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This overview article on diamond-like carbon (DLC) coatings in medical applications covers the interaction of cells and tissue with DLC and alloyed DLC to generate desired cell reactions as well as the release of toxic elements. The promising in vitro results of DLC to prevent thrombus formation in vascular applications are summarized and the problems of transferring these results to in vivo applications are described. Since DLC shows extremely low wear in technical applications, a desired implementation is also to build wear particle free, articulating joint replacements by coating the bearing surfaces. Several in vivo studies using DLC coatings on articulating joints resulted in a failure due to partial coating delamination some years after implantation. It will be shown that this delayed delamination was caused by crevice corrosion (CC) of the adhesion-promoting interlayer and the reason why different corrosion processes may prevent an easy transfer of a successful technical application of DLC onto an implant will be discussed. The main issue for successful, long-term, in vivo applications of DLC coatings on implants is to predict the in vivo survival time and especially the long-term adhesion stability of the coating. The formation at the interface of a few atomic layers of reaction products, usually a metal-carbide, will be addressed. Furthermore, any contamination from residual gas or any cross contamination will result in a different reactively formed interface material with different properties. Delamination can then occur by a slowly advancing crack in this thin carbidic layer governed by the laws of stress corrosion cracking (SCC). It will be shown that if a stable coating adhesion is obtained, DLC coated articulating implants show basically no wear of the coating up to 101 million articulations on a simulator corresponding to about 101 years of in vivo articulation.

RuO2/SnO2–Al2O3 has been recently reported as an industrial catalyst for Cl2 production through HCl oxidation. The stabilizing role of the alumina binder in the material, essential for its durable performance, is elucidated here. Al2O3 prevents chlorination of the SnO2 carrier under relevant reaction conditions, whereas, in its absence, SnO2 losses exceed 80 wt % in very short times owing to volatilization as SnCl4. Characterization by using X-ray diffraction, temperature-programmed reduction with hydrogen, and high-resolution TEM indicates expansion of the cassiterite cell in the SnO2–Al2O3 composite with respect to pure SnO2, which suggests the insertion of certain Al species upon mechanochemical and thermal activation of the oxide mixture. 27Al magic-angle spinning NMR and X-ray photoelectron spectroscopy studies reveal that the pentahedrally coordinated Al3+ cations interact with SnO2, generating an electron-depleted region near the surface of SnO2 particles. This induces some acidic character in cassiterite, which possibly makes it inert toward HCl. Besides this electronic effect, the presence of thin porous amorphous alumina films, partly covering the SnO2 surface, can offer additional geometric protection of the support. Mechanical mixing followed by calcination is essential to attain stabilization, and maximized effects are achieved with a high-surface area alumina. Other oxides such as SiO2 are ineffective in preventing tin losses during HCl oxidation. The practical implications of these findings are very important. The metal loading (fourfold decrease) and, thus, the cost of the catalyst can be significantly lowered without compromising its long-term stability.

The electroreduction of CO

Reactions in the gas phase are of primary technological importance for applications in nano- and microfabrication technology and in the semiconductor industry. We present exclusively gas-phase protocols to chemically passivate oxide-free Si(111) and Si(100) surfaces with short-chain alkynes. The resulting surfaces showed equal or better oxidation resistance than most existing liquid-phase-derived surfaces and rivaled the outstanding stability of a full-coverage Si(111)-propenyl surface.1,2 The most stable surface (Si(111)-ethenyl) grew one-fifth of a monolayer of oxide (0.04 nm) after 1 month of air exposure. We monitored the regrowth of oxides on passivated Si(111) and Si(100) surfaces by X-ray photoelectron spectroscopy (XPS) and observed a significant crystal-orientation dependence of initial rates when total oxide thickness was below approximately one monolayer (0.2 nm). This difference was correlated with the desorption kinetics of residual surface Si-F bonds formed during HF treatment. We discuss applications of the technology and suggest future directions for process optimization.

CrystEngComm, 18, ISSN:1466-8033

Diamond-like carbon (DLC) coatings are known to have extremely low wear in many technical applications. The application of DLC as a coating has aimed at lowering wear and to preventing wear particle-induced osteolysis in artificial hip joints. In a medical study femoral heads coated with diamond-like amorphous carbon, a subgroup of DLC, articulating against polyethylene cups were implanted between 1993 and 1995. Within 8.5 years about half of the hip joints had to be revised due to aseptic loosening. The explanted femoral heads showed many spots of local coating delamination. Several of these explanted coated TiAlV femoral heads have been analyzed to investigate the reason for this failure. Raman analysis and X-ray photoelectron spectroscopy (XPS) depth profiling showed that the coating consists of diamond-like amorphous carbon, several Si-doped layers and an adhesion-promoting Si interlayer. Focused ion beam (FIB) transverse cuts revealed that the delamination of the coatings is caused by in vivo corrosion of the Si interlayer. Using a delamination test set-up dissolution of the silicon adhesion-promoting interlayer at a speed of more than 100 μm year−1 was measured in vitro in solutions containing proteins. Although proteins are not directly involved in the corrosion reactions, they can block existing small cracks and crevices under the coating, hindering the exchange of liquid. This results in a build-up of crevice corrosion conditions in the crack, causing a slow dissolution of the Si interlayer.

