COMPARISON OF ULTRATHIN W/SI AND W/C MULTILAYERS FOR X-RAY OPTICS

New magnetic materials and x-ray mirrors have lead to the preparation of multilayered structures (MLS) with ultrathin periodic layers. However, physical limitations appear for periods below some tens of A. In particular, fabrication tolerances relative to these ultrathin layer thicknesses are critical for the realization of effective MLS. In sputtering, the deposition rate is easily reproducible and can be maintained at a constant and low value for several hours; for this reason we are able to perform a large number (more than 100) of periodic ultrathin layers by this system (3 to 1.5 nm period). High Resolution Transmission Electron Microscopy (HRTEM) and x-ray reflectivity measurements are used to compare interfaces and stacking regularities for different samples with 140 layers. The W/Si MLS present a better quality of interfaces and structures compared to the W/C MLS.