such as ta:C films are of growing interest for protecting surfaces of industrial machines and high capacity tools against wear and friction or for biomedical applications, more information about the structure‐to‐property relation is required. Therefore, core level X‐ray photoelectron sprectroscopy and X‐ray absorption spectroscopy and spectromicroscopy are used to derive chemical information about selected carbon species.     

Diamantartige Kohlenstoffschichten steigern die Effizienz

Diamond‐like carbon thin films enhance efficiency — laser arc deposition of ta‐C Rising prices for fossil fuels as well as the increasing effects of the climate change due to the emission of greenhouse gases reveal the necessity of saving energy. Low friction coatings have an enormous potential in saving energy. Carbon based coatings — named as DLC coatings — are especially well suited for low friction coatings. In particular hydrogen‐free tetrahedral amorphous carbon (ta‐C) coatings are of great interest due to their extraordinary low wear properties. In addition they show excellent low friction properties and especially in combination with specific lubricants the so‐called super low friction effect. For the deposition of ta‐C coatings PVD methods have to be applied instead of CVD methods as it is the case for conventional DLC coatings. We have developed a deposition method which is based on a pulsed arc steered by a laser (Laser‐Arc). This allows us to use large cathodes resulting in a high long‐term stability. Furthermore, the carbon plasma source can be combined with a filtering unit removing almost all droplets and particles, which usually are characteristic for an arc process. The resulting Laser‐Arc source allows for the deposition of smooth and virtually defect‐free ta‐C coatings with a competitive deposition rate.     

Superharter Kohlenstoff abgeschieden mit gepulstem Hochstrombogen als Nanoschutzschicht f�r Magnetspeicherplatten

Superhard amorphous Carbon films (ta‐C) deposited by pulsed High‐Current Arc (HCA) possess a good perspective to be used as future ultrathin protective coatings for magnetic hard disks. The ta‐C coatings meet all demands concerning the mechanical, chemical and tribological properties required for corrosion and wear protective coatings with thicknesses of 2‐3nm. From the current point of view the deposition technique also qualifies for an industrial mass production. Consequently there is a very good prospect that in near future the High‐Current Arc technique will be the method of choice for Carbon deposition in industrial hard disk drive production.     

Flächeneinfluss bei der PACVD‐Beschichtung

Impact of the active surface on properties of DLC films in the PACVD coating chamber. In the automotive industry, economic and stable industrial processes to apply hard coatings for tribological applications are required. Hence detailed knowledge about the influence of coating parameters on the film characteristics is essential. the following paper deals with the process of plasma activated chemical vapor deposition with focus on the effect of the parameter “active area in the coating chamber“ on the properties of diamond‐like‐carbons (DLC). the coatings are deposited in an industrial coating chamber using reactive magnetron sputtering with a pulsed bias voltage (40 kHz) and at constant pressure. During the investigation of the influence of active area and current density on the mechanical and tribological properties of the DLC films, the expected correlation between active area and current density could be confirmed. By regulating the current density, consistent film properties could be achieved, independently of the active area in the chamber. Furthermore improved wear characteristics of the film – crucial for the endurance of heavily loaded automotive components – were achieved by adapting the load pattern of the chamber.     

Influence of hydrogen on the mechanical properties and microstructure of DLC films synthesized by r.f.-PECVD

This paper aims to investigate the influence of hydrogen on the variation of mechanical properties and microstructure of diamond-like carbon (DLC) films synthesized by radio frequency plasma chemical vapor deposition (r.f.-PECVD). The DLC films were deposited on a silicon substrate (p-type). The reactant gases employed in this paper are a mixture of acetylene and hydrogen. The ratio of hydrogen in the gas mixture was successively varied to clarify its influence on the roughness, thickness, microstructure, hardness, modulus, residual stress and wear depth for the DLC films. The results reveal that increasing the concentration of hydrogen decreases thickness and roughness. Meanwhile, increasing the hydrogen concentration causes the decrease of sp³ ratio, hardness as well as modulus. Finally, wear behavior is correlated to the surface morphology and hydrogen concentration for deposition with hydrogen-containing reactant gas.     

