Tunable diode laser absorption spectroscopy of argon metastable atoms in Ar/C2H2 dusty plasmas (original) (raw)
Related papers
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.
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.
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)
In situ infrared absorption spectroscopy of dusty plasmas
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1996
In situ, time-resolved Fourier transform infrared spectroscopy was used to study particulate formation in rf discharges in mixtures of silane, argon, and nitrogen. The spectra were taken at a maximum rate of 20 Hz. The discharge conditions were chosen such that previous calibrations of the time evolutions of particle size and density could be used. The measurements indicate that the onset of the solid-state vibrational absorptions of the SiH and SiH 2 bands only takes place after the nucleation and coagulation phase have finished; it coincides with the previously predicted start of the deposition of amorphous hydrogenated silicon on the particles. The dissociation of the silane feed gas is found to be in the range of 30%, and its time development suggests that also the large-scale dissociation of silane only starts after the coagulation phase. This is in agreement with previously observed trends for the electron temperature. If silicon partilces are grown in the plasma, and the silane flow is stopped, the Si particles stay trapped in the glow. The infrared measurements, however, show that they almost completely oxidize: the SiH/SiH 2 vibrations disappear and a strong SiO vibration appears. If nitrogen gas is allowed into the plasma, the SiO vibration is replaced by a SiN vibration.
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 Plasma Physics, 2014
The formation of carbon nanoparticles in low pressure magnetized H2/CH4 and H2/C2H2 plasmas is investigated using infrared quantum cascade laser absorption, mass spectrometry, and electrostatic probe measurements. Results showed that dust formation is correlated to the presence of a significant amount of large positively charged hydrocarbon ions. Large negative ions or neutral hydrocarbon were not observed. These results, along with a qualitative comparison of diffusion and reaction characteristic, suggest that a positive ion may contribute to the growth of nanoparticles in hydrocarbon magnetized plasmas.
Thus, generation of the laserinduced dust gas plasma flows is possible in the case when the spectral energy ionization threshold for the matrix substance proves to be below the dustcomponent evaporation threshold. Such conditions are possible under the action of shortwave radiation on easily ablating poly meric media containing fine transparentdielectric particles. The electron concentration in plasma and the dustparticle charge achievable in this way enable us to carry out investigations in a previously unstudied range of parameters. The comparative analysis of the known data on the dustparticle charge with those obtained in this work shows that there exists a depen dence of the dustparticle charge on the electron con centration in the plasma carrier, which is close to that for the power (with the superscript equal to ~0.25). The effect of photoexcitation and step photoioniza tion of dust particles can be used for increasing the absorption coefficient for dust gasplasma flows with the purpose of increasing the efficiency of their further heating by the coherent IR radiation, which is of prac tical interest for solving urgent problems of designing plasma–photon energy installations of the highden sity power of various purposes with active plasma–dust media.
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.
Detection of dust particles in the plasma by laser-induced heating
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1996
Heating of dust particles suspended in a low pressure discharge by means of a high power pulsed laser was analyzed. A detailed model of particle heating and thermal decomposition was developed and experimentally verified using 1 m Teflon-like particles in a radio-frequency argon discharge. Laser-induced heating results in blackbody-like emission from the particles. This radiation can be easily recorded and a particle temperature of about 3500 K is determined by fitting the emission spectra. From the model it follows that the time resolved emission intensity gives valuable information about the particles: the time delay between the onset of the laser pulse and the blackbody-like emission corresponds to the heating time of the clusters and is dependent on their size. Moreover, the absolute emission intensity is proportional to the particle density.
Measurement of gas temperatures in dust-free and dusty argon discharges
Journal of Physics D: Applied Physics, 2019
Gas temperatures in an argon low-power capacitively-coupled rf discharge were measured by means of tunable diode laser absorption spectroscopy on 1s 5 metastable states. It was shown that the uncertainty of the measurements in dust-free plasma could be minimized to ±1 K. In the presence of dust, due to instabilities in the dust subsystem (e.g. dust density waves), the uncertainty of the temperature measurements increased several times. Nevertheless, an evidence of the gas temperature increase in the presence of dust was detected. This result suggests that the microparticle suspensions, immersed in the low-pressure plasmas, significantly modify the temperature fields of the neutral gas.