Dynamics of Ar* metastables atoms in dust free and dusty argon plasmas (original) (raw)
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Journal of Physics D: Applied Physics, 2010
Diode laser absorption at 772.38 nm is used to measure the time resolved density of Ar*(3 P 2) metastable atoms in a capacitively coupled radio-frequency (RF) discharge running in argon/acetylene mixture at 0.1 mbar. The RF power is pulsed at 100 Hz and the density of Ar*(3 P 2) atoms in the 5 ms ON time and in the afterglow are recorded. Different plasma conditions, namely: 1) pure argon, 2) argon + 7% acetylene before powder formation, 3) argon + 7% acetylene after dust particles have been formed and 4) argon with dust particles remained in the plasma volume but without acetylene are studied. The measured steady-state Ar*(3 P 2) density in the middle of the reactor is always about 10 times larger in dusty argon plasma than in pure argon discharge. This is mainly a consequence of the enhancement of electron temperature after dust formation. Both steady state densities and decay times in the afterglow indicate that the degree of dissociation of C 2 H 2 in the plasma volume can be as high as 99%. It is shown that in our plasma conditions on the surface of dust particles the loss of Ar*(3 P 2) atoms is negligible compared to their loss by diffusion to the electrodes.
Tunable diode laser absorption spectroscopy of argon metastable atoms in Ar/C2H2 dusty plasmas
New Journal of Physics, 2009
The tunable diode laser absorption spectroscopy method was used to measure Ar metastable density in order to study the dust growth process in hydrocarbon-containing plasmas. A simple model was proposed that successfully interprets the experimental results of pristine plasmas. The model is also suitable for explaining the influence of dust particle size on metastable density and for examining the dust growth process. The metastable density responded strictly to the formation of dust particles and their growth in processing plasmas. Using metastable density as an indicator is, therefore, a non-intrusive and effective method for the study of the dust growth process in hydrocarbon-containing plasmas.
Ion Molecule and Dust Particle Formation in Ar/CH4, Ar/C2H2 and Ar/C3H6 Radio-frequency Plasmas
Contributions To Plasma Physics, 2005
Molecule and particle formation in a capacitively coupled radio-frequency discharge has been investigated. Formation of molecular ions has been investigated by means of plasma process monitoring employing energydispersive mass spectrometry. Particle growth has been studied by recording the intensity of the transmitted and scattered laser light signal from the particle cloud. An oscillation of the transmitted laser intensity was observed which is caused by periodic formation and expansion of a central void. This behavior can be explained by multigeneration dust cloud formation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of argon–acetylene dusty plasma
Plasma Physics and Controlled Fusion, 2018
The properties of an Ar/C2H2 dusty plasma (ion, electron and neutral particle densities, effective electron temperature and dust charge) in glow and afterglow regimes are studied using a volume-averaged model and the results for the glow plasma are compared with mass spectrometry measurements. It is shown that dust particles affect essentially the properties of glow and afterglow plasmas. Due to collection of electrons and ions by dust particles, the effective electron temperature, the densities of argon ions and metastable atoms are larger in the dusty glow plasma comparing with the dust-free case, while the densities of most hydrocarbon ions and acetylene molecules are smaller. Because of a larger density of metastable argon atoms and, as a result, of the enhancement of electron generation in their collisions with acetylene molecules, the electron density in the afterglow dusty plasma can have a peak in its time-dependence. The results of numerical calculations are in a good qualitative agreement with experimental results.
Effects of process conditions on the chemistry of an Ar/C 2 H 2 dust‐forming plasma
Plasma Processes and Polymers, 2019
A volume-averaged model and numerical simulations are used to clarify the effects of process conditions on the plasma chemistry and species initiating the formation of nanoparticles in an Ar/C2H2 plasma. It is shown that Ar/C2H2 plasmas with low electron density, moderate input flux of acetylene and an electron energy distribution function (EEDF) close to the Druyvesteyn EEDF are the most suitable for the production of carbonaceous nanoparticles. These results are verified by a direct comparison with experimental data and enable to formulate recommendations for future experiments with a controlled growth of nanoparticles in chemically-active plasmas.
