LaAlO3 Single Crystal Substrates Research Articles

Enhanced thermoelectric performance in c-axis oriented Ca3Co4O9 films by Ag addition through multiple annealing

The [Formula: see text]-axis oriented Ca3Co4O9 (CCO) films without and with 5 wt.% Ag addition were prepared by chemical solution deposition (CSD) through multiple annealing processing on single crystal LaAlO3 (001) substrates. With Ag addition, the resistivity at 300 K is decreased to 2.25 m[Formula: see text]cm, the Seebeck coefficient at 300 K is enhanced to 106 [Formula: see text]V/K and the power factor at 300 K can reach as high as 0.5 mW[Formula: see text]K[Formula: see text]m[Formula: see text], which is the highest value among CCO films prepared by CSD. The results suggest that Ag addition is a very effective route to improve the thermoelectric properties of CCO films through multiple annealing processing.

Facile fabrication of micro-patterned LSMO films with unchanged magnetic properties by photosensitive sol-gel method on LaAlO3 substrates

We propose here a facile and inexpensive photosensitive sol-gel method to fabricate micro-patterned La0.67Sr0.33MnO3(LSMO) films with c-axis orientation on (001) LaAlO3 (LAO) single crystal substrates. The photosensitive LSMO sol-gel was first prepared using methanol as solvent, strontium acetate, manganese acetate and lanthanum nitrate as precursors, and 2,2'-Bipyridyl (Bpy) as chelating modifier. The sol-gel was photosensitive and was used to fabricate micro-patterned LSMO films directly in the absence of any photoresist. The as-prepared micro-patterned films exhibited regular microarray structure with smooth surface and clear edge. We also investigated the magnetic properties of LSMO films on LAO substrates. The overlapping of the magnetic momentum vs. temperature (M-T) curves as well the overlapping in the magnetic hysteresis loops of the micro-patterned and un-patterned LSMO films suggests that the photosensitive sol-gel method would be a promising technique to fabricate micro-patterned LSMO films without disturbing the original structure and functional properties.

High‐Speed Preparation of Highly (100)‐Oriented CeO2 Film by Laser Chemical Vapor Deposition

CeO2 films were prepared at deposition temperature ranged from 947 to 1096 K (corresponding laser power was from 52 to 185 W) on (100) LaAlO3 single crystal substrate by laser chemical vapor deposition. At deposition temperature of 1027–1096 K (laser power was from 115 to 185 W), highly (100)‐oriented CeO2 films with wedge‐caped columnar grains were prepared, whose epitaxial growth relationship was CeO2 [100]//LAO [100] (CeO2 [010]//LAO [011]). Their full width at half maximum of the ω‐scan on the (200) reflection and that of the ϕ‐scan on the (220) reflection were 0.8°–1.8° and 0.7°–1.2°, respectively. The highest deposition rate at which CeO2 film with pure (100) preferred orientation could be obtained was 30 μm h−1.

Characterization by X-Ray Diffraction of Non- <inline-formula> <tex-math notation="LaTeX">$c$</tex-math> </inline-formula>-Axis Epitaxial <inline-formula> <tex-math notation="LaTeX">${Bi}_{2}{Sr}_{2}{CaCu}_{2}{O}_{8+\delta}$</tex-math> </inline-formula> Thin Films

Thin films of Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) with the non-c-axis (117) orientation were grown by MOCVD on (110) LaAlO 3 single crystal substrate. XRD θ - 2θ scans show that films contain also (119) and (011)Bi-2212 impurity grains. We propose and report characterization of the non-c-axis films by XRD φ - ψ scans. By this approach, the assumed theoretical film-substrate relationship of the (117) Bi-2212 grains is demonstrated experimentally. The result also confirms twinning in the span rooflike (117) Bi-2212 grains. The impurity (119) and (011) Bi-2212 grains are also rooflike and in-plane aligned according to film-substrate relation and AFM images so that the film can be considered in-plane epitaxial.

Enhancement by La-Al-O Doping in Y-Ba-Cu-O Films Both in Self-Field and Under Magnetic Field

To enhance the J c of YBa 2 Cu 3 O 7-X (YBCO) films both in self-field and under magnetic field, an effective strategy is to introduce artificial pinning centers and keep a good YBCO matrix at the same time. Here, we propose a new dopant: LaAlO 3 (LAO), based on its chemical stability and small mismatch toward YBCO. A series of YBCO films with different LAO doping contents was fabricated on LAO single-crystal substrates by metal organic deposition. We observed by X-ray diffractometer measurements and scanning electron microscopy observations that although a large amount of LAO is added, YBCO still keeps a good epitaxial growth relationship with LAO. Compared with a pure YBCO film, the J c value of a 5.0% LAO-doped sample is enhanced more than three times in self-field 77 K and seven times at 77 K and 1.5 T, respectively. These results indicate that LAO doping can effectively enhance the J c of YBCO films both in self-field and in applied magnetic fields.

