LAO Substrate Research Articles

Substrate dependent structure and in-plane dielectric properties of Ba(Sn 0.15Ti 0.85)O 3 thin films

The structure, microstructure and in-plane dielectric properties of Barium tin titanate Ba(Sn 0.15Ti 0.85)O 3 (BTS) thin films grown on (100) LaAlO 3 (LAO) and (100) MgO single crystal substrates through sol–gel process were investigated. The films deposited on (100) LAO substrate exhibited a strong (100) preferred orientation while the film deposited on (100) MgO substrate showed polycrystalline structure. The in-plane ɛ– T measurements reveal that the films grown on (100) LAO substrate exhibited an obvious room-temperature ferroelectric state, while the film grown on MgO substrate showed paraelectric state in the temperature range of 10–130 °C. A high tunability of 52.11% was observed for the BTS films deposited on (100) LAO substrate at the frequency of 1 MHz with an applied electric field of 80 kV/cm, which is about two times larger than that of the BTS films deposited on (100) MgO substrate. The obvious differences in the dielectric properties could be attributed to the stress in the films, which come from lattice mismatch and difference in the thermal expansion coefficients between the film and substrates. This work clearly reveals the highly promising potential of BTS films for application in tunable devices.

Low-temperature growth of epitaxial PZT/LSMO/LAO film by excimer laser-assisted metal organic deposition (ELAMOD)

The preparation of the epitaxial Pb(Zr,Ti)O3:PZT film on SrTiO3: STO, LaAlO3: LAO, MgO and La0.7Sr0.3MnO3: LSMO / LAO substrates using the excimer laser-assisted metal organic deposition (ELAMOD) process was investigated. When using the STO substrate, the epitaxial PZT film was obtained by the ArF laser irradiation at room temperature using the 2-step irradiation method. On the other hand, when using the LAO and MgO substrates, no single phase of the PZT film was obtained by the ArF laser irradiation at room temperature. The LSMO buffer layer was prepared on the LAO substrate by thermal MOD at 1000°C, and the PZT film was then prepared on the LSMO / LAO substrate by ELAMOD at room temperature. The effects of the laser fluence, shot number and buffer layer thickness on the PZT epitaxial growth were investigated. An epitaxial PZT / LSMO / LAO film was successfully obtained by ArF laser irradiation at 80mJ/cm2 and room temperature. The formation mechanisms of the epitaxial PZT films by ELAMOD are also discussed.

Superconductivity in Pr0.4Ca0.6Ba2Cu3O7−δ epitaxial thin films

Pr0.4Ca0.6Ba2Cu3O7−δ thin films have been grown on SrTiO3 (STO) substrates by pulsed laser deposition. The dependence of growth orientation and superconducting properties on substrate temperature were studied. As characterized by X-ray diffraction (XRD), good quality c-axis and a-axis orientated films could be grown on STO by changing the substrate temperature. However, the highest TC0 (∼16.8K) was observed in samples with mixed orientations. Almost all samples exhibited a semiconducting-like temperature dependence of resistivity, which could be attributed to the scattering due to the localized electronic states. Furthermore, films grown on LAO, MgO and YSZ substrates were also studied.

Fabrication and characterization of epitaxial Ba0.6Sr0.4TiO3/LaNiO3 heterostructures

Epitaxial Ba0.6Sr0.4TiO3 (BST)/LaNiO3 (LNO) heterostructures were fabricated on LAO (100) substrates using pulsed laser deposition (PLD). Their structural properties were investigated by X-ray diffraction (XRD). The θ–2θ scans showed single crystalline BST and LNO layers with a (100) orientations perpendicular to the substrate plane. Phi scans (ϕ) on the (220) plane of BST layer indicated that the films have two in-plane orientations with respect to the substrate. The atomic force microscope (AFM) surface morphologies showed a smooth and crack-free surface with the average grain size of 55 nm and the root-mean-square (RMS) of 4.53 nm for BST films. Capacitance–voltage curves are measured. From the capacitance, a dielectric constant of 762, tunabilty of 82.81% and loss tangent of 0.032 are obtained. The current–voltage curve shows that the leakage current is 2.41 × 10−7 A/cm2 under an applied voltage of 2 V.

