The Effect Of Dust Charging And Growth On Plasma Parameters In Low Pressure Discharges

The dust particles exist extensively in interstellar and interplanetary spaces,planetary ionosphere and atmosphere,as well as laboratory plasma discharge devices and plasma processing reactors.Particularly in recent years,dusty plasmas have been found to be important in the gas discharge for material processing.On one hand,the dust particles can contaminate etching and deposition processes in microelectronics and affect the quality of semiconductor integrated circuits;on the other hand,the formation and growth of dust particles in discharges can provide new methods for powder synthesis,surface modification and plasma chemistry.These two aspects have led to a resurgence of interest in the behavior of dust particles and its impact on plasma parameters in low pressure discharges.In this thesis,we use the energy balance equation in plasma discharge to numerically study the variation of electron density and temperature in the evolution of the dynamical build-up of dust charging and growth processes and compare the results with experimental results.In Chapter 1,we briefly introduce the basic concept of dusty plasma physics,recent research progresses,and general study methods.In Chapter 2,we introduce the basic theory of dust charge process and the conserved quantities in plasma discharge analysis - the number of particle and energy conservations.In Chapter 3,we introduce the formation and growth of dust particles,and give a brief overview of the mechanisms of the rapid growth process(particles coagulation process) and the slow growth process.In Chapter 4,the dust charging process and its effect on plasma parameters in a specific experiment carded out at Dalian University of Technology is studied.We find that the electron density drops dramatically as the particles are charged and the fast increasing loss of electrons on the dust causes the particle balance to shift to a point with higher electron temperature.The dust charging process is a fast process,its characteristic charge timeτ～400μs with dust radius R_d = 40nm.Only considering the charging current from electrons and ions collected on the dust,the dust particles negatively charged and its total charge is about 111 electron charge.In addition,the total power absorbed is mainly used in collision ionization and excitation between electronics and neutral atom and the ion energy loss on wall and electron energy loss on dust are not significant in dust charge build-up process,and also the ion energy loss on wall is about 3%of the total energy,much larger than electron energy loss on dust.In Chapter 5,the dust slow growth process and its effect on plasma parameters is investigated.It is found that the electron temperature still increases,from 5.0eV to15.0eV, while the electron density decreases with time,as the drop rate of the electron density is reduced to small.Again,the total power absorbed is mainly used in ionization collision, accounting for about 50%of the total energy.Different from the charging process,the energy loss of ionization is greater than that of excitation energy in the slow growth phase.In addition,the ion energy loss on wall is increasing,which accounts for nearly half of the total absorbed power at the time of 100s,while electron energy loss on dust is also small.The increase of the ion energy loss on wall may affect stability of discharge for the deposition of thin films.Finally,a brief summary and future works end the thesis.