Biased Langmuir probe measurement for pulsed high-voltage glow discharge

High-voltage glow discharges (HVGD) are very versatile because they can be generated from practically any electrode geometries and gases. This technique is well suited for plasma implantation without the need of external plasma sources. In HVGD, the high voltage pulses serve the dual purpose of generating the plasma as well as accelerating ions to the target. Our results show that the discharge behaviour depends very much on the applied voltage, gas pressure, and pulsing frequency in HVGD. For a single pulse, there is a delay time which is determined by the bias voltage and working pressure. Our experimental results acquired from treated AISI304 stainless steel samples show that this process yields higher surface nitrogen concentration in spite of shallower penetration compared to conventional nitrogen plasma implantation employing hot filament glow discharge. In our work, we employ a biased Langmuir probe to measure the different discharge conditions with respect to the time-dependent electron density. The measurement technique imparts information on the voltage and pressure dependent discharge behaviour, discharge dynamics, and surface modification mechanism. Our data reveal that HVGD can yield high ion flux that is beneficial to elevated temperature plasma treatment.