Single-crystal oxide substrate dependent electrical properties of sputtered BiFeO3 thin films

A series of BiFeO3 thin films were prepared on SrRuO3-buffered (100) YAlO3, (La, Sr)(Al, Ta)O3, SrTiO3 and LaAlO3 single-crystal oxide substrates via radio-frequency magnetron sputtering. An excellent (00l)-oriented growth of BiFeO3 films with a dominant rhombohedral-like phase was identified by XRD analyses. The electrical properties, e.g. dielectric, ferroelectric and leakage current characteristics, of BiFeO3 films grown on these single-crystal substrates showed significant differences. It was found that the BiFeO3 film deposited on LaAlO3 substrate exhibited the best overall electrical properties among the four films. It showed low loss tangent (tanδ<0.05) and leakage current density (J<8×10−4A/cm2), as well as a remnant polarization of 2Pr~150μC/cm2 and a reduced coercive field of 2Ec~340kV/cm.

YDy&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Ba&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7-δ&lt;/sub&gt; Epitaxial Films Prepared by Chemical Solution Deposition

YBa2Cu3O7-δ (YBCO) coated conductors have wide-ranging potential in large scale applications, such as, superconducting maglev trains and superconducting electric cables, but low current carrying capability restrains the practical application of YBCO coated conductors at high temperatures and high magnetic fields. It is crucial to develop YBCO coated conductors with high flux pinning capability. In this paper, epitaxial, dense, smooth and crack-free YDyxBa2Cu3O7-δ (x = 0~0.5) films were prepared on a LaAlO3 (LAO) single crystal substrate via a fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The effects of Dy addition on the microstructure and superconducting character of YBCO films were investigated. The all films show a strong c-axis orientation and good texture in-plane and out of plane. The Dy addition to the YBCO film hardly affects the critical temperature of YBCO superconductor. The irreversibility fields of YBCO films can be improved with the Dy addition x = 0.5 compared to the pure YBCO film but decreased in the x = 0.3 sample.

Effect of Ba/Y Molar Ratio on Superconducting Properties of BaTiO3-Doped YBa2Cu3 O 7−δ Films

YBa2Cu3 O 7−δ (YBCO) films with BaTiO3 (BTO) nanostructures were prepared by using the precursor solutions with different cationic molar ratios of Y:Ba:Cu = 1.0:1.6–2.0:3.0 in the TFA-MOD process. These YBCO films were deposited on (00 l)-oriented LaAlO3 single-crystal substrates using a spin coater. The high superconducting critical current density (J C) (77 K, self-filed) of more than 10 MA/cm2 for the final BTO-doped YBCO film was obtained. Moreover, the effect of different Ba/Y molar ratios in the precursor solution on superconducting properties of BTO-doped YBCO films was investigated. Compared with the BTO-doped YBCO film deposited by using the precursor solutions with Ba/Y molar ratio of 2.0, an enhancement of J C in a magnetic field for the film from the solution with Ba/Y molar ratio of 1.9 was achieved. For Ba/Y molar ratios of 1.6 and 1.7, a reduction of J C in a magnetic field occurred. The J C enhancement may be mainly ascribed to the enhanced flux pinning by the Y2Cu2 O 5 nanostructures with the optimal number dispersing in YBCO matrix.

Magnetic and Raman spectroscopic study of laser ablated 100 (nm) thin film of La0.85Te0.15MnO3 deposited on LaAlO3

We report the magnetic and Raman spectroscopic study of 100 nm thin film of electron doped manganite system La0.85Te0.15MnO3 grown on (001) LaAlO3 single crystal substrate by pulsed laser deposition. The magnetization results show Paramagnetic to Ferromagnetic (PM–FM) phase transition. The film is assumed to be of orthorhombic in nature. A correlation of Raman modes with magnetic ordering has been observed. A softening of the 610 cm−1 (B2g) stretching mode is observed near and above the magnetic ordering temperature. The behaviour has been ascribed to magnetic interactions due to spin–phonon coupling terms.

Morphology-controlled synthesis of NiO films: the role of the precursor and the effect of the substrate nature on the films' structural/optical properties

NiO thin films were grown through MOCVD on quartz and LaAlO3 (001) single crystal substrates. The relationship between the precursor/substrate nature and film properties allowed to define the best conditions to grow good quality NiO films.

