J.G. Buijnsters | Delft University of Technology (original) (raw)

Papers by J.G. Buijnsters

Research paper thumbnail of Hydrogen quantification in hydrogenated amorphous carbon films by infrared, Raman, and x-ray absorption near edge spectroscopies

Abstract In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spe... more 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).

Research paper thumbnail of Nanodiamonds/poly(vinylidene fluoride) composites for tissue engineering applications

Poly (vinylidene fluoride) (PVDF) composites with different types of nanodiamond (ND) particles w... more 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.

Research paper thumbnail of Nanodiamond-TiO2 composites for heterogeneous photocatalysis

This is a pioneering study on the synthesis and application of composites based on micro- and nan... more 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.

Research paper thumbnail of Molybdenum Interlayers for Nucleation Enhancement in Diamond CVD Growth

Journal of Nanoscience and Nanotechnology, 2010

The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of mi... more The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films synthesized by hot filament chemical vapour deposition was studied. The MCD and NCD films were deposited using methane concentrations of 1% and 2%, respectively. The presence of a Mo nucleation layer enabled the formation of more uniform NCD films with reduced surface roughness (rms roughness ∼40 nm for a 750-nm thick layer) and with significantly less interfacial voids due to the superior nucleation densities and surface coverage in the early stages of NCD film formation. During the initial stages of MCD film growth, the nucleation density increased by one order of magnitude as compared to uncoated silicon. As a result, much thinner MCD films with smaller surface grain sizes and, thus, reduced surface roughness could be produced as well. The presence of a Mo nucleation layer not only leads to a structural optimization of NCD and MCD films but also allows fast nucleation and film growth kinetics at relatively low substrate temperatures (∼575 C), relevant for the coating of substrate materials that do not withstand high substrate temperatures.

Research paper thumbnail of Diffusion-modified boride interlayers for chemical vapour deposition of low-residual-stress diamond films on steel substrates

Thin Solid Films, 2003

The feasibility of using a boriding pretreatment for the chemical vapour deposition (CVD) of adhe... more The feasibility of using a boriding pretreatment for the chemical vapour deposition (CVD) of adherent, low-residual-stress diamond films on ferritic tool and AISI type 316 austenitic stainless steels was investigated. The steel samples were borided by means of a pack cementation process at a temperature of 950 8C using an interrupted thermal cycling process. Boriding of the alloy steels results in a very high surface hardness of approximately 3780 VHN due to the precipitation of alloy borides such as chromium boride in the predominantly FeB andyor Fe B case. The boriding conditions, and hence the microstructural state of the 2 as-borided steels, was found to have a strong influence on the diamond film characteristics, particularly on the adherence. Detailed characterisation of the as-borided steels, as well as the deposited diamond films and interlayer modification during the CVD process, is discussed based on scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy investigations. Under optimised conditions, adherent and continuous diamond films of good quality have been obtained on both the ferritic tool and austenitic stainless steels. In the case of borided surface structures without the presence of a FeB phase, diffusion-modified gradient microstructures were found to accommodate efficiently the high thermal stress expected between the steel substrate and the diamond film, resulting in low-residual-stress films. ᮊ

Research paper thumbnail of Direct deposition of polycrystalline diamond onto steel substrates

Surface and Coatings Technology, 2007

Research paper thumbnail of Gas nitriding of chromium in NH3–H2 atmosphere

Materials Science and Engineering: A, 2003

ABSTRACT Nitriding behaviour of pure chromium in an NH3–H2 atmosphere is discussed. Chromium samp... more ABSTRACT Nitriding behaviour of pure chromium in an NH3–H2 atmosphere is discussed. Chromium samples were nitrided for various times (1, 4, 24, 48, 72, 120 and 142 h) at 800 °C. The nitridation is accompanied by an increase in surface porosity, which leads to an enlarged surface brittleness. Vickers microhardness measurements along the direction of nitrogen diffusion show an overall increase in hardness as a result of the nitriding process resulting in a surface hardness as high as about 1200–1400 Vickers. X-ray diffraction studies reveal the formation of Cr2N, CrN and Cr(N) phases upon nitriding. Scanning electron microscopy and energy dispersive X-ray analysis (EDAX) show an increasing fraction of the CrN phase formed at the surface with increasing nitriding times. EDAX line profile analysis of the specimen nitrided for 120 h shows a three-layered structure. Though the surface layer and the second layer adjacent to it, both consist of a mixture of CrN and Cr2N phases, the fraction of CrN is much higher in the surface layer. Nitridation of Cr2N is suggested as the possible mechanism for CrN formation at the surface with increasing nitriding times, for the nitriding parameters chosen in the present study.

