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Abstract: Spectroscopic Ellipsometry was used to determine the optical and structural properties of amorphous carbon:gold nanocomposite thin films deposited by dc magnetron co-sputtering at different deposition power. The incorporation of gold as small particles distributed in the amorphous carbon matrix was confirmed by X-ray Diffraction, Rutherford Backscattering measurements and High Resolution Transmission Electron Microscopy. Based on these results, an optical model for the films was developed using the Maxwell–Garnett effective medium with the Drude–Lorentz model representing the optical response of gold and the Tauc–Lorentz model for the amorphous carbon. The gold volume fraction and particle size obtained from the fitting processes were comparable to those from the physical characterization. The analysis of the ellipsometric spectra for all the samples showed strong changes in the optical properties of the carbon films as a consequence of the gold incorporation. These changes were correlated to the structural modification observed by Raman Spectroscopy, which indicated a clustering of the sp 2 phase with a subsequent decrease in the optical gap. Finally, measurements of Reflection and Transmission Spectroscopy were carried out and Transmission Electron Microscopy images were obtained in order to support the ellipsometric model results. [Copyright &y& Elsevier]

Abstract: Amorphous niobium oxide thin films were deposited by unbalanced reactive magnetron sputtering under different conditions of pressure (2 to 4Pa) and oxygen percentage (9, 17, and 23%). The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, optical, mechanical, surface morphology and optical). The composition was determined by Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy. From the results of X-ray diffraction and the composition, we can conclude that for all of the deposition pressures and flow ratios used, the films were stoichiometric Nb2O5 and amorphous. Similarly, the mechanical and optical properties did not show significant variation between the different deposition conditions; all the films were transparent with a bandgap of about 3.4eV and a hardness around 5GPa. Concerning the electrochemical properties, the response of the films to DC polarization in a 0.89% NaCl solution was significantly different. The parameters used to compare the electrochemical response were the polarization resistance and the corrosion resistance obtained from the Tafel analysis. [ABSTRACT FROM AUTHOR]

Abstract: Composites of amorphous carbon films and silver were deposited by co-sputtering, where the target (10cm diameter) was of pure graphite with small inclusion of pure silver (less than 1cm2). The films were deposited under different powers, from 40 to 250W, and different target-substrate distances. The substrate was earthed and rotated in order to obtain a uniform distribution of the silver content. The addition of the Ag piece into the target increased the deposition rate of the carbon films, which could be related to the higher sputter yield of the silver, but there seems to be also a contribution from a larger emission of secondary electrons from the Ag that enhances the plasma and therefore the sputtering process becomes more efficient. Scanning electron micrographs acquired using backscattered electrons showed that the silver was segregated from the carbon matrix, forming nanoparticles or larger clusters as the power was increased. The X-ray diffraction pattern showed that the silver was crystalline and the carbon matrix remained amorphous, although for certain conditions a peak attributed to fullerene-like structures was obtained. Finally, we used Raman spectroscopy to understand the bonding characteristics of the carbon–silver composites, finding that there are variations in the D/G ratio, which can be correlated to the observed structure and X-ray diffraction results. [Copyright &y& Elsevier]

Abstract: Amorphous carbon films were deposited on SS316L substrates using a DC magnetron sputtering system, aiming at the application of the coated SS316L for biomedical implants. The biocompatibility and chemical stability of the carbon layers have been previously demonstrated. The films were deposited on top of sputtered titanium coatings introduced as a buffer layer to enhance film-substrate adhesion. The corrosion resistance of the a-C/Ti/SS316L systems was investigated by electrochemical techniques. The electrolyte used in this work was 0.89wt.% NaCl at pH 7.4, which simulates body fluid ionic concentrations. The coated samples displayed corrosion resistance values in the saline solution much higher than the stainless steel substrates and the role of the Ti coating thickness was analysed in order to determine the optimal system for biological applications. [Copyright &y& Elsevier]

The role of compressive stress in producing sp3 bonding in diamond-like carbon is of interest both technologically and scientifically. Stress limits the maximum thickness of adherent films, and it is desired to produce much thicker films for protective coatings and for making micro-electromechanical systems. Stress is important theoretically, because it is often linked to the deposition process. A strong correlation between macroscopic stress and sp3 fraction in diamond-like carbons has been noted, particularly for tetrahedral amorphous carbon (ta-C). However, a survey of data shows that a given stress produces films with sp3 contents between 20 and 85%, while for a given sp3 content, stresses between 2 and 19 GPa have been found. We propose that the main cause of stress is ion bombardment, and that a low energy of only 20 eV/ion is needed to produce films with an sp3 content over 70%. We discuss the various models linking stress and the sp3 fraction in ta-C. The role of densification vs. compressive stress in stabilising sp3 bonding is also discussed. [Copyright &y& Elsevier]

Abstract: It is now well established that all the different forms of amorphous carbon films are biocompatible and suitable for specific biomedical applications. On the other hand, bacterial adhesion on implant surfaces has also a strong influence on the healing and long-term outcome of biomedical devices and this has not been thoroughly studied for the carbon films. The purpose of this study was to evaluate the bacterial adhesion on graphite-like amorphous carbon (a-C) films in comparison to titanium (Ti) films and stainless steel (SS) substrates using different bacteria strains from the normal oral microbiota. Medical grade stainless steel discs of 15 mm in diameter were coated by either Ti or a-C films using magnetron sputtering. The bacterial adhesion of single species and a mixture of nine different microorganisms was tested on the three surfaces. The bacteria were anaerobically incubated on the surfaces for 24 h, then colony forming units (CFUs) were counted. The total amount of CFUs was found higher on the a-C and SS surfaces in comparison to Ti films when the nine strains were mixed together, suggesting that Ti surfaces are better than the a-C and SS to avoid bacterial adhesion. However, when single species were analyzed the individual strains showed different adhesion profiles. Some species like Aggregatibacter actinomycetemcomitans, Eikenella corrodens, Campylobacter rectus, and Fusobacterium nucleatum were found in higher counts on the a-C surfaces, while other species like Actinomyces israelii, Porphyromonas gingivalis, Prevotella intermedia and Streptococcus sanguinis were found in lower counts comparing to the Ti films. These results suggested that the determination of anti-bacterial properties of a surface by studying the bacterial adhesion of individual strains, as usually done, might not be representative of the in vivo response, where more than one strain are surely present. [Copyright &y& Elsevier]

The deposition and characterisation of tetrahedral amorphous carbon (ta-C) with an E04 optical gap of 3.5 eV and Tauc gap of 3 eV is presented. This is the highest optical gap reported in literature for ta-C and was directly measured using photothermal deflection spectroscopy (PDS) and UV-Vis spectrophotometry. Independent PDS, UV-Vis and electron energy loss spectroscopy (EELS) measurements confirmed the high gap. A large Urbach slope of 600 meV was measured, which indicated that there are many tail states. Electron spin resonance (ESR) measurements confirmed that this material has a high spin density of 7.5×1020 spins/cm3. Post-deposition vacuum annealing of the samples to 500 °C resulted in a small increase of the optical gap, E04∼3.6 eV, and a decrease of the defects to 2.7×1020 spins/cm3. Post-deposition annealing at this temperature did not significantly change the sp3 fraction, but caused a 2–3 order of magnitude increase of the conductivity and a significant reduction of the stress. Thus, this is the first demonstration that we can engineer the defects in ta-C by increasing the electron delocalisation whilst maintaining the high sp3 and optical gap of the material. [Copyright &y& Elsevier]