Plasma Immersion Ion Implantation Of Cylindrical Bore Based On Self Excited Radio-Frequency Glow Discharge

Surface modification has frequently been performed to improve the surface properties and lifetime of tube-like components. Ion implantation has been receiving much interest as an effective surface processing tool. However it is relatively difficult to implant the inner wall of cylindrical bore using this technique due to effect of line-of-sight. This desire presents a new approach based on self-excited radio-frequency (RF) glow discharge in the tube for purpose of ion implantation of the interior surface. The tube itself acts as a plasma source to generate required plasma within the tube and then biased negatively to achieve plasma ion implantation (PII) effect. In this thesis, the topics on development of power supply, uniformity of plasma density, dynamics of plasma sheath and ion implantation of inner wall of cylindrical bore have been focused on. The aim is to disclose the physical mechanism of ion implantation of cylindrical bore and provide a guide to treat the inner wall of tube-like components.The design and operation performance of this novel hybrid system coupling pulsed radio-frequency and pulsed high-voltage (HV) are very critical to achieve better ion implantation effect. The key problem is to protect the radio-frequency power supply from high-voltage damage and prevent the high-voltage pulser from the interference of radio-frequency system. The hard-ware system may run with multiple modes including high-voltage self-discharge PII and conventional PII depending on the time interval between the radio-frequency pulse and high-voltage pulse. The system may also operate with single RF/single HV and multiple RF/single HV.Steady discharge and plasma may be induced in the tube powered by RF system (non-uniformity is lower than 15﹪at the axial range from +75mm to -75 mm). With increasing RF power, the plasma density increases, however the uniformity firstly increases then decreases with the increasing of RF power. The working pressure has a slight influence on magnitude and uniformity of plasma density. The baffling plates near tow ends of the tube not only can not improve the uniformity of plasma density but also weaken substantially the glow discharge leading to a lower plasma density in the tube. A large tube diameter is helpful for better uniformity of plasma density. In contrast the tube length has a slight effect on the uniformity in the middle region. The plasma density near the central line of the tube is higher than that near the wall. The I-V curve of plasma density generated at high-frequency (e.g., 3kHz) pulse RF are similar to those at continue RF mode. In contrast at lower frequency pulsed RF case the plasma density is lower and varies with pulse configuration.Tow-dimensional particle-in-cell (PIC) model has been utilized to simulate the dymanics of ion implantation in the bore with non-uniform plasma. The expansion of plasma sheath and effect of instrumental parameters on ion dose and distribution have been investigated. The plasma sheath rapidly collides and the ions in the bore are mostly implanted with a perpendicular angle and the ions outside the tube possess a glancing injection angle. The incident dose is uniform in the middle region of the tube despite two peaks near two ends of the tube. With interest the dose right at the corner is very lower due to the focus effect of plasma sheath. The uniformity of incident dose may be improves with a large tube diameter, higher plasma density and lower tube bias.The stainless steel cylindrical bore has been implanted using this novel technique with the tube itself applied to RF power and high-voltage pulse. The XPS results demonstrate that there exists nitrogen element with injection range of 40nm in the inner wall at central sites of the tube. The nitrogen concentration in the middle section is relatively uniform except near two ends of the tube. The injection range of incident ions is similar no matter where they are implanted. Nitrogen implantation has improved substantially corrosion resistance and wear resistance of stainless steel tube. The results also show the uniform improvement along the tube axial. The tube with 30mm in diameter and 200mm in length has been successfully implanted leading to better surface properties.