Research paper thumbnail of Direct photothermal techniques for quantification of anthocyanins in sour cherry cultivars

Talanta, 2011

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and... more The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and of optothermal window (OW) method for quantification of total anthocyanin concentration (TAC) in five sour cherry varieties is compared to that of the spectrophotometry (SP). High performance liquid chromatography (HPLC) was used to identify and quantify specific anthocyanins. Both, PAS and OW are direct methods that unlike SP

Research paper thumbnail of DC substrate bias effects on the physical properties of hydrogenated amorphous carbon films grown by plasma-assisted chemical vapour deposition

Vacuum, 2007

Hydrogenated amorphous carbon (a-C:H) films have been grown from argon/methane gas mixtures by el... more Hydrogenated amorphous carbon (a-C:H) films have been grown from argon/methane gas mixtures by electron cyclotron resonance chemical vapour deposition (ECR-CVD) on silicon substrates. The effects of the application of a DC substrate bias on the structural, morphological and mechanical properties of the films have been explored by multiple analysis techniques such as infrared and micro-Raman spectroscopy, atomic force microscopy, nanoindentation and pin-on-disk wear testing. In general, within the range of applied substrate bias (i.e. from À300 up to +100 V) we have observed a strong correlation between all measured properties of the a-C:H films and the ion energy. This work shows that the properties can differ greatly and indicates a threshold energy in the order of 90 eV. For the production of hard, low-friction coatings energies above this value are required. r

Research paper thumbnail of Adhesion analysis of polycrystalline diamond films on molybdenum by means of scratch, indentation and sand abrasion testing

Thin Solid Films, 2005

Diamond films have been grown by hot-filament chemical vapour deposition (CVD) on molybdenum subs... more Diamond films have been grown by hot-filament chemical vapour deposition (CVD) on molybdenum substrates under different growth conditions. The films grown with increasing substrate temperatures show a higher interconnection of diamond grains, whereas increasing methane concentrations in the 0.5-4.0% range lead to a transition from micro-towards nanocrystalline films. X-ray diffraction analysis shows Mo 2 C interlayer formation. Indentation, scratch and sand erosion tests are used to evaluate the adhesion strength of the diamond films. Using steel ball indenters (F 750 Am), indentation and scratch adhesion tests are performed up to final loads of 200 N. Upon indentation, the load values at which diamond film failure such as flaking and detachment is first observed, increase for increasing temperatures in the deposition temperature range of 450-850 8C. The scratch adhesion tests show critical load values in the range of 16-40 N normal load for films grown for 4 h. In contrast, diamond films grown for 24 h at a methane concentration of 0.5% do not show any failure at all upon scratching up to 75 N. Film failure upon indenting and scratching is also found to decrease for increasing methane concentration in the CVD gas mixture. The sand abrasion tests show significant differences in coating failure for films grown at varying CH 4 /H 2 ratios. In contrast to the other tests, here best coating performance is observed for the films deposited with a methane concentration of 4%. D

Research paper thumbnail of Pitting corrosion behaviour of diamond coated tool steel

Surface and Coatings Technology, 2005

Using a hot filament chemical vapour deposition reactor, diamond films of approximately 2 -3 Am i... more Using a hot filament chemical vapour deposition reactor, diamond films of approximately 2 -3 Am in thickness were deposited on tool steel specimens with three different interlayer systems, namely CrN, Si and borided steel. The morphology, defect densities and residual stresses of the diamond films were strongly governed by the type of interlayer used. Electrochemical potentiodynamic polarisation studies have been carried out on the diamond deposited tool steel specimens in NaCl solutions of two different concentrations, 0.01 M and 0.50 M, respectively. The type of interlayer used for diamond coating on tool steel has a strong influence on the corrosion potential. The maximum shift in the equilibrium corrosion potential is observed for the silicon interlayer. However, it leads to selective dissolution of the carbide phase upon anodic polarisation. A near total resistance to pitting of the CrN coated tool steel specimens is observed with the introduction of a very thin diamond layer of 2 -3 Am. With increasing chloride ion concentration in the electrolyte, reverse trends in the shift of E corr are observed for the blank tool steels in comparison to the diamond-coated specimens. Detailed SEM characterisation of the corrosion-tested specimens indicates the possible operating mechanisms. D

