•UNCD and DLC films were modified by UV/O3 treatments, O2 or NH3-containing plasmas.•Surface composition, wettability and surface energy change upon modifications.•Higher efficiency of UNCD ...modifications was observed.•Cell attachment and growth were influenced by the surface termination and roughness.
Diamond and diamond-like carbon (DLC) films possess a set of excellent physical and chemical properties which together with a high biocompatibility make them attractive candidates for a number of medical and biotechnological applications. In the current work thin ultrananocrystalline diamond (UNCD) and DLC films were comparatively investigated with respect to cell attachment and proliferation after different surface modifications. The UNCD films were prepared by microwave plasma enhanced chemical vapor deposition, the DLC films by pulsed laser deposition (PLD). The films were comprehensively characterized with respect to their basic properties, e.g. crystallinity, morphology, chemical bonding nature, etc. Afterwards the UNCD and DLC films were modified applying O2 or NH3/N2 plasmas and UV/O3 treatments to alter their surface termination. The surface composition of as-grown and modified samples was studied by X-ray photoelectron spectroscopy (XPS). Furthermore the films were characterized by contact angle measurements with water, formamide, 1-decanol and diiodomethane; from the results obtained the surface energy with its dispersive and polar components was calculated. The adhesion and proliferation of MG63 osteosarcoma cells on the different UNCD and DLC samples were assessed by measurement of the cell attachment efficiency and MTT assays. The determined cell densities were compared and correlated with the surface properties of as-deposited and modified UNCD and DLC films.
Transformation from higher to ultra low friction coefficient was observed in ultrananocrystalline diamond film (UNCD) while changing the test atmospheric conditions. High friction coefficients were ...observed in dry argon and nitrogen atmosphere, however, low and ultra low friction coefficients were obtained in dry oxygen and in ambient atmospheric conditions, respectively. Wear rates follow the same trends as the friction coefficients. This fascinating behavior of friction and wear of UNCD film is explained by the chemical changes of sliding surfaces and extent of passivation of dangling covalent bonds.
Friction coefficients for the various samples under the various test conditions.
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► High to ultra low friction coefficient of UNCD film depends on atmospheric conditions. ► High friction coefficient was obtained in dry argon and nitrogen atmosphere. ► Ultra low friction coefficient was measured in ambient atmospheric condition. ► Chemical changes in wear track influence tribological properties of UNCD film.
Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films have been prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures. The complex nature of the ...coatings required the application of a variety of complementary analytical techniques in order to elucidate their structure. The crystallinity of the samples was studied by selected-area electron diffraction (SAED). The diffraction patterns revealed the presence of diamond crystallites within the films. From the images taken by transmission electron microscopy (TEM) the crystallite size was determined to be on the order of 3–5 nm. The results were confirmed by X-ray diffraction (XRD) measurements exhibiting broad (111) and (220) peaks of diamond from which the average size of the crystallites was calculated. The grain boundary width is 1–1.5 nm as observed by TEM images which corresponds to a matrix volume fraction of about 40–50%. This correlates very well with the crystalline phase content of about 50% in the films estimated from their density (2.75 g/cm
3 as determined by X-ray reflectivity). The bonding structure of the composite films was studied by electron energy loss spectroscopy (EELS) in the region of carbon core level. The spectra were dominated by a peak at 292 eV indicating the diamond nature of the investigated films. In addition, the spectra of NCD/a-C films possessed a shoulder at 284 eV due to the presence of a small sp
2 bonded fraction. This phase was identified also by X-ray photoelectron spectroscopy (XPS). The sp
2/sp
3 ratio was on the order of 10% as determined by deconvolution of the C1s XPS peak.
Diamond nanopillars with diameters of 1 μm down to 50 nm have been fabricated from two types of diamond thin films, namely nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD) using ...electron beam lithography (EBL) and reactive ion etching (RIE) in an inductively coupled oxygen plasma (ICP). Aim of the study was to investigate the suitability of these pillars to incorporate nitrogen‐vacancy (NV) color centers for applications in quantum information technology (QIT). The first part of the investigation is devoted to a characterization of the pillars, their shape, size, and properties. The second part of this investigation concerns the optical properties of NCD and UNCD nanopillars and the incorporation of NV centers within them. Among others, fluorescence mapping and photoluminescence measurements have been employed for this purpose. It turned out that NCD pillars are quite promising for the applications in QIT envisioned. At the present time, the opposite is the case for UNCD pillars. The reasons for these differences will be discussed on the basis of the differences of the two materials NCD and UNCD.
Nanocrystalline diamond films in an amorphous matrix have been deposited by microwave plasma chemical vapour deposition from CH
4/N
2 mixtures and characterized with respect to their morphology and ...structure, composition, crystallinity and bonding structure. The films turned out to be nanocrystalline with crystallite sizes on the order of 3–5 nm and a density of 2.75 g/cm
3. They contain approximately 0.5–1% nitrogen and 10% hydrogen. The nitrogen content of the gas phase has a strong influence on the growth rates and the morphology of the films, whereas the bonding structure is almost unaffected. Raman spectra prove the existence of sp
2 bonded carbon in the matrix; however, according to electron energy loss spectroscopy and X-ray photoelectron spectroscopy investigations the sp
2 content is rather small. Infrared spectra show that the hydrogen is bonded primarily in the form of sp
3 CH
x
groups.
