J.G. Buijnsters

Abstract In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spectroscopy, and x-ray absorption near edge structure (XANES) to quantify the hydrogen (H) content in hydrogenated amorphous carbon (aC: H) films. aC: H films with a hydrogen content varying from 29 to 47 at.% have been synthesized by electron cyclotron resonance chemical vapor deposition at low substrate temperatures (≪ 120 C) applying a wide range of bias voltage, V b,(-300 V≪ V b≪+ 100 V).

Poly (vinylidene fluoride) (PVDF) composites with different types of nanodiamond (ND) particles were produced by solvent casting. The variations of the morphological, structural, optical, thermal and electrical properties of the composites were studied as a function of nanofiller type (without and with air oxidation treatment) and concentration (in the range 0.1–1 wt%). No noticeable differences were found in the polymer crystallization process, the processing conditions and the filler determining the morphology and structure of the polymer. Nevertheless, ND nanofillers were useful for the tailoring of the optical properties, and also slightly contributed to the thermodynamic stability of the samples. An increase in the dielectric constant (∼2) of the ND composites, while maintaining constant the dielectric losses, was observed, independently of the filler concentration. On the other hand, solvent casted porous composites crystallize mainly in the electroactive γ-phase of PVDF. Those composite membranes were evaluated with pre-osteoblast culture tests and these revealed that the inclusion of ND nanoparticles does not induce cytotoxicity on the samples. Taking advantage of the properties of the polymer for cell culture and with the potential of the ND filler for protein functionalization and drug delivery, it is concluded that NDs/PVDF composites are a suitable platform for biomedical applications.

This is a pioneering study on the synthesis and application of composites based on micro- and nanodiamonds for the photocatalytic degradation of environmental water pollutants. Micro- and nanodiamond powders (with particle sizes of 1–3 μm and 2–10 nm, respectively) were combined with TiO2, by varying the carbon-phase content, and tested as composite photocatalysts for the degradation of diphenhydramine, which is a pharmaceutical water pollutant, under near-UV/Vis irradiation. These composites exhibited higher photocatalytic activity than the respective bare materials. In addition, composites prepared with pristine nanodiamonds were always more active than those prepared with microdiamonds of the same carbon content. A significant enhancement in the photocatalytic performance was observed on preparation of the composite with 15 wt % of nanodiamonds oxidised in air at 703 K; these oxidised nanodiamonds contained mainly carboxylic anhydrides, lactones, phenols and, to a lesser extent, carbonyl/quinone groups on their surface.

ABSTRACT By an extensive investigation of the principal growth parameters on the deposition process, we realized the epitaxial growth of crystalline wurtzite GaN thin films on single crystal (001) diamond substrates by metal organic chemical vapor deposition. From the influence of pressure, V/III ratio, and temperature, it was deduced that the growth process is determined by the mass-transport of gallium precursor material toward the substrate. The highest temperature yielded an improved epitaxial relationship between grown layer and substrate. X ray diffraction (XRD) pole figure analysis established the presence of two domains of epitaxial layers, namely (0001) 〈 10 0〉 GaN∥ (001)[110] diamond and (0001) 〈 10 0〉 GaN∥ (001) [10] diamond, which are 90∘ rotated with respect to each other. The presence of these domains is explained by the occurrence of areas of (2×1) and (1×2) surface reconstruction of the diamond substrate. When applying highly misoriented diamond substrates toward the [110] diamond direction, one of the growth domains is suppressed and highly epitaxial GaN on (001) diamond is realized.

We investigated the mechanical and tribological properties of hydrogenated amorphous carbon (aC: H) films on silicon substrates by nanoindentation, ball-on-disc tribotesting and scratch testing. The aC: H films were deposited from an argon/methane gas mixture by bias-enhanced electron cyclotron resonance chemical vapour deposition (ECR-CVD). We found that substrate biasing directly influences the hardness, friction and wear resistance of the aC: H films. An abrupt change in these properties is observed at a substrate bias of about− ...

Abstract In the present work, aC: H films have been grown from argon/methane gas mixtures by Electron Cyclotron Resonance Chemical Vapour Deposition (ECRCVD). The effect of the application of a dc bias voltage to the silicon substrate material on the structural, morphological and mechanical properties of the films has been explored by multiple analysis techniques such as IR and micro-Raman spectroscopy, AFM, nano-indentation and pin-ondisk wear testing. In general, within the range of–300 V to+ 100 V applied substrate ...

Gold (1 wt.%) was loaded on several types of carbon materials (activated carbon, polymer based carbon xerogels, multi-walled carbon nanotubes, nanodiamonds, microdiamonds, graphite and silicon carbide) using two different methods (sol immobilisation and double impregnation). Samples were characterised by N2 adsorption at −196 °C, temperature programmed desorption, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectrometry, high-angle annular dark-field imaging (Z-contrast), X-ray photoelectron spectroscopy and atomic absorption spectroscopy. The obtained Au/carbon materials were used as catalysts for the oxidation of cyclohexane to cyclohexanol and cyclohexanone, with aqueous H2O2, under mild conditions. The most active catalyst was prepared by supporting gold nanoparticles on carbon nanotubes by the sol method, achieving an overall turnover number of ca. 171 and an overall yield of 3.6% after 6 h reaction time. These values are comparable to the industrial process (that uses Co catalysts and high temperature), but were obtained at ambient temperature with considerable low loads of catalyst (Au catalyst to substrate molar ratio always lower than 1 × 10−3), which is of relevance for establishing a greener catalytic process for cyclohexane oxidation. Moreover, a very high selectivity towards the formation of cyclohexanol and cyclohexanone was achieved, since no traces of by-products were detected. The promoting effect of pyrazine carboxylic acid was observed and an optimum peroxide-to-catalyst molar ratio was found to be 2 × 104. Further increase of the oxidant amount results in decreased yield due to overoxidation reactions at higher H2O2 amounts. Catalyst recycling was tested up to six consecutive cycles for the most active catalytic system (gold deposited on carbon nanotubes by sol immobilisation), and it was found that the catalyst maintains almost the original level of activity after several reaction cycles (there was only a 6% drop in activity after the sixth cycle) with a rather high selectivity to cyclohexanol and cyclohexanone and with no catalyst leaching. The differences in activity for the other samples can be explained in terms of gold nanoparticle size and the textural properties of the carbon support.

Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by solution casting, were studied their chemical, mechanical, electrical and electro-mechanical properties evaluated. Few-layer graphene (FLG) nanoplatelets (G-NPL), graphene oxide (GO) and reduced graphene oxide (rGO) and single-walled carbon nanohorns (SWCNH)) were found to have a strong influence in the overall properties of the composites prepared with up to 5 wt% nanofiller contents. The mechanical strain of carbonaceous nanofillers/PVDF composites decreases from 15% to near 5% of maximum strain. The electrical percolation threshold depends on the nanofiller type, being below 1 wt% for rGO and near 2 wt% for the remaining nanofillers. The electrical conductivity shows a maximum increase of nine orders of magnitude, from s z 5 Â 10 À11 S/m of pure PVDF to s z 1 Â 10 À2 S/m for rGO/PVDF composites with 5 wt% nanofillers. The conduction mechanism being related to hopping between the carbonaceous nanofillers for concentrations higher than the percolation threshold. Furthermore, the composites show electro-mechanical properties, except for G-NPL materials, with rGO/PVDF composites with 5 wt% nanofiller content showing higher Gauge factor (GF) values, reaching GFz 11 for deformations between 0.5 and 2 mm in 4-point bending experiments. These results demonstrate the suitability of the composites for strain sensing applications.