Research paper thumbnail of Influence of external bias on the surface morphology of a-C:H films grown by electron cyclotron resonance chemical vapor deposition

Surface and Coatings Technology, 2007

We have studied the influence of an external bias on the surface morphology of a-C:H films grown ... more We have studied the influence of an external bias on the surface morphology of a-C:H films grown by electron cyclotron resonance chemical vapor deposition (ECR-CVD) on silicon substrates. We have deposited films for 1 h at different bias from + 100 V down to −250 V and analyzed their surface morphology by atomic force microscopy (AFM). For biases equal or higher than −80 V the film morphology is cauliflower-like, which is due to the shadowing geometry effects inherent to the deposition process. In contrast, for highly negative biases the films become ultrasmooth. Here, the film morphology is consistent with an Edwards-Wilkinson scaling behavior, which starts to operate at shorter length distances as the external bias becomes more negative. This morphology is likely due to the interplay of ion induced physical sputtering and enhanced downhill surface mobility.

Research paper thumbnail of Growth dynamics of ultrasmooth hydrogenated amorphous carbon films

Physical Review B, 2006

We have studied the growth dynamics of ultrasmooth hydrogenated amorphous carbon films deposited ... more We have studied the growth dynamics of ultrasmooth hydrogenated amorphous carbon films deposited on silicon substrates by electron cyclotron resonance chemical vapor deposition from argon/methane gas mixtures applying a high negative external bias. The surface morphology of films deposited for different growth times under the same experimental conditions was analyzed by atomic force microscopy. Our analysis leads to values of the growth, roughness, and coarsening exponents of 0, 0.1, and 0.5, respectively. As it has been recently proposed that the growth dynamics of amorphous films by ion-assisted methods should obey the Edwards-Wilkinson ͑EW͒ growth mode, we have analyzed the compatibility of our data with this model. Our analysis indicates that, although the scaling data could be interpreted in terms of the EW model, the relative large data error bars and the film ultrasmoothness preclude the unambiguous assessment of the EW growth mode for our film growth evolution. In our system, the interplay of shadowing, physical sputtering and enhanced surface mobility ion-induced effects contribute likely to the leveling and final ultrasmoothness of the film surface.

Research paper thumbnail of Novel morphology of chemical vapor deposited diamond films

physica status solidi (c), 2010

ABSTRACT We have obtained simultaneously nanocrystalline and {100} faceted large-grained polycrys... more ABSTRACT We have obtained simultaneously nanocrystalline and {100} faceted large-grained polycrystalline diamond films not only on different substrates but also on the same substrate in only one deposition run using a novel approach for substrate arrangement. Furthermore, interesting unusual morphologies and microstructures composed by non-faceted nanostructures and terminated with large smooth {100} facet-like belt are found near the edges of the top square sample. The morphology variation is likely caused by the so called edge effect, where a strong variation in temperature is also present. We have modelled the temperature distribution on the substrates by computer simulations using the finite element method. The novel feature, namely the coexistence of oval non-faceted nanocrystalline diamond grains and large smooth {100} facet-like belt in one diamond grain, is in the transition from {100} faceted polycrystalline diamond to cauliflower-like nanocrystalline diamond. The formation mechanism is discussed based on the temperature analysis and other simulation results described in the literature. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Formation of {100} facet-terminated nanocrystalline diamond by microwave plasma chemical vapor deposition: Edge effect

physica status solidi (a), 2010

... 1, each corner of sample PD1 has a large spot, which is actually a very big multi-twinned cry... more ... 1, each corner of sample PD1 has a large spot, which is actually a very big multi-twinned crystal of mm range size. As an example, Fig. 2b shows the much bigger multi-twinned crystal grown in the left corner as compared to the relatively smaller crystals grown along the edges. ...