Structure, mechanical and tribological properties of diamond-like carbon films on aluminum alloy by arc ion plating

The low hardness and poor tribological performance of aluminum alloys restrict their engineering applications. However, protective hard films deposited on aluminum alloys are believed to be effective for overcoming their poor wear properties. In this paper, diamond-like carbon (DLC) films as hard protective film were deposited on 2024 aluminum alloy by arc ion plating. The dependence of the chemical state and microstructure of the films on substrate bias voltage was analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical and tribological properties of the DLC films deposited on aluminum alloy were investigated by nanoindentation and ball-on-disk tribotester, respectively. The results show that the deposited DLC films were very well-adhered to the aluminum alloy substrate, with no cracks or delamination being observed. A maximum sp³ content of about 37% was obtained at −100 V substrate bias, resulting in a hardness of 30 GPa and elastic modulus of 280 GPa. Thus, the surface hardness and wear resistance of 2024 aluminum alloy can be significantly improved by applying a protective DLC film coating. The DLC-coated aluminum alloy showed a stable and relatively low friction coefficient, as well as narrower and shallower wear tracks in comparison with the uncoated aluminum alloy.     

Großflächenbeschichtung mit superhartem Kohlenstoff. Large area deposition of superhard carbon films

During the nineties the Laser‐Arc technology for the deposition of superhard amorphous carbon films (Diamor®) has been developed at the Fraunhofer Institute for Material and Beam Technology. This technology has now been scaled up by a factor of 4 compared to existing devices and integrated in an industrial large‐volume vacuum arc coater. First results demonstrate the possibility of depositing well adherent Diamor® films with a thickness of more than 2 microns and a hardness above 4000 HV on larger parts and tools. This opens a wide field of industrial applications.     

Slip‐rolling resistance of ta‐C and a‐C coatings up to 3,000 MPa of maximum Hertzian contact pressure

The slip‐rolling resistances of hard and stiff thin films under high Hertzian contact pressures can be improved by optimizing the “coating/substrate systems”. It is known from former investigations that the so‐called “egg‐shell” effect is no general hindrance for high slip‐rolling resistance of thin hard coatings. The coating stability depends more on specific deposition process and coating/substrate interface design. In this article it is experimentally shown, that pure amorphous carbon thin films with hardness between 15 and 63 GPa can be slip‐rolling resistant several million load cycles under a maximum Hertzian contact pressures of up to 3.0 GPa. Whereas all coatings were stable up to 10 million load cycles in paraffin oil at room temperature, reduced coating lifetime was found in SAE 0W‐30 engine oil at 120°C. It was shown how the coating hardness and the initial coating surface roughness influence the running‐in process and coating lifetime. No clear correlation between coating hardness and coating lifetime could be observed, but friction coefficients seem to be reduced with higher coating hardness. Very low friction down to ?0.03 in unmodified engine oils was found for the hardest ta‐C film.     

Micro‐Raman Studies on DLC coatings

Raman scattering is an excellent tool to characterize nanocrystalline clusters and the structural arrangement of carbon atoms in carbon‐based materials. Diamond‐like carbon (DLC) films are used in many industrial applications due to their hardness, wear resistance and biological compatibility. The properties of DLC coatings depend on the carbon coordination and incorporation of other elements, influences onto their Raman spectra will be reviewed.     

Minderung von Reibung und Verschleiß von Bauteilen aus Aluminium mit diamantähnlichen Kohlenstoffschichten (DLC)

Reduction of friction and wear for parts made of aluminium by diamond-like carbon coatings Reduction of friction and wear of machine parts and tools is usually achieved by separating the participating surfaces. This is predominantly done by liquid lubricants. Solid lubricant coatings replace them where hydrodynamic lubrication is not possible or not active. Among the hard and friction reducing layers diamond-like carbon films (DLC) have distinguished themselves as the most interesting representatives. They are deposited on metallic and ceramic parts in a glow discharge of a hydrocarbon gas at temperatures between 150 and 200 °C. Those low deposition temperatures, their very low dry sliding friction coefficient of 0.05 to 0.1, and an elastic recovery of 90 % differentiate them from PVD coatings to a high degree. DLC can also be deposited on light metals with thicknesses of more than 30 μm. For closed films an outstanding protection against corrosion is established. Machining and forming of light metals can be done without cooling lubricants.     

