Aluminum Fluoride, AlF3 for Optical Coating
Fluoride compounds are used in coatings for the UV to middle-IR regions. They provide the lowest refractive indices and therefore are essential components of anti-reflective coatings. Fluoride films display absorption bands in the IR regions 2.8-3.2 µm and 6.0-7.4 µm to varying depths, depending on the compound and the deposition method and parameters. High substrate temperatures, E-beam and IAD are methods that reduce the depths of the absorptions.
Aluminum fluoride, AlF3, is a well-known material which has previously been used as a coating material where a low index was required.* It is not affected by water and has good mechanical strength.
Applications of Aluminum Fluoride AlF3
AlF3 is used as a coating material for mirrors in excimer lasers. Excimer laser technology has applications in angioplasty in medicine and lithography in semiconductor processing.
Physical Properties of Solid Material Aluminum Fluoride AlF3
Evaporation Parameters of Aluminum Fluoride AlF3
AlF3 was test evaporated with an electron beam from graphite crucibles. The material was preconditioned for 5-15 minutes to dehydrate the particle surfaces and to create a melted, dense surface. AlF3 evaporated smoothly at 10-6 Torr at low E-beam power. No spitting occurred, and the vacuum pressure continued to decrease, indicating that no volatiles or water vapor were being emitted. A deposition rate of 10-20 Å/sec. and a substrate temperature of equal or greater than 250°C are suggested for highest density, water resistance and hardness.
Film Properties of Aluminum Fluoride AlF3
AlF3 coatings have a very low index compared with other fluorides. A loss of ~2% in transmission at wavelengths near 400 nm is attributed to a partial deficiency of fluorine content caused by decomposition in the E-beam evaporation. This depletion is aggravated by high energy processes, such as ion assisted deposition (IAD). The effect is minimal with resistance heated evaporation. Since the test evaporated film layer was ~1500 nm thick, this deficiency would be undetectable in the UV, where applications require layers one-tenth this thickness. AlF3 has promise for IR use although its absorption in the 10 µm region might be a little higher than desirable for high energy applications. The durability and adhesion of AlF3 films proved to be excellent. In the UV, AlF3 is finding applications in high energy laser coatings at wavelengths below 250 nm.
Forms and Sizes Available for Aluminum Fluoride AlF3
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Materion Advanced Chemicals offers other particle sizes for evaporation as well as sputtering targets. To view pricing on the items listed above, please visit the Materion Advanced Chemicals on-line catalog to search via the Materion Advanced Chemicals item number or chemical name. If you require a custom manufactured item, please submit your specific requirements via our Request for Information Form or by phone at 414-289-9800.
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Aluminum Fluoride, AlF3 for Optical Coating Reference
* Vacuum Evaporated Films of Aluminum Fluoride, W. Heitmann, Thin Solid Films, 5 (1970) 61-67.
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