Vicinal SrTiO3 Research Articles

Control of the growth and domain structure of epitaxial SrRuO3 thin films by vicinal (001) SrTiO3 substrates

We report the effect of both miscut angle (α) and miscut direction (β) of vicinal substrates on the epitaxial growth and domain structure of isotropic metallic oxide SrRuO3 thin films. The thin films have been grown on vicinal (001) SrTiO3 substrates with α up to 4.1° and β up to 37° away from the in-plane [010] axis. Single-crystal epitaxial (110)o SrRuO3 thin films were obtained on vicinal SrTiO3 substrates with a large miscut angle (α=1.9°, 2.1°, and 4.1°) and miscut direction close to the [010] axis. Decreasing the substrate miscut angle or aligning the miscut direction close to the [110] axis (β=45°) resulted in an increase of 90° domains in the plane. The films grown on vicinal substrates displayed a significant improvement in crystalline quality and in-plane epitaxial alignment as compared to the films grown on exact (001) SrTiO3 substrates. Atomic force microscopy revealed that the growth mechanism changed from two-dimensional nucleation to step flow growth as the miscut angle increased.

Substrate-mediated control of the microstructure of YBa 2Cu 3O 7−δ thin films

We have studied the surface of vicinal SrTiO 3(001) substrates and thereon deposited YBa 2Cu 3O 7−δ (YBCO) thin films by UHV-scanning tunneling microscopy (STM). We discuss the influence of the uniformity of substrate terraces on film growth. STM images indicate, that a combination of island and step-flow growth occurs on 1.2° miscut SrTiO 3. In particular, a regular nanoscale step structure of a 10° miscut SrTiO 3 surface generates an almost periodic surface structure of the YBCO films. Our findings indicate that a substrate-mediated control of the surface structure of YBCO films can be achieved.

The Effect of Miscut Angle and Miscut Direction of Vicinal (001) SrTiO3 Substrates on The Domain Structure of Epitaxial SrRuO3 Thin Films

ABSTRACTWe have grown epitaxial thin films of isotropie metallic oxide SrRuC>3 on both exact and vicinal (001) SrTiO3 substrates with miscut angle (α) up to 5.0° and miscut direction (β) up to 37° away from the in-plane [010] axis. The effects of both α and β on the epitaxial growth and domain structure of epitaxial SrRuC>3 thin films were studied by x-ray diffraction and atomic force microscopy (AFM). On vicinal SrTiO3 substrates with a large miscut angle (α = 1.7°, 2.0°, 4.1°, and 5.0°) and miscut direction close to the [010] axis, single crystal epitaxial (110)° SrRuO3 thin films were obtained. [The superscript o refers to the Miller indices based on the orthorhombic unit cell.] Decreasing the substrate miscut angle or aligning the miscut direction close to the [110] axis (β = 45°) resulted in an increase of 90° domains in the plane. The films grown on vicinal substrates displayed a significant improvement in crystalline quality and in-plane epitaxial alignment as compared to the films grown on exact (001) SrTiO3 substrates. AFM revealed that as the miscut angle increased the growth mechanism changed from two dimensional nucleation to step flow growth.

The Effect of Elastic Strain on the Electrical and Magnetic Properties of Epitaxial Ferromagnetic SrRuO3 Thin Films

ABSTRACTWe report the direct measurement of elastic strain effect on the electrical and magnetic properties of single domain epitaxial SrRuO3 thin films, using a lift-off technique. The as-grown films on vicinal (001) SrTiO3 substrates are subjected to elastic biaxial compressive strain within the plane and tensile strain normal to the plane. In contrast, the lift-off films prepared by chemical etching of SrTiO3 substrates, are completely strain free with bulk like lattice. Our measurements indicate that the elastic strain can significantly affect the electrical and magnetic properties of epitaxial ferromagnetic SrRuO3 thin films. For the strained films, the Curie temperature (Tc) was suppressed to 150K and the saturation magnetic moment (Ms) was decreased to 1.15μB/Ru atom as compared to a Tc of 160K and Ms of 1.45μB/Ru atom for the strain free films. These property changes are attributed to the structural distortion due to the elastic strain in the as-grown epitaxial thin films. Our results provide direct evidence of the crucial role of lattice strain in determining the properties of the perovskite epitaxial thin films.