Preparation of the La 0.8Sr 0.2MnO 3 films on STO and LAO substrates by excimer laser-assisted metal organic deposition using the KrF laser

La 0.8Sr 0.2MnO 3 films were prepared on SrTiO 3 (STO) and LaAlO 3 (LAO) substrates using excimer laser-assisted metal organic deposition (ELAMOD). For the LAO substrate, no epitaxial La 0.8Sr 0.2MnO 3 film was obtained by laser irradiation in the fluence range from 60 to 110 mJ/cm 2 with heating at 500 °C. On the other hand, an epitaxial La 0.8Sr 0.2MnO 3 film on the STO substrate was formed by laser irradiation in the fluence range from 60 to 100 mJ/cm 2 with heating at 500 °C. To optimize the electrical properties for an IR sensor, the effects of the laser fluence, the irradiation time and the film thickness on the temperature dependence of the resistance and temperature coefficient of resistance (TCR: defined as 1/ R·(d R/d T)) of the LSMO films were investigated. An LSMO film on the STO substrate that showed the maximum TCR of 3.9% at 265 K was obtained by the ELAMOD process using the KrF laser.

Effects of heat treatment and film thickness on microstructure and critical properties of YBCO film processed by TFA-MOD

We fabricated YBCO film on an LAO substrate using the TFA-MOD method and evaluated the effects of the heat treatment temperature and film thickness on the microstructure, degree of texture, and critical properties. The calcining and firing processes were performed in the temperature ranges of 370–460°C and 750–800°C, respectively. We found that the phase purity, grain size and orientation, and degree of texture varied with the calcining and firing temperatures.The films fired at 775°C after calcining at 400–430°C showed the highest critical temperature (TC-onset) of 89.5K and critical current (IC) of 40A/cm-width, which corresponds to a critical current density (JC) of 1.8MA/cm2. According to the XRD, pole-figure, SEM images, and Raman analysis, these highest critical properties are probably due to the formation of a purer YBCO phase and stronger biaxial texture. In the multi-coated films, the IC value increased from 39 to 169A/cm-width as the number of coatings increased from one to four, while the corresponding JC was measured to be in the range of 0.8–1.2MA/cm2. Both the IC and JC decreased when a further coating was applied due to the degradation of the microstructure.

Effect of internal strain on magnetic properties of La 0.7Sr 0.3MnO 3 films

Oriented La 0.7Sr 0.3MnO 3 (LSMO) films were grown on (100) LaAlO 3 (LAO) and SrTiO 3 (STO) substrates by the method of radio frequency magnetron sputtering. X-ray diffraction patterns of LSMO films deposited on LAO and STO substrates showed a slight shift of diffraction peaks as compared to the corresponding peaks of the bulk LSMO. The shift of diffraction peaks was believed to result from the in-plane lattice mismatch between the film and substrate. The distinguished strain effects of substrates were found to be effective on the magnetic properties and the surface morphology of LSMO films on both substrates. The results indicate that STO substrate may be the promising candidate for room-temperature applications of LSMO film.

Two-step growth of m-plane GaN epilayer on LiAlO 2 (1 0 0) by metal-organic chemical vapor deposition

The m-plane GaN (1 1¯ 0 0) epilayers have been grown on LiAlO 2 (1 0 0) substrate by a two-step growth method using a metal-organic chemical vapor deposition (MOCVD) system. The GaN buffer layer is introduced to overcome the drawbacks of thermal instability of LiAlO 2 (LAO), and to relieve the strains due to large thermal mismatch between LAO and GaN. The results of X-ray diffraction (XRD) and polarized Raman scattering spectra demonstrate that the GaN (1 1¯ 0 0) epilayer is single crystal as the growth temperature of the buffer layer is in the range of 850–950 °C. Moreover, it is found that the surface nitridation process on LAO substrate can result in the formation of the GaN poly-crystalline films, which is due to the unintentional growth of a thin layer of c-phase AlN on LAO surface.

