产品资料

Ossila/Sapphire Substrates/Standard \/ 1/5

Sapphire substrates are ideal for use instead of glass substrates when optical transmission is required in the ultraviolet (above 200 nm) or infrared (below 5 μm) range. Low-temperature optical measurements will also benefit from the higher thermal conductivity of sapphire substrates, and they may also be used in high temperature environments up to 2300 K.

Product Specifications

We offer sapphire substrates with two different surface finish qualities. Our 'Standard' sapphire substrates have been polished to a surface quality of 60/40 scratch-dig, have an RMS roughness of ~0.3 nm, and are suitable for most applications (including spectroscopy or thin-film deposition).

In comparison, our 'Ultra Smooth' sapphire substrates have been polished to a surface quality of 10/5 scratch-dig, have an RMS roughness of ~0.1 nm, and are suitable for applications involving atomic force microscopy, 2D materals, or any application where surface quality is crucial.

Properties	Standard	Ultra Smooth
Substrate size	20 mm x 15 mm	20 mm x 15 mm
Thickness	1.1 mm	1.1 mm
Material	Synthetic sapphire	Synthetic sapphire
Surface finish (scratch-dig)	60/40 (both sides polished)	10/5 (both sides polished)
Surface roughness (RMS)	~0.3 nm	~0.1 nm
Surface orientation	C-plane	C-plane
Applications	UV/optical/NIR spectroscopy	Atomic force microscopy, 2D material substrate

sapphire substrate AFM — Atomic force microscope images of the surface of sapphire substrates. Left: 'Standard' surface finish (scratch-dig 60/40). Right: 'Ultra Smooth' surface finish (scratch-dig 10/5).

Comparison Between Float Glass and Sapphire

Properties	Float Glass	Sapphire
Hardness (Mohs)	5.5	9
Density (g/cm³)	~2.5	3.975
Compressive strength (MPa)	1000	2000
Transmission window (nm)	~350-2000	~200-5000
Refractive index n (k) 300 nm 600 nm 2000 nm 5000 nm	1.55 (5.0×10^-5) 1.52 (4.5×10^-7) 1.50 (4.4×10^-6) 1.39 (3.0×10^-3)	1.91 (1.7×10^-8) 1.76 (2.0×10^-8) 1.74 (2.5×10^-8) 1.62 (3.1×10^-8)
Thermal conductivity (W/m.K) 30 K 300 K	0.2 0.9	10000 40
Melting point (K)	950	2300
Specific heat capacity (J/K.kg)	870	750

Chemical Properties

Sapphire is a crystalline form of aluminium oxide (Al₂O₃). It is formed of Al³⁺cations and O^2- anions arranged in a hexagonal lattice. It is extremely unreactive and chemically-resistant to acids and alkalis, including hydrofluoric acid.

Mechanical Properties

Sapphire is exceptionally hard with a Mohs hardness of 9, second only to diamond (which has a hardness of 10). For comparison, glass has a hardness of ~5.5. This makes it extremely scratch-resistant.

sapphire crystal structure planes — The crystal structure of sapphire (left) has numerous symmetry planes (right), along which the properties of the material differ slightly.

Optical Properties

Sapphire is birefringent, meaning that its refractive index depends on the direction at which the light propagates through the crystal and its polarisation. While birefringence has uses in various optical elements, it is generally undesirable in a substrate used for optical measurements.

To overcome this, our sapphire is cut along the C-plane which eliminates polarisation-dependent birefringence for normally-incident light. Sapphire is transparent to wavelengths of light between 200 nm and 5 µm, making it an excellent choice for UV and near/mid-IR applications. Sapphire has a refractive index of ~1.76 in the visible spectrum.

Below is a comparison of the optical transmission between our sapphire substrates and our quartz-coated glass substrates, showing the superior UV transmission of sapphire. Note: The lower transmission of sapphire in the wavelength range from 350nm - 1000nm is due to its higher real refractive index (n) causing greater reflection of incident light at the air-substrate interface.

sapphire optical transmission spectrum — Comparison between the optical transmission of a sapphire substrate (blue line) and a quartz-coated substrate (grey line).

Thermal Properties

Sapphire has a high thermal conductivity of ~40 W/m.K at room temperature. This is almost 50 times higher than glass, and twice as high as stainless steel. This value increases to ~10000 W/m.K as temperature is reduced. This makes sapphire highly suitable for low-temperature optical measurements where thermal equilibrium between the sample and cryostat is required. It is also suitable for use in high-temperature environments up to 2300 K. Our sapphire substrates are polished to optical quality, and have an RMS roughness significantly below than that of our glass substrates.

To the best of our knowledge the technical information provided here is accurate. However, Ossila assume no liability for the accuracy of this information. The values provided here are typical at the time of manufacture and may vary over time and from batch to batch.