Yves Tessier

Dust particles in low-pressure plasmas: Formation and induced phenomena*

Formation of dust particles is a common mechanism in low-pressure plasmas. These big particles (in comparison with other plasma species) are sometimes the desired final products of the process, but they may also constitute a severe drawback in certain contexts. In either situation, it is necessary to understand growth mechanisms well, in order to control or avoid dust particle formation. One of the problems that has to be overcome is that dust particle growth is usually a continuous mechanism: once started, it can enter into a cyclic regime where new generations of dust particles are succeeding one after the other. This cyclic phenomenon often induces a side effect consisting of instabilities of a few tens of Hz. This paper discusses the main characteristics of dust successive generations, and particularly the importance of dust-free spaces (void) involved in this process. Finally, some aspects related to deposition when several generations coexist will be presented.

Direct measurements of the energy flux due to chemical reactions at the surface of a silicon sample interacting with a SF6 plasma

Energy exchanges due to chemical reactions between a silicon surface and a SF6 plasma were directly measured using a heat flux microsensor (HFM). The energy flux evolution was compared with those obtained when only few reactions occur at the surface to show the part of chemical reactions. At 800 W, the measured energy flux due to chemical reactions is estimated at about 7 W cm−2 against 0.4 W cm−2 for ion bombardment and other contributions. Time evolution of the HFM signal is also studied. The molar enthalpy of the reaction giving SiF4 molecules was evaluated and is consistent with values given in literature.

Carousel Instability in a Capacitively Coupled RF Dusty Plasma

Rotating plasma spheroids are observed in a capacitively coupled radio-frequency discharge containing grown dust particles. These plasma spheroids are regions of slightly enhanced emission that rotate along the circumference of electrodes. This effect is not observed systematically, and when it occurs, the number and the speed of the spheroids can vary with the discharge parameters. These spheroids have been evidenced by using high-speed imaging.

Instabilities during the growth of dust successive generations in silane-based plasmas

Dust growth in silane-based plasmas is known to be a cyclic phenomenon as long as silane is provided. This continuous dust growth leads to an unstable behavior of the complex plasma, characterized by well-defined instabilities. In this paper, a complete study of these instabilities is presented. The electrical analysis is corroborated by an optical one, and high speed video imaging is used to get an insight in the dust cloud behavior. A possible cause of this instability phenomenon is also discussed.

Plasma Emission Modifications and Instabilities Induced by the Presence of Growing Dust Particles

Formation of dust particles in a plasma can strongly change its properties due to electron attachment on dust surface. An easy way to detect dust formation is to analyze modifications of the plasma emission. In this paper, changes in the plasma emission are related to the growth of dust particles. We particularly show that dust formation induces low-frequency plasma instabilities. Another interesting induced effect is the formation of an enhanced emission region which is dust free and usually named ldquovoidrdquo.

Nanostructured Silicon Thin Films Deposited Under Dusty Plasma Conditions

Silane-based dusty plasmas are widely used in plasma-enhanced chemical vapor deposition processes to synthesize silicon nanoparticles and/or nanostructured thin films. Under certain conditions, it is possible to access to the inner structure of the thin film by scanning electron microscopy, using the ldquoholerdquo due to dust particles that moved when the sample is brought back to atmospheric pressure.

Determination of boron by (p, a) reaction

A method for boron determination based on 11B(p, a)8Be reaction is described. The irradiations were performed with 800 keV protons and the alphas were counted with 2 PIPS detectors at an angle of 150° to the beam direction. The method is simple and permits the determination of boron at μg/g level in biological materials and sub-μg/g level in metals, alloys etc.

TCP Plasma Sputtering of Nanostructured Fuel Cell Electrodes

A transformer-coupled plasma sputtering reactor is used for depositing porous carbon-platinum proton exchange membrane fuel cell electrodes. Carbon nanocolumns decorated by platinum nanoclusters are thus obtained.

Particular Threshold Behavior of Dusty Plasma Instabilities

We show that some experimentally observed instabilities, concerning the void region of a dust cloud, are similar to oscillations obtained in chemical systems or neuronal dynamics. The time evolution of these instabilities follows a well‐defined process particularly visible in the instability shape and frequency.

Dust Successive Generations in Ar/SiH4 : Dust Cloud Dynamics

Silane‐based plasmas are widely used to deposit nanostructured silicon thin films or to synthesize silicon nanoparticles. Dust particle formation in Ar/SiH4 plasmas is a continuous phenomenon: as long as silane precursors are provided, new dust generations are formed. Successive generations can be monitored thanks to various electrical (Vdc/3H) and optical (OES, video imaging) diagnostics. Experiments presented in this paper have been performed in a capacitively‐coupled radiofrequency discharge, at low pressure (12 Pa) in an Argon/Silane mixture (92:8).