Aluminum Oxide for Optical Coating
Aluminum oxide, Al2O3, is a medium index, low absorption material usable for coatings in the near-UV (<300 nm) to IR (9 µm) regions. Typical applications include near-UV laser AR and dielectric mirror designs. Alumina can be used in combination with silicon dioxide layers to form multi-layer structures with high damage thresholds for UV laser applications.
Film Properties of Aluminum Oxide Al2O3
Completely oxidized alumina films are absorption-free over the range below 300 nm to at least 5 µm. Slight dissociation and oxygen loss occurs during evaporation. Adhesion is good to glass, most other oxides, some polymers, and to metals such as aluminum and silver. The films generally grow with a crystalline microstructure and low packing density and exhibit index changes when vented to moist air. Adsorption of water is often evident as rings of discoloration which reach a uniform appearance after moisture penetration is complete. This instability effect is exaggerated under low energy evaporation, low substrate temperature, or excessive background pressure evaporation conditions.
The refractive index responds to high energy deposition techniques and to high substrate temperature because both parameters decrease the void volume by increasing the packing density of the microstructure. Post-deposition baking in air can also raise the refractive index.
Refractive Index of Aluminum Oxide Al2O3
The refractive indices are dependent on the degree of oxidation, the substrate temperature and the film density achieved. For example, on a substrate at temperature of 300° C, n=1.63 for 550 nm. Approximate values are plotted below [1]. Since less dissociation occurs for Al2O3 than with SiO2 evaporation, less background oxygen is required to obtain low absorption film layers of alumina.
REFRACTIVE INDEX FOR ALUMINUM OXIDE (note scale discontinuity)
Material Behavior of Aluminum Oxide Al2O3
Recommended preconditioning consists of slow sweeping of the electron beam to heat the top surfaces to white hot and fuse them. Avoid hole drilling. Replace the charge when it becomes dark colored.
Evaporation Parameters of Aluminum Oxide Al2O3
Physical Properties of Solid Material for Aluminum Oxide Al2O3
Forms and Sizes Available for Aluminum Oxide Al2O3
| Item # | Purity | Description |
| 122741 | 99.99% | 1-5 mm pieces, clear, single-crystal sapphire |
| 122742 | 99.9% | 1.7 mm - 3.4 mm |
| 122698 | 99.8% | 3 - 12 mm, highly sintered, opaque |
| 122735 | 99.8% | 1-3 mm, highly sintered, opaque |
Learn How Materion Can Help You
Materion offers other particle sizes for evaporation as well as sputtering targets. To view pricing on the items listed above, please visit the Materion on-line catalog to search via the Materion item number or chemical name. If you require a custom manufactured item, please submit your specific requirements via our Request a Quote Form or by phone at 414-289-9800.
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Applications of Aluminum Oxide Al2O3
Because of its low absorption below wavelengths of 300 nm, alumina films can be combined in multilayers with silicon dioxide (n = 1.48) for UV laser applications. Adherent coatings can be deposited on low temperature substrates. Thin alumina films sometimes are useful in promoting adherence between two dissimilar materials. In contrast to the parent crystalline sapphire form, alumina films never obtain equivalent density, hardness or water impermeability.
Aluminum Oxide, Al2O3 for Optical Coating Reference
T. S. Eriksson, A. Hjortsberg, G. A. Niklasson, and C. G. Granqvist, Applied Optics 20Ý(5), 2742 (1981).
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