Single Crystalline LaAlO3 Research Articles

Growth and characterization of pyrochlore-type (Ca,Ti)2(Nb,Ti)2O7 thin films

Pyrochlore-type (Ca,Ti)2(Nb,Ti)2O7 thin films have been grown on single-crystalline LaAlO3 and yttria-stabilized zirconia substrates by a magnetron sputtering system. Atomic-scale interface structure and growth mode of the (Ca,Ti)2(Nb,Ti)2O7 films on the substrates with different crystal structures have been investigated by advanced electron microscopy techniques. In both heterosystems, the film/substrate orientation relationship of [100](001)film//[100](001)substrate has been determined. In the heterosystem of (Ca,Ti)2(Nb,Ti)2O7/yttria-stabilized zirconia, the films directly grow on the substrates. In contrast, in the (Ca,Ti)2(Nb,Ti)2O7/LaAlO3 heterosystem, a perovskite-type Ca1-□(Ti,Nb)O3 interlayer with a few unit cells in thickness forms at the interface and interfacial reconstruction occurs at the (Ca,Ti)2(Nb,Ti)2O7/Ca1-□(Ti,Nb)O3 interface. Our findings indicate that the formation of the interlayer and the (Ca,Ti)2(Nb,Ti)2O7/Ca1-□(Ti,Nb)O3 interface reconstruction can accommodate the film/substrate dissimilarities in the crystal structures and facilitate the growth of single-crystalline pyrochlore-type films on the perovskite-type substrates.

Influence of oxygen partial pressure on SmBa2Cu3O7-δ film deposited by laser chemical vapor deposition

ABSTRACT Laser chemical vapor deposition (LCVD) was applied to prepare SmBa2Cu3O7-δ (SmBCO) superconductive films on single-crystalline LaAlO3 (100) substrates. The effect of oxygen partial pressure (P O2) on the crystal orientation, microstructure, and superconducting property of SmBCO film were investigated thoroughly. The results of X-ray diffraction (XRD) and Raman showed that the crystal orientation of SmBCO film was pure c -axis orientation at the P O2 of 200 Pa, and the a- axis orientation grains gradually emerged in SmBCO film with the increase of P O2. The deposition rate, critical temperature (T c), critical current density (J c) firstly increased and then decreased with the increase of P O2. At the P O2 of 200 Pa, the SmBCO film had smooth and dense surface, the lowest FWHM of φ-scan (1.1°), the highest T c (89.2 K) and J c (2.04 MA/cm2), which indicated that SmBCO superconductive films possessed excellent crystal structure and superconducting performance.

Low‐Pressure Mechanical Switching of Ferroelectric Domains in PbZr0.48Ti0.52O3

AbstractLow‐energy switching of ferroelectrics is currently being investigated for energy‐efficient nanoelectronics. While conventional methods employ electrical fields to switch the polarization state, mechanical switching is investigated as an interesting alternative low‐energy switching concept, if low enough pressures could be achieved. Here, the thickness‐dependent mechanical and electrical switching behavior of ferroelectric PbZr0.48Ti0.52O3/YBa2Cu3O7−δ (PZT/YBCO) epitaxial heterostructures grown on single crystalline LaAlO3‐(001)pseudo‐cubic (LAO) substrate is reported. Mechanical switching is found under relatively low force (600 nN; estimated pressure ≈0.21 GPa) in atomic force microscopy‐based measurements. Mechanically switched domains can be erased by small electric fields and, interestingly, exhibit a surface potential change similar to electrically poled areas. The feasibility of switching these heterostructures with very low pressure makes them promising candidates for nanoscale electromechanical devices.

