Order an optical evaporation source by its starting chemistry and physical form; qualify the deposited film by its measured composition and optical properties. Those are related requirements, but they are not interchangeable. In particular, SiO feedstock is not SiO₂, and Ti₃O₅ can be a source for reactive TiO₂ deposition rather than a promise of a Ti₃O₅ film.
This guide compares four entries in the Basis Materials Evaporation Materials collection and explains what to specify for each source. The technical discussion is general process context; product listings and literature examples do not establish the properties of a coating made in your equipment.
Choosing an Optical Evaporation Material at a Glance
| Material | Common optical role | Key purchasing question |
|---|---|---|
| MgF₂ pieces | Low-index coatings and anti-reflection systems. | What purity, piece size and deposition arrangement are required? |
| SiO pieces | Starting source for silicon-oxide film development. | What source chemistry and final film oxidation state are intended? |
| Ta₂O₅ pieces | Starting oxide for high-index dielectric coatings. | What oxide chemistry, impurity limits and deposition method are required? |
| Ti₃O₅ granules | Suboxide source for selected titanium-oxide film processes. | What final TiOₓ composition and oxygen environment are intended? |
1. Connect source selection to the intended optical function
Anti-reflection coatings, dielectric mirrors, optical filters and other multilayer interference coatings depend on contrasts between optical layers. MgF₂ is commonly used as a low-index material; tantalum and titanium oxides are used in higher-index systems. “Low” and “high” describe a comparison within a design and wavelength range, not a universal specification for every deposited film.[1]
Understanding Refractive Index: Why Wavelength and Deposition Conditions Matter
The real refractive index, n, describes optical phase propagation; the extinction coefficient, k, describes absorption within the material. Both depend on wavelength, so an index without its wavelength is incomplete. Optical thickness depends on physical thickness together with n; absorption described by k must also be considered when assessing a film.[7]
A deposited film can differ from bulk reference material in density, porosity, composition and microstructure. Deposition conditions and subsequent treatment can change those features. Starting chemistry therefore does not uniquely determine the film's n and k. Ask for data covering the intended wavelength range, the relevant film state and the measurement method, rather than choosing a source by one catalog index.
One literature example: Reuna and colleagues reported n ≈ 1.36 at 632.8 nm for an electron-beam-deposited MgF₂ film at a stated substrate deposition temperature of 240 °C. These are the rounded value and conditions in the authors' published abstract, which also reports that deposition temperature and later annealing changed the index.[6] This is one study's film result, not a recommended temperature or a Basis product specification; it does not establish k or the index at another wavelength.
For purchasing, identify the intended film chemistry, wavelength range and application. Keep these separate from the source-material acceptance requirements. A source-material COA does not verify the optical constants, stress, adhesion or transmission of the coating.
2. Compare the four starting materials
SiO: specify the source and desired oxide separately
The formulas SiO and SiO₂ indicate different nominal oxygen-to-silicon ratios. A request for “silicon oxide” can therefore leave the starting material ambiguous. Write SiO when that is the required source, then describe the intended film separately. Equipment-supplier guidance confirms that reactive evaporation from SiO is possible, while also emphasizing source-interaction considerations.[2] Specify the intended oxidation state and verify the deposited film rather than inferring SiO₂ from the source name.
MgF₂: a familiar low-index role still needs process qualification
MgF₂ is widely used for optical anti-reflection layers. Both thermal and electron-beam evaporation are documented, but source configuration and deposition conditions remain important. Equipment guidance notes that substrate temperature affects film density and hardness.[3] Request the relevant impurity information and usable piece-size range, then qualify the resulting film in the actual process. Match any reference density or optical data to the film state and wavelength used in the design.
Ta₂O₅: control the oxide requirement, not just the material name
Ta₂O₅ is an established starting chemistry for high-index oxide coatings. Oxygen-related film behavior remains a process question; the nominal source formula does not eliminate the need to evaluate stoichiometry and absorption. Canon Optron's optical-material guidance identifies oxygen considerations for tantalum-oxide source formulations.[1] Specify whether the purchase concerns Ta₂O₅ source chemistry, the desired film, or both.
Ti₃O₅: a suboxide source can serve a TiO₂-film process
Primary research reports reactive electron-beam evaporation of Ti₃O₅ to produce TiO₂ films and examines oxidation during deposition and after air exposure. The study found oxygen supply and substrate conditions important to the resulting optical behavior.[4] Keep the source formula and intended film composition as separate RFQ fields; substitution of TiO₂ for Ti₃O₅ needs process review.
3. Review the deposition method and source arrangement together
Thermal evaporation heats the charge through a source such as a boat or heated container. Electron-beam evaporation delivers energy to the charge using an electron beam. Match the material, source geometry and required film to the equipment's limits.
For Ta₂O₅, Lesker recommends electron-beam deposition over conventional thermal evaporation because of the thermal burden required for useful evaporation rates.[5] Treat that as equipment guidance, not a claim that every e-beam source or liner is suitable. For each material, give the source-pocket or boat dimensions, liner material if used, and any equipment restrictions that affect charge size or handling.
Where reactive oxygen is part of the process, its introduction, control and interaction with the system require an equipment-specific procedure. Preconditioning, heating sequence and stability assessment also belong to process development. Record the actual oxygen conditions, substrate temperature, power, rate and conditioning sequence in the qualified process.
