Papers by Author: I. Popović

Abstract: Matching of pulse plasma generators to various gas discharges for surface treatment of materials depends on plasma processing equipment. In order to investigate the influence of pulse plasma generator and gas discharge parameters on electrical signal waveforms during the process of unipolar pulse plasma nitriding, equivalent electrical circuit was introduced. The influence of parasitic inductance of interconnection lines and vacuum chamber physical properties was also included in the given equivalent circuit. Gas discharge characteristics at different process parameters were investigated. It was found that the gas discharge and pulse plasma generator properties, as well as the electrical characteristics of interconnecting lines determined the system electrical signal response. From the analysis of optical signals emitted by the gas discharge it was found that the optical signal response might be represented by a typical RC integrator circuit response with the time constant higher than that of the equivalent electrical circuit of generator load. The conclusion was drawn that the process of charge particles generation is followed by the process of active species generation responsible for thermo-chemical processes on the cathode surface. Thus, the increase of the pulse plasma frequency is limited by the thermo-chemical process efficiency, and not only by the generator switching characteristics or by gas discharge electrical properties.

Abstract: The electrical and optical signal waveforms of nitrogen/hydrogen glow discharges used for plasma nitriding process were recorded and analyzed. The shape of the discharge voltage and current signals is dependent on the process parameters, pulse plasma generator properties and cathode geometry. It has been found that the dynamic parameters of the electrical signal waveforms contain information related to the charged particles generation, which is relevant to the homogeneity of different gas discharge surface treatment processes. On the other hand, information related to the active species generation responsible for thermochemical processes at the cathode surface is stored in the optical emission waveforms. The generation and quenching of the active ingredients during the voltage pulses switch on and off influence the shape of the emitted light signals. From the optical signal analysis it was found that the thermochemical processes are influenced by the plasma generator properties such as pulse duty cycle, frequency, applied discharge voltage level and process parameters like working gas composition, operating temperature and pressure.

Abstract: Introduction of pulse plasma power supply is one of the major contributions to plasma surface engineering. The voltage and current waveforms of nitrogen and nitrogen/hydrogen glow discharges in the vacuum total pressure range from 0.1 to 15 mbar were recorded and analyzed concerning the shape, typical operating values and the influence of surface treatment process parameters. It was found that the waveform shape of the voltage and current contains information on pulse generator output parameters and vacuum system properties during normal glow, hollow cathode discharge and arcing. We have also performed the scoping of dynamic parameters and static characteristic, in order to obtain information for the generator and chamber modeling, to be used in a future plasma materials treatment processes control. The influence of process parameters such as total pressure, cathode temperature and biasing voltage on current-voltage characteristics was also considered.