Exchange bias effect in Fe/LaAlO3: An interface induced effect

The present work reports the appearance of the exchange bias (EB) effect at low temperatures in epitaxial Fe thin film deposited on single crystalline LaAlO3(001) substrate. The observed EB effect vanishes around 30 K indicating that it could be due to the formation of antiferromagnetic FeO layer at the interface between Fe and LaAlO3 substrate. The EB in Fe/LaAlO3(001) is further substantiated by comparing the observations with polycrystalline Fe film deposited on silicon substrate, kept adjacent to LaAlO3 substrate during the deposition. Magnetic microstructure measured by Kerr microscopy corroborates the structural data of Fe film i.e., cubic four-fold anisotropy and isotropic nature for Fe film deposited on LaAlO3 and silicon substrates, respectively. Further, low temperature Kerr microscopy results reveal that the magnetization reversal process significantly gets modified due to the induced unidirectional anisotropy as a consequence of FeO layer formation at Fe/LaAlO3 interface.

Mechanical and correlated electronic transport properties of preferentially orientated SmNiO3 films

Although the correlated rare-earth nickelate perovskites (such as SmNiO3) exhibit remarkable metal to insulator transitions (MIT) beyond conventional semiconductors, their respective variations in mechanical properties during MIT remain yet unknown. Exploring the intrinsic mechanical properties of SmNiO3 is largely prohibited since it is theoretically impossible to grow the single crystalline samples in a large size as required for conventional characterizations. For the first time, we performed nano-indentation tests of preferentially oriented SmNiO3 films with thickness approaching micrometer scale epitaxy on single crystalline LaAlO3 substrates, and the corresponding temperature-dependent mechanical properties are characterized. As-grown SmNiO3 thick films experience sharp transitions in electrical resistivity across MIT, while their insulating phases exhibit thermistor transportation behaviors with the negative temperature dependence of resistance within a broad range of temperature. Nano-indentation tests at room and elevated temperature regions (25–200 °C) are performed for harvesting the Vickers hardness and elastic modulus at different temperatures. In addition, it is also interesting to note that these mechanical properties remain relatively stable during MIT, despite the structural twisting in their NiO6 octahedron during the MIT as previously known for SmNiO3. The SmNiO3 is shown to be relatively soft among the family of perovskite oxides, while its mechanical properties are insensitive to increase temperature across its metal to insulator transitions. It paves the way for further applying rare-earth nickelates in the field of correlation electronics.

Orientation-dependent physical properties of layered perovskite La1.3Sr1.7Mn2O7 epitaxial thin films

In this paper, the resistivity and magnetization of orientation-engineered layered perovskite La1.3Sr1.7Mn2O7 epitaxial thin films have been investigated. Epitaxial thin films were deposited on single-crystalline LaAlO3 (LAO) (001), (110) and (111) substrates by pulse laser deposition (PLD) technique. It is found that only the (100)-oriented thin film performs insulator behavior, whereas the (110) and (111)-oriented thin films exhibit obvious metal-insulator transition at 70K and between 85 and 120K, respectively. Moreover, the same spin freezing temperature and different spin-glass-like transition temperatures have been observed in various oriented films. The observed experimental results were discussed according to the electron-transport mechanism and spin dynamics.

Metal-Organic Deposition of Epitaxial La<sub>0.7</sub>Sr<sub>0.3</sub>CoO<sub>3</sub> Thin Films on LaAlO<sub>3</sub> Substrates

La0.7Sr0.3CoO3 (LSCO) thin films were epitaxially grown on (001)-single crystalline LaAlO3 substrates by metal organic deposition. The evolution of the crystallinity of the films having various thicknesses and obtained at various annealing temperatures is investigated using Raman spectroscopy. The Raman mode associated to the Jahn-Teller distortions in the LSCO films is found to be dependent on the annealing temperature and sensitive to the strain state evolution with film thickness. The microstructure and morphology of the obtained films were investigated using transmission electron microscopy observations on cross-sections and atomic force microscopy. The obtained films are characterized by nanocrystalline morphology, with an average roughness around 5 nm. By increasing the annealing temperature to 1000℃ and the film thickness to 100 nm, the electrical resistivity was decreased by several orders of magnitude. The film resistivity reaches approximately 2.7 × 10–4 Ω•cm in a wide interval of temperature of 77 - 320 K, making this material a promising candidate for a variety of applications.

