X-ray diffraction study of Co-Cu superlattices

Epitaxial Co/Cu superlattices were grown by molecular beam epitaxy on sapph ire substrates and investigated by high-resolution x-ray diffraction at roo m temperature. Detailed analysis of x-ray scattering along the [10.L] recip rocal-lattice rows revealed that about 80% of Co was hexagonal close packed (h.c.p.) and only 20% was face-centred cubic (f.c.c.). A combination of mo delling of x-ray scattering from superlattices with measurements of coheren ce lengths of individual components of the scattering suggests that the f.c .c. Co grows as a single block at the beginning of Co layers and the growth presumably starts from islands rather than from continuous Co layers. The h.c.p. structure is one-dimensionally disordered by stacking faults which a ppear after approximately every 12 layers of Co on average. Upon heating in ultrahigh vacuum to 700 degrees C the coherent superlattice structure was completely destroyed and the resulting structure consisted of relaxed layer s of Co and Cu.