Richard Clergereaux

Ultrasmooth silver thin film electrodes with high polar liquid wettability for OLED microcavity application.

For a lab-on-chip application, we fabricate a blue bottom emitting strong microcavity organic light emitting diode (OLED), using very smooth and optically thin (25 nm) silver film as anode on a glass substrate. To improve the hole injection in the OLED device, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid)) has been used, so the silver anode must present not only a very smooth surface but also a strong adherence on the glass and a high wettability to allow a good PEDOT-PSS spin coating deposition. To obtain these physical properties, different 5 nm thick nucleation layers (germanium, chromium, and hydrogenated amorphous carbon) have been used to grow the silver thin films by e-beam deposition. The Ge/Ag bilayer presents all the desired properties: this bilayer, investigated by ellipsometry, optical profilometry, contact angle measurements, and XPS analysis, highlights an ultrasmooth surface correlated with the film growth mode and a high wettability related to its surface chemical composition.

Particle formation in acetylene very low-pressure high density magnetized plasmas

Particle formation in cold plasmas is a matter of a large number of studies in capacitive, high-pressure, and low-density discharges. Conversely, under very-low working pressure and high plasma density conditions, as in microwave multipolar plasma excited at distributed electron cyclotron resonance (MMP-DECR), particle formation is generally not favored: the gas phase interaction probability is low due to the very-low working pressure. However, in this work, we report observations and analyses of particles formed in acetylene MMP-DECR discharges. It is proposed that the presence of the magnetic field compensates for the very-low working pressure inducing an increase in the gas phase interaction probability: negative ions are repelled by the sheath and confined within the magnetic field. Thus, particles can be formed similarly to in rf plasma.

Cyclic evolution of the electron temperature and density in dusty low-pressure radio frequency plasmas with pulsed injection of hexamethyldisiloxane

Optical emission spectroscopy was used to analyze the very-low-frequency cyclic evolution of the electron energy and density caused by repetitive formation and loss of dust nanoparticles in argon plasmas with pulsed injection of hexamethyldisiloxane (HMDSO, [CH3]6Si2O). After elaborating a Boltzmann diagram for Ar high-lying levels and a collisional-radiative model for Ar 2p (Paschen notation) states, temperatures characterizing the low- and high-energy parts of the electron population were calculated. Relative electron densities were also estimated from relative line emission intensities. Both temperatures increase when the dust occupation increases, and then decrease when dust is lost. The opposite trend was observed for the electron density. Such cyclic behaviors of the electron energy and electron density in the HMDSO-containing plasmas are in good agreement with the evolution processes in dusty plasmas, in which the formation of negative ions followed by an electron attachment on the surfaces of the ...

Experimental and modelling study of organization phenomena in dielectric barrier discharges with structurally inhomogeneous wood substrates

The spatial organization of dielectric barrier discharges operating at atmospheric pressure in the presence of complex wood substrates was analysed using optical imaging, current?voltage (I?V) characteristics, and optical emission spectroscopy combined with a collisional?radiative model to extract the average electron energy. The structural inhomogeneities of selected wood species produced non-uniform light emission patterns while maintaining homogeneous-like I?V characteristics and spatially uniform average electron energy. Based on a simple electrical model of the discharge, this localization was ascribed, at least partially, to a spatial modulation of the relative dielectric permittivity on ?early? versus ?late? wood affecting the local voltage applied to the gas, and thus the local discharge current.

Organization of Dielectric Barrier Discharges in the Presence of Structurally Inhomogeneous Wood Substrates

The spatial organization of atmospheric-pressure plasmas controlled by dielectric barriers in the presence of complex wood substrates was analyzed using optical imaging and current-voltage (I-V) characteristics. While all wood species investigated yielded homogeneous-like I-V characteristics, the structural inhomogeneities of selected wood species produced nonuniform light emission patterns with less intense emission on early versus late wood sections.

Spatially Modulated Emission of ECR Plasmas in Helium

Space modulation of the optical emission is observed in electron cyclotron resonance plasmas depending on the operating pressure. In contrast with low-pressure condition, where the plasma emission highlights a fairly homogeneous spatial structure, a spatial modulation appeared as the pressure increased: both color and intensity modulations were observed. This phenomenon is attributed to the establishment of a standing wave that modulate the plasma characteristics.

Trajectories of Dust Particles in Low-Pressure Magnetized Plasma

The growth of dust particles in electron cyclotron resonance plasma is highly related to the confinement of species in the magnetic field. Nanoparticles formed in these regions draw curved trajectories observable by naked eyes, related to their velocity, mass, and charge.

Characterization of magnetically confined low-pressure plasmas produced by an electromagnetic field in argon-acetylene mixtures

Dust particles formation was investigated in magnetically confined low-pressure plasma produced in argon-acetylene mixtures. The plasma characteristics were measured in order to identify the species involved in the dust particles formation. Their dependence on the operating conditions including magnetic field intensity, acetylene fraction in the gas mixture and operating pressure was examined. In contrast with noble gases, in the presence of acetylene, the electron temperature increases with the magnetic field intensity, indicating additional charged particles losses in the plasma. Indeed, in these conditions, larger hydrocarbon ions are produced leading to the formation of dust particles in the plasma volume. The observed dependence of positive ion mass distribution and density and relative negative ion density on the operating parameters suggests that the dust particles are formed through different pathways, where negative and positive ions are both involved in the nucleation.

Optimization of Ultra-Smooth Silver Thin Film Electrodes for Micro-Cavity OLED Application

For a Lab-on-Chip applications a strong micro-cavity OLED is required. Its silver anode, deposited on nucleation layers (germanium, chromium, amorphous-hydrogenated-carbon), was investigated by FEG-SEM, XPS, contact-angle, ellipsometry, optical-profiler. Ge-Ag electrodes gives the more stable micro-cavities. Article not available.