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A power-modulated radio-frequency (f = 13.56 MHz) argon plasma supplied by reactive acetylene to deposit an amorphous hydrocarbon film on the electrodes is studied. The effects of gradual film deposition on electron density, electron temperature, argon metastable Arm(3P2) density, and dc-bias voltage are investigated. The time evolutions of plasma parameters during a pulsing cycle are studied as a function of the applied RF power and the thickness of the deposited film. Analytical estimations show a slower expansion of the sheath size and a slower decay of the ion flux after film deposition on the electrodes. The observed changes in the plasma parameters during the power-on and afterglow phases of the pulsed plasma can be correlated with the presence of impurities desorbed from the chamber walls in the discharge volume. [ABSTRACT FROM AUTHOR]

Plasma-enhanced chemical vapor deposition methods are frequently used to deposit barrier layers, e.g. on polymers for food packaging. These plasmas may suffer from particle (dust) formation. We report on a flexible monitoring system for dust. It is based on scanning a 3D plasma volume for particles by laser light scattering. The lower size limit of particles detected in the presented system is 20 nm. We report on existence diagrams for obtaining dust free or dust loaded capacitively or inductively coupled rf-plasmas in C2H2 depending on pressure, flow and rf-power. We further present growth rates for dust in these plasmas and show that monodisperse particles are only obtained during the first growth cycle. [ABSTRACT FROM AUTHOR]

A non-invasive diagnostic technique for measurements of ion fluxes and ion densities in low-pressure pulsed radio-frequency (RF) discharges is described. The ion flux towards an electrode is determined from the change in electrode dc-bias in the plasma afterglow. The measurements in various gas mixtures (Ar, N2, Ar/C2H2 and Ar with nanoparticles) show an increase in ion flux with the applied RF power. Ion densities are estimated from the ion fluxes and the plasma density at the plasma–sheath boundary, assuming the afterglow electron temperature to be known. Very good agreement between the estimated ion densities and independently measured electron densities is found in the bulk of dust-free plasmas assuming an afterglow electron temperature of 0.05 eV for argon and argon/acetylene plasmas and 0.2 eV for the nitrogen plasma. In dusty plasmas, the ion density at the plasma–sheath boundary can be determined from the measured ion flux and assuming an afterglow electron temperature of 0.05 eV. For the estimation of ion density in the dusty plasma bulk, the ion density distribution, influenced by the negatively charged dust particles, has to be taken into account. [ABSTRACT FROM AUTHOR]

This study for the first time confirms the presence of plasma bullets in a MHz argon atmospheric pressure plasma jet. Bullet characteristics are investigated by phase-resolved optical emission measurements. Regarding the jet's reactive component output, its ozone production rates are investigated by two independent diagnostic techniques yielding complementary results. The first method--UV-absorption spectroscopy in the Hartley band--determines space-resolved distribution of the ozone concentration in the jet effluent. The second method--quantum cascade laser-absorption spectroscopy in the mid-infrared spectral region--yields high sensitivity results of the average ozone concentration in a multipass cell, in which the effluent is directed. The results of both diagnostic techniques show excellent agreement. [ABSTRACT FROM AUTHOR]

High power impulse magnetron sputtering (HIPIMS) is a plasma vapour deposition technique used for deposition of dense coatings. In order to contribute to a better understanding of the dynamics of a HIPIMS plasma discharge, time- and wavelength-resolved measurements of the light emitted from the plasma were performed. Lateral images of the HIPIMS plasma were recorded using an ICCD camera with a gate width of 1µs. For each picture, Abel inversion was performed to compute the radial emissivity profile of the plasma. Band-pass interference filters were used to isolate the desired wavelength in order to observe lines of ions and neutrals of metal and argon (Ar) in HIPIMS plasma discharges with an aluminium (Al), titanium (Ti) or chromium (Cr) target in Ar atmosphere. The result is the temporal evolution of the radial emissivity profile of metal and gas neutrals and singly charged ions. [ABSTRACT FROM AUTHOR]

Space- and time-resolved measurements of Ar (3P2) metastable atoms at the exit of an atmospheric pressure radio-frequency micro-plasma jet are performed using tunable diode laser absorption spectroscopy. The discharge features a coaxial geometry with a hollow capillary as the inner electrode and a ceramic tube with a metal ring as the outer electrode. Absorption profiles of metastable atoms and optical emission measurements reveal the dynamics and the filamentary structure of the discharge. Single filaments with a diameter of 125µm and metastable densities of about 1013 cm-3 are observed. The average spatial distribution of Ar metastables is characterized with and without a target in front of the jet, showing that the target potential and, therewith, the electric field distribution substantially change the filaments' expansion. Together with a detailed analysis of the ignition phase and the discharge's behavior under pulsed operation, the results give an insight into the excitation and de-excitation mechanisms. [ABSTRACT FROM AUTHOR]

