Spatially resolved study of spokes in reactive HiPIMS discharge

Abstract

Understanding mechanisms behind the formation and propagation of ionisation zones, so-called spokes, have been highly important since the first observations in HiPIMS discharges. To this day, however, a complete description is still lacking. This contribution gives an insight into the spokes in reactive Ar-N2 atmosphere using titanium target. The aim of this study is to describe not only global parameters of spokes such as their shape, length and propagation velocity but also provide a description of parameters evolving over the spoke, such as floating potential and spectral emission. The measurements of the latter clearly showed which species emission is most prominent and how it changes with transition from non-reactive argon discharge towards the discharge driven in a pure nitrogen atmosphere. Implications on the gas dynamics and discharge transitions are discussed.

Thermodynamic quasi-equilibria in high power magnetron discharges: a generalized Poisson–Boltzmann relation

“…• The localized ionization zone (spokes) that develop in high power magnetron discharges are of macroscopic size [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. They measure typically a centimeter, which is comparable to the length and curvature radius of a magnetic field line, as well as the mean free path.…”

“…Next, we analyze the temporal regimes of a typical high power magnetron discharge. The discharge is operated in argon at a pressure of p = 1 Pa and a temperature of T g = 800 K. The cathode radius is R C = 25 mm but a more typical scale is L = 10 mm which reflects the field line length in the ionization region and the size of the observed structures [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. We select two sets of parameters, one for the ionization region, the other for the outer region.…”

Spoke-resolved electron density, temperature and potential in direct current magnetron sputtering and HiPIMS discharges

“…The synchronization scheme proposed here builds upon our previous work [12], but uses the approach of Šlapanská et al of normalizing the varying spoke widths to a common value [20,21]. A peak finding algorithm (scipy.signal.find_peaks [22]) is used to detect the maxima in the reference probe signal.…”

Spatially resolved optical emission analysis of spokes in HiPIMS utilising Al, Cr, Cu, Ti, and W targets

“…A wide range of optical and electrical diagnostic methods have been used to conduct extensive investigations of the spokes. Optical methods [7] include optical screening techniques, such as fast cameras with optical filters [8][9][10] or without filters [1][2][3], as well as photomultipliers [11,12], optical emission spectroscopy (OES) [13][14][15], Thomson scattering diagnostics [16], and laser-induced fluorescence [17]. Electrical probes diagnostics * Author to whom any correspondence should be addressed.…”

“…The application of these diagnostic techniques has promoted the determination of various global properties of the spokes, such as their shape [2,3,13,27], the number of spokes along the racetrack [1,3,13,28], and their velocity [2,3,25,27]. Moreover, these methods have provided insights into structural properties, including the evolution of plasma and floating potentials [19,29], temperature of species [14,15], emission characteristics of species [9,14,15], electron density [19,30], and electron temperature [19,30] within individual spokes.…”