Nanocrystalline diamond/amorphous carbon (NCD/a-C) composite thin films have been deposited by microwave plasma chemical vapour deposition from methane-rich CH
4/N
2 mixtures. The films have been ...thoroughly characterized with respect to basic properties such as growth rates, morphology and structure, composition, crystallinity, and bonding environment. They consist of diamond nanocrystals with diameters of 3–5 nm, which are embedded in an amorphous carbon matrix. Further studies are aimed at application relevant properties.
I/
V and Hall measurements showed that the films are p-type conductive with a resistitivity of 0.14 Ω cm, a carrier concentration of 1.9
×
10
17 cm
−
3, and a carrier mobility of 250 cm
2/Vs. Reflection, scattering and ellipsometric measurements revealed a refractive index of 1.95–2.1 in the visible region and an rather high extinction coefficient of about 0.14 at 400 nm. The films possess a hardness of ca. 40 GPa and a Young's modulus of ca. 390 GPa. Nano tribo test and nano scratch tests proved a low friction coefficient, and a strong protective effect and good adhesion on silicon substrates. First biomedical tests showed that the films are not cytotoxic but bioinert. Finally, the deposition of multilayers nano/polycrystalline diamond with improved properties is demonstrated.
The initial growth phase of ultrananocrystalline diamond/amorphous carbon nanocomposite films (UNCD/a-C) has been investigated by scanning electron microscopy, atomic force microscopy and especially ...Raman spectroscopy. As due to resonance effects Raman spectra of carbon materials strongly depend on the excitation wavelength, a multiwavelength analysis has been performed with
λ
exc ranging from the UV region (325
nm) over the visible range (488 and 514
nm) to the IR region (785
nm). In addition, a set of measurements has been performed with a confocal Raman microscope, i.e. depth resolved, with a wavelength of 532
nm. The samples investigated were deposited with constant parameters, the deposition time being the only parameter varied, resulting in film thicknesses from 100 to 500
nm. It turned out that the diamond fraction and also the grain boundary material do not vary during that stage whereas there are slight but distinct changes of the nature of the amorphous matrix which reflect, among others, in a shift of the graphite-related G band to higher wavenumbers and in an increase of the ratio of D and G bands with increasing film thickness. These changes are discussed in terms of the above mentioned resonance effects; the major changes are a transition of hydrogen containing sp
2 chains to hydrogen-free condensed sp
2 rings when the material is no longer in the surface region of the films but becomes incorporated within the film bulk.
► Investigation of the first stages of UNCD growth. ► Multiwavelength Raman spectroscopy. ► Confocal Raman spectroscopy.
We have investigated the stability of the surface termination of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films after their modification with UV/O3 treatments or ...NH3-containing plasmas. The films were prepared by microwave plasma chemical vapor deposition from CH4/N2 mixtures and possess the H-termination typical for all CVD grown diamond films. The treatment with UV/O3 or NH3/N2 plasma resulted in a change of the surface termination as revealed by contact angle measurements and X-ray photoelectron spectroscopy (XPS). Both processes rendered the as-grown hydrophobic UNCD surface hydrophilic; the influence of the treatment time as well as that of the carrier gas (N2 or Ar) for the plasma process were investigated. The main task of this investigation was to determine the stability of the surface termination with storage time and storage conditions and upon exposure to standard organic solvents, like acetone, ethanol and i-propanol. It was found that for the UV/O3 treated UNCD surfaces the storage in air, and after NH3/N2 plasma modification package under reduced pressure preserved to a great extent the achieved hydrophilic properties in a period up to three months. The changes that occur predominantly during the first days after the modification step were due mostly to interchange of surface groups with the ambient. Similar processes were observed after exposure of the UNCD surfaces to standard organic solvents.
► UNCD/a-C films were modified by UV/O3 treatments or NH3-containing plasmas. ► Stability of surface termination of UNCD/a-C films after the modifications was studied. ► Storage conditions preserving the achieved hydrophilic properties were established. ► Exposure to organic solvents influences the surface termination.
Ultrananocrystalline diamond/amorphous carbon nanocomposite films (UNCD/a-C) have been deposited by microwave plasma chemical vapor deposition from a 17% CH4/N2 mixture. The films consist of diamond ...nanocrystallites of 3–5nm embedded in an amorphous carbon matrix of 1–1.5nm width. In a first series of experiments it is shown that as-grown UNCD/a-C films are hydrogen-terminated, conductive and very stable. Furthermore, by plasma- and photochemical treatments the H-termination can either be improved or replaced by terminating OH or F functionalities, whereas chemical room temperature processes to change the termination failed. A second set of investigations concerns the functionalization of differently terminated UNCD surfaces. Processes are discussed to bind DNA on H-terminated UNCD and to deposit an anti-fouling poly(ethylene glycol) layer on OH-terminated films. A third series of experiments shows that UNCD surfaces are not prone to unspecific interactions with highly-fouling proteins such as bovine serum albumin (BSA) but nevertheless some interaction will take place. However, the amount of adsorption and also the ratio of BSA and fibrinogen adsorption, which is of importance for the hemocompatibility of a surface, can be adjusted by the surface termination. Finally, it will be shown that continuous as-grown UNCD surfaces are bioinert and not cytotoxic for a variety of different cell lines.
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).