Document the source lot and process conditions used for qualification. If a source form, composition or lot changes, decide which checks are needed before treating the process as equivalent. Select film-thickness, composition and wavelength-dependent optical measurements appropriate to the research question.
4. Make each purchasing line item unambiguous
The current catalog identifies the chemical names and forms linked above. It does not, by itself, confirm a requested purity, piece-size distribution, packaging protocol or batch-documentation scope. Put those requirements into the inquiry and obtain confirmation.
| Material | Information to specify | What requires confirmation |
|---|---|---|
| SiO pieces | Exact starting chemistry; purity and impurity basis; piece-size limits; requested mass; thermal or e-beam arrangement. | Chemistry documentation, size suitability and packaging/handling; intended film chemistry remains a separate process objective. |
| MgF₂ pieces | Fluoride identity, critical impurities, piece sizes, quantity, source/liner arrangement and handling requirements. | Reported analysis and lot identification, physical-form agreement and any requested moisture/cleanliness controls. |
| Ta₂O₅ pieces | Oxide identity, purity basis, size, requested quantity, e-beam/source arrangement and required batch records. | Material and documentation scope; suitability for the named source setup and any requested packaging. |
| Ti₃O₅ granules | Exact suboxide formula, granule-size range, purity basis, quantity and intended reactive-deposition process. | Starting-material identity, available composition evidence and source-fit requirements; final TiO₂-film properties need process verification. |
Request a measured lot analysis when it is needed, and identify critical impurities rather than assuming “optical grade” has a universal definition. Confirm which tests or records can accompany the shipment. For the separate question of physical feedstock selection, see the pellets, granules, pieces and wire guide.
5. Separate deposited-film mass from source consumption
The Thin Film Material Calculator estimates theoretical deposited-film mass from coated area, thickness and film density, including multilayer inputs where appropriate. Use a justified film-density input; source identity does not establish the density of a particular deposited film.
Reactive oxides: account for oxygen supplied by the environment
In a process intended to convert SiO source material into SiO₂ or another SiOₓ film, oxygen from the surrounding gas can contribute to the deposited mass. The same accounting issue arises when a Ti₃O₅ source produces a titanium-oxide film with a different oxygen content. Final film mass must not automatically be treated as mass transferred from the purchased source.
- Starting material mass: distinguish the amount purchased or loaded from the amount actually consumed.
- Source-derived mass in the film: count the part of the source that is retained on the intended substrates; not all consumed material reaches them.
- Environment-derived mass: retained oxygen or other supplied species may add mass. Gas introduced into the chamber is not necessarily incorporated.
- Deposited-film mass: the calculator estimates this from film density, coated area and thickness. It includes all retained species, regardless of origin.
- Utilization and losses: define a consistent source-material basis, including deposition elsewhere, conditioning and remnants. A percentage alone does not establish the reactive chemical balance.
- Requested purchase quantity: state the customer's actual required amount separately from film mass and source-consumption estimates.
Idealized atom accounting: 2 SiO + O₂ → 2 SiO₂ is balanced, with two Si atoms and four O atoms on each side. It illustrates oxygen addition if source-derived Si and O are retained and extra oxygen completes that oxide. It does not assume that an actual run achieves full conversion, perfect sticking or any known utilization.
The calculator's optional utilization arithmetic is a user-supplied planning model, not a species balance. It does not automatically subtract gas-derived oxygen or convert the mass of a TiOₓ film into a Ti₃O₅ purchase amount. Establish the appropriate source-equivalent requirement separately when the source and film chemistries differ.
Practical loading may also depend on source remnants and minimum charge requirements. Avoid counting a loss twice when adding a planning allowance. Enter the actual requested purchase quantity in the RFQ; keep it separate from calculated film mass.
6. Hypothetical multi-material research inquiry
Select and copy this checklist for each material line:
For application context, visit Optics & Photonics. Send the completed material lines through Request a Quote; chemistry, form, quantity and documentation requirements are reviewed individually.
Technical references
- Canon Optron: vapor-deposition materials list. General optical-material roles and oxygen considerations; listed vendor properties are not Basis specifications.
- Kurt J. Lesker: silicon-dioxide films from silicon-monoxide pieces. Reactive-evaporation context; numerical operating guidance is not adopted here.
- Kurt J. Lesker: MgF₂ evaporation process notes. General deposition and film-property considerations, not equipment-independent guarantees.
- R. Linsbod, E. Ritter and K. Leitner, Evaluation of the oxidation of TiO₂ films during reactive evaporation of Ti₃O₅ and during exposure of the films to the atmosphere, Applied Optics 42(22), 4580–4583 (2003), DOI: 10.1364/AO.42.004580. Abstract verified; experimental conditions are not a universal recipe.
- Kurt J. Lesker: preferred method for depositing tantalum-oxide films. Equipment-supplier process guidance.
- J. Reuna and colleagues, Influence of ex-situ annealing on the properties of MgF₂ thin films deposited by electron beam evaporation, Optical Materials 96, 109326 (2019), DOI: 10.1016/j.optmat.2019.109326. The numerical example uses the authors' public abstract; no value is interpolated.
- J.A. Woollam, Light and Materials and Optical Constants, equipment-manufacturer tutorials on n, k, wavelength and film-thickness analysis.
Before ordering, confirm the exact source formula, acceptable physical form, actual purchase quantity and agreed lot documentation. Qualify the film's optical constants in the intended process, with its wavelength range and material balance stated explicitly.