Unwanted physiological reactions, caused by particle release in articulating joints, are still a major concern in total hip arthroplasty. Diamond-like carbon coatings (DLC) show very low wear values in many technical applications. Attempts to transfer these outstanding tribological properties to in-vivo load bearing articulating joints turned out to be extremely problematic. A DLC coated metallic metatarsophalangeal (MTP) prosthesis, with both articulating surfaces coated, was explanted after approximately 4 years. The DLC-coating was removed from the entire face of the phalangeal component and from most of the face of the metatarsal component. It appeared that the coating was scratched and then delaminated parallel to the scratches. To retrospectively investigate the reason for the in-vivo failure, the explanted prosthesis was analyzed by X-ray photoelectron spectroscopy (XPS) depth profiling and cross sectional scanning electron microscope (SEM) analysis. The coating consisted of an approximately 180 nm thick DLC film and a circa 120 nm thick silicon based adhesion promoting interlayer on a CoCrMo base material. SEM observation of transversal cuts showed that the delamination of the DLC-coatings was mainly caused by a slow in-vivo corrosion of the whole Si interlayer due to crevice corrosion. Additionally, a weak mechanical bond between the CoCrMo substrate and the Si-based interlayer further facilitated the access of body liquid below the Si interlayer. The instability of Si toward crevice corrosion was also demonstrated by a separate crevice experiment using silicon single crystals.

Diamond-like carbon (DLC) coatings are promising candidates for improving the mechanical wear and chemical resistance of load-bearing implants. However, in view of medical data showing severe problems due to film delamination, the application of DLC layers to the medicotechnical field is not yet recognized. In an extension to an earlier publication, in which we established that coating delamination in phosphate-buffered saline (PBS) solution is driven by stress–corrosion cracking, we present for the first time a detailed structural and chemical analysis of the interface region of DLC-coated CoCrMo. High-resolution and scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy shows that a 5 nm thick carbide layer with an average Me:C stoichiometry of 2:1 is formed at this interface. It is shown that the failure of DLC-coated CoCrMo in PBS is due to the instability of Co carbides at the film–implant interface.

The corrosion mechanisms of Al Cr Fe and Al Cu Fe Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al Cr Fe surface is exhibited from 1 M H2SO4 to 1 M NaOH solutions which was confirmed by ICP OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy hydroxide film. Although Al Cu Fe Cr showed passivation during potentiodynamic polarization heavy active corrosion at OCP was revealed by ICP OES. For the Al Cu Fe Cr alloy the 10 content of Cr is insufficient to maintain a protective "chemically stable" Cr oxide/hydroxide. (c) 2011 Elsevier Ltd. All rights reserved.

The evolving usefulness of organic conducting polymers, of metallic or semiconducting type, is primarily dependent on their mechanisms of electrical conduction and degradation. Understanding these mechanisms is crucial for improving the effi ciency and lifetime of technologies derived from this class of polymers. There is demand for a model that provides a vivid and more precise evaluation of the electrical conduction mechanism in these polymers – especially when they act as hosts to guest species, such as acid dopant ions and nanoparticles. If, for example, the motional behavior of a host–guest organic conducting polymer structure, as related to dynamic stability, is either asynchronous or synchronous, is this refl ected in the mechanism of electrical conduction and does it account for the pace of material’s degradation? Here, we demonstrate that the answer is affi rmative: asynchronous structural motions arising due to loosely bound or free guest species within the host polymer lead to anomalous electrical conduction mechanisms, increased fragility and short lifetime, at odds with the synchronous behavior.

Low friction and wear resistant coatings have a long history of successful applications in industry. It has long been hoped that these coatings, especially diamond-like carbon (DLC), could also be used successfully in load-bearing joint implants, extending implant life time considerably. However, despite several medical studies carried out so far, no regular DLC-coated implants are available on the market. In most cases, failure was due to insufficient long-term stability of the adhesion of such coatings on implants in vivo. That is because introducing a coated implant not only brings the coating into contact with the body environment but also the interface that controls the adhesion. This usually reactively formed interface must be considered to be at least one additional material which must be not only biocompatible, but also unsusceptible to corrosive attack. The aim of this paper is to analyze in detail the interface, i.e., the transition region between the substrate and the coating. This knowledge is necessary in order to find the right measures to ensure the long-term stability of the adhesion. Results for DLC coatings on a cobalt–chromium–molybdenum alloy are presented. It is shown that a very thin interface layer is formed, with the alloy on one side and the carbon film on the other side. This layer consists of a mixture of carbides from all the metals of the base material. This result is obtained by means of measuring depth profiles using X-ray photoelectron spectroscopy because these spectra yield not only the chemical composition of the interface but a detailed analysis provides information on the chemical states across the interface.

The influence of chemical and thermal aging effects on catalytic activity was analyzed for a vehicle (bifuel) aged pre- and underfloor three-way catalyst (p-/u-TWC) as well as an engine aged diesel oxidation catalyst (DOC). The conversion results were compared with the respective new catalysts. Although the vehicle aged p-TWC showed massive thermal aging, its CO conversion rate was comparable to that of the vehicle aged u-TWC. On the other hand, the conversion rate for methane abatement was significantly affected above 325 °C. Methane conversion appeared as the parameter mostly affected by (thermal) aging. The DOC showed massive chemical aging with typical engine oil based contaminants like P and Zn but also with Si. The contamination is likely responsible for the shift of propene and NO light-off curves to higher temperatures by about 70 °C.

Coatings from diamond-like carbon (DLC) have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the total joint replacement field, layer performance, stability and adhesion in realistic physiological setups are quintessential and these aspects have not been consistently researched. In our team's efforts to develop long-term stable DLC implant coatings, test results gained from a simplified linear spinal simulator setup are presented. It is shown that metal-on-metal (MoM) pairs perform well up to 7 million loading cycles, after which they start to generate wear volumes in excess of 20 times those of DLC-coated implants. This is attributed to the roughening observed on unprotected metal surfaces. Furthermore, we illustrate that in contrast to DLC-on-DLC, MoM tribopairs require protein-containing media to establish low-friction conditions. Finally, results of defect monitoring during testing are presented, showing catastrophic failure of layers whose interfaces are too weak with respect to the stress-corrosion-cracking mechanism encountered in vivo.

