Oxide Interfaces and Multilayers

Functional oxides with a perovskite structure as well as structurally related compounds have attracted great interest recently. It had been shown, that between interfaces of such epitaxial oxides novel electronic structures can be formed or that the biaxial strain induced by the lattice mismatch may affect the physical properties significantly in these materials. Well-defined and nearly perfect single crystal surfaces of oxide perovskites are important for the preparation of oxide superlattices with smooth interfaces. Therefore, single terminated surfaces of SrTiO3, LaAlO3, NdGaO3 and YAlO3 having steps of one unit cell height and atomically flat terraces were obtained by selective etching using various pH controlled hydrofluoric acid solutions. (Fig. 1) It has been demonstrated that perfect surfaces can be achieved with a proper selection of both the annealing temperature and the etching parameters with respect to substrate miscut angle.

Pulsed laser deposition was used in combination with in-situ RHEED observation to prepare single layers as well as heterostructures on these single terminated atomically flat substrates. The heteroepitaxial growth of materials as SrRuO3, LaAlO3, La2-xBaxCuO4 or LaCoO3 was studied with this technique. X-ray measurements confirmed the good quality of the grown multilayer structure as shown for a 9x(9 ML SrTiO3 / 9 ML LaCoO3)  architecture in Figure 2. Additionally, the layer-by-layer growth mode was confirmed by atomic force microscopy (Fig. 3).

Figure 1: AFM images of single terminated substrates: (a) SrTiO3; (b) NdGaO3; (c) YAlO3; (d) LaAlO3
Figure 2: X-ray reflectivity measurement and corresponding simulation of a [(LaCoO3)9|(SrTiO3)9]9 multilayer; (b) High resolution ??2? scan around the (002)substrate peak, the superlattice peaks of the order m are indicated by SLm.
Figure 3: AFM images of: (a) 60 monolayers LaCoO3; (b) 6 monolayers LaAlO3 grown on SrTiO3

Related Publications

S. Trommler, R. Hühne, A.D. Rata, L. Schultz, B. Holzapfel
Growth of strained La1-xSrxCoO3 films and multilayers using layer-by-layer growth
Thin Solid Films 519 (2010) 69-73