Table 1 Hardness of the common materials versus TiN, AlN and TiAlN for surface coloring. The Bragg coating is a commercially available mirror (EKSMA Optics, 042-5135)

Metallic coatings

angle-independent

Yes

Au

2.5-3

<1.5 (30-nm-thick on c-Si, <10B pencil)

Al

2.5-3

<3 (30-nm-thick on c-Si, 5H pencil)

Cu

3

<3 (30-nm-thick on c-Si, 4H pencil)

Pt

3.5

∼3 (30-nm-thick on c-Si, 10 H pencil)

TiN

9

7-9 (50-nm-thick on sapphire, >quartz; <sapphire)

Semiconductor coatings

angle-independent

Yes

Ge

6

<3 (30-nm-thick on sapphire, 8H pencil)

Si

6-7

<3 (30-nm-thick on sapphire, 8H pencil)

TiAlN

9

7-9 (50-nm-thick on sapphire, >quartz; <sapphire)

Dielectric coatings

angle-independent

No

AlN

9

7-9 (100-nm-thick on glass, >quartz; <sapphire)

Bragg coatings

angle-independent

No

Multilayer dielectrics

∼

5.5-6.3 (6.5 μm on glass, <stainless steel)

SM-type coating

angle-independent

Yes

Si(50nm)-Au(50nm)

∼

<2 (substrate: Si wafer, 6B pencil)

Ge(50nm)-Au(50nm)

∼

<2 (substrate: Si wafer, 6B pencil)

Si(50nm)-Cu(50nm)

∼

<2.5 (substrate: Si wafer, 3H pencil)

Si(50nm)-Al(50nm)

∼

<2.5 (substrate: Si wafer, 4H pencil)

Si(50nm)-Ag(50nm)

∼

<2.5 (substrate: Si wafer, 4H pencil)

Si(50nm)-Pt(50nm)

∼

<3 (substrate: Si wafer, 8H pencil)

Si(30nm)-TiN(50nm)

∼

<3 (substrate: Si wafer, 9H pencil)

TiAlN(30nm)-TiN(50nm)

∼

7-9 (substrate: Si wafer, >quartz; <sapphire)

FROC-type coating

angle-independent

Yes

TiAlN-TiN-AlN-TiN

∼

5.5-6.5 (130-nm-thick on sapphire, >glass; <c-Si)