Results from a study conducted between National Metrology Institutes (NMIs) for the measurements of the absolute thicknesses of ultra-thin layers of SiO2 on Si are reported. These results are from a key comparison and associated pilot study under the auspices of the Consultative Committee for Amount of Substance. ‘Amount of substance’ may be expressed in many ways, and here the measurand is the thickness of the silicon oxide layers with nominal thicknesses in the range 1.5–8 nm on Si substrates, expressed as the thickness of SiO2. Separate samples were provided to each institute in containers that limited the carbonaceous contamination to approximately < 0.3 nm. The SiO2 samples were of ultra-thin on (100) and (111) orientated wafers of Si. The measurements from the laboratories which participated in the study were conducted using ellipsometry, neutron reflectivity, X-ray photoelectron spectroscopy or X-ray reflectivity, guided by the protocol developed in an earlier pilot study. A very minor correction was made in the different samples that each laboratory received. Where appropriate, method offset values attributed to the effects of contaminations, from the earlier pilot study, were subtracted. Values for the key comparison reference values (agreed best values from a Consultative Committee study) and their associated uncertainties for these samples are then made from the weighted means and the expanded weighted standard deviations of the means of these data. These results show a dramatic improvement on previous comparisons, leading to 95% uncertainties in the range 0.09–0.27 nm, equivalent to 0.4–1.0 monolayers over the 1.5–8.0 nm nominal thickness range studied. If the sample-to-sample uncertainty is reduced from its maximum estimate to the most likely value, these uncertainties reduce to 0.05–0.25 nm or ∼1.4% relative standard uncertainties. The best results achieve ∼1% relative standard uncertainty. It is concluded that XPS has now been made fully traceable to the SI, for ultra-thin thermal SiO2 on Si layers, by calibration using wavelength methods in an approach that may be extended to other material systems. © Crown copyright 2009. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

In this work, the ability of ashless anti-wear additives to form protective tribofilms on diamond-like carbon (DLC) and steel surfaces was investigated and compared to the reactions of ZnDTP. Reciprocating sliding tests were performed under mild tribological conditions for steel/steel and DLC/DLC contacts to avoid wearing through the DLC coating. A comparison of the friction behavior of ZnDTP with two ashless additives, a butylated triphenyl phosphorothionate (b-TPPT) and an amine phosphate (AP), indicated that the latter additive behaved in a different manner to the first two. b-TPPT shows the lowest friction coefficient for DLC/DLC contacts whereas the AP give the lowest friction coefficient for steel sliding against steel. AFM and ESEM were performed to analyze the surfaces and showed the build up of tribofilms from ZnDTP and b-TPPT onto both the steel and DLC surfaces. No evidence of such a film formation on DLC was observed when the AP were used.

Increasing use of DLC coatings in oil-lubricated, mechanical systems has led to a great deal of interest in optimising the interactions between lubricant additives and coatings. We have looked at the formation of a tribofilm from ZnDTP on diamond-like carbon (DLC) when sliding in oil against DLC on a polished steel substrate under very low wear conditions. It was found that the tribofilm formed in the absence of iron adhered very weakly to the surface and could be removed by washing in an ultrasonic bath. The wear was too low to be detected with laser profilometry. AFM imaging of the surfaces of steel and DLC after sliding of steel/steel and DLC/DLC showed that the tribofilm formed on DLC had a very different morphology to that formed on steel. EDX was used to demonstrate that the tribofilm contained zinc, sulphur and phosphorus. ToF-SIMS measurements showed that iron was neither present at the DLC surface nor in the tribofilm.

Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI 3 ) at room temperature. InI 3 has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III–V semiconductors.

We report on mechanical dissipation measurements carried out on thin (∼100 nm), single-crystal silicon cantilevers with varying chemical surface termination. We find that the 1-2 nm-thick native oxide layer of silicon contributes about 85% to the friction of the mechanical resonance. We show that the mechanical friction is proportional to the thickness of the oxide layer and that it crucially depends on oxide formation conditions. We further demonstrate that chemical surface protection by nitridation, liquid-phase hydrosilylation, or gas-phase hydrosilylation can inhibit rapid oxide formation in air and results in a permanent improvement of the mechanical quality factor between three- and five-fold. This improvement extends to cryogenic temperatures. Presented recipes can be directly integrated with standard cleanroom processes and may be especially beneficial for ultrasensitive nanomechanical force- and mass sensors, including silicon cantilevers, membranes, or nanowires.

The structural evolution of a Ag–Cu/AlN nano-multilayer (NML), as prepared by magnetron-sputtering on a α-Al2O3 substrate, was monitored during fast heating by real-time in situ XRD analysis (at the synchrotron), as well as by ex situ microstructural analysis using SEM, XPS and in-house XRD. The as-deposited NML is constituted of alternating nano-layers (thickness ≈ 10 nm) of a chemically inert AlN barrier and a eutectic Ag–Cu40at% nano-alloy. The nano-alloy in the as-deposited state is composed of a fcc matrix of Ag nano-grains (≈6 nm), which are supersaturated by Cu, and some smaller embedded Cu rich nano-grains (≈4 nm). Heating up to 265 °C activates segregation of Cu out of the supersaturated Ag nano-grains phase, thus initiating phase separation. At T > 265 °C, the phase-separated Cu metal partially migrates to the top NML surface, thereby relaxing thermally-accumulated compressive stresses in the confined alloy nano-layers and facilitating grain coarsening of (still confined) phase-separated nano-crystallites. Further heating and annealing up to 420 °C results in complete phase separation, forming extended Ag and Cu domains with well-defined coherent Ag/AlN interfaces. The observed outflow of Cu well below the eutectic melting point of the bulk Ag–Cu alloy might provide new pathways for designing low-temperature nano-structured brazing materials.

