Role of growth temperature on nanostructure and field emission properties of PLD thin carbon films

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 (λ = 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 Eth and field enhancement factor β) have been evaluated using variable anode-to-cathode distance method. Samples deposited at low T sub have shown the best emission properties, presenting lower Eth and larger β values than those deposited at higher T sub. This is mainly attributed to thesensible density variation, which is in competition with the slighter augment of mean nanoparticle size.