LiH thin films for small d spacing multilayer reflectors

Gregory Thompson, David D. Allred

Department of Physics and Astronomy, Brigham Young University, PO Box 24636,
Provo, UT 84604-4636.

We report the preparation and optical characterization of LiH
thin films.  These, due to their low absorption, may have a role
as spacer layers in x-ray multilayer reflectors.  LiH's
crystalline properties may provide a basis of a new generation of
multilayer reflectors.  We are currently developing a novel group
of x-ray multilayers which are entirely crystalline, grown
eptiaxially one layer on another.  This epitaxial crystalline
growth, layer by layer, could play a role in developing a small d
spacing multilayer (d<5nm).  It has been shown that atomic abrupt
interfaces can be obtained in such crystalline materials.  These
materials include oxides and, to a lesser extent, nitrides. 
These materials have been prepared for other multilayer
applications, such as Josephson junction studies.  They have
generally been ignored in x-ray optics because of their low
theoretical reflectance.  However, some of the nitride based
crystalline structures paired with a suitable crystalline spacer
layer (such as LiH) could generate respectable theoretical
reflectance.  This, coupled with the abrupt interfaces, suggests
that the actual reflectivity of a small d spacing crystalline
multilayer could exceed the reflectance of a comparable
traditional multilayer.  Experimental results of LiH based
multilayers will be discussed.