Metastable states and nitriding plasmas

The results of investigations of slow diffusive effects in pre-breakdown nitrogen discharges, the effects of quenching by impurities, and the influence of surface conditions on metastable-particle-surface interactions are discussed briefly. This work suggests that two distinct neutral metastable species may be active in nitrogen plasmas used for surface nitriding. The electronically excited metastable N-2(A(3) Sigma(u)(+)) state has been positively identified; the second species, a more slowly diffusing state, remains unidentified. Evidence is emerging however, indicating that the more slowly diffusing species exists in a variety of excited states including electronically excited states and highly vibrationally excited ground states. The implications of this for plasma nitriding are discussed, including the possible significance to the use of temperatures similar to 500 degrees C in the commercial nitriding of steels. (C) 1997 Elsevier Science S.A.