Abstract: Beryllium has extremely low absorption ($LSEQ 4 $MUL 10$+4$//cm) for wavelengths below the carbon K absorption edge at 44 angstrom. This property makes Be a potentially useful spacer material for x-ray multilayer mirrors in the water window region of the spectrum (24 - 44 angstrom). In addition, Be based mirrors would have high reflectivities for wavelengths above the Be K edge ($lambda $GRT 114 angstrom), making them useful for applications in the spectral region around the Si L edge (at 124 angstrom). However, because thin films of this material have not been previously studied in detail, relatively little is known about the optimum conditions for Be growth. We have adapted a Riber 1000 Molecular Beam Epitaxy system, formerly used for epitaxy of GaAs, for deposition of beryllium films. We have grown hcp beryllium epitaxially on (001) sapphire substrates and have fabricated several beryllium/germanium and beryllium/bismuth multilayers. Ge and Bi were chosen as candidates for the absorber layers in our initial growth studies because of their expected low reactivity with Be as well as high predicted reflectivities (up to 53%) in the wavelength regions of interest. Characterization of our beryllium films and multilayers includes studies with reflection high energy electron diffraction, low and high-angle 0 - 20 x-ray diffraction, scanning electron microscopy, scanning tunneling microscopy, Auger depth profile analysis, Rutherford backscattering spectrometry, and ion beam channeling. !26
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