A global model for the afterglow of pure argon and of argon with negatively charged dust particles

Abstract

Zero-dimensional, space-averaged global models of argon dust-free and dusty afterglow plasmas are developed, which describe the time behaviour of electron n e(t) and Ar* metastable n m(t) densities. The theoretical description is based on the assumption that the free electron density is smaller than the dust charge density. In pure argon, fairly good agreement with the experimentally measured densities and their decay times in the afterglow is obtained when the electron energy loss term to the chamber walls is included in the electron energy balance equation. In dusty plasma afterglow, the agreement between theory and experiment is less satisfactory. The calculated metastable density is 3 times smaller than the measured one and the electron decay is much faster in the late afterglows. The difference should probably arise from the assumption that the electron energy distribution function is Maxwellian. Different sources of secondary electrons in the dusty plasma afterglow are analysed. Comparison of the model with experimental results of argon dusty plasma suggests that the metastable pooling could be the source of the experimentally observed electron density increase in the early afterglow but electron generation from metastable–dust interactions cannot be fully discarded.

Ion chemistry in H2-Ar low temperature plasmas

“…Other reactions of excited Ar, such as the reaction Ar m + Ar m → Ar + + Ar + e − , are not relevant for our plasma conditions due to the low pressure. However, for pressures higher than 1 Pa this reaction cannot be neglected 48,49 . For the wall loss of Ar m Eqn.…”

Modelling the effects of nitrogen doping on the carbon nanofiber growth via catalytic plasma‐enhanced chemical vapour deposition process

“…where n sj (= j 0 ) is the surface concentration of neutral atoms, [31,32] j is the surface coverage by the respective species, 0 is the adsorption sites per unit area, J j (=n j th /4) is the flux of neutral impinging species on the catalyst nanoparticle surface from the plasma, J…”

“…is the surface diffusion coefficient, D s0 = a 2 0 , a 0 (=0.34 nm) is the carbon atoms' interatomic distance, s (=0.3 eV) is the energy barrier for carbon species diffusion through the catalyst nanoparticle surface, [31] 6 eV) is the energy barrier for carbon species bulk diffusion through catalyst nanoparticle, [31] P(≈20 GPa) is the pressure exerted by graphene layers on catalyst nanoparticle, k = A k exp(− inc /k B T S ) is the carbon species incorporation speed in the graphene layers, [13] A k = a 0 , inc = (0.4 eV) is the carbon species energy barrier to diffuse along the nanofiber-catalyst interface, cnf is the nanofiber density, m cat is the mass of the metal catalyst particle, and cat is the density of metal catalyst nanoparticle. D m [=D m0 exp(− SD /k B T s )] is the metal atoms' diffusion coefficient, [31] and E th (=1.87 eV) is the energy for thermal dehydrogenation of hydrocarbons. [33] All complex processes involved in Equation 13 to describe the growth mechanism of N-CNFs on the catalyst nanoparticle are listed in Table 4.…”

“…At high temperatures, bulk diffusion dominates, and at low temperatures, surface diffusion dominates, whereas at intermediate temperatures, both are significant for growth. [31,34,[37][38][39] Therefore, in the present paper, we have taken both the diffusion processes into account because the temperature of the catalyst nanoparticle is assumed to be constant through the growth process. The dissociation of hydrocarbons and the diffusion of carbon species is a key step for nanostructure growth.…”

Low-temperature plasmas in carbon nanostructure synthesis

“…100,102 It should be also mentioned that the density of nanoparticles can reach $10 7 cm À3 in the pulsed symmetric Ar-C 2 H 2 capacitively coupled discharges; in this case, the charged nanoparticles can significantly affect the plasma properties. 103…”