Fig. 3-8 2.7 MeV 4He+ RBS spectra from the Nb/Cu (each 50 nm thick) multilayer (sapphire substrate) The energy and number of the back scattered helium ions from the multilayer gives information on the depth profile of the components to 10 nm accuracy. The analyzing beam of 4He+ was incident on (red spectrum) and off (blue spectrum) the crystal axis.

Fig. 3-9 Crystal quality of multilayered films vs. sapphire-substrate temperature during electron-beam evaporation The crystal disorder was estimated from the yield of back-scattered 4He+ ions (the height ratio of red and blue lines in Fig. 3-8). We find that good quality single crystals can be obtained from the sapphire substrate at temperatures higher than 500 degrees cent.

A structure with multiple layers of different metals, each with nanometer (10-9m) thickness, is expected to be one of the 2-dimensional model materials for high-Tc oxide superconductors, as well as a reflecting material for soft x-rays. For these applications, it is important to prepare single-crystalline multilayer films of refractory materials, which have sharp and immiscible interfaces on the atomic scale. We examined epitaxial growth of Nb, a highly refractory metal, and Cu, which has a high thermal conductivity. Their crystals of 50 nm thickness were grown one after the other on a single-crystalline sapphire substrate (alpha-Al2O3), and we succeeded for the first time in fabricating a Nb/Cu single-crystalline multilayer film. We also assessed the periodicity and crystal quality of the Nb/Cu multi-layered films, using Rutherford back scattering (RBS) /channeling analysis. The layered structure was prepared by using electron-beam evaporation, with the substrate kept at a controlled temperature. Very sharp interfaces were obtained by stacking of the Cu (111)/ Nb (110), the closest packed plane, and they were not destroyed by mutual diffusion of the two metals even at temperatures as high as 750 degrees cent.

Reference S. Yamamoto et al., Characterization of Single-crystalline Cu/Nb Multilayer Films by Ion Analysis, Proc. 4th Int. Symp. on Functionally Graded Materials, Oct. 21-24, 1996, Tsukuba, Japan.

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