Film Properties: Completely oxidized Hafnia films are absorption-free over the range below 300 nm to at least 10 µm. Evaporation causes some amount of dissociation and oxygen loss, which must be restored by supplying a partial pressure of oxygen during reactive deposition. Adhesion is excellent to glass, most other oxides, and to metals such as Aluminum and Silver. Under low energy evaporation conditions such as low substrate temperature, or with excessive background pressure, the films grow with a porous crystalline microstructure of low packing density and can exhibit index changes when vented to moist air. It is recommended that high energy deposition techniques such as IAD or sputtering or high substrate temperature be used to decrease the open void volume by increasing the packing density of the microstructure. Post-deposition baking in air can raise the refractive index of electron-beam depositions. Some amount of index in homogeneity can appear with increasing layer thickness or layer number as the material is consumed. The effect can be reduced by providing sufficient oxygen backfill during evaporation while avoiding excessive background pressure. IAD often improves homogeneity. For critical applications where the incorporation of micro-particles can reduce the laser damage threshold or increase light scatter, reactively evaporating Hafnium metal in an oxidizing atmosphere is recommended for producing particulate-free films.

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