Effect of surface roughness of substrate to grazing incidence X-ray optics

Grazing incidence specular reflectance and near specular scattering of uncoated and multilayer coated substrates are measured at Al-K alpha (1.486 keV) and Cu-K alpha (8.047 keV). Substrates included superpolished fused silica, SiO2 wafer, superpolished and precision ground Zerodur, float polished BK7 glass, and precision ground silicon carbide. Surface topography of these substrate had been measured with the Scanning Probe Microscope (SPM) and a Talystep mechanical profiler. The results showed that roughnesses obtained from 100 mu m x 100 mu m SPM images and 100 mu m Talystep profiles were in good agreement with that calculated from the Al-K alpha X-ray measurements. X-ray measurements of the multilayers deposited on these substrates are very important. The results of this study can be used as a foundation of calculating the X-ray specular reflectance and diffuse scattering at grazing incidence from multilayer coated mirrors. We coated these substrates with Pt/C multilayers. Tts periodical length were 40 Angstrom and number of layer pairs was 40. The measured reflectivity showed no significant correlation between interfacial roughness of multilayers and the substrate surface roughness. The interfacial roughness of most samples scattered around 3 - 4 Angstrom except for the precision ground silicon carbide and the precision ground Zerodur. The surface roughness of these exceptional substrates are considerably larger value of 6 Angstrom and 9 Angstrom rms from Talystep measurement. When the surface roughness of the substrate is small enough, typically less than 3 Angstrom interfacial roughness of multilayers are considered to be independent from substrates.