MPCVD Diamond Window Anti reflective Coating Er₂O₃ vs HfO₂
MPCVD Diamond Window Anti reflective Coating
Er₂O₃ vs HfO₂
| Er₂O₃ (Erbium Oxide) | HfO₂ (Hafnium Oxide) | |
|---|---|---|
| Chemical formula | Er₂O₃ | HfO₂ |
| Material class | Rare-earth sesquioxide | Transition-metal oxide |
| Refractive index (visible–NIR) | ~1.6–2.1 (depends on film & λ) | ~1.9–2.1 (high-index coating) |
| Bandgap | ~4–6 eV | >5 eV |
| Transparency range | UV → mid-IR | UV → IR (broad) |
| Thermal expansion (CTE) | ~8.8 × 10⁻⁶ /K | ~5–6 × 10⁻⁶ /K (typical literature range) |
| Melting point | ~2400 °C (very high) | ~2750 °C (very high) |
| Thermal stability | Excellent (stable >900 °C films) | Excellent (used in high-temp coatings) |
| Mechanical robustness | Moderate (stress issues possible) | High (hard, dense, durable) |
| Density | ~8.6 g/cm³ | ~9.7–10 g/cm³ |
| Dielectric constant | ~7–20 | High (~20–25 typical) |
| Optical role in coatings | Often single-layer AR (IR) | High-index layer in multilayers |
| Index match to diamond | Good (closer to diamond n≈2.4) | Moderate (used in stacks instead) |
| Stress on diamond substrate | Higher (CTE mismatch) | Lower (better mechanical compatibility) |
| Deposition methods | ALD, sputtering, MOCVD | ALD, sputtering, e-beam |
| Typical use cases | IR windows, specialty AR coatings | Laser optics, interference filters, durable coatings |
| Key advantage | Optical matching + IR AR performance | Mechanical durability + multilayer flexibility |
| Key limitation | Interface stress / adhesion challenges | Needs multilayer design for optimal AR |
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