AFM Observations on the Growth Mechanisms of Epitaxial Perovskite Oxide SrRuO3 Thin Films

ABSTRACTThe growth mechanism and surface morphology of epitaxial SrRuO3 thin films deposited on exact and vicinal (001) SrTiO3 and exact (001) LaAlO3 substrates has been studied. Vicinal substrates with miscut angle, a, up to 4° toward [010] direction were used. Atomic force microscope images show that the films grown on exact (001) SrTiO3 substrate had a growth mechanism involving two dimensional nucleation. In contrast, characteristic step patterns were observed on the films deposited on vicinal substrates, suggesting that these films had a step flow growth mode. The films deposited on exact (001) LaAlO3 substrates had a three dimensional island growth, due to the incoherence between the film and substrate lattice. These results were found to be consistent with the results of x-ray diffraction analysis of the in-plane domain structure.

Periodic step structure of clean and YBa 2Cu 3O 7 − δ-covered vicinal SrTiO 3(001) surfaces

We have studied the structure of a stable vicinal SrTiO 3(001) surface by UHV scanning tunneling microscopy. We find that the regular nanoscale step structure on the vicinal surface strongly influences the growth of c-axis-orientedYBa 2Cu 3O 7 − δ (YBCO) thin films. It generates an almost periodic surface structure of the YBCO films. This substrate-mediated control of the film growth is particularly important, because the resultant YBCO microstructure leads to an in-plane anisotropy of the transport properties in the high-temperature superconducting material.

Surface Morphology Control of YBa2Cu3Ox Thin Films Grown by Metalorganic Chemical Vapor Deposition Using Vicinal SrTiO3 Substrates

We have used vicinal SrTiO3 substrates for improving and controlling the surface roughness of a YBa2Cu3Ox film. If we use a SrTiO3(100) substrate, the surface morphology of the film is abruptly degraded over a thickness equivalent to 15 unit cells. In contrast to using a SrTiO3(100) substrate, good surface morphology is maintained, even at 20-unit-cell thickness, when using a vicinal SrTiO3(100) substrate misoriented by 2°. The reason is that the effective terrace width produced by 2° misorientation is almost equal to the migration length of species on the growing surface. This is suitable for controlling the surface morphology of a YBa2Cu3Ox film.

Single Variant Orientational Growth of Yba2Cu3O7-x on Vicinal (011) SrTiO3 Substrates.

AbstractThe results of a transmission electron microscopic (TEM) and X-ray microanalysis (EDS) study of Yba2Cu3O7-x (YBCO) films grown on vicinal (011) SrTiO3 substrates are presented. The YBCO films tend to be single crystalline grown in single variant orientation with c-axis =;45° from the surface. Cracks, second phase precipitates (CuO and Y2O3), and a few small YBCO grains in other orientations were revealed in the films.

Epitaxy of PbTio3 on (100) SrTio3 and Vicinal (100) SrTio3 by Pulsed Laser Deposition

AbstractEpitaxial PbTiO3 films have been grown on (100) SrTiO3 substrates by pulsed laser deposition. X-ray diffraction analysis indicates pure c-axis oriented PbTiO3 films with a rocking curve FWHM of 0.25° for the 002 reflection. Thicker films (˜ 2000 Å) grown on 4° miscut SrTiO3 show mixed aaxis and c-axis PbTiO3 due to twinning along {1011} planes. The [100] axis of the a-axis domains are misoriented by 3.4° - 3.8° toward <001> substrate directions with respect to the substrate normal. In contrast to growth on well-oriented (100) SrTiO3 surfaces where the four equivalent tilts of the [100] axis of the a-axis domains are equally likely, on vicinal SrTiO3 the a-axis domains are preferentially oriented (˜ 90 vol. %) in an uphill direction with respect to the miscut substrate.

