Lenka Dosoudilová

Investigation of helium barrier discharges with small admixtures of oxygen

Barrier discharges in helium and in helium with small admixtures of oxygen were investigated by electrical measurements, the spatiotemporally resolved optical emission spectroscopy and surface charge diagnostics via the electro-optic Pockels effect. As already known, in pure helium a diffuse discharge is typically formed because of the significant role of the metastable species. However, even a very small oxygen admixture (0.025 vol.%) causes the transition to a filamentary mode as a result of the effective quenching of helium metastables by oxygen molecules. This effect was indicated by a significant decrease of N-2(+) the first negative system emission. The transition region was characterized by several Townsend-like discharge breakdowns becoming more and more unstable with an increasing O-2 admixture. The formation of the atmospheric pressure Townsend-like discharge was confirmed by the spatiotemporally resolved emission. The development of the surface charges agrees qualitatively and quantitatively well with the transported charge during the discharge breakdown calculated from the discharge current.

Determination of titanium atom and ion densities in sputter deposition plasmas by optical emission spectroscopy

The thorough characterizations of deposition plasma lead to important achievements in the fundamental understanding of the deposition process, with a clear impact on the development of technology. Measurement of the spatial and, in the case of pulse excited plasma, also temporal evolution, of the concentrations of sputtered atoms and ions is a primary task in the diagnostics of any sputter deposition plasma. However, it is difficult to estimate absolute number densities of the sputtered species (atoms and ions) in ground states directly from optical emission spectroscopy, because the species in the ground levels do not produce any optical signal. A method using effective branching fractions enables us to determine the density of non-radiating species from the intensities of self-absorbed spectral lines. The branching fractions method described in the first part of this paper was applied to determine the ground state densities of the sputtered titanium atoms and ions. The method is based on fitting the theoretically calculated branching fractions to experimentally measured ratios of the relative intensities of carefully selected resonant titanium atomic and ionic lines. The sputtered species density is determined in our experimental setup with a relative uncertainty of less than 5% for the dc driven magnetron and typically 15% for time-resolved measurements of high- power impulse magnetron sputtering (HiPIMS) discharge. In the second part of the paper, the method was applied to determine the evolution of titanium atom and ion densities in three typical cases ranging from the dc driven sputter process to HiPIMS.

Atmospheric pressure RF discharge in neon and helium

Radio frequency (13.56 MHz) capacitive discharges at atmospheric pressure in neon and helium were studied by ICCD imaging. The discharges were generated between parallel plate metal electrodes with a gap of 2 mm. At certain conditions, a homogeneous discharge burning in α-mode can be generated both in helium and neon. The time-resolved images of discharges reveal similarities in atomic excitation mechanism in both gases.

Diffuse α-mode atmospheric pressure radio-frequency discharge in neon

In this work, a radio-frequency (RF) atmospheric pressure glow discharge burning in neon between planar metal electrodes is achieved for the first time. The RF discharge can operate in two stable modes: in a diffuse α-mode with uniformly covered electrode surfaces and in a constricted γ-mode. Similarities are revealed when the discharge is compared against the RF atmospheric pressure glow discharge in helium, namely both discharges show a discontinuity and a hysteresis in the current–voltage characteristic at the mode transition; the spatio-temporal profiles of the light emission in the α-mode from neon, helium and atomic oxygen are also similar.