A kinetic model for an argon plasma containing dust grains
Physics of Plasmas, 2004
A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann equation for the electrons and fluid equations for the ions. Local effects, such as the spatial distribution of the dust density and external electric field, are included, and their effect on the electron energy distribution, the electron and ion number densities, the electron temperature, and the dust charge are investigated. It is found that dust particles can strongly affect the plasma parameters by modifying the electron energy distribution, the electron temperature, the creation and loss of plasma particles, as well as the spatial distributions of the electrons and ions. In particular, for sufficiently high grain density and/or size, in a low-pressure argon glow discharge, the Druyvesteyn-like electron distribution in pristine plasmas can become nearly Maxwellian. Electron collection by the dust grains is the main cause for the change in the electron distribution function.
Interaction of dust particles with metastable atoms
Spatial density and temperature profiles of neon metastables produced in a radio frequency (rf) discharge were investigated by means of tunable diode laser absorption spectroscopy. The experiments were performed in the PULVA1 reactor, which is designed for the study of complex (dusty) plasmas. The line averaged measured density is about 1.5 × 10 15 m −3 in the bulk and drops almost linearly in the plasma sheath. The gas temperature is in the range of 370-390 K. The flow of metastable atoms in the plasma sheath deduced from the spatial density distribution is dominated by the flow towards the rf electrode. The sheath length is supposed as the effective diffusion length in the plasma sheath region. This approximation was used to investigate the interaction of injected particles with the plasma. The observations and estimation provide evidence for a significant interaction between metastable atoms and powder particles which is important for energy transfer from the plasma to the particles. The power per unit area absorbed by dust particles due to the collision of metastable atoms with the dust particle surface is in the range of a few tens of mW m −2 .
Journal of Applied Physics, 2017
The formation of dust particles in low-pressure plasmas is a 3-step process. The first one corresponds to nucleation and growth of nanoparticles by chain reactions between ions and gas molecules, the second one is agglomeration of the nanoparticles to form larger particles, and finally, the particles grow by radical deposition on their surfaces. In this work, the nucleation time for carbon dust particles was studied in low pressure acetylene/argon radio frequency (RF) plasmas. Since the self-bias voltage on a powered electrode was drastically affected by the transition from the nucleation to the agglomeration phases, the nucleation time was measured by observing the self-bias voltage time evolution. The nucleation time increases with the gas temperature and decreases when the gas pressure and the RF power are increased. A kinetic model, involving balance between diffusion and charging times of the nanoparticles as well as the chain reactions, is used to explain the exponential dependence of the nucleation time on the gas temperature. The balance between the times was especially indispensable to get good agreement between the model and the experimental results.
Discharging of dust particles in the afterglow of plasma with large dust density
Physical Review E, 2013
The discharging of dust particles in the afterglow of plasma with large dust density is studied. We used measured electron and metastable dependencies to calculate the rate describing collection of electrons by dust particles by solving the electron balance equation. This rate is compared with the rate calculated using the orbital motion limited (OML) theory. It is found that the OML theory may not be applied for description of dust charging at large afterglow times, and the energetic electrons generated in metastable-metastable collisions significantly affect charging of dust particles. The time dependence for dust charge is calculated by two different approaches: first, the "standard" approach is used, which assumes that ion and electron fluxes to the dust particles are different in the afterglow. Second, the dust charge is calculated by assuming that desorption of electrons from dust particles is very fast. Both approaches gave similar results for dust charging. In addition, the effects of secondary emission due to ion-dust and metastable-dust collisions on dust discharging are investigated. The main source of dust charging in the late afterglow of plasma with large dust density are the energetic electrons generated in Ar m metastable-metastable collisions.