The aim of this Thesis was on one side to contribute to a better understanding of the phases formed in the TiAlSiN(O) system and the influence of impurities on their properties. On the other side it was also aimed in the Thesis to individually study the phases forming the nanocomposite.
In each chapter the individual conclusions from that particular chapter are presented, a summary of the most relevant conclusions and achievements is listed below.
¡à Ti1-xAlxN(O) coatings
The optical properties of Ti1-xAlxN(O) coatings were investigated. By changing the Al content in the coatings the properties change from the metallic character of TiN to dielectric character of AlN allowing to obtain spectrally selective coatings. For high Al content the films show low infrared reflectance and high emittance resulting in low equilibrium temperature, characteristics suitable for example for satellite temperature control. While the low emittance and high absorptance of low Al content are adequate for solar absorbers.
The thermal stability of the low Al content coatings was investigated and the coatings are stable up to 400 ¨¬C without much change in the optical properties.
¡à SiyNz(O) coatings
The silicon oxynitride coatings proved to be themselves interesting for their optical properties, specially the refractive index. The control of the microstructure was the key factor to control the optical properties of the coatings. Low energetic conditions in pure nitrogen atmosphere lead to the formation of closed porosity (nanovoids). The Raman results proved the encapsulation of nitrogen in the pores.
Changing the N2 fraction in the gas mixture during deposition allows (at low power) to produce coatings with similar composition and mechanical properties presenting different refractive index by the introduction of the closed porosity.
The closed porosity in the coatings is stable in N2 and vacuum up to 900 ¨¬C.
Changing the target-substrate distance allows to produce coatings with different size of nanovoids.
The possibility to extend the deposition of porous (close porosity) coatings to other systems is demonstrated. Porous silicon coatings were deposited by this method.
¡à nc-Ti1-xAlxN/a-SiyNz(O) coatings
It was found from the XRD, SAED, EELS and XPS results, of coatings deposited under low energetic conditions, that the coatings are composed of a nanocrystalline cubic (Ti,Al)N phase embedded in an amorphous silicon oxynitride phase.
The presence of oxygen impurities was identified particularly in non biased samples and estimated to be around 10 at% as the upper limit in these particular samples. Oxygen seems to be outside the nitride nanocrystallites, and mainly bond to silicon, forming amorphous silicon oxynitride phases and confirmed to occupy preferentially nitrogen positions (confirmed by HAADF and EFTEM) at the column boundaries.
The application of substrate bias and substrate heating during deposition proved to be very efficient in reducing the oxygen incorporation in the coatings originating also denser coatings with improved mechanical properties.
The different energetic conditions (either kinetic or thermal) at which the coatings were exposed during growth and the consequently obtained structures express the need for growth models were the transitions between zones can be achieved by a combination of substrate bias and substrate temperature.
| Identifer | oai:union.ndltd.org:BICfB/oai:ulb.ac.be:ETDULB:ULBetd-02222011-092310 |
| Date | 18 February 2011 |
| Creators | Godinho, Vanda v |
| Contributors | Segers, Luc, Godet, Stephane, Delplancke-Ogletree, Marie-Paule, Fernandez, Asuncion, Trujillo, Francisco Javier, Garcia, Francisco Javier |
| Publisher | Universite Libre de Bruxelles |
| Source Sets | Bibliothèque interuniversitaire de la Communauté française de Belgique |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://theses.ulb.ac.be/ETD-db/collection/available/ULBetd-02222011-092310/ |
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