Diamond-like carbon (DLC) coatings are a class of materials and, depending on the deposition conditions and the tribological system, different outstanding tribological properties can be obtained. The most important subclasses of DLC are hydrogenated amorphous carbon (a-C:H) and hydrogen free tetrahedral amorphous carbon (ta-C). When DLC slides against a metal, the formation of the so-called transfer layer on the metallic counterpart can protect the metal from further wear. Adhesion and cohesion of this transfer layer is a critical issue and is also influenced by the environmental atmosphere including the relative humidity. When DLC is running against a hard and chemically inert counterface, such as sapphire, the formation of a transfer layer is not observed but low wear is still obtained. This is attributed to the lubricating properties of the graphitic wear residues. Due to its unique combination of properties, DLC is already used in different industrial applications such as magnetic storage media, diesel injection pumps, sliding bearings, car valve rockers, gears, tappets of racing motorcycles, laser barcode scanner windows in supermarkets, VCR head drums, textile industry parts, motor cycle forks, razor blades, etc. In medical applications, i.e. the coating of load bearing joints that slide against ultra high molecular weight polyethylene (UHMWPE), the different in vitro experiments apparently showed contradicting results, mainly due to the different experimental setups and especially the different liquids used as lubricants. However, when DLC slides against DLC in medical applications low wear rates could be demonstrated in different in vitro tests.

A study was carried out for the measurement of ultrathin SiO on (100) and (111) orientation silicon wafer in the thickness range 1.5-8 nm. XPS, medium-energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), SIMS, ellipsometry, gazing-incidence x-ray reflectometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM) were used for the measurements. Water and carbonaceous contamination about 1 nm were observed by ellipsometry and adsorbed oxygen mainly from water at thickness of 0.5 nm were seen by MEIS, NRA, RBS and GIXRR. The different uncertainty of the techniques for the scaling constant were also discussed.

Diamond-like carbon (DLC) films are well known for their outstanding tribological properties, which has been shown in many studies. Because of their extreme hardness, low coefficient of sliding friction (often after some running-in time) and especially their ability to form a transfer layer on the counter-body of the frictional pair, these coatings have found different areas of application. There are many different types of these coatings on the market depending on the deposition process and on the deposition parameters used. The dependence of the film properties on the deposition conditions allows the tailoring of certain film properties to specific applications. Additionally, alloying with different elements allows further adaptations. A special tribological problem is found in applications where almost no or only little motion takes place and therefore no transfer layer can build up. In this case a special coating is needed which has a low coefficient of friction already at the very beginning of any motion. A similar situation is found in low-load applications where neither a transfer layer is created nor the transformation of the topmost surface layer into a more graphitic-like state takes place. In this study, silicon containing DLC films are produced in a RF plasma-activated chemical vapor deposition system. A mixture of acetylene and an organosilicon gas is used to deposit silicon containing DLC films onto hardened steel sample plates. On top of a supporting coating, a 30-nm thick DLC layer with varying silicon content is deposited using different selected self-bias voltages. The coefficient of static friction against a hardened stainless steel surface is then measured in dependence of the silicon content in the film and of the self-bias used during deposition. The films display a constant coefficient of static friction even after many single measurements. The results are compared to results obtained for pure DLC films.

Hydrogenated amorphous carbon films or diamond-like carbon films have shown their outstanding tribological properties in many studies and in many applications. This is due to their extreme hardness, low coefficient of sliding friction (after some running-in time) and especially, their property to form a transfer layer on the counter-body of the frictional pair. Hydrogenated amorphous carbon coatings describe a large class of different coatings with properties ranging from relatively soft to extremely hard, from highly amorphous to more graphitic-like and from high hydrogen contents to hydrogen free, as well as any combination of these. A special problem is found in applications, where almost no or only little motion takes place, because either the static friction cannot be overcome or the running-in cannot be completed, because the transfer layer cannot form. In all these cases, a special coating is needed, which has a low coefficient of friction, already at the very beginning of any motion. A similar situation is found in low load applications, where neither a transfer layer is created nor a transformation of the topmost surface layer into a more graphitic-like state takes place. Diamond-like carbon films in this study are produced in a r.f. plasma-activated chemical vapour deposition system from acetylene and deposited onto hardened steel plates. The coefficient of static friction against a hardened stainless steel surface is then measured in dependence of the self-bias, used for the topmost coating layer. Different measurement methods have been used to prove the reproducibility. It was furthermore shown that these films displayed a constant coefficient of static friction even after 200 single measurements. The overall average coefficient of static friction in air was 0.158±0.002, and in a dry nitrogen atmosphere 0.126±0.003 as compared to 0.210±0.011 for uncoated surfaces in air.