Growth of DyBa2Cu3O7−x thin films on vicinal (100) SrTiO3 substrates

We report studies of the initial stages of epitaxial growth of DyBa2Cu3O7−x films on vicinal (100) SrTiO3 substrates using in situ reflection high energy electron diffraction (RHEED), transmission electron microscopy, and atomic force microscopy. Two sets of substrates, with misorientations of 2.2° and 4.4° off (100) towards (110) were used. These substrates were prethinned and annealed prior to deposition. DyBa2Cu3O7−x films were grown by ozone‐assisted molecular beam epitaxy. The annealed substrates were reconstructed and had stepped surfaces. Films nucleating preferentially at the steps giving rise to an interconnected network of islands, as observed in plan view transmission electron microscopy. In situ RHEED showed intensity oscillations of the specular spot consistent with such an interpretation, and exhibited behavior dominated by surface diffusion. The higher density of nucleation sites on vicinal surfaces appears to reduce the fraction of a‐axis outgrowths. The films grown on vicinal substrates a...

Synthesis and properties of a-axis and b-axis oriented GdBa2Cu3O7−δ high T c thin films

We report the growth and properties of a-axis oriented GdBa2Cu3O7−δ high Tc thin films on (100) SrTiO3 substrates by dc magnetron sputtering. It is found that GdBa2Cu3O7−δ films on (100) SrTiO3 exhibit a-oriented growth at higher substrate temperatures compared with YBa2Cu3O7−δ films. By utilizing low-temperature-grown a-axis GdBa2Cu3O7−δ films (200 Å in thickness) as a self-template, pure a-axis films can be grown at elevated temperatures. The growth of b-axis film on vicinal (100) SrTiO3 under similar growth conditions is also reported.

Single domain high T c La2−xSrxCuO4 films with tilted CuO2 planes

The two fold degeneracy inherent to epitaxial growth of high Tc films on (101) perovskite substrates has been removed successfully. This is demonstrated by single domain, (103) oriented La2−xSrxCuO4 films of 0.04≤x≤0.34 on vicinal (101) SrTiO3 substrates using 90° off-axis sputtering. (101) substrates that have the surface normal rotated about [010] by 0.5°–3.5° produced essentially single crystal films with the c-axis direction determined by the sense of the miscut. Misoriented antidomains (103)′ have been eliminated effectively to a percentage less than 1 part in 104. The mechanism for symmetry breaking is understood on the basis of a surface step model in which the energetics promoting single domain growth is derived from nucleation and epitaxy on the (001) face found at surface steps of vicinal substrates. Furthermore, the incommensuration of the c axis interplanar spacings with the a, b, plane lattice parameters in the La2−xSrxCuO4 structure provides a natural selection of (103) domains over (103)′ domains. The model predicts the application to other high Tc materials such as the Bi2Sr2CanCun+1Ox, and the Tl2Ba2CanCun+1Ox families.

Microstructure of Bi 2(Sr,Ca) 3Cu 2O x thinfilm on vicinal SrTiO 3 substrates

The microstructure of epitaxial Bi 2(Sr,Ca) 3Cu 2O x films prepared on vicinal SrTiO 3 substrates was studied by cross-sectional high-resolution transmission electron microscopy. The films were prepared in situ by ion beam sputtering on the vicinal SrTiO 3 substrates oriented off[001] by about 4° toward [111] with Bi 2Sr 2CuO x buffer layers. The films grew without 90° misorientation defects (“twinning”). The surface of the substrates consisted of [001] terraces and ledges. The b-axis was aligned with the step direction of the substrate. The c-axis was oriented normal to the [001] terrace surface, not to the macroscopic substrate surface. As a result, the a, b-plane tilted 4° from the substrate surface. While many anti-phase defects were found in the film near the substrate surface, there were relatively few defects in most regions.