Investigation of Plasma-Assisted Functionalization of Graphitic Materials for Epoxy Composites

In this study we evaluated the effect of microwave vacuum plasma for the surface functionalization of graphitic fillers (graphite and graphene); we also showed the effect of the functionalization on the mechanical and electrical properties of epoxy composites. Optimized conditions of plasma treatment were defined to obtain high plasma density and increased surface hydrophilicity of the fillers, with high stability of functionalization over time and temperature. However, the extent of such treatments proved to be limited by the high temperatures involved in the curing process of the resin. The use of specific gas mixtures (He/O2) during functionalization and the use of a high surface filler (graphene) can partially limit these negative effects thanks to the higher thermal stability of the induced functionalization. As a consequence, mechanical tests on graphene filled epoxies showed limited improvements in flexural properties while electrical resistivity is slightly increased with a shift of the percolation threshold towards higher filler concentration.

DRIFT-ALFVEN INSTABILITY IN A 2D MAGNETOTAIL CONFIGURATION – THE ADDITION OF BOUNCING ELECTRONS

To explain the possible destabilization of a 2D magnetic equilibrium such as the Near-Earth magnetotail, we developed a kinetic model describing the resonant interaction of electromagnetic fluctuations and bouncing electrons trapped in the magnetosphere, characterized by a high plasma density gradient. A small-β approximation is used in agreement with a small field line curvature. It has been found that for a quasi-dipole configuration, unstable electromagnetic modes may develop in the current sheet in westward direction with a growth rate of the order of a few tenth of seconds provided that the typical scale of density gradient slope responsible for the diamagnetic drift effects is over one Earth radius or less. This instability growth rate is large enough to destabilise the current sheet on time scales often observed during substorm onset.

Collisional effects on the relativistic current-filamentation instability in dense plasmas

Collisional effects on the current-filamentation instability (CFI), accounting for the space charge effect (SCE), are investigated kinetically for a relativistic beam propagating in dense plasmas. It is shown that collisions can completely suppress the SCE in low temperature dense plasma, leading to enhancement of the CFI. This kind of decoupling mechanism is quite different from the well-known resistive mechanism [Molvig (1975). Phys. Rev. Lett. 35, 1504]. In particular, we find the present decoupling mechanism can well explain the recent numerical simulation results [Karmakar et al. (2008). Phys. Rev. Lett. doi: 101, 255001]. In the parameter regime related to the laser-solid interaction and fast ignition scenario (FIS), the CFI growth rate with SCE included is enhanced in the low plasma density region through the decoupling mechanism. In the high plasma density region, it is enhanced mainly through the resistive mechanism.

Dynamic Temperature Profiles of Plasma Neutralization Induced by Microwave Irradiation

This paper investigates the thermal profiles of plasma neutralization induced by microwave radiation by the chronological examination of their thermal distributions. Single triangular, circular, and bowtie-shaped copper tapes were trimmed to investigate the plasma neutralization burst under microwave irradiation. The infrared thermal images showed that the copper tape with a more acute angle and with a narrower gap between the bowtie-shaped electrodes was inclined to generate high plasma density. A high plasma-density area was eventually observed, generating a higher temperature peak based on the experimental results. Thermal dissipation under room temperature was found critical in determining peak temperature after burst. These results may provide basis for the development of an inexpensive, microwave-induced local heating.

Characterization of Thin Film CdTe photovoltaic materials deposited by high plasma density magnetron sputtering

ABSTRACTA new magnetron sputtering strategy is introduced that utilizes high plasma density (~5mA.cm-2) to avoid or reduce high temperature processing. The technique uses magnetrons of opposing magnetic polarity to create a “closed field” in which the plasma density is enhanced without the need for high applied Voltages. A batch system has been used which employs a rotating vertical drum as the substrate carrier and a symmetrical array of linear magnetrons. The magnetrons are fitted with target materials for each of the thin films required in the photovoltaic (PV) stack including the CdTe absorber layer, CdS window layer, metal contact using the conventional superstrate configuration. The “closed field” sputtering technology allows scale up not only for larger batch system designs but it is also configurable for “in-line” or “roll to roll” formats for large scale production. The morphology of each of the layers is characterized using a variety of structural and optical techniques including Field Emission Gun SEM and X-ray diffraction (XRD).

Feature Evolution During Sub 100NM Gap-Fill and Etch

Inductively coupled plasma (ICP) reactors are being used at low gas pressure (<100mTorr) and high plasma density ([e] > 1013/cm2) processes in semiconductor fabrication. In these reactors plasma is generated by inductively coupled electric field while positive ions are accelerated anisotropically by applying a negative bias RF to the substrate. Semiconductor manufacturers face many challenges as wafer size increases while device geometries decrease. Two key challenges for both process design and electronics processing equipment design are (a) scale up of process from 200mm to 300mm diameter substrate, and (b) deposition and etching features with high aspect ratios. A unified phenomenological model to explain profile evolution trend as a function of aspect ratio for deposition (gap fill) and trench etch using ICP reactors is presented. Trends for feature evolution as a function of pressure for gap fill and trench etch are reviewed and explained. The article emphasizes importance of low pressure for sub-100nm gap-fill and trench-etch applications in ICP processing reactors.