FABRICATION OF LSMO SINGLE LAYERS AND LSMO/YBCO DOUBLE LAYERS

( La , Sr ) MnO 3 (LSMO) single-layer and LSMO/YBCO double-layer films have been grown on LAO and MgO substrates using ion beam sputtering. For LSMO single-layer films, the highly epitaxial films can be grown at lower substrate temperatures down to 500°C. The epitaxy of the films, which is degraded with increasing TS, can be restored by supply of plasma oxygen. Smaller lattice mismatch of LSMO on LAO gives two-dimensional step-and-terrace type growth, whereas on MgO grain type growth is observed due to larger mismatch. For the double-layer films, LSMO layer can be grown epitaxially on a-oriented YBCO underlayer, but a part of the underlying a-YBCO is changed into c-YBCO during the deposition of overlayer. For c-YBCO underlayer, a part of the underlying c-YBCO is changed into (110)-oriented phase after the deposition of overlayer. Then it is necessary to deposit the overlayer at lower temperatures.

Study on the hydrolytic property and thermal stability of LiAlO 2 substrate

The hydrolytic property and thermal stability of LiAlO 2 (LAO), important factors for its application, were examined by AFM and X-ray rocking curve. We found that H 2O may be deleterious for LAO surface polishing when the root mean square (RMS) value is less than 1 nm. However, when the RMS value is more than 1 nm it may be useful for LAO polishing. (1 0 0)-plane LAO substrates are annealed in the range of 850∼900 °C in flux N 2, slick AlN layer probably is produced on the substrate surface. M-plane GaN layer has grown on the substrate by metal–organic chemical vapor deposition (MOCVD) method. Theses results show that LiAlO 2 crystal is a promising substrate of fabricating high-efficiency LEDs by MOCVD.

Effects of deposition conditions on the phase formation of YBCO films prepared by spray pyrolysis method

YBa2Cu3Oy superconducting films were deposited on LaAlO3(100) single crystal substrates by spray pyrolysis method. Two types of ultrasonic and concentric nebulizer were used in order to generate fine droplets of metal-inorganic precursor solution. c-Axis oriented films were obtained at deposition temperature of 750–850°C and at working pressures of 100Torr and 500Torr. In case of ultrasonic nebulizer, the films showed rough surface morphology due to the presence of enormous droplets, whereas smooth and dense films were obtained for concentric nebulizer. The good c-axis oriented YBCO films were formed at the wide range of the oxygen partial pressure. Oxygen which is generated via the decomposition of nitrate precursors is considered to participate in the formation reaction of YBCO film. Microstructures of YBCO films varied depending on oxygen partial pressure and rod-like grains were appeared when the oxygen partial pressure was lower than 30Torr. YBCO films were deposited epitaxially on LAO(100) substrate. Δϕ of in-plane and Δω of out-of-plane texture were measured as 3.3° and 1.0°, respectively. A transport Jc value of 0.50MA/cm2 at 77K and self-field was achieved for the YBCO film deposited on LaAlO3(100) single crystal substrate.

The effects of the firing temperature of YBCO coated conductors fabricated by TFA-MOD process

We fabricated YBCO films on LAO substrates using the TFA-MOD method and evaluated the effects of the heat treatment temperature on the microstructure, degree of texture, and critical properties. The phase formation and microstructure were characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM) and the degree of texture was evaluated by pole-figure analysis.The firing was performed in the temperature range of 750–800°C and we found that the phase purity, grain size and orientation, degree of texture, and oxygen content varied with the firing temperature. The films fired at 775°C showed the highest critical temperature (TC-onset) of 89.5K and critical current (IC) of 40A/cm-width, which corresponds to a critical current density (JC) of 1.8MA/cm2. According to the results of the XRD, pole-figure, SEM and Raman analyses, these optimum critical properties can probably be attributed to the formation of a pure YBCO phase, stronger c-axis orientation and higher oxygen content.