Metal-on-metal (MOM) hip joint bearings are considered one of the alternatives to the generally used metal-on-polyethylene bearings. In order to control and minimize wear of MOM bearings, an in-depth understanding of the acting wear mechanisms is essential. In a recent study it was suggested that layers of decomposed proteins are generated due to high pressures between contact spots of the cobalt–chromium alloy bearing. It was further suggested that these tribochemical reaction products greatly influence the wear behavior of the MOM articulation. Since these conclusions were limited to in-vitro test observations, the purpose of this study was to compare retrieved McKee–Farrar prostheses with the previously utilized in-vitro specimens to investigate tribochemical layer presence, composition and role in the overall wear process. Forty-two retrieved McKee–Farrar prostheses with a complete clinical record were compared to the in-vitro specimens. Ninety-three percent of the cups and 83% of the heads of the retrieval collection showed macroscopically and microscopically similar layers than the in-vitro bearings. SEM revealed a varying layer thickness with scratched or smeared sections. Combined SEM and EDS analysis suggested the presence of carbon and oxygen in most of the layers, while some layers showed traces of sodium, magnesium, calcium, nitrogen, sulfur, phosphorus and chlorine, too. These observations were quantitatively verified using XPS. By means of protein standards the organic origin of the layers was shown. Since the latter covered large areas of the contacting surfaces, adhesion is minimized and abrasion is reduced. Thus, the layers have a solid lubricating effect and the general wear behavior of the MOM bearing is affected by generation and delamination of the tribochemical reaction layers.

Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), is a class of materials with excellent mechanical, tribological and biological properties. By the addition of other elements into the DLC all of these properties can be changed within a certain range. It will be shown that the ratios of the different proteins adsorbed on the surface can be influenced by the addition of different elements into the DLC film. These proteins will then subsequently influence cell attachment, cell proliferation and cell differentiation. Certain toxic elements such as Cu, Ag, V, embedded in the DLC will, when exposed to a biological media, be released and cause toxic reactions. This allows the preparation of surfaces with a tunable antibacterial effect. DLC has proven its outstanding tribological properties in many technical applications due to the transformation of DLC into graphite (a solid lubricant) and the build up of a transfer layer on the counterpart. However, it is questionable if this effect takes place in artificial joints. Contradicting results on DLC coated hip joints are found in the literature, some indicating an improvement and some a change for the worse. DLC coatings have an excellent haemocompatibility, which is expressed in a decreased thrombus formation. When exposed to blood, an increased ratio of albumin to fibrinogen adsorption as well as decreased platelet activation is observed on coated surfaces. DLC coated cardiovascular implants such as artificial heart valves and stents are already commercially available.

Chemical patterns on smooth wafer substrates comprising areas with two different metals have been produced by vacuum metal deposition and photolithographic techniques. The combination of metals has been chosen from the series titanium (Ti), aluminium (Al), vanadium (V) and niobium (Nb), producing patterns (dots and stripes with dimensions of 50, 100 and 150 micrometer) with one of the metals as the background and with the second metal (foreground pattern) deposited on the background metal. The structure and chemical composition of the patterned surfaces were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy and imaging time-of-flight secondary-ion mass spectrometry. The surfaces proved to be geometrically well defined with the expected surface-chemical composition, i.e. a surface oxide (passive) film essentially composed of TiO(2),Al(2)O(3),V(2)O(5), or Nb(2)O(5). Ti/Ti patterned surfaces were produced as controls and found to show no chemical composition contrast. The surface roughness of the pattern was greater than that of the background by a factor of 2-3, but was still extremely smooth with Ra2nm. The patterns serve as model surfaces for studying in vitro the behaviour of cells as well as the adsorption of serum proteins on different metal oxides, which will be reported in a companion paper. These surfaces can be used to compare and contrast the response of osteoblasts to Ti and other alloy components, such as Al, V, or Nb, which are used in load-bearing medical implants.

Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), is a class of material with variable properties. Depending on the deposition conditions and the setup used in tribological experiments, varying and even controversial results are obtained. Additionally, hydrogen, oxygen and the relative humidity have a crucial influence on the tribological behavior. The amorphous nature of a-C:H opens the possibility to introduce different amounts of other elements into the coating and still maintain the amorphous phase of the coating. By this technique film properties such as thermal stability, hardness, tribological properties, electrical conductivity, surface energy and biological reactions of cells in contact with the surface can be tuned within a certain range. Commercial applications of DLC and alloyed DLC are for example: magnetic storage media, diesel injection pumps, sliding bearings, car valve rockers, gears, tappets of racing motorcycles, laser barcode scanner windows in supermarkets, VCR head drums, textile industry parts. DLC has excellent tribological properties in technical applications, however, the literature shows contradicting results on the wear behavior of DLC-coated hip joints.

Nanostructures of sizes comparable to protein dimensions are created on Si and Ti surfaces by local anodic oxidation (LAO) using the atomic force microscope (AFM). The characterization of the surface by X-ray photoelectron spectroscopy (XPS) reveals that this method assures a modification of the topography of the surface without a change of its chemical composition. Surfaces structured by LAO therefore represent ideal systems to study the dependence of protein adsorption on topography. We are able to visualize the created nanostructures with an AFM and successively adsorb the proteins in situ, rinse and image the new surface. The densities of adsorbed proteins on the nanostructured and neat surfaces are compared and we find that the protein arrangement depends on the underlying nanostructures, showing that proteins can “sense” the topography of surfaces at the nanometer scale. This result can be considered as the nanoscale analogous of the adsorption found for cell systems on micrometer structures.

