Ultra-precision grinding of chemically vapor deposited silicon carbide mirrors for synchrotron radiation

Chemically vapor deposited silicon carbide (CVD-SiC) is the most important material of mirrors for high-brightness synchrotron radiation beamlines, though the material is too difficult to be machined. It takes quite a long time to polish SiC substrate to make mirrors. This paper intends to reduce the machining time to make CVD-SiC miners by using ultraprecision grinding technology. The CVD-SiC sample has been ground into 0.4nm mrs in surface roughness by a resinoid-bonded diamond wheel and an ultra-precision surface grinder having a glass-ceramic spindle of extremely-low thermal expansion. The surface roughness of ground samples were measured with TOPO-3D and AFM. 88.7% reflectivity has been obtained on the ground CVD-SiC flat surface, measured with X-ray of 0.834nm in wavelength at the grazing incident angle of 0.7-0.95 degree. The reflectivity depends upon the angle between the direction of incident beam and grinding marks on the sample. The relationship between the surface roughness and grinding conditions was also discussed.