Effect of lattice-mismatch strain on the structural and dielectric properties of (Pb,Sr)TiO 3 thin films grown by pulsed laser deposition

Pb 0.35Sr 0.65TiO 3 (PST) thin films have been fabricated on LaAlO 3 (LAO) and MgO substrates using the pulsed laser deposition technique. The microstructure characteristics of the films were examined by means of X-ray diffraction, atomic force microscopy, scanning electron microscopy and Raman spectroscopy, and the results indicate that the films are epitaxially grown and show good crystallinity. The dielectric constant dependence on DC bias voltage and temperature were measured in a planar capacitor configuration for these films. Compared to the PST thin film grown on LAO, the film grown on MgO showed a higher temperature of the capacitance maximum and a higher dielectric constant at zero bias. We explain the results by taking into account the lattice-mismatch strain between the substrate and the film. In contrast to the in-plane compressive strain induced by the LAO substrate, the in-plane tensile strain induced by the MgO substrate enlarges the unit cell of PST and enhances the magnitude of dipole moments, which increases the dielectric constant. These results indicate that a reasonable in-plane tensile strain could improve the dielectric properties of PST thin films.

TFA-MOD법을 이용한 YBCO 박막의 열처리 온도와 두께의 영향

We fabricated the YBCO films on LAO substrate using the TFA-MOD method and evaluated the effects of heat treatment temperature and film thickness on the microstructure, degree of texture, and critical properties. The calcining and firing were peformed at the temperature range of , respectively. For the films fired at after calcining at showed highest critical temperature (Tc-onset) of 89.5 K and critical current (Ic) of 40A/cm-width which corresponds to critical current density (Jc) of . The highest critical properties are probably attributed to the formation of purer YBCO phase, stronger biaxial texture, and higher oxygen content, according to the XRD, pole-figure, SEM, Raman analysis. From the multi-coated films, the Ic increased from 39 to 169 A/cm-width as the coating repeated to four times, while the corresponding Jc was measured from once to be in the range of . Both Ic and Jc degraded as the coating repeated further, indicating that the optimum thickness is in the range of .

Fabrication and characterization of epitaxial Sr0.6Ba0.4Nb2O6/La0.7Sr0.3CoO3 heterostructures

Abstract Epitaxial Sr 0.6 Ba 0.4 Nb 2 O 6 (SBN60)/La 0.7 Sr 0.3 CoO 3 heterostructures were fabricated on LAO(0 0 1) substrates using pulsed laser deposition (PLD). Their structural properties were investigated by X-ray diffraction. The θ –2 θ scans showed single crystalline Sr 1− x Ba x Nb 2 O 6 (SBN) and La x Sr 1− x CoO 3 (LSCO) layers with a 〈0 0 1〉 orientations perpendicular to the substrate plane. Phi scans on the (2 2 1) plane of SBN layer indicated that the films have two in-plane orientations with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ±18.4° as well as ±45° with respect to the LAO substrate. This rotation was explained by considering the lattice matching between films and substrate, and minimization of electrostatic energy. Spectroellipsometry (SE) was used to characterize the depth profile, the microstructural inhomogeneities, including voids and surface roughness, refractive indices and extinction coefficients of the films.

Heteroepitaxial growth of YBCO/STO thin films for voltage tunable varistors

SrTiO 3 (STO) ferroelectric (FE) thin films associated with high-temperature superconductors (HTSC) is a good compromise for tunable microwave components. The great challenge encountered for frequently used coplanar structured devices based on FE/HTSC (A/B means A is on B) thin films is that it is difficulty to simultaneously keep good superconductivity of HTSC thin films and optimized non-linear dielectric properties of ferroelectrics. Stripline structured devices based on HTSC/FE thin films are prepared in this paper. In the HTSC/FE structured devices, STO thin films with smooth surface were heteroepitaxial grown on LaAlO 3 (1 0 0) (LAO) substrate. The STO thin film showed not only good out-of-plane orientation, but also identical in-plane orientation with substrate. The crystallographic orientation relationship between LAO substrate and STO thin film in a– b plane is [1 0 0] STO∥[1 0 0] LAO. Highly out-of-plane textured YBCO thin films with good superconducting properties were grown onto the STO thin films, and interdigital capacitors with relative capacitance change of 20% and Q-factor of 286 were made from the YBCO/STO/LAO thin films. The experiment results showed that the HTSC/FE multilayers is a good candidate for high- Q varistors.