Research paper thumbnail of The applicability of ultra thin silicon films as interlayers for CVD diamond deposition on steels

physica status solidi (a), 2003

ABSTRACT In this study, the use of thin Si interlayers (35–150 nm) for promoting diamond depositi... more ABSTRACT In this study, the use of thin Si interlayers (35–150 nm) for promoting diamond deposition onto steel is investigated. The diamond films are deposited by hot filament CVD onto AISI type 316 stainless and high-speed steels. Single stage deposition at substrate temperatures ranging from as low as 475 to 750 °C is found to result only in non-continuous films with low number densities of diamond crystallites. A composite film of diamond and carbides is formed at intermediate temperatures of about 650 °C. It is believed that the formation of iron silicide phases at the exposed steel substrate surfaces leads to diffusion barriers for free iron from the steel matrix, so that graphitic soot formation is significantly avoided.Utilizing a two-stage deposition process, the density and uniformity of the deposited diamond films areincreased and a nearly continuous cauliflower shaped diamond film is obtained. Micro-Raman spectros-copy, scanning electron microscopy and X-ray diffraction techniques are employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers.

Research paper thumbnail of Surface morphology stabilization by chemical sputtering in carbon nitride film growth

Journal of Physics D: Applied Physics, 2008

We have studied the influence of chemical sputtering effects on the morphology of carbon nitride ... more We have studied the influence of chemical sputtering effects on the morphology of carbon nitride films grown on silicon substrates by electron cyclotron resonance chemical vapour deposition. This study has been performed by comparing the evolution of their morphology with that of hydrogenated amorphous carbon films grown under similar conditions, where these effects are not present. When chemical sputtering effects operate we observe a film surface stabilization for length scales in the 60-750 nm range after a threshold roughness of about 3-4 nm has been developed. This stabilization is explained on the basis of the re-emission of nitrogen etching species, which is confirmed by growth experiments on microstructured substrates.

Research paper thumbnail of Molybdenum Interlayers for Nucleation Enhancement in Diamond CVD Growth

Journal of Nanoscience and Nanotechnology, 2010

The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of mi... more The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films synthesized by hot filament chemical vapour deposition was studied. The MCD and NCD films were deposited using methane concentrations of 1% and 2%, respectively. The presence of a Mo nucleation layer enabled the formation of more uniform NCD films with reduced surface roughness (rms roughness ∼40 nm for a 750-nm thick layer) and with significantly less interfacial voids due to the superior nucleation densities and surface coverage in the early stages of NCD film formation. During the initial stages of MCD film growth, the nucleation density increased by one order of magnitude as compared to uncoated silicon. As a result, much thinner MCD films with smaller surface grain sizes and, thus, reduced surface roughness could be produced as well. The presence of a Mo nucleation layer not only leads to a structural optimization of NCD and MCD films but also allows fast nucleation and film growth kinetics at relatively low substrate temperatures (∼575 C), relevant for the coating of substrate materials that do not withstand high substrate temperatures.

Research paper thumbnail of Atomic force microscopy studies on the surface morphology of {111} tabular AgBr crystals

Journal of Crystal Growth, 2000

Both ex situ and in situ atomic force microscopy have been applied to study the {111} and {100} s... more Both ex situ and in situ atomic force microscopy have been applied to study the {111} and {100} surfaces of tabular silver bromide crystals grown from dimethyl sulphoxide–water solutions. This resulted in observations of monosteps, macrosteps, etch pits, pinning of steps and nucleated crystals showing twin planes. These examinations indicate that the growth and dissolution of both the {100} and

Research paper thumbnail of Morphology and growth mechanism of multiply twinned AgBr and AgCl needle crystals

Journal of Crystal Growth, 1999

In this study the morphology and growth mechanism of AgX (X=Cl, Br) needle crystals will be revea... more In this study the morphology and growth mechanism of AgX (X=Cl, Br) needle crystals will be revealed. The silver halide needles are grown by two different techniques. AgBr needles are grown with an extractive crystallization in a dimethylsulfoxide–water mixture and AgCl needles are grown from the vapor phase. All needles contain nonparallel twin planes. The morphology of the AgBr needles

Research paper thumbnail of Hydrogen quantification in hydrogenated amorphous carbon films by infrared, Raman, and x-ray absorption near edge spectroscopies

Abstract In this study, we have employed infrared (IR) absorption spectroscopy, visible Raman spe... more 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).

