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Thin nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films and amorphous diamond-like carbon (DLC) films were prepared by three methods: microwave plasma chemical vapour deposition (MWCVD) from methane/nitrogen mixtures (NCD/a-C), RF magnetron sputtering of a pure graphite target in argon/methane ambients, and pulsed laser deposition (PLD) in vacuum or argon atmosphere (DLC). The films prepared by the three techniques were comprehensively characterized with respect to their bonding structure by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma chemical vapour deposition (MWCVD) from CH4/N2 mixtures. The films have been thoroughly characterized by a variety of methods with respect to their composition, morphology, structure and bonding environment. Thereafter, the bioproperties of these films have been investigated. Tests with osteoblast-like cells and pneumocytes proved that the NCD/a-C films are not cytotoxic. In addition, exposure of the films to a simulated body fluid revealed that they are bioinert. Further experiments addressed the question whether biomolecules such as RNA or proteins bind unspecifically on the surfaces of NCD/a-C films. By means of atomic force microscopy (AFM) and scanning force spectroscopy measurements it was established that, in contrast to control experiments with mica and glass, no interaction between the nanocrystalline diamond and either RNA or protein molecules took place. The results of these experiments concerning the biologically relevant properties of NCD/a-C films are discussed in view of possible future applications, e.g. as a material for the immobilization of biomolecules and their characterization by AFM measurements and related techniques. [Copyright &y& Elsevier]

Abstract: Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films have been deposited by microwave plasma chemical vapour deposition from CH4/N2 mixtures. They consist of diamond nanocrystals of 3–5 nm grain size, embedded in an amorphous matrix with a thickness of 1–1.5 nm. The matrix is mainly sp3 bonded, with about 20–30% sp2 material, and contains 10% hydrogen in the form of sp3 CH x units. The influence of the substrate temperature on the growth and the properties of the films was investigated in the range from 520 to 770 °C. The growth rate increases with increasing temperature, indicating a thermally activated process. The apparent activation energy of 0.38±0.02 eV is lower than the values found for standard diamond deposition, thereby proving that differences between both processes exist. X-ray diffraction revealed that the crystalline properties of the NCD films (e.g. the grain size) are not affected by the temperature. From Raman and infrared measurements, it becomes evident, however, that the properties of the matrix are distinctively different at low and high temperatures, respectively. Possible reasons for these observations are discussed in some detail. [Copyright &y& Elsevier]

We present investigations of the sorption behaviour of amorphous nitrogen-rich carbon nitride films (CNx) towards water vapour and volatile organic compounds, for example methanol, ethanol, i-propanol and acetone, in order to evaluate their potential as sensitive layers for cantilever-based chemical sensor applications. The CNx films were deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) utilizing transport reactions from a solid carbon source. In order to study the influence of the thickness of the sensitive layer on its sensitivity and selectivity, two series of cantilevers coated with 120 nm and 240 nm CNx films were prepared. We found that the variation of the film thickness affected the sorption process of the CNx film quantitatively as well as qualitatively. For thin films (120 nm), the sensor dynamic responses (frequency shift) increased with increasing molecular weight of the analytes. The largest responses were observed towards acetone and i-propanol ; here, the cantilever acted as a resonant microbalance. When the film thickness was increased from 120 to 240 nm, the analytes with higher dipole moments caused stronger response signals. In this case we observed, for example, an increase of the sensitivity towards methanol by a factor of more than three. The performance of the cantilever-based sensors functionalised with CNx coatings was compared to that of organic polymers, and the observed peculiarities were explained by the chemical nature of the sensitive materials. [ABSTRACT FROM AUTHOR]

Nitrogen-rich carbon nitride films were prepared by three different deposition methods on fused silica, stainless steel and silicon cantilever substrates. Their optical properties were studied by spectroscopic ellipsometry and UV spectrometry. Mechanical properties such as plastic and Vickers microhardness, Young’s modulus, adhesion and film stress were also tested. The results were compared with the properties of films with lower nitrogen concentrations. [ABSTRACT FROM AUTHOR]

