3.1. Discharge current waveforms
Discharge current density waveforms for sputtering of Ni at different current/pulse power densities are shown in Fig. 4 for the on-time of 300 μs. Increasing the duty cycle, the pulse power was decreasing. For low pulse powers, a typical HiPIMS current evolution is seen when the discharge current peaked at about 40 μs and then decreased as a result of substantial gas rarefaction [24]. For higher pulse powers, self-sputtering became pronounced and the current was rather stable throughout the remainder of the pulse [25]. In the case of Ti sputtering (Fig. 5), there were relatively small differences between the shapes of the current waveforms at different pulse power densities, although the peak current density was very different. No distinct current peak can be seen for low peak powers in contrast to Ni.