André Plain

Particle generation and behavior in a silane‐argon low‐pressure discharge under continuous or pulsed radio‐frequency excitation

The generation and behavior of particles in a low‐pressure silane‐argon discharge have been analyzed under continuous and pulsed radio‐frequency (rf) excitation conditions. In the continuous rf excitation regime, the influence of parameters such as gas temperature and silane partial pressure are determined. By using rf pulsed excitation, it is shown that gas‐flow effects play a predominant role for particle dynamics when the excitation is stopped. Radio‐frequency regimes with short and adjustable rf off sequences are used to study both the inhibition of particle formation and the elimination of particles from the dusty plasmas. The electrical properties of the discharge are shown to be sensitive to the presence of the particles. Simple models for particle trapping in the plasma edge and for particle dynamics when the discharge is turned off are presented.

Measurements of particle size kinetics from nanometer to micrometer scale in a low‐pressure argon‐silane radio‐frequency discharge

The time evolution of the size of particles produced in a silane‐argon low‐pressure radio‐frequency discharge has been determined in the nanometer to the micrometer range using transmission electron microscopy. Highly ‘‘monodisperse’’ distributions are observed and their temporal evolution is followed. These studies are combined with laser light scattering measurements to obtain particle densities, which are of the order of 107 cm−3. For short plasma durations (Δt<5 s), a fast (10 nm/s) linear increase in diameter is measured.

Particle–particle interactions in dusty plasmas

High densities of submicron particles have been created in an Ar/SiH4 parallel plate radio‐frequency (rf) discharge. The particles were collected and measured by electron microscopy and the mean particle diameter was found to be 230±60 nm. Laser scattering from the dense clouds of such particles showed that the concentration was 1×108 cm−3. A laser Doppler anemometer was used to measure the particle velocity distribution and hence the mean particle mass. This is consistent with the specific density of the hydrogenated amorphous silicon. The mean velocities of particles were measured at two different gas flows when the discharge was extinguished, so that the particles are neutral and do not interact, and the particles move with the gas velocity. However, during the discharge the particles have almost no mean axial velocity, even though the gas flow is as large as before. This is due to the strong interparticle interactions that keep the particle cloud, as a whole, stationary. The charge on the particles is estimated, leading to a value of the Coulomb coupling parameter of Γ=10. This large value suggests that the particle cloud can be viewed as a Coulomb liquid.

Influence of the power on the particles generated in a low pressure radio frequency nitrogen-rich methane discharge

Particles are generated in low pressure radio frequency (13.56 MHz) CH4/N2 discharges containing 90% of nitrogen. The influence of the radio frequency power supply on the particle presence within the plasma is studied. Particles are evidenced by laser light scattering. The particle formation leads to modifications in the discharge electrical parameters such as the dc self-bias voltage and the phase angle third harmonic. The plasma is analyzed by optical emission spectroscopy by following the temporal evolution of excited species such as CN, N2, N2+, Ar, and He. Finally, the particle morphology and size are analyzed by scanning electron microscopy. The correlation between these results allows a better understanding of the power influence on the particle growth within the plasma.

Nitrogen effect on the dust presence and behavior in a radio frequency CH4∕N2 discharge

In this paper, we have studied the effects of the nitrogen percentage on particles generated in low pressure radio frequency CH4∕N2 discharges. The particle behavior has been analyzed by laser beam extinction and scattering. The nitrogen percentage in the mixture influences the particle presence, behavior, and size in the discharge. For nitrogen percentages greater than 50%, we have evidenced a particle multigeneration and oscillations in particle clouds. These oscillations have been correlated with the discharge electrical parameters.

Determination of the electron temperature by optical emission spectroscopy in a 13.56 MHz dusty methane plasma: Influence of the power

Optical emission spectroscopy is applied to the study of a radiofrequency (13.56 MHz) discharge in methane used to obtain hydrogenated carbon films and particles. The methane dissociation allows the creation of species in the plasma bulk as H2, H, and CH. The emission lines of these species are studied as a function of time and of incident rf power. The electron temperature is determined from the two line radiance ratio method and the corona balance model using the Balmer lines (Hα, Hβ, and Hγ). The incident rf power enhancement in the range 40–120 W leads to the increase in the emission line intensities as the electron temperature decreases. The temporal variations of CH and hydrogen emission lines, of the dc self-bias voltage, and of the electron temperature are correlated both with the particle behavior and growth in the plasma, and with the coating that grows onto the powered electrode.

Photoluminescence of hydrogen amorphous carbon nitrile particles obtained in a 13.56 MHz dusty plasma

In this article, we report the photoluminescence (PL) of small particles generated in CH4/N2 radiofrequency (13.56 MHz) discharges. The particles have been produced with various mixtures of N2 and CH4 gases. The particle PL has been analysed using fluorescence microscopy in air with an Ar+ laser at 488 nm. It appears that the photoluminescence intensity is in relation to the particle size. However, the incorporation of nitrogen modifies the peak position of the PL spectrum.

DETERMINATION OF THE SIZE, OPTICAL INDEX AND DENSITY OF PARTICLES IN AN ARGON-SILANE RADIO-FREQUENCY DISCHARGE

We have determined, by laser light scattering experiments at three different angles (90°±9°) and by use of the Mie theory, the temporal evolution of particle size (in the range 40–110 nm) in an argon silane radio frequency discharge. The results are in good agreement with values previously determined by transmission electron microscopy. The evolution of the optical indices (absorption and refraction) has been calculated as a function of the particle size at λ=514 nm. We have also shown that these variations are independent of the electrical charges of the particles. The particle density in the discharge is about 108 cm−3.

Particle Collecting in a 13.56-MHz Radio-Frequency Methane Discharge

Radio-frequency methane plasmas are widely used for deposition of amorphous hydrogenated coatings a-C:H in PECVD reactors. According to our experimental conditions, particles are also generated in the plasma. The study of the chemical nature of these particles requires a sufficient quantity to be collected at the end of the experiment. We show that a modification of the electrical field lines above the grounded electrode improves particle collecting.

Determination of the Electron Temperature in a Low Pressure Dusty Radiofrequency Methane Plasma

The particles are obtained by PECVD in radiofrequency (13.56 MHz) low pressure plasmas (90%CH4‐10%Ar). During the particle growth, the particles trap electrons and modify the EEDF, and the electrical and optical characteristics of the plasma. The plasma is analyzed by Optical Emission Spectroscopy. The excitation temperature and the electron temperature are calculated from the Hα, Hβ, Hγ Balmer hydrogen line intensities and from Ar ones. The temporal evolutions of the temperatures during the particle formation are compared and discussed.