After annealing at high temperature in vacuum for 12h the Al2O3 alpha phase substrate, it has turned into black and it is not transparent anymore. It is a black mirror. XRD peaks don't suggest anything.
These are impurities of organic compounds that become carbon during heating in a vacuum. For example, fingerprints on sapphire's surface turn black. Also traces of oil from the pump brings carbon into the furnace chamber.
You can remove this black layer if you then heating your sapphire in an air furnace at about 700°C.
These are impurities of organic compounds that become carbon during heating in a vacuum. For example, fingerprints on sapphire's surface turn black. Also traces of oil from the pump brings carbon into the furnace chamber.
You can remove this black layer if you then heating your sapphire in an air furnace at about 700°C.
First,the colour and shape of nanoparticles depend on the particle sizes. the exemple to illustrate is that it is difficult to confound yellow colour of silver with white colour of Gold...but when silver is precipitated in small particles it turns into black colour and caused by scattering. For your case , it could not change if you use much more little size of your substrate after annealing the particles settle down but particular peaks don't appear.
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