Role of the substrate on the magnetic anisotropy of magnetite thin films grown by ion-assisted deposition

Magnetite (Fe3O4) thin films were deposited on MgO (001), SrTiO3 (001), LaAlO3 (001) single crystal substrates as well on as silicon and amorphous glass in order to study the effect of the substrate on their magnetic properties, mainly the magnetic anisotropy. We have performed a structural, morphological and compositional characterization by X-ray diffraction, atomic force microscopy and Rutherford backscattering ion channeling in oxygen resonance mode. The magnetic anisotropy has been investigated by vectorial magneto-optical Kerr effect. The results indicate that the magnetic anisotropy is especially influenced by the substrate-induced microstructure. In-plane isotropy and uniaxial anisotropy behavior have been observed on silicon and glass substrates, respectively. The transition between both behaviors depends on grain size. For LaAlO3 substrates, in which the lattice mismatch between the Fe3O4 films and the substrate is significant, a weak in-plane fourfold magnetic anisotropy is induced. However when magnetite is deposited on MgO (001) and SrTiO3 (001) substrates, a well-defined fourfold in-plane magnetic anisotropy is observed with easy axes along [100] and [010] directions. The magnetic properties on these two latter substrates are similar in terms of magnetic anisotropy and coercive fields.

The effect of stress on the piezoelectric properties of BNT–BT–ST thin films

The Bi0.5Na0.5TiO3–BaTiO3–SrTiO3 (BNT–BT–ST) thin films were grown on the LaNiO3 buffered MgO, SrTiO3 and LaAlO3 single crystal substrates, respectively. A systematic stress change of the thin films was obtained. The effect of increasing tensile stress on phase transition temperature is attributed to the suppression of in-plane polarization. The tensile stress reduces the unit cell along electric field, remnant polarization and dielectric permittivity, while enhances the piezoelectric response in this study. The high strain level (0.25%) and piezoelectric coefficient (d33*=200pm/V) were obtained. These results suggest that the piezoelectric properties of BNT–BT–ST thin films can be adjusted by choosing different stress magnitude.

The Effects of Elements Doping on the Properties of YBCO Epitaxial Films Prepared by Chemical Solution Deposition

YBa2Cu3O7−δ (YBCO)-coated conductors have wide-ranging potential in large-scale applications such as superconducting magnets and superconducting electric cables, but low current carrying capability restrains the practical application of YBCO-coated conductors at high temperatures and high magnetic fields. It is crucial to develop YBCO-coated conductors with high flux pinning capabilities. In this paper, YBa2Cu3−x Fe x O7−δ (x = 0, 0.0005, 0.001, 0.002, 0.005) and YDy x Ba2Cu3O7−δ (x = 0∼0.5) films were prepared on a LaAlO3 (LAO) single crystal substrate via a fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The effects of elements doping on the properties of YBCO in different positions of the lattice were investigated. The superconducting critical temperature (T c) decreases, and the superconducting transition width broadens with the Fe and Dy doping. However, the critical current densities (J c) improve at 77 K with Fe doping quantities of xless than 0.005 and Dy doping quantities of xless than 0.5. It means that the current carrying capability of a YBCO film can be improved by doping with appropriate amounts of Fe and Dy.

The effect of annealing atmosphere on magnetoelectric coupling of the La0.7Sr0.3MnO3/BaTiO3 layered heterostructure

The epitaxial La0.7Sr0.3MnO3/BaTiO3 (LSMO/BTO) layered heterostructure was grown on (001) oriented LaAlO3 single-crystal substrate by pulsed laser deposition. Our results showed that the in-situ annealing process in oxygen made the LSMO/BTO interface possess higher oxygen content than that of the one annealing in vacuum, which leaded to the LSMO film presented higher magnetic permeability and higher saturated magnetization. The P–E hystersis loop only could be detected in the sample annealing in oxygen. The ME voltage coefficient of the LSMO/BTO heterostructure annealing in oxygen was higher than that of the one annealing in vacuum, which suggested a more effective ME coupling. It was a combined effect of the two main ME coupling mechanisms, including strain mediation, and polarized carrier mediation.

