Introduction
Scandium oxide, Sc2O3, produces high-index film layers that are transparent to wavelengths as short as 225 nm in the UV region. The films are insoluble and hard.
Film Properties
Scandium oxide films require an electron-beam source to reach evaporation temperature. Amorphous films can be deposited below 150° C substrate temperature.
| Region of transparency: | ~250 nm to >5 µm |
| Refractive index: | 300 nm: 1.95 400 nm: 1.90 500 nm-700 nm: 1.85 |
Physical Properties of Solid Material
| Molecular Weight: | 137.91 |
| Melting Point: | 2300° C |
| Color: | White |
| Crystal Density: | 3.86 g/cc |
Evaporation Parameters
| Electron beam source container: | Graphite |
| Pressure: | ~5 x 10-5 Torr. |
| Rate: | <5 Å/sec. |
| Substrate temperature: | 200-250° C. |
Evaporation Procedure
Keep the material in a dry atmosphere, preferably heated to reduce moisture adsorption. Precondition with a low power sweep until spitting and outgassing subside as a rate of 1Å/sec is approached (~15 min). Evaporation is by sublimation. Continue sweeping to prevent burrowing.
Applications
The high index value, transparency, and layer hardness make scandium oxide suitable for the high index component of UV, AR, and bandpass coatings. High damage thresholds have been reported for combinations with silicon dioxide or magnesium fluoride for use in AR, beamsplitters, and bandpass filter coatings at 248 nm and 351 nm.