Fabrication of diamond-based microplasma devices

• Main Author: Allen, Monika Jozefa
• Published: University of Bristol 2014
• Subjects: 660
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.653084

Plasmas and microplasmas in particular have a great potential for expanding their range of applications if improvements can be made to the lifetime of the devices housing them, and their operating pressure can be increased. Using a hollow-cathode geometry and scaling down the devices to micron size allows for their work in atmospheric pressure, while using diamond as the main material greatly increases their lifetime. Polycrystalline undoped diamond was used as the insulating layer for creating sandwich structured microplasma devices, with electrodes of either evaporated titanium/gold or thin films of polycrystalline boron-doped diamond created by chemical vapour deposition (CVD). The hollow cathode cavities and holes were micromachined using an Oxford laser system and the quality of the electrode thin films was tested using Raman spectroscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. Successful ignition of several samples at below- and above-atmospheric pressure was achieved, thus proving that CVD diamond can be used as the material for microplasma devices. Three types of devices were created: diamond insulator with metal electrodes, diamond insulator with boron-doped diamond electrodes, and diamond insulator with one metal and one boron-doped diamond electrode. Varying the thickness of the insulating layer and the size of the cavity or hole allowed the micro plasma to ignite at different pressures. The devices showed no sign of reaching the end of its life in the time it took a comparable device made of previously used materials (metal and glass) to break down. This thesis describes the fabrication of these devices. as well as the refinement process of the architecture which eventually led to a successful ignition of a microplasma at above-atmospheric pressure.