Novel nanostructured carbon films for high performance devices
Creators: name: Moafi, Ali
Publisher: name: RMIT University
Year: 2024

description: The next generation of advance technologies require novel materials to meet demands in the energy and high performance device sectors. Novel carbon materials, such as nanostructured carbon films, are promising since they can exhibit a wide range of desirable properties depending on their structure and they are generally low-cost which is vital for industrial applications. Whilst functionalized CNTs and graphene based devices offer good performance and low power consumption their preparation typically includes the manipulation of individual sheets/tubes, precluding compatibility with large scale silicon device processing. In addition, large scale production of CNTs having the necessary degree of ordering between each tube so that properties can be optimised for device applications is problematic. By using a filtered cathodic vacuum arc (FCVA) deposition system, it is possible to synthesise carbon thin films with a variety of microstructures including diamond-like amorphous, graphite-like oriented or carbon nitride (CNx). However, it is a challenge to find the deposition parameters which can produce films with the desired microstructure on any given substrate type. <br><br>This first aim of this thesis is to map out the microstructures that are possible in CNx films as the most important deposition conditions of temperature, gas pressure and substrate bias are varied. While some work has been done previously in this area, this is the first comprehensive study and will allow researchers in the field to choose the most appropriate conditions in order to synthesise CNx films with a particular microstructure. <br><br>The second aim of this thesis is to find an alternative method to direct substrate biasing in order to alter the deposition energy, a key parameter which determines microstructure and properties in carbon based films prepared using FCVA. An alternative method is urgently required since direct substrate biasing is problematic if electrically insulating substrate are required. The use of a biased mesh placed in front of the substrate within the plasma stream was found to be an effective alternative to direct substrate biasing for varying the energy of the depositing flux. This opens the way for the deposition of the full range of carbon film types that are possible on electrically conducting substrates to be deposited on any substrate type.<br><br>While the excellent properties of carbon based films are well known, there is the opportunity to extend their use in a range of real world applications. In this thesis, the use of carbon films with a microstructure consisting of highly oriented graphitic carbon as thermal and electrical interconnects is investigated. This thesis also investigates the use of carbon based films for use in hydrogen gas sensing. In the latter case, it was found that hydrogen exposure increases the resistance between two catalytic metal contacts placed on the carbon material. The mechanism for gas sensing was found to involve hydrogen “spillover” from the catalytic metal into the carbon leading to carbon-hydrogen bonding, the removal of free electrons and an increase in resistance.<br>