Advances in Science and Technology Vol. 48

Abstract: We have succeeded to grow high quality phosphorus doped n-type diamond thin films on {111} diamond substrates. Although the ionization energy of phosphorus donor is large (0.57 eV), the n-type conductivity is clearly observed by Hall measurements. The Hall mobility is as high as 660 cm2/V-sec at room temperature. In this paper, current status of n-type diamond research are mentioned mainly focused on the growth of high mobility n-type diamond and its electrical properties. High quality diamond growth has been carried out by surface pre-treatment of diamond substrate. The Hall measurements performed in a wide temperature range gives detailed information about the n-type conductivity nature.

Abstract: In this study, we present our recent work on microplasma synthesis in liquid (or liquid solution) and supercritical fluid (SCF) for carbon nanostructured materials. For microplasma synthesis in liquid (or liquid solution), we easily fabricated graphites, carbon nano-onions, carbon nanotubes (CNTs) and distinctive self-organized carbon nanostructures. On the other hand, for microplasma synthesis in supercritical CO2 (scCO2), carbon nanostructured materials, such as CNTs and carbon nanopolyhedrons, were synthesized with the arc plasma using sc CO2 as a processing medium and raw starting material. Additionally, we showed the film deposition of carbon nanostructured materials by using a dielectric barrier discharge under scCO2 environments.

Abstract: In the present work, a-C: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 bias we have observed a strong correlation between all measured properties of the grown a-C:H films and the ion energy. Though it is known that the ion energy is one of the crucial parameters in plasma grown films, this work clearly shows that the properties of the a-C:H layers can differ greatly and indicates a threshold energy for the production of hard, low-friction coatings in the order of 80-90 eV. Moreover, this threshold energy is also combined with a sharp transition from rough, cauliflower-like film surfaces towards ultrasmooth, featureless topographies. This correlation suggests that at energies higher than 80 eV the ion bombardment affects simultaneously the surface morphology and the internal bonding structure.

Abstract: In this paper, porous carbon was made from biomass derived carbonaceous mesophase and carbonaceous fillers, and further applied as the substrate for CVD grow of nano carbon materials. With the assistance of microwave plasma, the acetone gas was decomposed into carbon and grew on the surface of the porous carbon, which produce ballas diamonds, carbon tubes, nets, petal, and other structures.

Abstract: In this work the method of single-wall carbon nanotube synthesis based on chemical vapor deposition from ethanol vapor has been developed. The films grown have been characterized in detail by the electron microscopy and the Raman scattering techniques. A typical split tangential mode (at 1592 cm-1) and a number of "breathing" modes (150-270 cm-1) have been revealed in the Raman spectra for a variety of synthesis regimes. It was possible to change the geometrical parameters of nanotubes by playing with the synthesis conditions. A key role of the catalyst (Co, Co:Mo) preparation has been revealed. A special procedure of the catalyst crystal growth has been developed.

Abstract: Since their discovery, carbon nanotubes received a great deal of attention because of unique physical and chemical properties. However, in order to become of interest in the field of super resistant fibers for nanocomposite materials or in the production of textile material, very long carbon nanotubes are needed. Massive samples of well packed, vertically aligned and very long selfstanding multi wall carbon nanotubes (MWNT) were synthesized on uncoated silicon by a very efficient thermal CVD process, which involved the co-evaporation of camphor and ferrocene in a nitrogen atmosphere. We obtained structures with diameter between 20 and 80 nm with an average growth rate of about 400 nm/s, organized in thick carpets of entangled nanotubes. By the weight of the deposited carpet of MWNTs (density circa 0.8 g/cm3) the conversion of about 30% of the total hydrocarbon feedstock was calculated. Morphology and physical properties were characterized by electron microscopy techniques, Micro- Raman spectroscopy and thermogravimetric analysis. The analyses performed showed the absence of secondary carbonaceous products, whereas only 6% in weight of ferromagnetic iron clusters are present. BET analysis was used to calculate the porosity and the specific surface area density of the as grown samples, which resulted approximately 70 m2/g. Hydrophobicity of the CNT carpet was also investigated.

Abstract: 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.

Abstract: 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.