Structural Transition in Thickness Dependent CSD Grown Nanostructure Manganite Thin Films

In this report, manganite thin films of La0.7Sr0.3MnO3(LSMO) of various thicknesses are carried out by using Chemical Solution Deposition (CSD) technique on(100)– oriented single crystalline LaAlO3(LAO) substrate. Desired film thickness was achieved via control of the number of deposition sequences. X-ray diffraction (XRD) study shows that 1stand 3rdcoatings of LSMO films have the cubic structure while 5thand 7thcoatings of LSMO films have hexagonal structure. As the film thickness increases, increase in lattice parameter(c)was observed. Surface morphological study was carried out using Atomic Force Microscopy (AFM). RMS roughness and grain size were found to increase with the thickness. It is interesting and noticeable that the structural transition occurs from cubic to hexagonal are clearly observed through XRD and AFM results. In electrical resistivity measurement, show the resistivity of all the samples decreases as the film thickness or grain size increases, but the trend inverts for the film with 7 coatings and the maximum MR with the value of 21.35 %, in Hexagonal structure.

Laser Induced Thermoelectric Voltage Effect of LaNiO<sub>3</sub>/LaAlO<sub>3</sub> Multilayer

LaNiO3 single layer, LaNiO3/LaAlO3 superlattice on vicinal-cut single crystalline LaAlO3 (100) and LSAT (100) substrates were prepared by pulsed laser deposition technique. Single-phased LaNiO3 polycrystal target, which is synthesized by sol-gel method, is employed in the thin film deposition process. The structure and physical properties of both the targets and thin films are analyzed. X-ray diffraction results show LaNiO3 single layer is of c-orientation and textural growth, therefore LaNiO3/LaAlO3 forms not superlattice but multilayer. The ultra-violet LITV (laser induced thermoelectric voltage) effects of the LaNiO3/LaAlO3 mutilayer and LaNiO3 single layer were investigated. A comparison study of the influence of LaNiO3 targets prepared by different sol-gel method on the physical property, and LITV effect of thin films was performed as well.

Highly anisotropic magnetic properties of ultrathin (La,Na) MnO3 films on LaAlO3 (001) substrates

AbstractMagnetic measurements and resonance measurements have been carried out on ultrathin (20 nm) films of sodium‐doped lanthanum manganite fabricated by magnetron sputtering on single crystalline LaAlO3 (001) substrates. Complex behavior of magnetization and magnetic anisotropy has been revealed. It is shown that an out‐of‐plane alignment of the film magnetization is characteristic of the films at low temperatures. As temperature increases, a spin‐reorientation transition occurs at about 160 K and in‐plane alignment of magnetization becomes more preferable. Further increase in temperature results in an isotropic behavior of magnetization as temperature approaches and crosses the Curie point (≈270 K). It is concluded that anisotropy energy, originated from a substrate‐induced compressive strain, is responsible for the unusual behavior of the ultrathin films of sodium‐doped manganites.

Defect dynamics and spectral observation of twinning in single crystalline LaAlO3 under subbandgap excitation

We have investigated the photoluminescence and ultrafast dynamics of LaAlO3 crystal. The photoluminescence consists of a broad spectrum and two sharp peaks, which arise from various defect levels within the bandgap. A doublet splitting of roughly 6 nm is seen in these two sharp peaks. An Al displacement of 0.09 Å in a sublattice, which is possible because of twinning, is adequate to explain the spectral splitting. Femtosecond pump probe experiments reveal further that many of these defect levels have a few picosecond decay times while the lowest defect states have decay times longer than nanosecond to the valence band.

