Investigation on heteroepitaxy of I-VII compounds and their surface propeties

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The results of the present research are summarized.(1)Heteroepitaxy of cuprous halide and their surface propertiesCuprous halide CuX (Ib-VII compounds) belongs to tetrahedrally coordinated binary compounds with zinc blende crystal structure and forms the end points of isoelectronic sequences through IV,III-V,II-VI and I-VII compounds. In this sense CuX is positioned between covalent and ionic materials. We have examined the growth of CuCl, CuBr and CuI on GaAs and Si substrates with various crystal faces and clarified the growth nature. The surface atomic structure differs between crystal faces just like Si and GaAs. However, the dangling bond on CuX surfaces is less active than that of Si and GaAs.(2)Growth of a polar NaCl (111) surfaceA (111) surface of rocksalt crystals is a polar surface consisting of either cations or anions and is expected to show very peculiar surface properties. Up to now such a surface was obtained only by oxidizing a metal surface and was stable for films wit … More h several layrs. We have stabilized a flat NaCl (111) surface by growing such complicated haterostructure as NaCl/CuCl/CuBr/GaAs (111) with use of molecular beam epitaxy. There exist about half layr copper atoms on the (111) surface, which might cancel the macroscopic electric field arising from accumulation of dipole layrs along the [111] direction. The present result opens a way to form a polar surface of another materials such as metal oxides, which might achieve a novel surface in the field of catalysis, low dimensional physics and so on.(3)In-situ optical measurement of alkali halide ultrathin filmsGrowth mode of alkali halide (Ia-VII compounds) on foreign alkali halide substrates has been classified to three types by our previous experiments. That information was obtained by presise RHEED measurement. We have devised a new experimental apparatus consisting of a growth chamber and an optics chamber, where optical absorption measurement could be done in UHV condition for the grown film without breaking vacuum. Use of this system enables the measurement of an ultrathin film with nm thickness. We have investigated the exciton energy for alkali halide thin films, which were grown heteroepitaxially on foreign alkali halide substrates. From the peak energy shift, we could calculate the strain at the interface, which agrees well with the value estimated from the RHEED measurement. Less