Abstract
Abstract This thesis describes the development of microplasma devices architecture by hybrid diamond as cathode. These microplasma devices are suitable for UV emission sources and corresponding applications. The cathode boundary layer (CBL) discharge device structure has been implemented in this study, which consist of 2 mm cylindrical cavity in the centre of anode. Here, two types of devices were fabricated, such as two electrode and novel three electrode devices. These devices were tested with Ar (10 %) + N2 (90 %) gas used as discharge medium for generation of UV emissions. The current – voltage relationship and optical emission spectra were studied for two devices, while HiD (nanocrystalline diamond/ultrananocrystalline diamond) coated Si tip cathode. The microplasma illumination behavior was investigated for different diamond films including microcrystalline diamond (MCD), ultrananocrystalline diamond UNCD, planar HiD and HiD coated Si tip cathodes for the case of two-electrode microplasma device. From these results, the HiD coated over Si tip shows the better plasma illumination intensity compared with other electrodes due to its excellent electron field emission property (E0 = 9.1; Je = 4.53 @ 18.1 V/µm; β = 1605). The lifetime stability of the microplasma devices were studied by means of electrode degradation by plasma damage and variation of plasma intensity for two-electrode device. However, the electrode degradation causes the limitation of the lifetime stability in two electrode device due to high filed strength on cathode, which leads to ion bombardment. To overcome this problem, the third electrode has been added to the two electrode devices, which results in lower applied voltages on diamond cathode for longer lifetime. The cathode material in case of the three electrode microplasma device has been exhibited longer lifetime than the two electrode device. In case of the HiD/Si tip based two-electrode device operated at current density of ~ 3.5 mA/cm2 with applied voltage of 500 V, the device shown the lifetime stability of 2.9 hr. In case of the three-electrode device, which operated at anode current density (Ja) = 3.2 mA/cm2 (applied voltage 440 V) and cathode current density (Jc) = 1.8 mA/cm2 (applied voltage 160 V), the stability of the device came up to 4.3 hr without any decay in current density. The plasma intensity of the three electrode device was markedly higher in comparison with two electrode device due to the additional third electrode, which results in generation of extended positive column. We observed the near UV emissions for both devices, which arising from N2 second positive. The resultant near UV emissions attained at wavelengths of 296.5 nm, 315.5 nm, 336.5 nm, 353.1 nm, 357.3 nm, 375.1 nm and 379.8 nm. Therefore, this hybrid diamond based three electrode CBL device has great potential for practical applications as a robust UV source.