Study of subsurface damage in Ge optics machined by SPDT

Single point diamond turning (SPDT) allows to finish Ge surfaces with a high shape accuracy, low surface roughness and low subsurface damage. We use SPDT for X-ray crystal optics, which poses stringent requirements for surface quality. A study of the surface and subsurface properties of the nanomachined Ge crystal surfaces using AFM, micro-Raman imaging and RBS-channeling methods was done. A surface roughness of 0.9 nm (RMS) is shown in AFM image from $10 \times 10 \mu m^{2}$ area. The RBS-channeling as a complementary method to micro- Raman imaging confirmed, that no amorphous phase of Ge remains on the nanomachined surface and the crystallinity is very good up to the very surface.