Diamond like carbon (DLC) coatings have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the orthopaedic field, layer performance, stability and adhesion in physiologically relevant setups are crucial and not consistently investigated. In vitro wear testing as well as adequate corrosion tests of interfaces and interlayers are of great importance to verify the long term stability of DLC coated load bearing implants in the human body. DLC coatings were deposited on articulating lumbar spinal disks made of CoCr28Mo6 biomedical implant alloy using a plasma-activated chemical vapor deposition (PACVD) process. As an adhesion promoting interlayer, tantalum films were deposited by magnetron sputtering. Wear tests of coated and uncoated implants were performed in physiological solution up to a maximum of 101 million articulation cycles with an amplitude of ±2° and −3/+6° in successive intervals at a preload of 1200 N. The implants were characterized by gravimetry, inductively coupled plasma optical emission spectrometry (ICP-OES) and cross section scanning electron microscopy (SEM) analysis. It is shown that DLC coated surfaces with uncontaminated tantalum interlayers perform very well and no corrosive or mechanical failure could be observed. This also holds true in tests featuring overload and third-body wear by cortical bone chips present in the bearing pairs. Regarding the interlayer tolerance towards interlayer contamination (oxygen), limits for initiation of potential failure modes were established. It was found that mechanical failure is the most critical aspect and this mode is hypothetically linked to the α-β tantalum phase switch induced by increasing oxygen levels as observed by X-ray diffraction (XRD). It is concluded that DLC coatings are a feasible candidate for near zero wear articulations on implants, potentially even surpassing the performance of ceramic vs. ceramic., International Journal of Molecular Sciences, 15 (6), ISSN:1422-0067

A specific feature of diamond-like carbon (DLC) tribological behaviour is the increase of its friction coefficient with increasing ambient humidity levels and the loss of its self-lubricating properties at very high humidity. In a previous study it was shown that alloying DLC with small amounts of Si provided a significant reduction in friction coefficient at high relative humidity and allowed the friction coefficient to be stabilised over a wide humidity range. For example, the addition of approximately 4 at.% Si allowed friction coefficient to be held approximately constant at 0.08±0.01 over the humidity range 5–85% R.H. sliding against a steel counterface [Surf. Coat. Technol. 133–134 (2000) 437]. In this study, the possibilities for optimising and tailoring the tribological humidity response of DLC has been further investigated for the alloying elements F and Ti and the results compared with those obtained for Si. The addition of Ti was found to lower friction coefficient slightly both under dry and humid conditions. The addition of F was found to produce a dramatic increase in friction coefficient especially at low humidity, resulting in a friction coefficient as high as 0.9 against steel.

We study the protein adsorption on surfaces in order to investigate their predominant role in biocompatibility. Nanostructures are created by local anodic oxidation on titanium using the atomic force microscope. A remarkable specificity of the actin filament adsorption on the nanostructure height is noticed. F-actin is observed to have a low adsorption on nanostructures of a height of 4 nm and the adsorbed proteins appear to be randomly oriented. In contrast high protein adsorption is observed for structure height between 1 and 2 nm, moreover the filaments adsorb preferentially parallel to the nanostructured pattern.

Diamond-like carbon (DLC) has become one of the most widely used wear-protective low-friction coatings due to its outstanding mechanical and tribological properties. However, a major disadvantage of DLC is the deterioration of its lubricating properties at high relative humidity, limiting its use in certain tribological applications for which ambient humidity may be subject to significant variations. The addition of small amounts of Si to DLC has been reported as an effective method for reducing friction coefficient at high humidities. In this paper we have characterised the tribological behaviour of a reference DLC coating prepared using a PACVD technique in the relative humidity range 5–85%, sliding against steel, alumina and DLC counterfaces, and directly compared this to similar coatings alloyed with small amounts of Si (

Nowadays a variety of different hard coatings are commercially available, the most widely used ones are TiN, TiC, TiCN, TiAlN, CrN, Al 2 O 3 , and combinations thereof, as well as some coatings with lubricating properties such as diamond-like carbon (DLC), WC/C or MoS 2 . To fulfil the industrial demands for improved coatings, a lower friction, a longer lifetime, a desired biological behavior or a better thermal stability in different environments, improved and application adapted coatings are developed. The different properties of a coating can be tuned to a desired value by alloying with suitable elements. Composite materials such as multilayer coatings and isotropic nanocomposite coatings, having structures in the nanometer range, can even show properties which can not be obtained by a single coating material alone. The authors review research and development work on the improvement of the overall coating performance, It mainly addresses alloying, the development of multilayer systems and the recently emerged field of nanocomposite coatings.

Amorphous hydrogenated carbon (a-C : H) coatings, also called diamond-like carbon (DLC), have many properties required for a protective coating material in biomedical applications. The purpose of this study is to evaluate a new surface coating for bone-related implants by combining the hardness and inertness of a-C : H films with the biological acceptance of titanium. For this purpose, different amounts of titanium were incorporated into a-C : H films by a combined radio frequency (rf) and magnetron sputtering set-up. The X-ray photoelectron spectroscopy (XPS) of air-exposed a-C : H/titanium (a-C : H/Ti) films revealed that the films were composed of TiO2 and TiC embedded in and connected to an a-C : H matrix. Cell culture tests using primary adult rat bone marrow cell cultures (BMC) were performed to determine effects on cell number and on osteoblast and osteoclast differentiation. By adding titanium to the carbon matrix, cellular reactions such as increased proliferation and reduced osteoclast-like cell activity could be obtained, while these reactions were not seen on pure a-C : H films and on glass control samples. In summary, a-C : H/Ti could be a valuable coating for bone implants, by supporting bone cell proliferation while reducing osteoclast-like cell activation.