Research paper thumbnail of Nanodiamonds/poly(vinylidene fluoride) composites for tissue engineering applications

Poly (vinylidene fluoride) (PVDF) composites with different types of nanodiamond (ND) particles w... more 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.

Research paper thumbnail of Nanodiamond-TiO2 composites for heterogeneous photocatalysis

This is a pioneering study on the synthesis and application of composites based on micro- and nan... more 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.

Research paper thumbnail of Molybdenum Interlayers for Nucleation Enhancement in Diamond CVD Growth

Journal of Nanoscience and Nanotechnology, 2010

The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of mi... more The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films synthesized by hot filament chemical vapour deposition was studied. The MCD and NCD films were deposited using methane concentrations of 1% and 2%, respectively. The presence of a Mo nucleation layer enabled the formation of more uniform NCD films with reduced surface roughness (rms roughness ∼40 nm for a 750-nm thick layer) and with significantly less interfacial voids due to the superior nucleation densities and surface coverage in the early stages of NCD film formation. During the initial stages of MCD film growth, the nucleation density increased by one order of magnitude as compared to uncoated silicon. As a result, much thinner MCD films with smaller surface grain sizes and, thus, reduced surface roughness could be produced as well. The presence of a Mo nucleation layer not only leads to a structural optimization of NCD and MCD films but also allows fast nucleation and film growth kinetics at relatively low substrate temperatures (∼575 C), relevant for the coating of substrate materials that do not withstand high substrate temperatures.

Research paper thumbnail of Diffusion-modified boride interlayers for chemical vapour deposition of low-residual-stress diamond films on steel substrates

Thin Solid Films, 2003

The feasibility of using a boriding pretreatment for the chemical vapour deposition (CVD) of adhe... more The feasibility of using a boriding pretreatment for the chemical vapour deposition (CVD) of adherent, low-residual-stress diamond films on ferritic tool and AISI type 316 austenitic stainless steels was investigated. The steel samples were borided by means of a pack cementation process at a temperature of 950 8C using an interrupted thermal cycling process. Boriding of the alloy steels results in a very high surface hardness of approximately 3780 VHN due to the precipitation of alloy borides such as chromium boride in the predominantly FeB andyor Fe B case. The boriding conditions, and hence the microstructural state of the 2 as-borided steels, was found to have a strong influence on the diamond film characteristics, particularly on the adherence. Detailed characterisation of the as-borided steels, as well as the deposited diamond films and interlayer modification during the CVD process, is discussed based on scanning electron microscopy, X-ray diffraction and micro-Raman spectroscopy investigations. Under optimised conditions, adherent and continuous diamond films of good quality have been obtained on both the ferritic tool and austenitic stainless steels. In the case of borided surface structures without the presence of a FeB phase, diffusion-modified gradient microstructures were found to accommodate efficiently the high thermal stress expected between the steel substrate and the diamond film, resulting in low-residual-stress films. ᮊ

Research paper thumbnail of Direct deposition of polycrystalline diamond onto steel substrates

Surface and Coatings Technology, 2007

Research paper thumbnail of Gas nitriding of chromium in NH3–H2 atmosphere

Materials Science and Engineering: A, 2003

ABSTRACT Nitriding behaviour of pure chromium in an NH3–H2 atmosphere is discussed. Chromium samp... more ABSTRACT Nitriding behaviour of pure chromium in an NH3–H2 atmosphere is discussed. Chromium samples were nitrided for various times (1, 4, 24, 48, 72, 120 and 142 h) at 800 °C. The nitridation is accompanied by an increase in surface porosity, which leads to an enlarged surface brittleness. Vickers microhardness measurements along the direction of nitrogen diffusion show an overall increase in hardness as a result of the nitriding process resulting in a surface hardness as high as about 1200–1400 Vickers. X-ray diffraction studies reveal the formation of Cr2N, CrN and Cr(N) phases upon nitriding. Scanning electron microscopy and energy dispersive X-ray analysis (EDAX) show an increasing fraction of the CrN phase formed at the surface with increasing nitriding times. EDAX line profile analysis of the specimen nitrided for 120 h shows a three-layered structure. Though the surface layer and the second layer adjacent to it, both consist of a mixture of CrN and Cr2N phases, the fraction of CrN is much higher in the surface layer. Nitridation of Cr2N is suggested as the possible mechanism for CrN formation at the surface with increasing nitriding times, for the nitriding parameters chosen in the present study.

