Silicon on Sapphire
Silicon on Sapphire wafers are comprised of R-Plane (1102) sapphire wafers with a deposited layer of silicon on their polished surface.
When cut at the R-plane the oxygen atoms of the sapphire wafer mirror the symmetry of the silicon crystal at (100) orientation enough that silicon crystal can be grown on the surface.
Silicon on Sapphire wafers are used in radio frequency integrated circuits (RFIC). Chips made using Silicon-on-Sapphire are used in mobile devices and other electronics where the low power consumption, resistance to radiation and durability and stability over a wide temperature range allow them to out-perform other Silicon-on-Insulator devices.