Search

Thin carbon films have been deposited in vacuum (?10-4 Pa) on Si substrates by pulsed laser ablation of a graphite target using a Nd:YAG laser operating in the near infrared region (?=1064 nm). The samples have been deposited at different substrate temperatures (T sub) ranging from room temperature (RT) to 800°C. X-ray diffraction analysis established the progressive formation of nanosized graphene structures as T sub increased. In fact, film structure evolves from almost amorphous to nanostructured phase characterized by graphene layers oriented perpendicularly to the film plane. The film density, evaluated by X-ray reflectivity measurements, is strongly affected by T sub. At RT the film density is similar to the graphite one, while it decreases at higher T sub. The electrical properties of the samples have been characterized by field emission measurements. The parameters describing the emitter properties (threshold field E th and field enhancement factor ?) have been evaluated using variable anode-to-cathode distance method. Samples deposited at low T sub have shown the best emission properties, presenting lower E th and larger ? values than those deposited at higher T sub. This is mainly attributed to the sensible density variation, which is in competition with the slighter augment of mean nanoparticle size.

PLD and CVD methods, plasma or bias assisted, have been used to prepare thin films of nano-clustered graphite. The experimental conditions (vz. deposition apparatus, substrate temperature, working pressure, inert sustaining gases parent species, and applied voltage) have been changed with the final aim of obtaining small graphene particles with the basal planes oriented along the growth vector and perpendicular to the n-Si substrate. Pulsed laser ablation (Nd:YAG, 2nd harmonic: lambda=532 nm, hnu=2.33 eV, tau=7 ns, nu=10 Hz, Phiapproximate to7 J/cm(2)), assisted by an RF-plasma, of a pyrolytic graphite target gave good results for nano-structure formation, provided high substrate temperature and high inert gas pressure are maintained. CVD methods, in the presence of high substrate temperature and a DC bias, showed a good attitude to drive a longitudinal growth of graphene layers and nano-wires from a reactive gas flow of Argon/Hydrogen and Methane. The morphology of the films grown at different conditions have been characterised by scanning electron microscopy (SEM). Film quality and nano-particle dimensions have been estimated by Raman spectroscopy.