Measurements of electric-field strengths in ionization fronts during breakdown

Using laser-induced fluorescence-dip Stark spectroscopy, we performed time-resolved, direct measurements of electric-field strengths during the breakdown phase of a low-pressure, pulsed discharge in xenon. With this experimental technique we could for the first time quantitatively measure the time evolution of the driving force of the plasma breakdown process: the electric field. Moving ionization fronts were measured with submicrosecond resolution. These ionization fronts were sustained by a spatially narrow, rapidly moving region of strong electric field.     

Evolution of a dust void in a radio-frequency plasma sheath

The onset and growth of a dust void are investigated in a radio-frequency (rf) sheath of a capacitively coupled argon plasma. A circularly symmetric void emerges and grows with increasing rf power and pressure in the central region of the dust cloud levitating in the sheath. Experimental measurements of the void diameter are compared with the predictions of a simple phenomenological theory, based on a balance of forces on dust grains.     

Quantitative measurement of different ceramide species from crude cellular extracts by normal-phase high-performance liquid chromatography coupled to atmospheric pressure ionization mass spectrometry

Normal-phase high-performance liquid chromatography (NP-HPLC) coupled to atmospheric pressure ionization mass spectrometry (APCI-MS) allows quantitative analysis of endogenous ceramide and dihydroceramide species from crude lipid extracts. Qualitative information for the species comes from observation of differences in chromatographic and mass spectrometric behavior between species (Pettus et al. Rapid Commun. Mass Spectrom. 2003; 17: 1017-1026). Quantitative analysis is achieved by (1) use of a synthetic internal standard as an extraction and injection control, (2) lack of salt adduction, ion suppression, or other matrix effects in APCI mode, and (3) consistent fragmentation and ionization of external standards across the physiologically relevant concentration range found in endogenous lipid samples. Application to the analysis and quantitation of ceramide and dihydroceramide from various cell lines is demonstrated. The results from APCI-MS analysis corroborate and enhance information acquired from use of the diacylglycerol kinase assay for total ceramide measurement. This technique readily allows simultaneous quantitation of ceramide and dihydroceramide species.     

Laser-particulate interactions in a dusty RF plasma

The interaction of particulates formed in an argon RF discharge containing 1-5% CCl₂F₂ admixture with a pulsed infrared laser (Nd:YAG, intensity ~10⁹ W m^-2, pulse duration ~10^-4 s) has been studied in situ. The white light emitted during this process has been monitored as a function of time and wavelength using a fast photo diode and an optical multichannel analyser. The spectra have been fitted with blackbody curves with a standard deviation of 5%. A spectral temperature of about 3500 K has been obtained for various plasma conditions and attributed to the decomposition temperature of the particulate material. A model based on laser heating, internal heat conduction and chemical decomposition is compared with the experimental results. This model predicts the time constants for heating and decomposition of the particulates and explains the dependence of the measured emission intensity on the laser intensity     

Fast deposition of amorphous hydrogenated carbon films using a supersonically expanding arc plasma

Experiments concerning the growth rate and quality of an amorphous hydrogenated carbon film deposited in a reactor based on the supersonic expansion of an arc plasma are reported. In order to be able to calculate the deposition rate, an existing flow model has been completed with chernical reaction rate equations. The methane gas that is injected in the arc appears to be dissociated and ionized completely. The calculated deposition rates agree well with the experimental values obtained within-situ ellipsometry. The growth rates are an order of magnitude larger than those reported in the literature. Still, the film quality, expressed in terms of refractive index, optical bandgap, and hardness, is similar to those obtained by other authors.     

In-situ diagnostics for plasma surface processing

A survey is given of in-situ diagnostics of plasma and surface for application in plasma etching and deposition. Especially those diagnostics that increase the fundamental understanding of the elementary processes occurring both within the plasma and at the surface are highlighted. In general, diagnostics are performed to determine the value of a physical parameter. This value is fed into models of plasma or surface, and in that way the understanding of the process is enhanced. In the paper first the most interesting physical parameters are defined. Subsequently the diagnostic techniques currently available to determine those parameters are reviewed.     

Elastic electron deuteron scattering on a tensor polarized solid ND3 target

Elastic electron deuteron scattering has been measured at the Bonn 2.5 GeV electron-synchrotron using a tensor polarized ND₃ target. The scattered electrons and deuterons were detected in coincidence by two magnetic spectrometers. Data were taken at an average value of four momentum transfer ofQ ²=0.495 (GeV/c)² in order to separate the electric monopole and quadrupole form factors of the deuteron. To have a sufficient control of systematic effects, both polarized and unpolarized cross sections were measured with an identical experimental set up. In the ratioR _EXP=dσ_pol/dσ_unp systematic effects are expected to cancel. This ratioR _EXP is related to the theoretical polarized cross section d dσ _T where the spin quantization axis for the deuterons is orientated in the ed-scattering plane, perpendicular to the virtual photon direction. Our final result for the corresponding recoil tensor polarization ist ₂₀=?2.01±1.13.     

Analysis of the Evolution of a Supersonically Expanding Plasma

A supersonically expanding arc plasma in argon is analyzed both experimentally and theoretically. The plasma is created in a cascaded arc and extracted through a hole in the anode. It emanates in a large vacuum system, where it expands supersonically. This expansion is limited by a shock wave. After the shock wave a subsonic plasma beam is created. A quasi one-dimensional model, based on the conservation of mass, momentum and energy is presented. The shock wave is treated as a discontinuity. The electron density, the gas velocity and the gas temperature are measured as a function of the position in the expansion by means of Stark broadening and Doppler spectroscopy. The model calculations agree well with the measurements, especially in the first part of the supersonic flow.     

The energy balance of a plasma in partial local thermodynamicequilibrium

The energy balance for electrons and heavy particles constituting a plasma in partial local thermodynamic equilibrium is derived. The formulation of the energy balance used allows for evaluation of the source terms without knowledge of the particle and radiation transport situation, since most of the contributions that arise from that situation (diffusion, local capture of radiation, etc.) are taken into account in the nonequilibrium term. The small correction for the contribution of the loss of excited states, which is slightly overestimated in this approach, can usually be neglected. The overpopulation factor, which can often be evaluated from measurements of the pressure, electron density, and temperature, becomes one of the most important plasma parameters; in the energy balance it accounts for most of the phenomena which may be difficult to evaluate otherwise. As an illustration, some rate coefficients are given for an argon plasma, and the evolution of the several terms of the electron energy equation in a flowing cascaded arc is discussed     

On the determination of energy fluxes at plasma–surface processes

A summary is given of different methods for the determination of the energy influx and its influence on the thermal balance and energetic conditions of substrate surfaces during plasma processing. The discussed mechanisms include heat radiation and kinetic and potential energy of charged particles and sputtered neutrals. For a few examples such as magnetron sputtering of a-C:H films, sputter deposition of aluminum on microparticles, and titanium deposition in a hollow-cathode arc evaporation device the energetic balance of substrates during plasma processing is presented. Received: 6 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001