» Plasma Modeling Chemical kinetics simulations

Plasma simulations are a viable way for understanding the complexity of plasma processing.

Plasma processing involves basically three phenomena. First, the breakdown of the neutral gas, which results in the discharge with the production of the plasma state.

Second, the evolution of the composition of the plasma state induced by the chemical reactions and by the diffusion processes. Third, the transport phenomena followed by the interaction of the plasma species with the material surface. While the effects of the plasma processing depend on the latter, a feed-back exists among each of these phenomena. Numerical simulations of these phenomena have been implemented for several interesting molecular gases.

1) Efficiency of ozone production in a dielectric barrier discharge (DBD) in air has been studied [1]. Ozone can be employed in sterilization or water treatment.

 

2) The feasibility of the plasma reforming of hydrogen from methane can be studied numerically. Under suitable discharge conditions, complete transformation can be accomplished. Argon-methane plasmas for diamond -like carbon deposition (DLC) have been studied too [2]

 

3) The production of atomic fluorine in a low pressure discharge has  been studied [3]. Such plasma can be used for the fluorination of material surface, improving their hydrorepellence and water vapour barrier property.

 

Database: we have collected a rather extended set of reaction rates relevant for the simulation of plasma chemical kinetics of several gas mixtures. A few datasets are collected here in the form of rate tables (in postscript files).For electron impact reactions, rates have been evaluated at a fixed electron temperature Te = 4 eV, a typical value in gas discharges.

1) Argon-hydrogen-light hydrocarbons mixture 

2) Nitrogen-oxygen mixture:

•  low pressure conditions 
• atmospheric pressure conditions 

3) Sulphur hexafluoride-fluorine mixture 

» Monte Carlo simulations of Complex Systems

The Monte Carlo simulations cover four main areas: the chemical kinetics in laboratory plasmas, electric discharges in cold plasmas, rough surfaces treated with plasmas, and the analysis of time series recorded from plasma processes, and other complex systems such as financial markets. Few examples are given below.

1) Discharge patterns in plasmas: Discharge patterns produced by 4 electrons moving under the action of an applied dc-electric field. The intensity of the field is 45000 kV/cm.Ionization of Ar atoms occur and secondary electrons are emitted. The resulting internal Coulomb fields are fully taken into account.

2) Rough surfaces produced with plasmas: A rough surface generated with a fractal algorithm, characterized by a Hurst exponent H=0.2, to simulate a surface treated with a plasma.

 

3) Econophysics: The minimal spanning tree (MST) (lines) for a set of 445 stocks (full circles) taken from the Standard & Poors 500 index. The MST has been constructed from the time series of logarithmic returns over a period of 1600 days in which the internal `metric’ of the market has been defined from the cross-correlation matrix.

 

» Further information is available in papers published in scientific and popular reviews:

[1] “Chemical kinetics simulation for atmospheric pressure air plasmas in a streamer regime”

R.Barni, P.Esena and C.Riccardi,

Journal of Applied Physics 97, 073301.1-7 (2005).

[2] “Gaseous precursors of diamond-like Carbon films in CH4/Ar plasmas”

C.Riccardi, R.Barni, M.Fontanesi and P.Tosi,

Chemical Physics Letters 392, 66-70 (2000).

[3] “Modeling and diagnostic of a SF6 RF plasma at low pressure”

C.Riccardi, R.Barni, F.De Colle and M.Fontanesi,

IEEE Transactions on Plasma Science 28, 278-287 (2000).