REACTIVITY OF A DC-PULSED PLASMA - PLASMA DIAGNOSTICS AND NITRIDED SAMPLE ANALYSIS

The growing use of pulsed discharge in surface treatment processes req uires time-resolved plasma diagnostics in order to determine the bette r conditions leading to the creation of a high density of active speci es in the vapour phase. A low frequency DC-pulsed nitriding plasma has been studied by means of optical emission spectroscopy and Langmuir p robe measurements; both of these diagnostics are carried out with a ti me resolution of 1 mu s across the plasma period. The analysis of the plasma by an electrostatic probe allows us to determine the time varia tion of the electron density and energy distribution function. From th ese results we show the importance of the vibrational excitation of th e nitrogen molecules during the afterglow and we explain some fundamen tal kinetic processes leading to an enhancement of the plasma reactivi ty. On the other hand, the spectroscopic measurements performed as a f unction of various plasma parameters (pressure: discharge and afterglo w duration) lead to the determination of some plasma conditions that s eem to improve the nitriding process. These favourable plasma conditio ns are discussed with regard to the characterization of nitrided sampl es. (C) 1997 Elsevier Science S.A.