Erik Von Wahl

Modelling of argon-acetylene dusty plasma

The properties of an Ar/C2H2 dusty plasma (ion, electron and neutral particle densities, effective electron temperature and dust charge) in glow and afterglow regimes are studied using a volume-averaged model and the results for the glow plasma are compared with mass spectrometry measurements. It is shown that dust particles affect essentially the properties of glow and afterglow plasmas. Due to collection of electrons and ions by dust particles, the effective electron temperature, the densities of argon ions and metastable atoms are larger in the dusty glow plasma comparing with the dust-free case, while the densities of most hydrocarbon ions and acetylene molecules are smaller. Because of a larger density of metastable argon atoms and, as a result, of the enhancement of electron generation in their collisions with acetylene molecules, the electron density in the afterglow dusty plasma can have a peak in its time-dependence. The results of numerical calculations are in a good qualitative agreement with experimental results.

How the emission spectroscopy can determine the effects of dust particles on the plasma

Summary form only given. Dusty plasmas [1] are found in many astrophysical environments such as comet tails, planetary nebulae and rings or in fusion devices like the future ITER. In industrial and laboratory reactors, these dust particles [2] become a huge problem, particularly in microelectronics. However, these particles could be used in many industrial applications related to nanotechnology. So it is important to study the production of these solid particles. At GREMI laboratory, several methods are used to create dust particles in a plasma. They are mainly based on reactive gases or material sputtering. In this work, experiments are performed in a capacitively-coupled RF discharge in the PKE-Nefedov reactor [3], where dust particles are grown by sputtering a polymer layer in Ar or Kr plasmas. The presence of dust particles in plasmas can strongly change their properties like the light emission. This modification is due to a change in the plasma parameters such as electron temperature and density. Emission spectroscopy is used to analyze the light emission, more precisely to study the spatiotemporal evolution of the Ar emission and the molecules involved in the dust particle growth like: CN, CH and C2. When dust particles are growing in the plasma, a laser at 685 nm is also used to highlight their presence. Their localization is determined by recording the scattered light with the spectrometer. Other diagnostics are also used to follow dust particle growth like a CCD camera and the measurement of the discharge current.

Mass spectrometry to control dust particle growth in an acetylene plasma

Summary form only given. Dust particles are involved in a wide range of applications like thin film deposition or the manufacturing of microelectronic devices. They are an essential subject of research in the growing field of nanotechnology due to their interesting chemical and physical properties. In this study, nanoparticles are formed in a capacitively coupled asymmetric discharge running in an Ar/C2H2 mixture at a frequency of 13.56 MHz and RF-power of 9 W. The presence and growth of dust particles in a plasma change its properties like electron density or temperature. So to understand the formation and the growth of nanoparticles, it is necessary to study the complex physicochemical reactions in occuring hydrocarbon plasmas. Acetylene is used to provide the reactive species leading to dust particle growth. This cyclic process can be monitored in situ thanks to several methods [1]. Particularly, the different stages of dust particle growth like the nucleation and agglomeration can be evidenced by correlating the evolution of the electrical characteristics of the discharge with time resolved mass spectrometry. In this presentation, the evolution of the self-bias voltage [2] can be correlated with the acetylene concentration during nanoparticle growth.

Electrical measurements for the control of nanoparticle growth in an acetylene plasma

Nanoparticles are not only of fundamental interest due to their remarkable properties but also of practicle importance in material processing. Controlling their growth in plasmas is regarded as a new route to prepare nanoparticles of well defined size and composition. However, the processes during their formation are yet to be fully understood. Especially the early stages of the particle growth are not well investigated since they are experimentally inaccessible by standard methods like Mie-scattering. A novel collection method based on neutral drag was tested in order to get a better insight into the early stages of particle growth. The experiments were performed in a capacitively coupled discharge, where multiple growth cycles can be obtained. Size distributions of the nanoparticles at different stages of the growth cycle were determined ex-situ by electron microscopy. The obtained size distributions were correlated with in-situ measurements of the bias voltage and the phase angle between discharge current and voltage. The observed correlations, which can be used for prediction of the particle growth, are qualitatively explained.