On aspects of chemical processes in surface modification plasma processes The current work is focused on the study of two surface modification plasma processes (i) the active screen plasma nitriding (ASPN) and nitrocarburizing (ASPNC) for the hardening of ferrous surfaces and (ii) the microwave plasma assisted chemical vapor deposition (MW PACVD) for the synthesis of single crystal and doped diamond. Conventional and active screen plasma nitriding processes have been investigated in a cylindrical industrial scale ASPN reactor with a volume of about 1 m3 using low pressure pulsed dc H2 N2 plasmas with admixtures of CH4 or CO2. The experiments were carried out (i) with the plasma at an internal model probe (ii) with the plasma at the active screen (floated model probe) and (iii) with the plasma at the active screen and an additional plasma at the biased model probe. For deeper insights in ASPN and ASPNC processes a laboratory scale plasma nitriding monitoring reactor PLANIMOR has been constructed. The main feature of this reactor is the linear configuration of the electrode setup combined with a tubular glass vessel overcoming the experimental disadvantages of cylindrical laboratory scale ASPN reactors. With the help of infrared laser absorption spectroscopy (IRLAS) the rotational temperature of the stable molecules in the gas phase and the concentrations of the precursor CH4 and the reaction products (NH3 HCN C2H2 C2H4 CO CH3) could be determined in both reactors depending on the plasma power the gas mixture the plasma at the model ... Niederdruckplasma Plasmanitrieren Diamant Gasphasenabscheidung Laserspektroskopie Absorptionsspektroskopie