Depth-graded Co/C multilayers prepared by reactive sputtering

We have used reactive sputtering with nitrogen to deposit both periodic and depth-graded Co/C X-ray multilayers intended for use at grazing incidence for astronomical applications. In comparison to Co/C films deposited nonreactively, reactively-sputtered films show lower stress and lower roughness. Consequently we have been able to fabricate Co/C multilayers that have much smaller periods relative to what can be achieved using non-reactive sputtering. We have thus far produced several prototype Co/C multilayers, including a depth-graded film containing 500 bilayers for use below 10 keV, and a depth-graded film containing 1100 bilayers for use up to 100 keV. Both of these films show excellent X-ray performance, low film stress, and excellent temporal stability.