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The objective of this project was to develop new, plasma based, technologies for sub-micron sized powder engineering. The size and the structure of highly monodisperse particles are engineered by using an appropriate control and modification of the plasma chemistry during or after the particles growth process.
The project is divided into three tasks:
1/ Particles in silane plasmas: Complete understanding of the particle nucleation and growth process in silane plasmas has been obtained. It has been demonstrated in various ways that the smallest particles (up to 5 nm diameter) can be crystalline. Amorphous, hydrogenated silicon films can be deposited at higher rates and with better film quality if plasma conditions are chosen in a regime close to where dust formation takes place.
2/ Nanomaterial synthesis: The small crystallites which are present in silane discharges have been deposited on a surface. Subsequently, amorphous silicon was deposited on top of it. After annealing, micro-crystalline silicon films are resulting, of which the grain size can be influenced by the surface density of the nanocrystallites. If the nanocrystals are embedded in a transparent, conducting, matrix material, then photoluminescent films and electroluminescent devices can be produced. Solar cells produced with nanostructured silicon films, consisting of an amorphous matrix in which ordered silicon nanoparticles are embedded show a stable efficiency of 10%: the traditional decrease of the efficiency by 50 % in the first few days of liht soaking does not occur.
3/ Submicron scale new catalysts: In a first step the possible use of SiC and Si3N4 as support for metal (palladium) catalysts have been tested, together with their performances for the methane total oxydation. Then stable, mono-disperse submicron ceramic powders (SiC and Si3N4) have been grown in RF plasmas in mixtures of silane, methane, ammonia, and nitrogen. The powders can be coated with palladium by adding Pd vapour to the discharge. The Pd coating has the form of small, nm sized speckles on the surface of the carrier particle. For catalysis, this is about the ideal geometry. Within this task, the main remaining problem is the upscaling of the throughput, which is too small (1 mg in 10 minutes) at the moment. Especially the discharge geometry requires further investigation.
We propose to develop new technologies for sub-micron size powders engineering.

The scientific insight acquired in a 2 year BE project on particulates formation and behavior in surface processing plasmas gives a world leader position to European laboratories. This has already a significative industrial impact (previous endorser statement). This work reveals spectacular possibilities in controlling the size and the structure of highly monosized particles spectacular possibilities in controlling the size and the structure of highly monosized particles (few nm up to *m diameter) through an appropriate control and modification of the plasma chemistry during or after the particles growth process (by using their strong electrostatic trapping in plasma reactor). This entirely new and promising micro-powder processing technology requires a cooperative research in order to test significative applications with the benefit of the acquired know-how and association of new specialists. Three applications are under the scope of the project :

1. Nanomaterial synthesis : using the knowledge on nanometric Silicon particles plasma elaboration the project is to develop optical active systems by embedding them in a thin layer matrix or by using them as seeds for well controlled microcrystalline films elaboration.

2. Submicron scale new catalysts : achieve 0.2 *m diameter ceramic (Si3n4, SiC) powders together with a surface (few nm scale) treatment conferring catalytic properties proved on massive materials (Pt, alloys deposition). The same plasma reactor will be used to control powder growth and metal coverage.

3. Dust control in PECVD plasmas reactors : new way for higher speed and good quality thin films deposition by PECVD technologies will be investigated through dust control in dusty reactors. The industrial throughputs of this new technology are expected in various fields, as shown by this work-programme. The unequivalent expertise acquired by partners involved in the project seems open a chance to develop breakthroughs in the technologies involving submicron powders processing.

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