Optical properties of ZnO thin film on γ-LiAlO 2 substrate grown by pulsed laser deposition

Optical properties were investigated of ZnO thin films grown on (100) γ-LiAlO 2 (LAO) substrates by pulsed laser deposition method. C-axis oriented ZnO film was grown on (100) LAO substrate at the substrate temperature of 550 °C. The transmittances of the films were over 85%. Peaks attributed to excitons were seen in the absorption spectra, indicating that the thin films have high crystallinity. Photoluminescence spectra were observed at room temperature; the peak at 550 nm is ascribed to oxygen vacancies in the ZnO films caused by the diffusion of Li from the substrate into the film during deposition.

Microstructural and electrical properties of La0.7Ca0.3MnO3 thin films grown on SrTiO3 and LaAlO3 substrates using metal-organic deposition

La 0.7 Ca 0.3 MnO 3 (LCMO) thin films have been prepared on LaAlO3 and SrTiO3 (STO) (001) single-crystal substrates by the metal-organic deposition process. These films were characterized by transmission electron microscopy (TEM) and temperature dependence of the resistance R(T). The microstructure of the LCMO films and LCMO/substrate interfaces were investigated through cross-sectional TEM observations. High-resolution TEM (HRTEM) observations and electron-diffraction patterns demonstrate the (001) epitaxial growth on both the LAO and STO substrates. The local structure of the LCMO film depends on the type of substrate. HRTEM observations along the LCMO/STO interface display a good epitaxy throughout the entire film without any microstructural defects. On the contrary, in the LCMO film and in the region close to the LAO substrate, we note the presence of misfit dislocations and twins. The temperature coefficient of resistance (TCR) was calculated from the temperature dependence of the resistance measurements. The LCMO/LAO system exhibits a TCR value of 27.5%∕K compared with the 10%∕K measured for the LCMO/STO system.

Microstructures and Enhancement of Critical Current Density in<tex>$rm YBa_2rm Cu_3rm O_7$</tex>Thin Films Grown by Pulsed Laser Deposition on Various Single Crystal Substrates Modified by Ag Nano-Dots

YBa/sub 2/Cu/sub 3/O/sub 7/ (Y123) thin films were grown by pulsed laser deposition (PLD) on YSZ (100), SrTiO3 (100), and LaAlO3 (100) single crystal substrates. Prior to the film deposition, a discontinuous layer of Ag nano-dots was deposited on the substrates. The Y123 films grown on such surfaces modified with Ag nano-dots were characterized by Atomic Force Microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), AC susceptibility and DC magnetization. The effects of the density of Ag nano-dots, which was controlled by the numbers of PLD shots, on the microstructures and resultant critical current density J/sub c/ have been studied systematically. Results showed that at fixed physical deposition conditions J/sub c/ increased monotonically with number of Ag shots, n, for films grown on both STO and LAO substrates. At 77 K, the J/sub c/ increased from 10/sup 6/ to 3.2/spl times/10/sup 6/ A/cm/sup 2/ for LAO and from 8/spl times/10/sup 5/ to 3.5/spl times/106 A/cm/sup 2/ for STO as n increased from 0 to 150. At 5 K, the enhancement of J/sub c/ was approximately four times at both low and high fields. However, for films grown on YSZ substrate, J/sub c/ increased from 2/spl times/10/sup 5/ to 2/spl times/10/sup 6/ A/cm/sup 2/ as Ag shots increased from 0 to 30, and decreased to 9/spl times/10/sup 5/ for n/spl ges/60. Detailed microstructure investigations indicated that the crystallinity and ab alignment gradually improved as the number of Ag-nano-dots increased.

Critical Current Density Enhancement in<tex>$rm YBa_2rm Cu_3rm O_7-delta$</tex>Thin Films by Twin Domains of<tex>$rm LaAlO_3$</tex>Substrates

Magnetic flux penetration into a 0.2 /spl mu/m-thick YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin film grown on a crystalline LaAlO/sub 3/ (LAO) substrate was studied using magneto-optical imaging techniques. Enhanced critical current density J/sub c/ was observed at the location corresponding to twin domains on the underlying substrate. We attribute this J/sub c/ enhancement to increased pinning defects in the YBCO layer induced by the naturally formed nano-scaled surface roughness on the LAO substrate. Our results suggest that the substrate surface roughness might be helpful in J/sub c/ improvement of YBCO thin films grown on metal substrates by pulsed laser deposition.