The different properties of a-C:H can be tuned, either by alloying additional elements into the amorphous a-C:H or by building multilayer structures composed of two different types of a-C:H. This allows the design of optimized coatings for a wide range of applications. Multilayered a-C:H films, composed of a 60 nm Si-a-C:H adhesion layer and 300 nm multilayer structure have been deposited by a periodical variation of the sample self-bias voltage during deposition. The single layer thickness has been varied from 4 to 20 nm. The wear rate (determined by pin-on-disk measurement against a steel ball) of multilayer structures having a single layer thickness in the range of 12–14 nm, showed a drastic decrease by one decade down to 4×10 −18 m 3 Nm −1 , compared to the multilayer systems composed of thicker or thinner single layers. Amorphous hydrogenated carbon films containing titanium in different concentrations (a-C:H/Ti) were deposited by a combined RF-PACVD and DC magnetron sputtering process. The titanium content in the carbon matrix caused cellular reactions of bone marrow cells (BMC) like enhanced cell proliferation together with a reduced osteoclast cell activity. This could make a-C:H/Ti a valuable hard coating for bone implants, by enhancing bone ingrowth through osteoblast differentiation while reducing bone resorption through osteoclast inhibition.

Amorphous hydrogenated carbon films (a-C : H) containing different amounts of Ti or V were produced by combined plasma-activated chemical vapour deposition and d.c. magnetron sputtering. New bioactive materials resulted from the combination of the excellent tribological and biological properties of the a-C : H matrix with the biological response to the incorporated metals. By adding Ti to the a-C : H matrix, an enhanced differentiation of osteoblast- and reduced osteoclast-like cell activity was achieved, leading to a coating that is valuable for bone implants: enhancing bone ingrowth through increased osteoblast activity and reducing bone resorption through osteoclast-like cell inhibition. The a-C : H/V films reduced lysosomal activity as well as neutral red uptake in bone marrow cell cultures, thus being an interesting coating for short-term implants where reduced cell attachment is required. Prior to cell culture tests, the surfaces of the metal-containing a-C : H films were investigated by x-ray photoelectron spectroscopy. The relation between chemical surface composition and cellular response is discussed.

A new microelectrode is presented, based on an electrochemically etched Pt/Ir needle with a high aspect ratio and a radius of curvature smaller than 1 μm. The needle is electrically insulated by a thin (15 to 20 nm) insulation film made of hydrogenated amorphous carbon (a-C:H). In order to use the needle as a microelectrode, the very end is made conductive again through a local oxygen plasma. The localization of the plasma is achieved in a specially designed scanning tunneling microscope (STM) working in a high pressure oxygen atmosphere. The reduction of the total resistance after the local plasma treatment was proved by measuring the transition resistance between the needle and a 0.1 M NaCl solution. It is supposed that the two processes responsible for the decrease of the resistance are: (a) the reduction of the thickness of the a-C:H insulation by reactive oxygen ion etching, (b) transformation of the a-C:H film into a more graphitic-like state (increased content of sp2 bondings) by a thermal process. The functioning of this new type of electrode was tested by measuring the transmembrane potential of mouse liver cells in vitro.

ClTi(OiPr)3 reacts with Na[HB(R3R4R5pz)3] (where pz denotes pyrazolyl) to yield volatile isopropoxy(pyrazolylborate)titanium(IV) compounds. Methoxy- and tert-butoxy(pyrazolylborate)titanium(IV) complexes were isolated from the reaction of hydrido(trispyrazolylborate)trichlorotitanate with the sodium alcoholate. Using [HB(pz)3Ti(OiPr)3], thin amorphous TiO2 films were grown by metal organic chemical vapor deposition (MOCVD) in a low pressure reactor, in the temperature range 250–600 °C. The dependence of the growth on evaporation rate, oxygen flow, and substrate temperature is discussed. The influence of different co-reactants on texture and composition of the film, i.e., O2, N2, H2, and O2 with MeOH, was also investigated. The films were characterized by UV-vis and IR spectroscopy, X-ray diffraction (XRD), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS).

The excellent biocompatibility of titanium and its alloys is intimately related with the properties of the surface in contact with the biological environment, and therefore it is closely connected with the stable, passivating oxide layer that forms on its surface. In the present paper, the oxide layer on the alloy Ti6Al7Nb has been characterized using X-ray photoelectron spectroscopy, scanning Auger microscopy and pH-dependent lateral force microscopy. The alloying elements Al and Nb are incorporated in the oxide layer and detected in their most stable oxidized form, as Al2O3 and Nb2O5. Their distribution in the oxide reflects the underlying alpha-beta microstructure, with enrichment of Al in the alpha- and of Nb in the beta-phase (determined by electron microprobe). Friction measurements (lateral force microscopy) indicate slightly different, pH-dependent, lateral forces above the alpha- and beta-phase structures that point to small local variations in surface charges.

Nanoscaled multilayer coatings consisting of alternating layers of different types of amorphous hydrogenated carbon (a-C:H) films were deposited in a plasma activated chemical vapor deposition (PACVD) process. The thickness of the multilayer repeat unit as well as the interface width between these layers were varied by controlling the substrate bias voltage. The influence of the achieved multilayer structure on the tribological properties was investigated. At a certain range of thickness of the multilayer repeat unit, a decrease in wear rate by a factor of ten down to 4×10 −18 m3 Nm was observed. Another trend observed was the correlation between an abrupt interface and lower wear.

