Liang Wei-Hua

Influence of Ionization Degrees on the Evolutions of Charged Particles in Atmospheric Plasma at Low Altitude

A zero-dimensional model which includes 56 species of reactants and 427 reactions is used to study the behavior of charged particles in atmospheric plasmas with different ionization degrees at low altitude (near 0 km). The constant coefficient nonlinear equations are solved by using the Quasi-steady-state approximation method. The electron lifetimes are obtained for afterglow plasma with different initial values, and the temporal evolutions of the main charged species are presented, which are dominant in reaction processes. The results show that the electron number density decays quickly. The lifetimes of electrons are shortened by about two orders with increasing ionization degree. Electrons then attach to neutral particles and produce negative ions. When the initial electron densities are in the range of 1010 ~ 1014 cm−3, the negative ions have sufficiently high densities and long lifetimes for air purification, disinfection and sterilization. Electrons, O2−, O4−, CO4− and CO3− are the dominant negative species when the initial electron density ne0 ≤ 1013 cm−3, and only electrons and CO3− are left when ne0 ≥ 1015 cm−3 · N+2, N+4 and O+2 are dominant in the positive charges for any ionization degree. Other positive species, such as O+4, N+3, NO+, NO+2, Ar+2 and H3O+·H2O, are dominant only for a certain ionization degree and in a certain period.

Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas

A Monte Carlo simulation method with an instantaneous density dependent mean-free-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas. The ablated-particle density and velocity distributions are analyzed. The force distributions acting on the ablated particles are investigated. The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed. The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa. This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles.

Influence of Ionization Degrees on Conversion of CO and CO2 in Atmospheric Plasma near the Ground

A zero-dimensional model is used to study the processes of physical and chemical reactions in atmospheric plasma with different ionization degrees near the ground (0 km). The temporal evolutions of CO, CO2 and other main reactants (namely OH and O2), which affect the conversion of CO and CO2, are obtained for afterglow plasma with different initial values. The results show that the consumption rate of CO is largest when the initial electron number density ne0=1012 cm−3, i.e. the ionization degree is 0.000004%. The number density of CO2 is relatively small when ne0=1016 cm−3, i.e. the ionization degree is 0.04%, whereas they are very close under the condition of other ionization degrees. Considering the total number densities of CO and CO2 and the consumption rate of CO comprehensively, the best condition is ne0=1013 cm−3, i.e. the ionization degree is 0.00004% for reducing the densities of CO and CO2 in the atmospheric plasma. The temporal evolutions of N+, Ar+, CO+ and CO2+ are also shown, and the influences on the temporal evolutions of CO and CO2 are analyzed with increasing ionization degree.

Pressure ranges of velocity splitting of ablated particles produced by pulsed laser deposition in different inert gases

The transport of ablated particles produced by single pulsed-laser ablation is simulated via Monte Carlo method. The pressure ranges of velocity splitting of ablated particles in different inert gases are investigated. The result shows that the range of velocity splitting decreases with the atomic mass of the ambient gas increasing. The ambient gas whose atomic mass is more than that of Kr cannot induce the velocity splitting of ablated particles. The results are explained by the underdamping model and the inertia flow model.

First principles study of electronic and optical properties of Er-doped silicon nanoparticles with different densities

The structural stability, the electronic and the optical properties of Er-doped silicon nanoparticles are investigated by first principles based on the density functional theory. The results show that the structure is more stable when the doping concentration of Er atoms is smaller in silicon nanoparticles. The doping of Er atom in silicon nanoparticle introduces the impurity levels which result in the narrowing of band gap. A strong absorption peak occurs in the low-energy region of Er-doped silicon nanoparticles, and the intensity of the absorption peak decreases gradually, even disappears with doping concentration decreasing. The study provides the theoretical basis for the design of silicon-based materials.

Numerical simulation of NO x species behaviour in atmosphere plasma

A zero-dimensional model is used for studying the behaviors of NO x in atmosphere plasmas with different ionization degrees. The temporal evolutions of NO x (including NO, NO + , NO 2 , NO 2 + , N 2 O, N 2 O + , NO 3 and N 2 O 5 ), N and O 3 , the main important reactants which influence the producing and the consuming of NO x , are obtained in different initial densities for afterglow plasmas. The results show that the removal rates of NO and NO 2 are higher when n e0 =10 9 cm -3 , and the total nitrogen oxide density is lower, so it is suited for the removal of the pollution of NO x . Some important reactants such as N and O 3 varying with the increase of ionization degree are also analyzed.