Th. Dikonimos Makris

Carbon Nanotube Growth on PAN‐ and Pitch‐Based Carbon Fibres by HFCVD

Abstract Carbon nanotubes (CNT) were grown on carbon fibres, both PAN‐ and pitch‐based, by hot filament chemical vapour deposition (HFCVD) using H2 and CH4 as precursors. Nickel clusters were electrodeposited on the fibre surfaces to catalyse the growth, and uniform CNT coatings were obtained on both PAN‐ and pitch‐based carbon fibres. Ni cluster features varied, depending on the deposition parameters, showing on average larger dimensions and denser distribution on pitch fibres. Multi‐walled CNTs with smooth walls and low impurity content were grown. The morphological features, both before and after the growth process, were characterised by SEM. This novel material based on carbon fibres coated with CNT, shows a potential for applications in polymeric matrix composites.

Nanocrystalline Diamond Films by Bias Enhanced Nucleation and Argon Assisted Growth in a HFCVD System

The achievement of nanosmooth, ultrathin diamond coatings with nanosized grains is mandatory for the successful utilization of diamond in areas such as microelectromechanical systems, field emission and surface acoustic waves devices. The bias enhanced nucleation technique (BEN) allows to achieve high nucleation density diamond films, where the average distance between diamond nuclei can be as low as 10-20nm. Moreover by diluting the gas precursors (H2 and CH4) into noble gas (Ar, He) during growth, the formation of larger crystals can be inhibited, giving rise to nanocrystalline films without a degradation of the film quality, such as the presence of more graphitic bonds. In this paper we report the growth of ultrathin, smooth, high quality nanodiamond films obtained by combining the two techniques in a HFCVD reactor. A variety of nanocrystalline diamond films with a grain size as low as 10nm and thickness up to 1μm were obtained. The nucleation process and ensuing growth of the film were monitored by SEM observation. Spectroscopic measurements were also performed to study the microstructure and to assess the quality of the deposited material.

CVD SYNTHESIS OF CARBON NANOTUBES ON DIFFERENT SUBSTRATES

Carbon nanotubes (CNTs) were grown using three different chemical vapor deposition (CVD) processes. Optimized conditions were studied. CNTs were grown on differently supported Ni catalytic nanoparticles on flat and bulk substrates using H2 and CH4 as precursors. The different behavior of the same metal catalyst in the presence of the same precursor varying the gas activation by different energy sources, using Hot Filament, Plasma Enhanced (PE), and pure Thermal CVD processes, was studied. By properly choosing the process parameters, dense CNTs were grown by HFCVD on 3 nm Ni thin film deposited by Evaporation and Radio-frequency (RF) Sputtering onto flat Si substrates coated with an intermediate SiO2 layer 3 (Fig. 1a). Prior to the growth, the samples were heated in H2 atmosphere and the Ni clusters distribution shown in Fig. 2a was obtained. No CNT growth was obtained on the same sample in the thermal CVD reactor, but only cluster coalescence was observed (Fig. 2b). CNT grew sparsely in the PE CVD reactor. The different results were ascribed to: i) the catalytic decomposition of the precursors was more efficient where an additional activation source was present; ii) weak interaction between the Ni cluster and the SiO2 substrate could favour cluster coalescence, which was the dominant effect in the thermal CVD process. Flat Al2O3 substrate coated by a 3nm Ni film, deposited by RF Sputtering, were subjected to the same clustering and CNT growth process in Thermal and PE CVD. The thermal process failed as in the previous case giving rise to

Purification of Multi-Walled Carbon Nanotubes Grown by Thermal CVD on Fe-Based Catalyst

Aiming at the purpose of using carbon nanotubes as secondary phase in composite materials, removal of metal catalyst, catalyst support and amorphous carbon is crucial to make the most of the required properties. A purification method was developed to remove the metal catalyst from multi-walled nanotubes grown by thermal CVD. A nanosized Fe-based catalyst, prepared by coprecipitation of iron and aluminum ions, followed by solid state reaction, was used to catalyze the growth. Carbon nanotubes were subjected to acid purification and a comparison between nitric acid and a mixture of nitric and hydrochloric acid for the removal of Fe and Fe oxides is provided. Morphological and spectroscopic analyses of the materials were performed, both before and after the purification processes.