A reaction model for plasma coating of nanoparticles by amorphous carbon layers

Abstract

A detailed chemical kinetics scheme of the reactions occurring in a CH4∕H2 plasma, namely, electron-neutral, ion-neutral, and neutral-neutral reactions, is implemented for the prediction of the species fluxes toward the surface of a submicron particle in a low-pressure environment. Surface reactions at the particle surface are also accounted for. Kinetic theory is applied in the collisionless region within a distance of one mean free path away from the particle, while continuum theory is implemented to solve for species transport in the outer region where reactive-diffusive phenomena occur. These regions are bounded by appropriate boundary conditions. The self-consistent electric field is obtained by solving the Poisson’s equation in the continuum region. The charged and neutral species distributions are calculated and the growth rate of the amorphous carbon layer at the particle surface, as well as particle charging, are predicted. The predicted growth rate is within the range of experimental data from literature for similar conditions. This shows that the model reflects rather accurately the complicated physicochemical phenomena occurring in real systems.

Non-Heat Assistance Plasma-Enhanced Chemical Vapor Deposition of SiCxNyOzFilm Using Monomethylsilane, Nitrogen and Argon

“…Generally, the plasma process has been studied by taking into account the huge number of elementary reactions. [9][10][11][12][13] However, such a complicated reaction model is often not practical for easily adjusting and optimizing the film formation corresponding to the frequently changed parameters. Thus, a simple and practical evaluation method is expected by simplifying the expression of the chemical reaction paths.…”

Simulation study of nanoparticle coating in a low pressure plasma reactor

“…The two regions are connected by matching of the fluxes. 15,18 Inside the vacuum, sphere is treated as a collisionless medium and no reactions occur there except on the particle surface, so the relation between the flux on particle (C pj ) and flux (C kj ) at r ¼ k þ r p is given by…”

“…(15). The cumulative concentration of H 2 and CH 4 in the bulk plasma is assumed constant and obtained from the equation of state as ðC H 2 þ C CH 4 Þ 1 ¼ P tot =ðk B T gas Þ.…”

“…employed a multi-fluid reaction model for thin film coating of nanoparticles by amorphous carbon layer in a CH 4 /H 2 plasma. 15 They showed that the growth rate increases with increasing of the pressure but is independent from the particle size. Mangolini and Kortshagen developed a numerical model to describe the energy balance of nanoparticles in a nonthermal plasma.…”

On accuracy and performance of high-order finite volume methods in local mean energy model of non-thermal plasmas

“…In such a second-order hydrodynamic model [4][5][6][7][8]3,[9][10][11][12][13][14][15][16][17][18][19][20], the electron energy is conserved, and the ionization rate coefficient is an empirical function of the local mean electron energy. This is particularly useful in the simulation of plasma flows where full chemistry of the carrier gas is considered (see [17,21,20,22]). The first-order 'local field approximation model' [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37], on the other hand, is characterized by dependence of ionization on electric field.…”