Effect of strain-modulated lattice distortion on the magnetic properties of LaMnO3 films

LaMnO3 films with various thicknesses were deposited on LaAlO3 (001) single crystal substrate using a pulsed laser deposition technique (PLD) at oxygen pressure of 7.5mTorr to probe how strain affects the magnetic properties. Results show that the magnetic transition temperature (Tc) is enhanced about 3.4% as the thickness increasing from 13.9 to 88.5nm. Meanwhile, the saturation magnetization significantly increases almost 110.3%. The out-of-plane lattice parameter c was found to decrease from 3.97Å to 3.94Å with increasing the thickness of the film from 13.9 to 88.5nm because of the compressive-strain relaxation. Temperature dependence of Raman scattering for all the films were measured to investigate the lattice distortion in the films at different strain. It was found that the softening of the lattice distortion model was suppressed at low temperature by the compressive strain. The decreased Tc and saturation magnetization are ascribed to the strain-modulated lattice distortion and thus the orbital-spin-phonon (OSP) coupling.

Strain controlled orbital state and magnetization in insulating LaMnO3+δ films

LaMnO3+δ films with various thicknesses were grown on LaAlO3 (001) single crystal substrate to investigate the effect of in-plane compressive strain (∼−0.57%) on magnetic properties. All films exhibit a blocking temperature Tb at which the zero field cooled magnetization reaches a maximum, indicating the ferromagnetic (FM) nanoclusters are embedded in the background of antiferromagnetic (AFM) matrix. The onset temperature of FM transition Tc and Tb is increased by 24% and 89%, respectively, with the thickness decreasing from 82.4 nm to 9.2 nm. Simultaneously, the saturation magnetization greatly increases by 309%, which is ascribed to the strain-induced transition of AFM to FM phase due to the orbital order structure switching from x2− 1/y2−1 [A-type] to (x2− y2) + (z2− 1) [F-type].

Laser-induced thermoelectric voltage effect of La0.9Sr0.1NiO3 films

Laser-induced thermoelectric voltage effect signal was observed in the La0.9Sr0.1NiO3 (LSNO) thin films grown on LaAlO3 single crystal substrate which is cut with 5° tilting angle along the 〈100〉 direction by excimer pulsed laser deposition. The results of the LITV measurement demonstrated that the peak voltage of LSNO thin films was strong and could reach as large as 700mV when laser energy density is 2mJ/mm2. The rising time of LITV signal was less than 20ns. Moreover, the peak voltage increased linearly with the single-pulse laser energy density. Above characteristics indicate LSNO thin films are a potential candidate for laser energy/power detectors is an excellent choice.

Effect of thickness variation on the physical properties of La0.85Te0.15MnO3 thin films grown on LaAlO3 (001) by pulsed laser deposition

We report the effect of thickness on the structural, morphological, transport and magnetic properties of perovskite oxide La0.85Te0.15MnO3 thin films grown on LaAlO3 (001) single crystal substrate by pulsed laser deposition. We have observed that the transport and magnetic properties of the films depend on the film thickness, surface morphology, and epitaxial strain. The films were characterized by x-ray diffraction that confirms that the films have good crystalline quality, single phase and c-axis orientation. The Atomic force microscopic (AFM) results show that surface roughness and average grain size increase with film thickness. The resistivity measurements show an insulator to metal transition that correlates well with the magnetic ordering temperature. X-ray photoemission spectroscopy measurements suggests that Te ions are in the Te4+ state, while the Mn ions stay in the Mn2+ and Mn3+ valence states.

Effects of thickness on superconducting properties and structures of Y2O3/BZO-doped MOD-YBCO films**Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Beijing Natural Science Foundation, China (Grant No. 2152035).

We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7−x (YBCO) films with BaZrO3 (BZO) and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD). Comparing with pure YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores.

Solution processing of transparent conducting epitaxial La:BaSnO3 films with improved electrical mobility

As a type of perovskite transparent conducting oxides, La-doped BaSnO3 is considered as a very important material to construct all transparent perovskite devices. The difficulty in achievement of large-area films with high electrical mobility has hindered the development of La-doped BaSnO3 films. Here, we report the results about chemical solution deposition of Ba0.92La0.08SnO3−δ (BLSO) films. The post-annealing and atmosphere as well as lattice mismatch have been investigated. Post-annealing at 1000 °C can obviously improve the performance due to the enhanced crystallization. Under post-annealing in N2 atmosphere the room-temperature resistivity and electrical mobility can achieve 3.25 mΩ cm and 11.09 cm2 V−1 s−1, respectively, for the BLSO on LaAlO3 single crystal substrates due to the enhanced oxygen deficiencies. BLSO films with different orientation can be easily obtained by selection of the substrates, showing isotropic physical properties. Furthermore, the room-temperature resistivity and mobility are optimized to 1.8 mΩ cm and 23.04 cm2 V−1 s−1 when SrTiO3 single crystal substrates with smaller lattice mismatch are used due to the decreased dislocation density. The results will provide an alternative route to fabricate large-area transparent conducting alkaline-earth stannate films with high performance using low-cost chemical solution deposition.