Sapphire thermal treatment

Eigure 3.56 depicts LEIS spectra for two completely different types of AI2O3 sample, i. e. a-alumina (sapphire) and y-alumina (a powder with high specific surface area) which show very similar results in both cases after thermal treatment at 400 °C [3.142]. Reduction of the A1 signal in y-alumina was ascribed to shielding by hydroxyl groups formed by water molecules, which are typical adsorbates on y-alu-mina. 

Fig. 4.52 Effect of thermal treatments on initial yielding of a Czochralski and b Vemetiil sapphire crystals [19]. With kind permission of John Wiley and Sons...

Thermal treatment. Thermally treated sapphires are widespread while gamma irradiated stones are less common. Usually, pale yellow or colorless sapphires are heat treated in air in the temperature range 1500-1900°C to yield a dark yellow, golden, golden-brown, orange, or reddish-brown color due to the oxidation of Fe into to Fe ". Pink sapphire containing traces of chromium can be heat treated to yield a padparadscha orange-pink color, while dark blue... 

Figure 5 (a) M-plane sapphire, (b) Sawtooth patterns from the facets of sapphire after thermal treatment, (c) Deposition of thin films of block copolymer, (d) Highly ordered cylindrical microdomains oriented normal to the surface after solvent vapor annealing, (e and f) Atomic force microscopy (AFM) images of the block copolymer surface with thickness of (e) 24 nm and (f) 34 nm on a surface with facets having pitches of 130 and lOOnm with amplitudes of 14 and lOnm. Scale bars. 200nm. 

Adhesion to the film can be enhanced by surface treatment. The conventional method is corona discharge but more recently atmospheric pressure oxygen plasma treatments have been developed. The film can also be vacuum metallised to improve barrier performance, coated with copper for surface conductivity or with more advanced coatings such as sapphire. Mineral fillers can be used to provide higher modulus and to the control coefficient of thermal expansion in relation to particular coatings or specific applications. 

ZnO films can be prepared by many techniques, including chemical vapour deposition (CVD) [135], electron beam evaporation [136], molecular beam epitaxy (MBE) [137], pulsed laser deposition (PLD) [138], sol-gel [139], spray pyrolysis [140], sputtering [141] and chemical bath deposition [142]. Thermal oxidation of metallic Zn [143-149], ZnS or ZnSe [150-153] films has been used to prepare ZnO films. The Zn precursor films were deposited onto the substrates (glass, sapphire or Si) by magnetron sputtering, thermal/ electron-beam evaporation or filtered cathodic vacuum arc technique. Oxidation treatment was normally conducted in air or oxygen atmospheres in a wide temperature range typically from 300 to 1000°C. 

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