Multilayer performance optimization for x-ray applications between 0.1
keV and 100 keV. 

E. Ziegler (ziegler@esrf.fr) and K. Vestli

European Synchrotron Radiation Facility
BP 220, F-38043 Grenoble Cedex, France 

Nowadays, applications in X-ray instrumentation call for multilayers
optimized for various criteria, including reflectivity (transmissivity)
performance at a fixed angle or energy, constant reflectivity
(transmissivity) over a given energy (angular) range, heat resistance,
selectiviety, harmonic rejection, and degree of polarization. In this
paper we present an optimization of both the peak and the integrated
reflectivity of X-ray multilayers for the energy range from 0.1 keV up
to 100 keV.  To our knowledge the only exhaustive list of material
combinations that maximize multilayer reflectivity in the soft x-ray
domain was published by Rosenbluth. However, it was limited to a maximum
energy of 2 keV and to multilayers composed of pure elements and
operating under normal incidence. Our search includes alloys, as they
may be essential for a smooth growth and/or for stability under high
heat load. The material screening consisted of a list of up to 300
solids having a melting point above 100 C and that could be deposited in
a sputtering process. When using the complete list, a total of 45000
multilayer combinations are computed for each angle (or multilayer
d-spacing) and energy of operation, the only necessary input variables.
A list of the most promising multilayer pairs and performance is
presented. The results take into account a non-periodic design to
minimize absorption effects and other manufacturing concerns such as
minimum values for thickness (layer continuity) or for interface
roughness (~ 0.3nm).

Our computer program can also be used to optimize any of the other
criteria described above, through minor modification of the code. Some
examples will be given.