Temporal development of the plasma composition of a pulsed aluminum plasmastream in the presence of oxygen

We describe the temporal development of the plasma composition of pulsed al uminum plasma streams at various oxygen pressures. The plasma was formed wi th a vacuum arc plasma source and the time resolved plasma composition was measured with time-of-flight charge-to-mass spectrometry. The temporal deve lopment of the plasma composition as well as the Al average ion charge stat e was found to be a strong function of the oxygen pressure. Oxygen and hydr ogen concentrations of up to 0.36 and 0.32, respectively, were found in the first 50 mu s of the pulse at oxygen pressures of greater than or equal to 5x10(-5) Torr. The average charge state of aluminum ions was found to vary from +1.2 to +2.5 depending on the oxygen pressure and the time elapsed af ter ignition of the arc. These results are of fundamental importance for th e understanding of the evolution of the composition (through the plasma com position) and microstructure (through the Al ion flux energy) of alumina th in films produced by pulsed, reactive aluminum plasmas. (C) 1999 American I nstitute of Physics. [S0003-6951(99)01231-0].