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W. Schwarzenbach

Bio: W. Schwarzenbach is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Light scattering & Ion. The author has an hindex of 5, co-authored 5 publications receiving 250 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors used a Brownian free molecule coagulation model to determine the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering.
Abstract: To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities (incident and scattered light intensities with opposite polarization) measured at 135 degrees and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spherical particles again. The presence of strong cross-polarization intensities is accompanied by low-frequency instabilities detected on the scattered light intensities and plasma emission. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under our experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution. (C) 1996 American Institute of Physics.

90 citations

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TL;DR: In this paper, the frequency dependence of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive argon discharge, where the capacitive sheaths are thinner at high frequencies which accentuates the high frequency reduction in sheath impedance.
Abstract: The frequency dependence (13.56–70 MHz) of the ion energy distribution at the ground electrode was measured by mass spectrometry in a symmetrical capacitive argon discharge. Reduced sheath impedance at very high frequency allows high levels of plasma power and substrate ion flux while maintaining low levels of ion energy and electrode voltage. The lower limit of ion bombardment energy is fixed by the sheath floating potential at high frequency, in contrast to low frequencies where only the radio frequency voltage amplitude is a determinant. The capacitive sheaths are thinner at high frequencies which accentuates the high frequency reduction in sheath impedance. It is argued that the frequency dependence of sheath impedance is responsible for the principal characteristics of very high frequency plasmas. The measurements are summarized by simple physical descriptions and compared with a particle‐in‐cell simulation.

70 citations

Journal ArticleDOI
TL;DR: In this paper, measurements of anions and cations are reported for hydrocarbon and silane radio frequency capacitive glow discharges. And the general role of anion in particle formation is discussed in the light of these experiments.
Abstract: Measurements of anions and cations are reported for hydrocarbon and silane radio frequency capacitive glow discharges. Series of anions were observed by quadrupole mass spectrometry using power‐modulated plasmas, and their structures are interpreted from the form of the mass spectra. Various experiments in silane plasmas show that anion confinement results in particles and conversely, anion detrapping can inhibit particle formation. In contrast, the polymerized neutral flux magnitudes, mass spectra and dynamics are independent of the powder formation. Powder is known to form readily in deposition plasmas containing electronegative free radicals, and the general role of anions in particle formation is discussed in the light of these experiments.

70 citations

Journal ArticleDOI
TL;DR: In this article, the authors used particle-in-cell (PIC) simulations to reconstruct the profile of the time-averaged potential in the sheath of an argon plasma in a capacitive reactor.
Abstract: Charge-exchange collisions and radio frequency (RF) excitation combine to give peaks in the ion energy distribution measured at the ground electrode of an argon plasma in a capacitive reactor. These peaks are used as a diagnostic to reconstruct the profile of the time-averaged potential in the sheath. Particle-in-cell (PIC) simulations show that the method is accurate. The method is applied to investigate the sheath thickness as a function of excitation frequency at constant plasma power. The time-averaged potential is found to be parabolic in both experimental measurements and numerical simulations.

18 citations

Journal ArticleDOI
TL;DR: In this paper, a cross section of a capacitive discharge is illuminated with an expanded laser beam, and global scattered light is recorded by camera, and a small amount of particles trapped in an argon plasma is visualized using the scattered intensity.
Abstract: Understanding particle dynamics requires comparison of spatially resolved measurements with two-dimensional (2-D) simulations. In this work, a cross section of a capacitive discharge is illuminated with an expanded laser beam, and global scattered light is recorded by camera. Plasma equipotentials are visualized using the scattered intensity from a small amount of particles trapped in an argon plasma. At low RF voltages, good agreement is found with 2-D fluid simulations, whereas displacement of the power clouds toward the sheaths is observed at high voltage.

8 citations


Cited by
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01 Jan 1993
TL;DR: In this article, particle-in-cell (PIC) combined with Monte Carlo collision (MCC) calculations are used for simulation of partially ionized gases, with many of the features met in low-temperature collision plasmas.
Abstract: Many-particle charged-particle plasma simulations using spatial meshes for the electromagnetic field solutions, particle-in-cell (PIC) merged with Monte Carlo collision (MCC) calculations, are coming into wide use for application to partially ionized gases. The author emphasizes the development of PIC computer experiments since the 1950s starting with one-dimensional (1-D) charged-sheet models, the addition of the mesh, and fast direct Poisson equation solvers for 2-D and 3-D. Details are provided for adding the collisions between the charged particles and neutral atoms. The result is many-particle simulations with many of the features met in low-temperature collision plasmas; for example, with applications to plasma-assisted materials processing, but also related to warmer plasmas at the edges of magnetized fusion plasmas. >

1,022 citations

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TL;DR: In this article, the chemical reactions and physical processes which occur at the surface of hydrocarbon films during deposition from low-temperature hydrocarbon plasmas are reviewed and a framework for understanding film growth is presented.

334 citations

Journal ArticleDOI
02 Aug 2001-Vacuum
TL;DR: In this paper, a summary of different elementary processes influencing the thermal balance and energetic conditions of substrate surfaces during plasma processing is given, and various contributions to the energy balance are given in a modular mathematical framework form and examples for an estimation of heat fluxes and numerical values of relevant coefficients for energy transfer, etc.

325 citations

Journal ArticleDOI
TL;DR: An overview of dynamic self-organization phenomena in complex ionized gas systems, associated physical phenomena, and industrial applications is presented in this paper, where the most recent experimental, theoretical, and modeling efforts to understand the growth mechanisms and dynamics of nano- and micron-sized particles, as well as the unique properties of the plasma-particle systems (colloidal, or complex plasmas) and the associated physical effects are reviewed and the major technological applications of micro- and nanoparticles are discussed.

322 citations

Journal ArticleDOI
TL;DR: The fundamentals of nanocrystal formation in plasmas are discussed, practical implementations of plasma reactors are reviewed, the materials that have been produced with nonthermal plAsmas and surface chemistries that have be developed are surveyed, and an overview of applications of plasma-synthesized nanocrystals is provided.
Abstract: Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal pla...

292 citations