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

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. (c) 2007 Elsevier B.V. All rights reserved.status: publishe

Surface morphology stabilization by chemical sputtering in carbon nitride film growth

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.status: publishe

Growth dynamics of ultrasmooth hydrogenated amorphous carbon films

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 (EW) 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.status: publishe

Nanogold on nanodiamonds – A microscopic study

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Nucleation enhancement of nanocrystalline diamond thin films by using metal seed layers

oral presentation + abstract (NANO-66)status: publishe

Degradation of carbon fiber reinforced epoxy composites under sliding in ambient air

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Metallic seed nanolayers for nucleation enhancement of nanocrystalline diamond thin films

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Surface damage of unidirectional carbon fiber reinforced epoxy composites under reciprocating sliding in ambient air

For many technical applications friction and wear are critical issues. Reinforced polymer-matrix composites are widely used under vibrating contact condition in various automotive and aerospace applications as well as in structural engineering. In this paper, the friction and wear of bulk epoxy and unidirectional carbon fiber reinforced epoxy composite have been investigated under reciprocating sliding against either alumina or stainless steel balls in ambient air. The effect of sliding direction with respect to the long and unidirectional carbon fibers has been studied. We demonstrate that the carbon fiber reinforcement greatly improves the tribological properties of the thermoset epoxy: it reduces the coefficient of friction and the debris formation. It was found that on sliding in the anti-parallel direction a more significant degradation takes place than in the parallel direction. The coefficient of friction measured on bulk epoxy sliding against either stainless steel or alumina is around 0.65, whereas the coefficient of friction measured on epoxy reinforced with carbon fibers is significantly lower, namely down to 0.11. It was found that sliding with a stainless steel ball in a direction parallel to the fiber orientation results in a lower coefficient of friction than sliding in anti-parallel direction. The reduced coefficient of friction is largely influenced by the carbon fiber reinforcement due to the auto-protecting film formed as a paste in the contact area and along the wear track edges. The relationship between friction and degradation of the composite material including surface wear and debris formation are discussed based on an in-depth analysis of the worn surfaces by optical and scanning electron microscopy, micro-Raman spectroscopy, and white light interferometry. (C) 2011 Elsevier Ltd. All rights reserved.status: publishe

Surface wettability of macroporous anodized aluminum oxide

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Surface wettability of macroporous anodized aluminum oxide

The correlation between the structural characteristics and the wetting of anodized aluminum oxide (AAO) surfaces with large pore sizes (>100 nm) is discussed. The roughness-induced wettability is systematically examined for oxide films grown by a two-step, high-field anodization in phosphoric acid of three different concentrations using a commercial aluminum alloy. This is done for the as-synthesized AAO layers, after various degrees of pore widening by a wet chemical etching in phosphoric acid solution, and upon surface modification by either Lauric acid or a silane. The as-grown AAO films feature structurally disordered pore architectures with average pore openings in the range 140–190 nm but with similar interpore distances of about 405 nm. The formation of such AAO structures induces a transition from slightly hydrophilic to moderately hydrophobic surfaces up to film thicknesses of about 6 μm. Increased hydrophobicity is obtained by pore opening and a maximum value of the water contact angle (WCA) of about 128° is measured for AAO arrays with a surface porosity close to 60%. Higher surface porosity by prolonged wet chemical etching leads to a rapid decrease in the WCA as a result of the limited pore wall thickness and partial collapse of the dead-end pore structures. Modification of the AAO surfaces by Lauric acid results in 5–30° higher WCA’s, whereas near-superhydrophobicity (WCA ∼146°) is realized through silane coating. The “rose petal effect” of strongly hydrophobic wetting with high adhesive force on the produced AAO surfaces is explained by a partial penetration of water through capillary action into the dead-end pore cavities which leads to a wetting state in-between the Wenzel and Cassie states. Moreover, practical guidelines for the synthesis of rough, highly porous AAO structures with controlled wettability are provided and the possibility of forming superhydrophobic surfaces is evaluated.status: publishe