A study of Direct Current Corona Discharges in Gases and Liquids for Thin Film Deposition

The applicability of DC corona discharges with their lower temperatures and uniformity was investigated for the deposition of thin films. The deposition was done at atmospheric pressure and room temperature, which lowers the facility cost as no vacuum or low pressure facilities are required and also enables continuous processing rather than batch processing. The operating regimes and the structures of DC negative corona discharges for a point to plate electrode configuration for thin film deposition were studied. Traditionally DC coronas have been operated at extremely low currents. By modifying the circuit, the DC corona was operated at higher currents without spark breakdown. The DC negative corona discharge was operated in a new regime where a stable and diffuse glow was observed near the anode surface. This diffuse glow was observed in air and methane discharges. The discharge was characterized by voltage-current diagnostics. Optical emission spectroscopy (OES) was used to obtain spatially resolved temperature measurements and electric field measurements. The DC negative corona discharge was also observed to deposit films on the anode surface. The deposition of films and particles on the anode surface has introduced the possibility of using corona discharges as a novel method of materials deposition or surface modification at atmospheric pressure. The study of electrical breakdown in both conducting and dielectric liquids has gained interest due to various applications. These discharges in liquids are unsuitable for many applications due to their thermal nature. Non-thermal discharges in liquids are relatively unexplored. DC plasma discharges in liquids for a negative pin-to-plate electrode configuration were also investigated. The discharge was characterized by voltage-current characteristics and visualization. The corona discharge is observed to deposit films on the anode surface when operated in tetraethyl orthosilicate (TEOS). Deposition on the anode surface by the proposed method has introduced the possibility of using corona discharges as a method of materials deposition or surface modification directly in liquid phase. The proposed plasma enhanced liquid deposition (PELD) technique is encouraging because it is both simple and effective in depositing films without damaging the substrate material.M.S., Mechanical Engineering -- Drexel University, 200