Preparation and Structure of Artificial Superlattices of Oxides and Selenides

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We have investigated the structural and magnetic properties on thigh quality single crystals of the artificial superlattices. High quality single crystal films have been epitaxially grown on a single crystal by the evaporation. Important informations on the artificial superlattices have been obtained as follows.1. Proper selection of substrate crystals, evaporation rates (R_r), and substrate temperatures (T_s) must be taken for growth of good quality single crystals. For example, optimum conditions for growth of PbSe/SnSe superlattice on the rock salt by evaporation are T_s of 150゜C, and D_r of 1A/s. Hile, optimum conditions for growth of C0O/NiO superlattice on sapphire c plane by the reactive evaporation are T_s of 200゜C and D_r less than 1 A/s. Under these optimum conditions, the crystal may grow by layer growth mechanism, and results in the monolayer controlled superlattice.2. The crystalline quality estimated from a rocking curve significantly become higher with decreasing layer t … More hickness in PbSe/SnSe and CoO/NiO superlattices. It seems likely that a preudomorphous crystal below a critical thickness grows on a substrate crystal and the mismatch is adsorbed in each layer as homogeneous elastic strain. When each layer thickness is large, the interface contains the misfit dislocations and strain.3. The superlattices (PbS)_m(SnSe)_n have the SnSe type structure for m<equal or less than>6, n>(2/3)_m, the PbSe type structure for m<equal or less than>4, n<(2/3)_m, and the PbSe and SnSe structures in each layer for m>12, n>4, respectively.4. (CoO)_m(NiO)_n superlattices stacked with (111) plane show a well-defined magnetic peak in neutron diffraction pattern. The magnetic axis of the superlattices is most probably oriented within the film plane. The (CoO)_m(NiO)_n with m, n <equal or less than> 8 gives a unique T_n like a single phase material. However, (CoO)_m(NiO)_n superlattices with m, n <greater than or equal> 20 have two magnetic phases with different Neel temperatures. Less