The effects of plasma pre-treatment and post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of plasma pre-treatment and post-treatment on the DLC films were investigated. Experimental results show that the surface roughness of the substrate, ranging from 0.2 to 1.2 nm, created by the plasma pre-treatment, will affect the surface roughness of the DLC films deposited using methane as the carbon source. However, the film surface roughness (0.1-0.4 nm) is much smaller than that of the substrate. Raman analysis and hardness measurement by nanoindentation indicate that the structure and the hardness of the DLC films are relatively unchanged for the film surface roughness investigated. For the argon or hydrogen plasma post-treatment of the DLC films deposited using acetylene as the carbon source, it is found that surface roughness decreases with the post-treatment time. Although the hardness decreases after post-treatment, it remains relatively constant with increasing post-treatment time.     

Study of adhesion of carbon nitride thin films on medical alloy substrates

The adhesion improvement of biocompatible thin films on medical metal alloy substrates commonly used for joint replacement implants is studied. Diamond-like carbon (DLC) and carbon nitride (CN) thin films are, because of their unique properties such as high hardness, wear resistance and low friction coefficient, candidates for coating of medical implants. However, poor adhesion on substrates with high thermal expansion coefficient limits their application. We deposited CN films by pulsed DC discharge vacuum sputtering of graphite target on CoCrMo and Ti6Al4V substrates. Surface nitridation of the substrate, changing the deposition parameters and use of interlayer led to improved adhesion properties of the films. Argon and nitrogen gas flow, thickness of the film and frequency of the deposition pulses had significant influence on the adhesion to the substrate. Properties of deposited films were analyzed using Scanning Electron Microscopy, Raman spectroscopy and tribology tests.     

Diamond and diamond-like carbon films

Polycrystalline diamond films are grown from low pressure gas mixtures, the deposition techniques are Microwave Plasma Chemical Vapour Deposition and Hot filament Chemical Vapour Deposition, in both techniques the deposition temperature is close to 900°C. The film growth process is strongly dominated by the initial nucleation stage, after this stage, the film grows at a rate of one micron per hour. The carbon atoms in the diamond film are fully fourfold (sp³) co-ordinated and the film properties are close to those of single crystalline diamond: extremely hard, resistant and transparent from UV to IR.Diamond-like carbon (DLC) films are amorphous and contain a variable amount of hydrogen in their structure, the carbon atoms are partially threefold (sp²) co-ordinated. Films are obtained at temperatures below 250°C and deposited on almost any substrate. Film composition, structure and functional properties are strongly dependent on the level of ionic bombardment of the film during growth. DLC films are very hard, have a low friction coefficient and good wear resistance, are chemically inert and are transparent in the IR.     

Technisch‐wirtschaftlicher Review der Herstellung tetraedrisch‐amorpher Kohlenstoffschichten durch Lichtbogenverdampfen

Technical and economical review of the production of tetrahedral‐amorphous carbon films by vacuum arc evaporation Due to the high energy of the depositing species, vacuum arc evaporation is suited for the production of tetrahedral‐amorphous carbon coatings (ta‐C). As besides, the process allows for high deposition rates, it seems to be ideal for the deposition of ta‐C in industrial mass production. However, during the evaporation process inevitably macroparticles are formed, which also deposit on the parts to be coated, degrading the coating properties considerably. Therefore, measures are necessary in order to counter the formation and/or deposition of these particles. The following article intents to give an overview of possible measures and to subject them to a technical and economical evaluation in regard to their application in industrial mass production.     

Laser Processing of Advanced Bioceramics

In this article, laser processing of diamondlike carbon‐metal nanocomposite films, hydroxyapatite‐osteoblast composites, and Ormocer® microdevices for medical applications is described. Pulsed laser deposition has been used to process diamondlike carbon‐silver‐platinum nanocomposite films that provide hardness, wear resistance, corrosion resistance, and antimicrobial functionalities to cardiovascular, orthopaedic, biosensor, and MEMS devices. Laser direct writing has been used for fabricating integrated cell‐scaffold structures. Two photon induced polymerization has been used to create Ormocer® tissue engineering scaffolds and microneedles with unique geometries. Pulsed laser deposition, laser direct write, and two photon induced polymerization techniques may provide medical engineers with advanced biomaterials that possess unique structures and functionalities.     

