Hsin-Yi Lee

Structural characteristics of epitaxial BaTiO3/LaNiO3 superlattice

Artificial superlattices consisting of ferroelectric BaTiO3 (BTO) and conductive LaNiO3 (LNO) sublayers were epitaxially grown on Nb-doped SrTiO3(001) single crystal substrates by a dual-gun rf magnetron sputtering system. A symmetric sublayer structure with the designed thickness varying in the range from 3 nm to 70 nm was adopted. The formation of superlattice structure was confirmed from the (00L) Bragg reflection of x ray and the depth profile of secondary ion mass spectrometry. The in-plane diffraction shows that the BTO and LNO sublayers have the same in-plane lattice spacing for the superlattices with stacking periodicity below 16 nm. The lattice parameter obtained from in-plane diffraction also exhibits a partial but nearly constant relaxation of in-plane strain in the superlattices, even though the sublayer thickness is below the critical value for generation of misfit dislocations. X-ray reflectivity measurement reveals that all the above superlattices have about the same interface roughness of ...

Evaluation of Strain-Dependent Dielectric Properties in BaTiO3 ∕ LaNiO3 and ( Ba , Sr ) TiO3 ∕ LaNiO3 Artificial Superlattice Films on LaNiO3-Coated SrTiO3 Substrates

We formed strained artificial superlattices of BaTiO 3 /LaNiO 3 (BTO/LNO) and (Ba 0 . 4 8 Sr 0 . 5 2 )TiO 3 /LaNiO 3 (BST/LNO) on LaNiO 3 -coated SrTiO 3 (001) substrates by dual-gun radio-frequency magnetron sputtering. The (00L) crystal truncation rod intensity profiles confirm the formation of a superlattice structure. The BTO (or BST) sublayer in the artificial superlattice is under biaxial compressive stress whereas the LNO sublayer is under biaxial tensile stress. Both BTO/LNO and BST/LNO superlattices of total thickness -60 nm exhibit some degree of strain relaxation, even though the modulation length is less than the critical value to generate misfit dislocations. These BTO/LNO and BST/LNO artificial superlattices show a dielectric constant significantly enhanced relative to BTO and BST single layers of the same effective thickness. From a macroscopic point of view, the strain in the superlattice structure contributes significantly to the dielectric enhancement.

Structural and Dielectric Properties of Sputter-Deposited Ba0.48Sr0.52TiO3 / LaNiO3 Artificial Superlattice Films

Artificial superlattices consisting of dielectric Ba 0.48 Sr 0.52 TiO 3 (BST) and conductive LaNiO 3 (LNO) were fabricated on an Nb-doped SrTiO 3 (001) single-crystal substrate with radio-frequency magnetron sputtering at temperatures in the range of 500-700°C. A symmetric structure with a sublayer thickness of 3 nm was deposited at varied substrate temperatures; the superlattices contained 10 periods of BST/LNO bilayers. The microstructure of these films was characterized with measurements of X-ray reflectivity and diffraction at high resolution. The formation of a superlattice structure was confirmed through the appearance of both the Bragg peaks separated by Kiessig fringes in X-ray reflectivity curves and the satellite peaks of a (002) diffraction pattern and the secondary-ion mass spectrometry profile. The clearly discernible main feature and satellite features observed in the (002) crystal truncation rod indicate the high quality of the BST/LNO artificial superlattice structure formed on a SrTiO 3 substrate at all temperatures of deposition. The higher the temperature of deposition, the smaller the full width at half-maximum of the in-plane rocking curve and the better the crystalline quality. These BST/LNO artificial superlattices show a dielectric constant significantly enhanced relative to the BST single layers of the same effective thickness. Both the lattice strain and the interface quality affect the dielectric properties of the BST/LNO superlattices.

Physical Properties of Strained Artificial Superlattices of ( La0.7Ba0.3 ) MnO3 ∕ LaNiO3

Oxide superlattices composed of ferromagnetic La 0.7 Ba 0.3 MnO 3 (LBMO) and paramagnetic LaNiO 3 (LNO) were grown on SrTiO 3 (001) substrates with dual-gun radio-frequency magnetron sputtering. The (00L) crystal-truncation-rod intensity profiles confirm the formation of a superlattice structure. The LBMO layer in the artificial superlattice structure is under biaxial compressive stress, whereas the LNO layer is under biaxial tensile stress. Experiments involving X-ray scattering, absorption, and atomic-force microscopy provide structural information about the designed superlattices. The observed Curie temperature of LBMO epi layers exhibits a strong correlation with lattice strain. All superlattices are coupled ferromagnetically at low temperature.