Development of multilayer coatings (Ni/C-Pt/C) for hard x-ray telescopes by e-beam evaporation with ion assistance

Abstract

A number of X-ray astronomical missions of near future (XEUS, Constellation-X, SIMBOL-X, HEXIT-SAT, NEXT) will make use of hard X-ray (10-100 keV) optics with broad-band multilayer coatings. To this aim we are developing a multilayer deposition technique for large substrates based on the e-beam deposition technique, improved by the implementation of an ion beam assistance device, in order to reduce the interfacial roughness and improve the reflectivity. The e-beam deposition with ion assistance keeps the film smoothness at a good level and takes the advantage of a reduction of the interlayer stresses. This approach is well suited for the manufacturing of high-reflectance multilayer mirrors for hard X-rays space telescopes where, in addition to a high quality of the deposited films, a volume production is also requested. Moreover, we are also up-grading the replication technique by nickel electroforming, already successfully used for the gold coated soft X-ray mirrors of Beppo-SAX, XMM, JET-X/SWIFT missions, to the case of multilayer coated mirrors. In this paper we will present the technique under development and the implemented deposition facility. Some preliminary, very encouraging, results achieved with the X-ray (8.05 and 17.4 keV) and topographic characterization on flat samples will be discussed.