Irreversibility field up to 42 T ofGdBa2Cu3O7-δ thin films grown by PLD and its dependence on deposition parameters

We investigated the irreversibility field ofGdBa2Cu3O7 − δ thin films grown epitaxially by pulsed laser deposition on single crystallineLaAlO3(100) substratesin pulsed magnetic fields up to 42 T and at temperatures between 50 and 100 K. The critical temperatureTc reached valuesof 93.5 K with a ΔTc of 0.6 K and an inductively measured self-field critical current densityJc at 77 Kof 3.7 MA cm − 2. The pulsed magnetic field measurements yield a strong dependence ofHirr on the deposition rate, but the film thickness has a small influence on theresistive transition in high magnetic fields. A maximum irreversibility fieldHirr of 40.1 T was measured at a temperature of 50 K for a 300 nm thick film.

Tc Optimisation of GdBa2Cu3O7 thin films grown by pulsed laser deposition

GdBa2Cu3O7 thin films were deposited on single crystalline LaAlO3(100) substrates by pulsed laser deposition (PLD) in on-axis geometry. The deposition parameters temperature, laser repetition rate and oxygen partial pressure were optimized with respect to critical temperature Tc and self-field critical current density Jc of the films. We obtained the best films with a deposition temperature of 910 °C, an oxygen partial pressure of 0.3 mbar and a laser frequency of 2 Hz. This film had a Tc of 93.3 K with a ΔTc of 0.6 K. The self-field Jc at 77 K measured inductively was above 1.5 MA/cm−2.

Extrinsic origin of ferromagnetism in single crystalline LaAlO3 substrates and oxide films

Commercial LaAlO3 substrates were thermally cycled simulating a procedure similar to those followed during TiO2 and SnO2 dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO2 films is of extrinsic origin.

Structure Stability of LaAlO3 Thin Films on SiSubstrates

A series of amorphous and single-crystalline LaAlO3 (LAO) thinfilms are fabricated by laser molecular-beam epitaxy technique on Sisubstrates under various conditions of deposition. The structurestability of the LAO films annealed in high temperature and variousambients is studied by x-ray diffraction as well as high-resolutiontransmission electron microscopy. The results show that the epitaxialLAO films have very good stability, and the structures of amorphous LAOthin films depend strongly on the conditions of deposition andpost-annealing. The results reveal that the formation of LAOcomposition during the deposition is very important for the structurestability of LAO thin films.

Chemical solution deposition and properties of La0.8Na0.1A0.1MnO3 (A = Ca, Na, Sr) films

Chemical solution deposition as an alternative method for colossal magnetoresistance films is used to prepare the La0.8Na0.1A0.1MnO3 (A = Ca, Na, Sr) on single crystalline LaAlO3 (h00) substrates. The results show that all the derived films are highly (h00)-oriented and have rather large magnetoresistance values near the room temperature. Moreover, for the three films, it is found that the insulator–metal transition temperature (TIM) is higher than that of the paramagnetic–ferromagnetic transition (Tc). It is interesting to find that in the Na-doped manganites the maximum MR value and TIM as well as Tc can be synchronously improved.

Magnetoresistance in polymer-assisted deposited Sr- and Ca-doped lanthanum manganite films

We have grown epitaxial films of La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO) on single crystalline LaAlO3 substrates by a cost effective polymer-assisted deposition technique. Film crystallinity, microstructure, resistivity, magnetization, and magnetoresistance (MR) were highly dependent on the annealing temperature in the film processing. High negative MR values of −50% (at 305K) and −88% (at 250K) were observed at magnetic field of 5T, for high temperature annealed LSMO and LCMO films, respectively. These results are comparable to those for films grown by pulsed laser deposition and rf sputtering techniques.

Anisotropic behaviour in the magnetic field dependence of the low temperature electrical resistance of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering

We report about the magnetoresistive properties of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering on single crystalline LaAlO3 and MgO substrates. Two orientations of the magnetic field with respect to the electrical current have been studied: (i) magnetic field in the plane of the film and parallel to the electrical current, and (ii) magnetic field perpendicular to the plane of the film. The film grown on LaAlO3 is characterised by an unusual magnetoresistive behaviour when the magnetic field is applied perpendicular to the film plane: the appearance of two bumps in the field dependence of the resistance is shown to be related to the occurrence of anisotropic magnetoresistive effects in manganate films.