Bio: C. Courteille is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Silane & Particle. The author has an hindex of 8, co-authored 10 publications receiving 342 citations.
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.
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.
TL;DR: In situ Fourier transform infrared absorption spectroscopy has been used to study the composition of particles formed and suspended in radio-frequency discharges of silane-oxygen-argon gas mixtures.
Abstract: In situ Fourier transform infrared absorption spectroscopy has been used to study the composition of particles formed and suspended in radio-frequency discharges of silane-oxygen-argon gas mixtures. The silane gas consumption was observed by infrared absorption. The stoichiometry of the produced particles depends on the silane flow rate and was compared with commercial colloidal silica. A small proportion of silane gas produces nanometric stoichiometric particles whereas a large proportion produces larger under-stoichiometric particles. Absorption spectroscopy was sufficiently sensitive to reveal particles too small to be visually observed by laser light scattering. Post-oxidation of hydrogenated silicon particles trapped in an argon plasma was obtained by adding oxygen. Mass spectrometry of negative and positive ions showed an extensive range of ionic clusters which may be at the origin of the observed particle formation. A model based on an iterative reaction sequence gives a good agreement with the measured positive ion mass spectrum.
TL;DR: In this paper, partial-depth modulation of the rf power in a capacitive discharge is used to investigate the relative importance of negative ions and neutral radicals for particle formation in low-power low-pressure silane plasmas.
Abstract: Partial-depth modulation of the rf power in a capacitive discharge is used to investigate the relative importance of negative ions and neutral radicals for particle formation in low-power low-pressure silane plasmas. For less than 85% modulation depth, anions are trapped indefinitely in the plasma and particle formation ensues, whereas the polymerized neutral flux magnitudes and dynamics are independent of the modulation depth and the powder formation. These observations suggest that negative ions could be the particle precursors in plasma conditions where powder appears many seconds after plasma ignition. Microwave interferometry and mass spectrometry were combined to infer a rough estimate of anion density of similar to 7 x 10(9) cm(-3) which is approximately twice the free electron densit in these modulated plasmas.
TL;DR: Particle formation has been investigated experimentally from the initial molecular precursors up to the final micron-sized particles in a low pressure silane rf capacitive discharge.
Abstract: Particle formation has been investigated experimentally from the initial molecular precursors up to the final micron-sized particles in a low pressure silane rf capacitive discharge. Neutrals and ions were studied by quadrupole mass spectro- metry in power-modulated plasmas: Whole series of negative ions were observed, ranging from monosilicon anions through to nanometric clusters. Anion confinement results in particles and conversely, anion de-trapping can inhibit particle formation. Plasma polymerisation is considered in terms of neutral and ionic species. Laser light scattering measurements show that particles appear during a rapid coalescence phase and possible mechanisms are discussed.
TL;DR: In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and the phonon broadening of these lines is considered.
Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.
TL;DR: A review on macromolecular plasma chemistry illustrates the continuing interest in achieving controlled surface modification under plasma conditions, and the potential of plasma-chemistry for advancing future technologies.
Abstract: It is now well established that exposing inorganic and organic polymeric substrates to cold-plasma species represents an unusually convenient and versatile surface-modification and coating technology. The uniqueness of non-equilibrium plasma processes is related to the fact that they permit the conversion of a wide range of organic materials and organic compounds containing main group elements, including organometallic derivatives, into charged and neutral molecular-fragments and atomic species. These fragments can then promote surface-functionalization reactions or generate macromolecular thin layers as a result of recombination of nascent species on the surfaces that confine the plasma. In earlier work the control of the composition of polymeric films generated via plasma treatment was focused predominately on synthesis of unique, highly cross-linked polymers produced under relatively high power conditions. However, interest recently increased in providing less cross-linked, more highly functionalized films. Modern non-equilibrium plasma technologies are ‘par excellence’ surface modification processes which result in surface material layers that retain the inherent advantages of the substrates while providing more exact film chemistry control, and as a result they have potential appeal in many applications. Most of the prior research related to discharge-mediated surface-modification reactions involved low-pressure cold-plasma environments. However, in recent last years, atmospheric pressure non-equilibrium plasma installations have been designed, developed and tested with great success. This review on Macromolecular Plasma Chemistry illustrates the continuing interest in achieving controlled surface modification under plasma conditions, and the potential of plasma-chemistry for advancing future technologies.
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.
Abstract: The chemical reactions and physical processes which occur at the surface of hydrocarbon films during deposition from low-temperature hydrocarbon plasmas are reviewed. Special emphasis is placed on the chemical reactions of atomic hydrogen, the interaction of energetic particles with the solid, and the synergistic effects between them. The interaction of energetic particles with the surface of the growing film has been simulated in the binary collision approximation by means of the TRIM.SP computer code. The sputtering and displacement yields were calculated for hydrogen and carbon ions in the energy range from 25 to 500 eV. In addition, the depth distributions of the damage and implantation profiles are shown. The validity of this binary collision approach is discussed and compared with molecular dynamics simulations. The dominant ion-induced effect in this energy range is displacement of bonded hydrogen atoms. The microscopic processes of atomic hydrogen interacting with a carbonaceous surface, such as adsorption, abstraction, addition, and etching, are briefly reviewed and summarized. Furthermore, investigations of synergistic effects using thermal, atomic hydrogen and low-energy hydrogen ion beams are discussed. The film growth of hydrocarbon films from hydrocarbon plasmas was investigated experimentally by real-time, in-situ ellipsometry and a variety of ex-situ analyses. The real-time possibilities and the submonolayer sensitivity of ellipsometry allow detailed investigation of the growth process in the plasma environment. The temperature dependence of the growth and the interaction of atomic hydrogen and energetic particles with the film surface were thoroughly investigated. The experimentally observable net deposition rate represents a competition between a temperature-independent deposition process and the temperature-dependent erosion by atomic hydrogen. At very low ion energies the synergistic interaction between atomic hydrogen and the ions leads to `ion-assisted chemical erosion'. The interaction of ions with the surface generates a modified layer on top of the film surface. This modified layer is an intrinsic property of the deposition as well as the erosion process at ion energies above about 30 eV. The deposition results are discussed on the basis of the reviewed microscopic processes and a framework for understanding film growth is presented.
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.
Abstract: An overview of dynamic self-organization phenomena in complex ionized gas systems, associated physical phenomena, and industrial applications is presented. 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 phenomena are reviewed and the major technological applications of micro- and nanoparticles are discussed. Until recently, such particles were considered mostly as a potential hazard for the microelectronic manufacturing and significant efforts were applied to remove them from the processing volume or suppress the gas-phase coagulation. Nowadays, fine clusters and particulates find numerous challenging applications in fundamental science as well as in nanotechnology and other leading high-tech industries.
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...