Research paper thumbnail of Direct photothermal techniques for quantification of anthocyanins in sour cherry cultivars

Talanta, 2011

The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and... more The analytical performance of the newly proposed laser-based photoacoustic spectroscopy (PAS) and of optothermal window (OW) method for quantification of total anthocyanin concentration (TAC) in five sour cherry varieties is compared to that of the spectrophotometry (SP). High performance liquid chromatography (HPLC) was used to identify and quantify specific anthocyanins. Both, PAS and OW are direct methods that unlike SP

Research paper thumbnail of DC substrate bias effects on the physical properties of hydrogenated amorphous carbon films grown by plasma-assisted chemical vapour deposition

Vacuum, 2007

Hydrogenated amorphous carbon (a-C:H) films have been grown from argon/methane gas mixtures by el... more Hydrogenated amorphous carbon (a-C:H) films have been grown from argon/methane gas mixtures by electron cyclotron resonance chemical vapour deposition (ECR-CVD) on silicon substrates. The effects of the application of a DC substrate bias on the structural, morphological and mechanical properties of the films have been explored by multiple analysis techniques such as infrared and micro-Raman spectroscopy, atomic force microscopy, nanoindentation and pin-on-disk wear testing. In general, within the range of applied substrate bias (i.e. from À300 up to +100 V) we have observed a strong correlation between all measured properties of the a-C:H films and the ion energy. This work shows that the properties can differ greatly and indicates a threshold energy in the order of 90 eV. For the production of hard, low-friction coatings energies above this value are required. r

Research paper thumbnail of Adhesion analysis of polycrystalline diamond films on molybdenum by means of scratch, indentation and sand abrasion testing

Thin Solid Films, 2005

Diamond films have been grown by hot-filament chemical vapour deposition (CVD) on molybdenum subs... more Diamond films have been grown by hot-filament chemical vapour deposition (CVD) on molybdenum substrates under different growth conditions. The films grown with increasing substrate temperatures show a higher interconnection of diamond grains, whereas increasing methane concentrations in the 0.5-4.0% range lead to a transition from micro-towards nanocrystalline films. X-ray diffraction analysis shows Mo 2 C interlayer formation. Indentation, scratch and sand erosion tests are used to evaluate the adhesion strength of the diamond films. Using steel ball indenters (F 750 Am), indentation and scratch adhesion tests are performed up to final loads of 200 N. Upon indentation, the load values at which diamond film failure such as flaking and detachment is first observed, increase for increasing temperatures in the deposition temperature range of 450-850 8C. The scratch adhesion tests show critical load values in the range of 16-40 N normal load for films grown for 4 h. In contrast, diamond films grown for 24 h at a methane concentration of 0.5% do not show any failure at all upon scratching up to 75 N. Film failure upon indenting and scratching is also found to decrease for increasing methane concentration in the CVD gas mixture. The sand abrasion tests show significant differences in coating failure for films grown at varying CH 4 /H 2 ratios. In contrast to the other tests, here best coating performance is observed for the films deposited with a methane concentration of 4%. D

Research paper thumbnail of Pitting corrosion behaviour of diamond coated tool steel

Surface and Coatings Technology, 2005

Using a hot filament chemical vapour deposition reactor, diamond films of approximately 2 -3 Am i... more Using a hot filament chemical vapour deposition reactor, diamond films of approximately 2 -3 Am in thickness were deposited on tool steel specimens with three different interlayer systems, namely CrN, Si and borided steel. The morphology, defect densities and residual stresses of the diamond films were strongly governed by the type of interlayer used. Electrochemical potentiodynamic polarisation studies have been carried out on the diamond deposited tool steel specimens in NaCl solutions of two different concentrations, 0.01 M and 0.50 M, respectively. The type of interlayer used for diamond coating on tool steel has a strong influence on the corrosion potential. The maximum shift in the equilibrium corrosion potential is observed for the silicon interlayer. However, it leads to selective dissolution of the carbide phase upon anodic polarisation. A near total resistance to pitting of the CrN coated tool steel specimens is observed with the introduction of a very thin diamond layer of 2 -3 Am. With increasing chloride ion concentration in the electrolyte, reverse trends in the shift of E corr are observed for the blank tool steels in comparison to the diamond-coated specimens. Detailed SEM characterisation of the corrosion-tested specimens indicates the possible operating mechanisms. D