ist davon auszugehen, dass auchT riethoxysilane , die eine Aminoalkylkette tragen, leicht undohne !u§eren Katalysator hydrolysiert werden. DieseGrundfunktionalit!t schw!cht die starke Si-O-Bindung (einPh!nomen, das aSelbstkatalyseO genannt werden kann, umauszudr"cken, dass eine chemische Spezies sowohl Substratals auch Katalysator ist). Eine nachfolgende oxidative Ab-spaltung der Aminoalkylkette sollte ein Silanol ergeben, dasf"r weitere Reaktionen mit Aminoalkyltriethoxysilan-Mole-k"len bereit ist. Zusammengenommen k#nnte man sich die inSchema 1 skizzierte Reaktion unter Beteiligung von 3-Ami-nopropyltriethoxysilan, W asser und Ozon (O

Multilayer coatings of metallic (Au, Ni, Pb or PbO) and MoS 2 nanometer-scale layers were deposited by r.f. magnetron sputtering on 440C steel with a Cr adhesion layer. The structure, composition and thickness of the multilayers were studied by Rutherford back-scattering (RBS) and X-ray diffraction (XRD) spectroscopies. Pin-on-disk tribometer tests were performed in humid air of 50% RH. In order to investigate chemical and mechanical aspects of wear in humid air, the worn surfaces of the multilayers and of the counter parts were studied by scanning Auger microscopy (SAM) and scanning electron microscopy (SEM) after different sliding distances. The chemistry of wear was found to be associated with elimination of Mo from the contact surfaces. Relative to pure sputter-deposited MoS 2 coatings, lower values and more stable mean friction coefficients were observed for the metal–MoS 2 multilayers studied at higher loads. A correlation between the morphology and sliding properties of multilayers was found to be associated with an increased preferred basal orientation of MoS 2 in nanoscaled layers. The role of metal is most likely associated with a structural modification of MoS 2 rather than “gettering” of oxygen during sliding. It is concluded that the improvement in the tribological performance of sputter-deposited metal–MoS 2 multilayers in humid air can be generally attributed to the optimization of MoS 2 morphology in nanostructured multilayer coatings.

Nanoscaled multilayer coatings consisting of alternating layers of hard and soft amorphous hydrogenated carbon (a-C:H) films have been deposited by modulation of the substrate bias voltage in a plasma activated chemical vapor deposition (PACVD) process. Alternating hard/ soft a-C:H nanolayers is a model system to investigate the correlation of the different layers and interfaces with the final tribological and mechanical properties. The substrate bias voltage determines the ratio of sp2/sp2 bonded carbon, the internal stress and the hydrogen content in the different a-C:H layers, all of which contribute to the mechanical properties. Different bias voltage functions (sinusoidal, triangular, rectangular, etc.) were used to obtain soft, graded or sharp interfaces between the layers. The mechanical and tribological behavior of the multilayer structures have been characterized by tribological tests.

Pure TiN and MoSX, as well as Au/TiN, Ti/TiN and MoSX/Pb multilayers (multilayer layer thickness 4–50 nm), have been prepared by magnetron sputtering at room temperature. The characteristics of these films have been investigated using atomic force microscopy, X-ray diffraction and reflection, Auger depth profiling and Rutherford backscattering. The wear properties of the films have been determined using pin-on-disc measurements and the hardness of the films have been examined using nanoindentation techniques. Results show that the mechanical properties depend on multilayer thickness and that oxygen contamination from the background vacuum result in a degradation of film performance.

CuCl reacts with Na[HB(R3R5pz)3] and phosphine (PR3) or isonitrile (CNR) to yield volatile (pyrazolylborate)copper(I) complexes. These compounds were evaluated as MOCVD precursors. Using [{HB(pz)3}Cu(PEt3)] and [{HB(pz)3}Cu(PMe3)], thin copper films were grown by thermal metal organic chemical vapor deposition in a low pressure reactor in the temperature range 150–350°C. Polycrystalline Cu-phases were obtained at temperatures as low as 150°C. The metallic films were characterized by four-point-probe resistivity measurements, AES, and XPS, as well as AFM and SEM. Selective deposition on metal-seeded surface sites was observed on Pt, Au, Al, and W versus SiO2. Anti-selective deposition was found to occur on Pd-seeded samples.

We report successful introduction of negatively charged nitrogen-vacancy (NV(-)) centers in a 5 nm thin, isotopically enriched ([(12)C] = 99.99%) diamond layer by CVD. The present method allows for the formation of NV(-) in such a thin layer even when the surface is terminated by hydrogen atoms. NV(-) centers are found to have spin coherence times of between T2 ~ 10-100 μs at room temperature. Changing the surface termination to oxygen or fluorine leads to a slight increase in the NV(-) density, but not to any significant change in T2. The minimum detectable magnetic field estimated by this T2 is 3 nT after 100 s of averaging, which would be sufficient for the detection of nuclear magnetic fields exerted by a single proton. We demonstrate the suitability for nanoscale NMR by measuring the fluctuating field from ~10(4) proton nuclei placed on top of the 5 nm diamond film.

Chemistry of Materials, 25 (9), ISSN:0897-4756

One of the widely used materials for medical implants is titanium, because it readily forms a passivation layer of titanium dioxide which is known to be of excellent biocompatibility. However, under mechanical loads this passivation layer may locally be removed resulting in a black residue of TiO2 particles around the implant. Hard diamond-like carbon (DLC) coatings on the other hand are known to be biocompatible and to have excellent mechanical and chemical stability. A combination of the two materials in the form of TiO containing DLC coatings is expected to show further improvements of the bio-mechanical properties of medical implants. In this paper we present X-ray photoelectron spectroscopy investigations of TiO containing amorphous hydrogenated carbon films. These films are produced by r.f.-plasma chemical vapor deposition using mixtures of acetylene and titanium(IV) ethoxide as feed gases. The chemical states of the different elements in as-deposited tiO DLC films are analyzed.