Structural characteristics of epitaxial BaTiO3/LaNiO3 superlattice

Abstract

Artificial superlattices consisting of ferroelectric BaTiO 3 ͑BTO͒ and conductive LaNiO 3 ͑LNO͒ sublayers were epitaxially grown on Nb-doped SrTiO 3 (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 BTO/LNO. Consequently, nearly the same extent of dielectric enhancement results from the strained BTO layer, along with a highly conductive interface zone in the superlattiecs.

Real-time X-ray study of roughness scaling in the initial growth of epitaxial BaTiO3/LaNiO3 superlattices

“…On investigating the scaling behavior of surface and interface roughness in the initial growth of BaTiO 3 /LaNiO 3 (BTO/LNO) superlattices as a function of d and N, we here report the results of experiments on real-time X-ray scattering in situ with synchrotron radiation. The BTO/LNO superlattice was chosen for this purpose because of its remarkable dielectric properties compared to the single-layer BTO film of the same effective thickness, and also because strain between constituent compounds in the initial several N has a large influence in determining the evolution of surface and interface roughness in a superlattice, further influencing the dielectric performance of superlattice [9].…”

In situ characterization of lattice relaxation of the BaTiO3/LaNiO3 superlattices epitaxially grown on SrTiO3 substrates

“…In previous work on a BaTiO 3 /LaNiO 3 (BTO/LNO) superlattice we observed a significant dielectric enhancement [6], which we attributed to the large lattice strain in the heteroepitaxial superlattice [3,6]. In general, lateral lattice matching between heteroepitaxial layers occurs up to only a critical thickness, beyond which misfit dislocations become generated at the interface to compensate the accumulated lattice strain induced from the difference of lattice parameters between the hetero-layers in the superlattice system.…”

“…; here a || BTO is the in-plane lattice parameter of a BTO layer in a superlattice derived from (0 K 0) CTR spectra [6], a bulk BTO that of an unstrained BTO film, and a STO is the lattice parameter of the STO substrate. The measured strain relaxation is 28% in the superlattice with 24 bilayers, but only $4% in the superlattice with ten bilayers.…”

“…In the case of a BTO/LNO superlattice, the dislocation lines at the (0 0 1) interface are parallel to the [1 1 0] and ½11 0 directions, and the Burgers vectors of the dislocations are of type 1 2 ah1 1 0i inclined at 451 to the (0 0 1) plane [42]. For a coherently free-standing BTO/LNO bilayer, we estimate the in-plane lattice parameter of the least strained bilayer according to the formula [6,11],…”

“…In general, lateral lattice matching between heteroepitaxial layers occurs up to only a critical thickness, beyond which misfit dislocations become generated at the interface to compensate the accumulated lattice strain induced from the difference of lattice parameters between the hetero-layers in the superlattice system. The critical thickness of a superlattice depends on the lattice mismatch and elastic properties of the constituent layers [7][8][9][10][11], but there is still a critical thickness for a superlattice having sublayers with individual thickness not exceeding the critical value [6,11]. The characterization of lattice relaxation during coherent growth of an epitaxial superlattice is therefore important for preparing pervoskite oxide superlattices with short periods.…”