Mechanical properties of nanostructured carbon layers grown by CVD and PLD techniques

Pulsed laser deposition (PLD) and chemical vapour deposition (CVD) have been proven to be among the most successful techniques for growing the entire spectrum of carbon films, which can be used in a wide range of technical applications. Here an investigation has been performed to explore the effect of different growing techniques (PLD and CVD) and process parameters (such as deposition time and substrate type) on the films' morphology and mechanical properties. The mechanical properties of the grown thin films were characterised by means of nano/micro indentation and scratch test techniques. It was observed that the thickness of the Al2O3 interlayer (between the Fe catalyst nanoparticles and the silicon substrate) is a critical parameter that can be used to significantly enhance the adhesion strength of PLD-grown carbon films. PLD-grown carbon films were in fact found to have higher adhesion to the substrate than CVD-grown carbon nanotubes (CNT), and the adhesion strength was found to increase with increasing thickness of the Al2O3interlayer. On the other hand, CVD-grown carbon films (made of aligned CNTs) seem to offer a greater response in terms of elastic modulus. A thorough scanning electron microscopy characterisation suggested that the observed mechanical responses might be correlated to the films' morphology at the nano/microscale. It was in fact observed that, in PLD-grown samples, an increasing deposition time and Al2O3content leads to a grain size increase and to a clustering effect, thus to a loss in film uniformity. © 2010 Taylor & Francis.