Kinetics of the pulsed erosion deposition process induced by high intensity plasma beams

Abstract

Intense pulsed ion and/or plasma beams can modify the surface properties of materials by melting their near surface region and doping and/or coating with foreign atoms reaching doses in the order of 10 17 cm −2 in a single pulse. Such processes can be performed using a Rod Plasma Injector (RPI), where plasma pulses are generated as a result of a low-pressure, high current discharge between two concentric, cylindrical sets of rod-type electrodes. The discharge is initiated by a HV pulse applied with a delay time τ d after the moment of injection of working gas into the inter-electrode space. Depending on τ d, two modes of operation are possible. If τ d is sufficiently long, the plasma contains almost exclusively the elements of the working gas (PID mode). For short τ d in addition to the generation of plasma of the working gas rapid erosion of the metallic electrodes also occurs (DPE mode). This metal is deposited and in some cases mixed into the substrate. The aim of the present work was to get insight into the kinetics of the DPE process. Several experiments with different working gases (N, Ar, and Xe), different electrode materials (Ti, W) and substrates (Al 2O 3, Cu) were performed. Energy density was approximately 5–7 J/cm 2 and pulse duration was approximately 1 μs, respectively. The two main conclusions have been derived. (a) Metal atoms eroded from electrodes do not undergo ionization and acceleration during the discharge (as it is the case with the working gas). Vapor and low energy ions reach the surface when it is already solidified after being melted first by the working gas plasma. The metallic coating is molten and mixed into the substrate during the subsequent pulse. (b) Erosion of electrodes is caused by some thermal effects as a result of heating by ions and electrons — but not by sputtering.