Abstract. Amorphous nitrogen-rich carbon nitride (CN[sub x]) films have been prepared by inductively coupled plasma chemical vapour deposition (ICP-CVD) utilizing transport reactions from a solid carbon source. The nitrogen atomic fraction N/(C + N) is about 1 or even higher as detected by various surface and bulk sensitive methods. An investigation of the chemical bonding structure showed that the films are composed of >C:N- units with a small fraction of -C is equivalent to N groups. Based on these findings, several structural units derived from cis- and trans-conjugated carbon-nitrogen chains are proposed. The optical properties of the CN[sub x] films were studied by transmission spectroscopy and spectral ellipsometry; the optical Tauc gap was determined to 2.1 +/- 0.05 eV. The photoluminescence characteristics were measured at three different excitation wavelengths (476, 488 and 515 nm) and revealed two individual contributions. These data are interpreted in terms of the different structural units comprising the nitrogen-rich CN[sub x] films. [ABSTRACT FROM AUTHOR]

Abstract. The humidity sensitive properties of carbon nitride (CN[sub X]) films deposited by two methods, inductively coupled plasma chemical vapour deposition utilizing transport reactions and pulsed laser deposition combined with an rf discharge, have been investigated. For this purpose capacitance humidity sensors with a CN[sub X] detecting element have been fabricated and tested. Fast and significant responses toward moisture am registered by the changes of the electrical parameters. The CN[sub X] films sensing mechanism has been discussed. The results obtained show unambiguously that CN[sub X] films appear to be a promising candidate as a humidity sensitive element in up-to-date electronic noses. [ABSTRACT FROM AUTHOR]

Abstract. A combined HFCVD/in situ STM setup is presented that allows the performance of in situ scanning tunneling microscopy measurements during hot-filament chemical vapour deposition of diamond thin films despite the adverse conditions required for diamond growth. Both parts of the setup, the hot filament reactor and the tunneling microscope, are described in detail. Performance tests show that STM measurements can be carried out irrespective of the high substrate and filament temperatures, the high pressures, and the high gas flows necessary for diamond deposition. First measurements under process conditions on a pre-grown diamond surface am presented, demonstrating the feasibility of STM measurements with high resolution and long-term stability during the growth of diamond thin films. [ABSTRACT FROM AUTHOR]

Abstract: The influence of the nucleation density on the development of the morphology of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films and their mechanical properties has been investigated by variation of the substrate pre-treatment used to enhance the nucleation. The films have been prepared by microwave plasma chemical vapour deposition from 17% CH4/N2 mixtures on silicon substrates. Their morphology and topography have been characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). It is shown that by successive addition of ultradispere diamond powder (3–5 nm average grain size) to the suspension of nanocrystalline diamond powder (250 nm average grain size) in n-pentane used for the ultrasonic pre-treatment, the nucleation density can be enhanced by two orders of magnitude from 1×108 cm−2 to higher than 1×1010 cm−2. This changes the morphology of the films from individual nodules to uniform coatings and reduces the thickness required to achieve closed films. The mechanical properties of these films have been investigated by nanoindentation and nanoscratch tests. The determined hardness was about 25–28 GPa for all samples under investigation, the elastic modulus 262–271 GPa, and the elastic recovery 62–65%, revealing the influence of the amorphous carbon matrix. The scratch tests proved a strong adhesion of the UNCD/a-C coatings and their protective effect on silicon substrates. The nucleation density has no distinct influence on the mechanical properties of the closed films. [Copyright &y& Elsevier]

Abstract: Ultrananocrystalline diamond (UNCD) films have been deposited by microwave plasma chemical vapor deposition from 17% CH4/N2 mixtures. In order to change the original hydrogen termination of the UNCD surfaces, the films have subsequently been subjected either to the so-called UV/O3 treatment which leads to OH-terminated surfaces, or to NH3/N2 plasmas which introduces NH2 groups but also a certain amount of OH groups. These three types of surfaces have been characterized by X-ray photoelectron spectroscopy, contact angle and ζ-potential measurements. The contact angle measurements have shown that as-grown UNCD surfaces are highly hydrophobic but became highly hydrophilic after both treatments. The ζ-potential measurements revealed that the isoelectric point of the H-terminated as-grown surface is distinctively higher than that of either UV/O3 or NH3/N2 plasma treated surfaces. Finally, the interactions of these surfaces with neurons of the cockroach Leucophaea maderae have been investigated. These studies have shown that especially the two treated surfaces allow for a fast, strong attachment of these cells without compromising their viability and without changing their normal physiological responses. These results will be discussed in terms of those obtained with the different surface characterization techniques. [Copyright &y& Elsevier]