Cover Picture: Laser Processing of Advanced Bioceramics (Adv. Eng. Mater. 12/2005)

In this article, laser processing of diamondlike carbon‐metal nanocomposite films, hydroxyapatite‐osteoblast composites, and Ormocer® microdevices for medical applications is described. Pulsed laser deposition has been used to process diamondlike carbon‐silver‐platinum nanocomposite films that provide hardness, wear resistance, corrosion resistance, and antimicrobial functionalities to cardiovascular, orthopaedic, biosensor, and MEMS devices. Laser direct writing has been used for fabricating integrated cell‐scaffold structures. Two photon induced polymerization has been used to create Ormocer® tissue engineering scaffolds and microneedles with unique geometries. Pulsed laser deposition, laser direct write, and two photon induced polymerization techniques may provide medical engineers with advanced biomaterials that possess unique structures and functionalities.     

CVD of hard DLC films in a radio frequency inductively coupled plasma source

Chemical vapor deposition (CVD) of hard diamond-like carbon (DLC) films on silicon (100) substrates from methane was successfully carried out using a radio frequency (r.f.) inductively coupled plasma source (ICPS). Different deposition parameters such as bias voltage, r.f. power, gas flow and pressure were involved. The structures of the films were characterized by Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The hardness of the DLC films was measured by a Knoop microhardness tester. The surface morphology of the films was characterized by atomic force microscope (AFM) and the surface roughness (R_a) was derived from the AFM data. The films are smooth with roughness less than 1.007 nm. Raman spectra shows that the films have typical diamond-like characteristics with a D line peak at 1331 cm⁻¹ and a G line peak at 1544 cm⁻¹, and the low intensity ratio of I_D/I_G indicate that the DLC films have a high ratio of sp³ to sp² bonding, which is also in accordance with the results of FTIR spectra. The films hardness can reach approximately 42 GPa at a comparatively low substrate bias voltage, which is much greater than that of DLC films deposited in a conventional r.f. capacitively coupled parallel-plate system. It is suggested that the high plasma density and the suitable deposition environment (such as the amount and ratio of hydrocarbon radicals to atomic or ionic hydrogen) obtained in the ICPS are important for depositing hard and high quality DLC films.     

Hochbelastbare kohlenstoffbasierte Mehrschichtsysteme für die Umformtechnik

Carbon based multilayer systems for highly loaded forming tools Amorphous hydrogenated carbon (metal‐free a‐C:H and metal‐containing a‐C:H:Me) films respond very sensitively to local overloads. For example during forming tool operations, hard abrasive particles and locally high stresses on the coating surface can cause crack initiation and early coating failure. Compared to the high hardness, wear resistance and excellent friction properties, in many cases the adhesion of a‐C:H films is relatively insufficient. Adhesion and overload resistance of a‐C:H and a‐C:H:Me, prepared by reactive sputtering, can be influenced in a wide range by different interlayer systems. In the present report the wear mechanism of amorphous carbon coatings and the influence of different metallic, metal nitride and metal carbide interlayers on the growth structure, the adhesion and the load resistance will be reported. Two well adapted multi‐coating systems, successfully tested for highly loaded tools and components, will be presented.     

Optical properties of hydrogenated hard carbon thin films

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass, silicon and germanium substrates. The films are transparent in the IR and are extremely hard (Mohs' hardness of about 8). The a-C:H coatings were prepared in an r.f.-excited discharge sustained by various hydrocarbon gases.The thickness, density, refractive index (at 0.3 μm and 2–10 μm) and relative hydrogen content were determined. Variations in the IR refractive index and the relative hydrogen content could be correlated with the deposition conditions. With a refractive index of approximately 2 a-C:H is an ideal antireflection coating for germanium (n = 4).Laser calorimetric measurements of optical absorption at 10.6 μm give a loss as low as 3% for a coating 1.3 μm thick on germanium (λ/4 for n = 2 at 10.6 μm).