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We have shown that high quality Be films may be grown on alpha-A12O3 Si( 111 ) and Ge( 111 ) Consistent with the relative lattice mismatches, films grown on Si( 111) are of higher quality than those grown on alpha-A12O3, and those grown on Ge(111) are of the highest quality. The epitaxial Be films grown on Ge during this grant period are the best quality Be films that we or anyone else have ever produced. Growth of these high quality films is a significant step toward single crystal heterostructures containing Be. Such Be-containing structures may he useful, not only in EUV optics, but also in IR optics electronic devices, and studies of thin-film superconductivity. We have been successful in growing epitaxial Co-on-Be, and Ge-on-Be, but not in making Co/Be or Ge/Be superlattices. In both cases the problem is related to limitations of our equipment. To pursue this work further would require an upgrade to our MBE apparatus. Our very recent successes with sputter-deposited Y- and B4C-based multilayers show that there is still much to he gained by studying and (optimizing the growth of carefully chosen new material pairs. jg

New material pairs are needed to provide useful mirrors at wavelengths where currently none exist, and to improve on performance at wavelengths where there are existing mirrors. In this paper we discuss our studies of selected new materials. Our studies take a surface analysis approach toward characterizing reactions at interfaces, the sharpness of interfaces, and the effect of the thin film growth mode on roughness. The studies were carried out in molecular beam epitaxy systems for two reasons: to study epitaxial growth of promising materials as a step toward single-crystal multilayer mirrors, and to exploit the powerful analytical tools available for surface analysis in a UHV environment. Growth of Be-, and B-based materials pairs have been studied with a wide variety of techniques including Auger, XPS, RHEED, LEED, and STM with the goal of determining interface structure, overlayer morphology, and crystal structure.