Research paper thumbnail of Influence of external bias on the surface morphology of a-C:H films grown by electron cyclotron resonance chemical vapor deposition

Surface and Coatings Technology, 2007

We have studied the influence of an external bias on the surface morphology of a-C:H films grown ... more We have studied the influence of an external bias on the surface morphology of a-C:H films grown by electron cyclotron resonance chemical vapor deposition (ECR-CVD) on silicon substrates. We have deposited films for 1 h at different bias from + 100 V down to −250 V and analyzed their surface morphology by atomic force microscopy (AFM). For biases equal or higher than −80 V the film morphology is cauliflower-like, which is due to the shadowing geometry effects inherent to the deposition process. In contrast, for highly negative biases the films become ultrasmooth. Here, the film morphology is consistent with an Edwards-Wilkinson scaling behavior, which starts to operate at shorter length distances as the external bias becomes more negative. This morphology is likely due to the interplay of ion induced physical sputtering and enhanced downhill surface mobility.

Research paper thumbnail of Growth dynamics of ultrasmooth hydrogenated amorphous carbon films

Physical Review B, 2006

We have studied the growth dynamics of ultrasmooth hydrogenated amorphous carbon films deposited ... more We have studied the growth dynamics of ultrasmooth hydrogenated amorphous carbon films deposited on silicon substrates by electron cyclotron resonance chemical vapor deposition from argon/methane gas mixtures applying a high negative external bias. The surface morphology of films deposited for different growth times under the same experimental conditions was analyzed by atomic force microscopy. Our analysis leads to values of the growth, roughness, and coarsening exponents of 0, 0.1, and 0.5, respectively. As it has been recently proposed that the growth dynamics of amorphous films by ion-assisted methods should obey the Edwards-Wilkinson ͑EW͒ growth mode, we have analyzed the compatibility of our data with this model. Our analysis indicates that, although the scaling data could be interpreted in terms of the EW model, the relative large data error bars and the film ultrasmoothness preclude the unambiguous assessment of the EW growth mode for our film growth evolution. In our system, the interplay of shadowing, physical sputtering and enhanced surface mobility ion-induced effects contribute likely to the leveling and final ultrasmoothness of the film surface.

Research paper thumbnail of Novel morphology of chemical vapor deposited diamond films

physica status solidi (c), 2010

ABSTRACT We have obtained simultaneously nanocrystalline and {100} faceted large-grained polycrys... more ABSTRACT We have obtained simultaneously nanocrystalline and {100} faceted large-grained polycrystalline diamond films not only on different substrates but also on the same substrate in only one deposition run using a novel approach for substrate arrangement. Furthermore, interesting unusual morphologies and microstructures composed by non-faceted nanostructures and terminated with large smooth {100} facet-like belt are found near the edges of the top square sample. The morphology variation is likely caused by the so called edge effect, where a strong variation in temperature is also present. We have modelled the temperature distribution on the substrates by computer simulations using the finite element method. The novel feature, namely the coexistence of oval non-faceted nanocrystalline diamond grains and large smooth {100} facet-like belt in one diamond grain, is in the transition from {100} faceted polycrystalline diamond to cauliflower-like nanocrystalline diamond. The formation mechanism is discussed based on the temperature analysis and other simulation results described in the literature. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Formation of {100} facet-terminated nanocrystalline diamond by microwave plasma chemical vapor deposition: Edge effect

physica status solidi (a), 2010

... 1, each corner of sample PD1 has a large spot, which is actually a very big multi-twinned cry... more ... 1, each corner of sample PD1 has a large spot, which is actually a very big multi-twinned crystal of mm range size. As an example, Fig. 2b shows the much bigger multi-twinned crystal grown in the left corner as compared to the relatively smaller crystals grown along the edges. ...

