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Diamond (C) Cubic Carbon
Diamond is used for transmission windows and domes, and offers a very wide transmission range. Type IIa is the hardest material available and has the highest thermal conductivity.
| Transmission Range | 300nm to 2.5 μm and 7 to >100 μm (1) |
| Refractive Index | 2.4175 @ 0.589 μm (1) |
| Reflection Loss | 30% at 0.589 μm (2 surfaces) |
| Absorption Coefficient | <0.07 cm-1 @ 8 to 12 μm |
| Reststrahlen Peak | n/a |
| dn/dT | 9.6 x 10-6 /°C (3) |
| dn/dμ = 0 | n/a |
| Density | 3.51 g/cc |
| Melting Point | 3497°C (Oxidises in air at 700°C - see notes) |
| Thermal Conductivity | 2600 W m-1 K-1 @ 273K (2) |
| Thermal Expansion | 1.0 x 10-6 /°C at 293K |
| Hardness | Knoop 5700 to 10400 |
| Specific Heat Capacity | 502 J Kg-1 K-1 at 273K (4) |
| Dielectric Constant | 5.68 @ 1.68Mhz at 300K (2) |
| Youngs Modulus (E) | 1050 GPa |
| Shear Modulus (G) | n/a |
| Bulk Modulus (K) | 442 GPa |
| Elastic Coefficients | C11=1076; C12=125; C44=577 |
| Apparent Elastic Limit | 276 MPa |
| Poisson Ratio | 0.16 to 0.29 |
| Solubility | Insoluble in water |
| Molecular Weight | 12.01 |
| Class/Structure | Cubic Diamond, Fd3m |
| μm | No |
|---|---|
| 0.232 | 2.6917 |
| 0.298 | 2.5429 |
| 0.405 | 2.4626 |
| 0.589 | 2.4175 |
| 0.656 | 2.4104 |
| 1.00 | 2.3905 |
| 2.00 | 2.3813 |
| 3.00 | 2.3795 |
| 4.00 | 2.3787 |
| 5.00 | 2.3783 |
| 6.00 | 2.3779 |
| 10.0 | 2.3765 |
| 20.0 | 2.3741 |
Diamond is available as single crystal (Type IIa) natural or synthetic or as polycrystalline CVD film. Single crystal is available economically up to about 4mm diameter. CVD diamond of 75mm diameter is available.
The IR transmission has a range of absorptions in the mid-IR between 2,5 and 7 microns due to inherent lattice resonances. The UV transmission may be limited to 350nm in poorer quality samples.
Single crystal diamond is selected into four forms:
Ia ~98% of natural yield (>100ppm Nitrogen – yellow)
Ib ~0.1% of natural yield (~100ppm Nitrogen)
IIa ~2% of natural yield (1ppm Nitrogen)
IIb – Synthetic only (100ppm boron for electronic applications)
Only Type IIa is used for optical applications. CVD diamond transmission and characteristics are very similar to Type IIa.
REFERENCES:
(1) Handbook Optical Constants, ed Palik, V1, ISBN 0-12-544420-6
(2) Properties Polycrystalline Diamond, Sussmann et. al. Diamond & Rel. Mat. 3(1994) 303-312
(3) Fontenella et. al. App. Optics 16, 2949 (1977)
(4) Slack & Bartram J.Appl. Phys. 46, 89 (1975)