Fast relaxation of the velocity distribution function of neutral and ionized species in high-power impulse magnetron sputtering

A super-exponential time-relaxation of the full width at half maximum of Ti and Ti(+) spectral lines was found during the off-time in a high-power impulse magnetron sputtering discharge studied by laser-induced fluorescence. After the estimation of the possible broadening mechanisms, the main contribution to the determined linewidths appeared to be the broadening due to ballistic motion of sputtered species with a minor contribution of the instrumental and Doppler broadenings. The deconvoluted linewidths depend both on pressure and distance from target, and their time-decay was attributed to the fast energy relaxation of the sputtered neutrals and ions during the off-time. (C) 2011 American Institute of Physics. [doi:10.1063/1.3644989]