R. Hippler

Spectroscopic Study of Plasma Polymerized a-C:H Films Deposited by a Dielectric Barrier Discharge

Plasma polymerized a-C:H thin films have been deposited on Si (100) and aluminum coated glass substrates by a dielectric barrier discharge (DBD) operated at medium pressure using C2Hm/Ar (m = 2, 4, 6) gas mixtures. The deposited films were characterized by Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS), Raman spectroscopy, and ellipsometry. FT-IRRAS revealed the presence of sp3 and sp2 C–H stretching and C–H bending vibrations of bonds in the films. The presence of D and G bands was confirmed by Raman spectroscopy. Thin films obtained from C2H4/Ar and C2H6/Ar gas mixtures have ID/IG ratios of 0.45 and 0.3, respectively. The refractive indices were 2.8 and 3.1 for C2H4/Ar and C2H6/Ar films, respectively, at a photon energy of 2 eV.

Resonance trapping effects in stepwise electron/laser excitation

Abstract This paper considers the relaxation processes in stepwise electron/laser excitations that are affected by radiation trapping. The pressure dependence of the observed linear and circular polarisations is examined and quantified. An extrapolation to zero pressure is found to be significantly different from a linear fitting procedure. This enables the extraction of true values of the state multipoles, which describe the alignment and orientation of the mercury 6 1 P 1 state immediately after electron-impact excitation.

Time resolved tunable diode laser absoption spectroscopy of dual High Power Impulse Magnetron Sputtering discharges

Time-resolved measurements have been performed during dual High Power Impulse Magnetron Sputtering (dual-HiPIMS) with two cathodes in a closed magnetic field configuration. The dual-HiPIMS system, operated at a repetition frequency f = 100 Hz and duty cycle of 1 %, was equipped with two different metallic targets (Ti, Cu). The effect of a delay between subsequent pulses on argon excited atom density and temperature was investigated by means of tunable diode laser absorption spectroscopy. It is shown that the peak densities of pulses vary strongly with the delay. We observed an enhancement of metastable density due to pre-ionization effect but more effective than that is the contribution of metal atoms which have smaller ionization energy compare to that of buffer gas atom. Associate with the enhancement of density, the temporal variation of metastable atom temperature in the Cu pulse also transforms from those of low current pulse into the high current one.

Photon angular correlations and pressure-dependent effects of helium 21P and 31P excitation by electrons

The orientation and alignment parameters of the 21P and 31P excited states of helium at an incident electron energy of 81.6 eV have been remeasured for electron scattering angles from 25 degrees to 5 degrees and extended down to 2 degrees . The studies investigate a wide range of experimental conditions and measurement techniques, including beam alignment, electron and photon angular distribution asymmetries in both the singles and coincidence detection modes, in order to establish better precision in the measurements. Nevertheless the present coherence lambda , chi and gamma a, parameters for He(21P) and He(31P) state excitation for scattering angles in the range theta e=2 degrees to 25 degrees are collectively not in good agreement with any single distorted wave, first Born or close coupling model predictions, although there are ranges of scattering angles where the individual measured parameters are in good agreement with a particular theory. Radiation trapping effects on the 31P state lifetime enabled the relative relaxation rates for the population, orientation and alignment, i.e. rank 0, 1 and 2 multipoles, of the excited state to be measured. The effects of these relaxation rates on the measured intensities and the coherence parameters are quantified. The lifetime, which can be measured an order of magnitude more quickly than the state parameters, reflects these relaxation rates and provides a reliable guide to radiation trapping effects. Radiation trapping influences the state parameters down to the lowest background operating pressure of 10-7 Torr at which the measurements have been made.