Development of nanostructured carbon thin films

Abstract

In this thesis, experimental investigation of the growth mechanism of unique nanostructured carbon films and their properties as well as different fabrication techniques of these films is reported. Using experimental results, the presented mechanisms have been evaluated and developed. This work has enabled a larger range of deposition parameters to create user-specific nanostructured carbon films. The parameters examined include heat, depositing ion energy, plasma density and post treatments such as laser and thermal annealing. Electrical, thermal and field emission properties of nanostructured carbon films have also been studied. First, the effects of deposition temperature and ion energy on the microstructure of the carbon films have been investigated. To do this, the microstructure of carbon films deposited at temperature range of 25 to 6000C and substrate bias range of 25 to 600 V have been studied by plan view and cross section transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and Raman spectroscopy. It is found that at low deposition temperatures ( 1500C) the microstructure of the film depends on the substrate bias. at low substrate biases (lower than 400V) the films are amorphous in the microstructure. Increasing the bias to 600V results in formation of preferred oriented nanocrystals in the microstructure. This is attributed to the formation of high temperature thermal spikes due to impinging of high energy ions to the growing film. Increasing the substrate temperature to 400 and 6000C leads to formation of preferred oriented nanocrystals even at floating substrate bias. The nature of the nanocrystals however depends on the applying bias. Low substrate biases (lower than 600V) results in the formation of graphitic like nanocrystals while at 600V tubular nanostructures are formed. This is due to higher formation enthalpy of tubular carbon structures compare to graphene sheets. In order to study the effect of plasma parameters, carbon films were prepared under two different plasma densities (2.5 and 12.5 mA/cm2) and different substrate biases (25 to 500 V). It is found that by applying high ion density plasma, nanocrystals are formed at room temperature even at low substrate biases (300 V). Meanwhile, decreasing the ion density increases the threshold ion energy for graphitization. More importantly it is experimentally shown that the nature of the nanocrystals strongly depends on the depositing ion energies. High ion energy (higher than 500 eV) results in formation of tubular nanostructures while lower ion energies (300 to 500 eV) results in formation of graphitic nanostructures. Stability of different nanostructures have been discussed in terms of the thermal spike temperature. The experimental results of the formation of different nanostructures have been proven by molecular dynamics simulations. Separately, the properties of textured nanostructure carbon films were also studied. The first property investigated was the electrical conductivity of the films. It is found that…