Dense layers with good hardness can be deposited by electron-beam evaporation or sputtering. Typical applications include near-UV laser AR and dielectric mirror designs. Hafnia can be used in combination with silicon dioxide layers to form high index-contrast multilayer structures with high laser damage thresholds. Evaporation causes some amount of dissociation and oxygen loss, which must be restored by supplying a partial pressure of oxygen during deposition.
Adhesion is excellent to glass, most other oxides, and to metals such as aluminum and silver.
The films generally grow with a crystalline microstructure. Under some evaporation conditions, such as low energy evaporation, low substrate temperature, or excessive background pressure, the films grow with low packing density and can exhibit index changes when vented to moist air. Some amount of index inhomogeneity can appear with increasing layer thickness and with layer number as the material is consumed. The effect can be reduced by providing sufficient oxygen backfill during evaporation, but not excessive pressure to create voids which will absorb water vapor upon venting the vacuum chamber. The refractive indices are dependent on the degree of oxidation and the film density achieved.