By investigating the atomic oxygen density in its effluent, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy measurements are for the first time performed in a cold argon/oxygen atmospheric pressure plasma jet. The measurements are carried out in ambient air and quenching by inflowing air species is considered. We propose a novel absorption technique in the VUV spectral range, where emission originating from within the discharge is used as light source to determine the inflow of atmospheric oxygen into the effluent. Furthermore, we propose a modelling solution for the on-axis density of inflowing ambient air based on the stationary convection-diffusion equation. [ABSTRACT FROM AUTHOR]

Micro-scaled plasma jets with reactive process gases, e.g. oxygen, are applied for localized surface treatment. Here, investigations of the development and the spatial distribution of atomic oxygen are reported in the post-discharge effluent of a micro-scaled atmospheric pressure plasma jet. These measurements are supplemented by installation of planar targets of various materials in the effluent. The reactive species are detected by means of two-photon laser-induced fluorescence spectroscopy from the discharge, through the free effluent, up to distances of about 200 µm in front of a planar surface. Ozone density profiles are measured by UV absorption spectroscopy. The effect of the effluent on gold and plastic substrates and vice versa is investigated. In the free effluent, the atomic oxygen density falls off exponentially to about 2 × 1015 cm-3 at a distance of 6mm from the jet's nozzle. The implementation of a plastic target does not disturb the O distribution, resulting in a strictly localized etching of the target. In contrast, mounting of a gold target increases the oxygen density and spreads its distribution close to the target. For correlation, surface modifications by plasma treatment of plastic and gold substrates are analysed by UV laser microscopy and x-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

Axial emission profiles in a parallel plate dc microdischarge (feedgas: argon; discharge gap d = 1 mm; pressure p = 10 Torr) were studied by means of time-resolved imaging with a fast ICCD camera. Additionally, volt-ampere (V -A) characteristics were recorded and Ar* metastable densities were measured by tunable diode laser absorption spectroscopy (TDLAS). Axial emission profiles in the steady-state regime are similar to corresponding profiles in standard size discharges (d ≈ 1 cm, p ≈ 1 Torr). For some discharge conditions relaxation oscillations are present when the microdischarge switches periodically between the low current Townsend-like mode and the normal glow. At the same time the axial emission profile shows transient behavior, starting with peak distribution at the anode, which gradually moves toward the cathode during the normal glow. The development of argon metastable densities highly correlates with the oscillating discharge current. Gas temperatures in the low current Townsend-like mode (Tg = 320-400 K) and the high current glow mode (Tg = 469-526 K) were determined by the broadening of the recorded spectral profiles as a function of the discharge current. [ABSTRACT FROM AUTHOR]

In Ar and He radio-frequency (RF) plasmas with admixtures of C2H2 and CH4 the hydrocarbon chemistry has been studied in relation to dust particle formation by means of infrared tunable diode laser absorption spectroscopy (TDLAS) combined with Fourier transform infrared (FTIR) spectroscopy. The experiments were performed in a RF capacitively coupled parallel plate reactor at a frequency of f = 13.56 MHz, a pressure of p = 0.1 mbar and a flow rate of Φ = 8 sccm of Ar or He with admixtures of 0.5 sccm C2H2 or 1 sccm CH4. The power was P = 15 W. Using TDLAS, the temporal evolution of the concentrations of the methyl radical and of four stable molecules, C2H2, CH4, C2H4 and CO, was monitored in the plasma. Simultaneously, the growth process of the dust particles was analysed by FTIR spectroscopy. The degree of dissociation of the acetylene precursor was found to be nearly constant in the range of 96% under stabilized conditions for both the Ar and He plasmas. In contrast, the degree of dissociation of the methane precursor varied between 45% and 90% depending (i) on the appearance of dust particles in the reactor volume and (ii) on the Ar or He plasma conditions. The methyl radical concentration was found to be in the range of 1011 molecules cm−3. The concentrations of all hydrocarbon species were strongly correlated with the dynamic of the dust formation. Fragmentation efficiencies of acetylene (RF (C2 H2) = 3.2 × 1016 molecules J−1) and of methane (RF (CH4) = (0.16–2.5) × 1016 molecules J−1) and conversion efficiencies to the produced hydrocarbons (RC = (0.23–8.5) × 1014 molecules J−1) could be estimated in dependence on the discharge conditions in the RF plasma. [ABSTRACT FROM AUTHOR]