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In this paper, the novel technique of THz time domain spectroscopy has been applied to obtain time-resolved measurements of the plasma density in the active zone of a HiPIMS discharge with a titanium target. The obtained peak values are in the range of 1012–1013 cm−3 for discharge current densities of 1–4 A cm−2 at 0.5 and 2 Pa argon pressure. The measured densities show good correlation with the discharge current and voltage and the intensity of various atomic and ionic lines. The well known phases of the discharge have been identified and related to the variation of the electron density. The measurement results show that the plasma density remains nearly constant during the runaway/self-sputtering phase. Based on that, it is conjectured that singly charged titanium ions are the dominant ion species during this phase. [ABSTRACT FROM AUTHOR]

A typical dc discharge is configured with the negative cathode at one end and a positive anode at the other end, separated by a gas filled gap, placed inside a long glass cylinder. A few hundred volts between the cathode and anode is required to maintain the discharge. The type of discharge that is formed between the two electrodes depends upon the pressure of the working gas, the nature of the working gas, the applied voltage and the geometry of the discharge. We discuss the current–voltage characteristics of the discharge as well as the distinct structure that develops in the glow discharge region. The dc glow discharge appears in the discharge current range from μA to mA at 0.5–300 Pa pressure. We discuss the various phenomena observed in the dc glow discharge, including the cathode region, the positive column, and striations. The dc glow discharge is maintained by the emission of secondary electrons from the cathode target due to the bombardment of ions. For decades, the dc glow discharge has been used as a sputter source. Then it is often operated as an obstructed abnormal glow discharge and the required applied voltage is in the range 2–5 kV. Typically, the cathode target (the material to be deposited) is connected to a negative voltage supply (dc or rf) and the substrate holder faces the target. The relatively high operating pressure, in the range from 2 to 4 Pa, high applied voltages, and the necessity to have a conductive target limit the application of dc glow discharge as a sputter source. In order to lower the discharge voltage and expand the operation pressure range, the lifetime of the electrons in target vicinity is increased through applying magnetic field, by adding permanent magnets behind the cathode target. This arrangement is coined the magnetron sputtering discharge. The various configurations of the magnetron sputtering discharge and its applications are described. Furthermore, the use of dc discharges for chemical analysis, the Penning discharge and the hollow cathode discharges and some of its applications are briefly discussed. [ABSTRACT FROM AUTHOR]

The spatial and temporal dynamics of the Ar metastable () density and temperature is studied by an extended Tunable Diode Laser Absorption Spectroscopy set-up (TDLAS) within a High Power Impulse Magnetron Sputtering (HiPIMS) pulse. A beam expander in combination with a photo diode array is used to simultaneously measure the spatial and time resolved absorption profile of an transition. HiPIMS discharges are known for their complex physics, e.g. drifting ionisation zones called spokes, that occur in a discharge with crossed magnetic and electric fields. By analysing the Doppler shift of the absorption line, we found evidence for a small azimuthal velocity of the in direction. However, this observed azimuthal velocity is three orders of magnitude slower than the reported ion drift velocities and four orders of magnitudes slower than the drift velocity. This finding may be caused by the weak coupling between the plasma rotation driven by drift and the background gas, providing an estimate of the coupling between the plasma drifting in direction and the neutral background gas. [ABSTRACT FROM AUTHOR]