Research paper thumbnail of The applicability of ultra thin silicon films as interlayers for CVD diamond deposition on steels

physica status solidi (a), 2003

ABSTRACT In this study, the use of thin Si interlayers (35–150 nm) for promoting diamond depositi... more ABSTRACT In this study, the use of thin Si interlayers (35–150 nm) for promoting diamond deposition onto steel is investigated. The diamond films are deposited by hot filament CVD onto AISI type 316 stainless and high-speed steels. Single stage deposition at substrate temperatures ranging from as low as 475 to 750 °C is found to result only in non-continuous films with low number densities of diamond crystallites. A composite film of diamond and carbides is formed at intermediate temperatures of about 650 °C. It is believed that the formation of iron silicide phases at the exposed steel substrate surfaces leads to diffusion barriers for free iron from the steel matrix, so that graphitic soot formation is significantly avoided.Utilizing a two-stage deposition process, the density and uniformity of the deposited diamond films areincreased and a nearly continuous cauliflower shaped diamond film is obtained. Micro-Raman spectros-copy, scanning electron microscopy and X-ray diffraction techniques are employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers.

Research paper thumbnail of Surface morphology stabilization by chemical sputtering in carbon nitride film growth

Journal of Physics D: Applied Physics, 2008

We have studied the influence of chemical sputtering effects on the morphology of carbon nitride ... more We have studied the influence of chemical sputtering effects on the morphology of carbon nitride films grown on silicon substrates by electron cyclotron resonance chemical vapour deposition. This study has been performed by comparing the evolution of their morphology with that of hydrogenated amorphous carbon films grown under similar conditions, where these effects are not present. When chemical sputtering effects operate we observe a film surface stabilization for length scales in the 60-750 nm range after a threshold roughness of about 3-4 nm has been developed. This stabilization is explained on the basis of the re-emission of nitrogen etching species, which is confirmed by growth experiments on microstructured substrates.

Research paper thumbnail of Molybdenum Interlayers for Nucleation Enhancement in Diamond CVD Growth

Journal of Nanoscience and Nanotechnology, 2010

The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of mi... more The use of a 50-nm thick Mo interlayer on silicon substrates for the nucleation enhancement of microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films synthesized by hot filament chemical vapour deposition was studied. The MCD and NCD films were deposited using methane concentrations of 1% and 2%, respectively. The presence of a Mo nucleation layer enabled the formation of more uniform NCD films with reduced surface roughness (rms roughness ∼40 nm for a 750-nm thick layer) and with significantly less interfacial voids due to the superior nucleation densities and surface coverage in the early stages of NCD film formation. During the initial stages of MCD film growth, the nucleation density increased by one order of magnitude as compared to uncoated silicon. As a result, much thinner MCD films with smaller surface grain sizes and, thus, reduced surface roughness could be produced as well. The presence of a Mo nucleation layer not only leads to a structural optimization of NCD and MCD films but also allows fast nucleation and film growth kinetics at relatively low substrate temperatures (∼575 C), relevant for the coating of substrate materials that do not withstand high substrate temperatures.

Research paper thumbnail of Atomic force microscopy studies on the surface morphology of {111} tabular AgBr crystals

Journal of Crystal Growth, 2000

Both ex situ and in situ atomic force microscopy have been applied to study the {111} and {100} s... more Both ex situ and in situ atomic force microscopy have been applied to study the {111} and {100} surfaces of tabular silver bromide crystals grown from dimethyl sulphoxide–water solutions. This resulted in observations of monosteps, macrosteps, etch pits, pinning of steps and nucleated crystals showing twin planes. These examinations indicate that the growth and dissolution of both the {100} and

Research paper thumbnail of Morphology and growth mechanism of multiply twinned AgBr and AgCl needle crystals

Journal of Crystal Growth, 1999

In this study the morphology and growth mechanism of AgX (X=Cl, Br) needle crystals will be revea... more In this study the morphology and growth mechanism of AgX (X=Cl, Br) needle crystals will be revealed. The silver halide needles are grown by two different techniques. AgBr needles are grown with an extractive crystallization in a dimethylsulfoxide–water mixture and AgCl needles are grown from the vapor phase. All needles contain nonparallel twin planes. The morphology of the AgBr needles

Research paper thumbnail of High-performance graphene-based carbon nanofiller/polymer composites for piezoresistive sensor applications

Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by ... more 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.