X-ray Diffraction Φ-scans Research Articles

NdSrNi0.8Cu0.2O4−δ thin films epitaxially grown by pulsed laser deposition on LaAlO3 and SrTiO3: A potential electrode for epitaxial regrowth of perovskite structure-based oxides

NdSrNi0.8Cu0.2O4−δ (NSNCO) thin films were grown by pulsed laser deposition (PLD) on LaAlO3 and (110)SrTiO3 substrates. NSNCO thin films were (00l) and (103) oriented on (100) LaAlO3 and (110)SrTiO3, respectively, as evidenced by the θ−2θ X-ray diffraction. The high crystalline quality was illustrated by low value of rocking curve (Δω=0.1–0.5° for (00l) films and about 1° for (103) films). In-plane ordering was probed by X-ray diffraction ϕ-scans, evidencing the epitaxial growth on both substrates. The microstructure of films investigated by scanning electron microscopy was strongly influenced by deposition conditions. Four probe electrical resistivity measurements were performed versus temperature in the range 77–300K. The resistivity was found to be 0.004Ωcm at room temperature. Some bilayers combining a ferroelectric oxide and NSNCO, i.e. SrBi2Nb2O9 (SBN) and NdSrNi0.8Cu0.2O4−δ, were grown by PLD on both substrates. The possibility to control (00l)- and (116)-oriented epitaxial SBN thin films was proved by the X-ray diffraction analysis.

Epitaxial Growth of ZnO by Sol-Gel Method

Epitaxial films of ZnO have been synthesized by the sol-gel method using ZnO buffer layers on sapphire (001) substrates. The buffer layers of 50-nm ZnO were epitaxially grown by metal organic chemical vapor deposition prior to the sol-gel process and significantly improved the crystallinity of the sol-gel ZnO. The six-fold symmetry observed in X-ray diffraction φ-scan spectra confirmed the epitaxial nature of the sol-gel ZnO films. Excitonic recombinations were dominant in the photoluminescence, while defect-related emissions around 3.31 to 3.32 eV, which are commonly observed in polycrystalline sol-gel films, were not observed in the sol-gel ZnO with ZnO buffer layers.

Formation of CeO 2 buffer layer using multi-plume PLD

The CeO 2 buffer layer was fabricated using the multi-plume pulsed laser deposition (PLD) method with different deposition rates controlled by the excimer laser energy and frequency on the Gd 2Zr 2O 7 template tape formed by the ion-beam assisted deposition (IBAD) with 14° of Δ φ (full width at half maximum (FWHM) value of X-ray diffraction φ-scan for Gd 2Zr 2O 7 (2 2 2) pole). The laser conditions with high pulse energy and low frequency resulted in a highly textured in-plane grain alignment (Δ φ). The surface roughness and Δ φ values were improved by increasing the thickness of the CeO 2 buffer layer. YBCO films with the thickness of 1 μm and 1.6 μm were further deposited by the advanced trifluoroacetates–metal organic deposition (TFA–MOD) on the CeO 2 buffered substrates with the deposition rate of 0.15 and 0.5 μm/min. The J c values of 2.5 MA/cm 2 and 2 MA/cm 2 were obtained, respectively. High J c films could be deposited on the CeO 2 buffer layer even at high deposition rate by the multi-plume deposition.

Evaluation of buffer materials for fluorine contained solid phase epitaxy of 123 films on MgO substrates

Recently solid phase epitaxial YBa 2Cu 3O 7− δ films such as metal organic deposition using trifluoroacetate (TFA-MOD) technique, chemical solution-based coating pyrolysis, and BaF 2 ex situ post reaction process have been improving their crystalline quality. In order to grow thick films, larger thermal expansion coefficient substrates than that of YBCO are preferable. From the viewpoint of thermal expansion coefficient, MgO is a promising substrate. However, it is difficult for solid phase epitaxial YBa 2Cu 3O 7− δ films to grow directly on the MgO substrate, because fluorine reacts with Mg in the substrate. Therefore we evaluate buffer layer materials to protect MgO substrates against fluorine. Buffer layer are grown by pulsed laser deposition at around 730 °C on polished MgO substrates. Thin CeO 2 buffer layers are difficult to grow directly on the MgO substrates. However, CeO 2-capped double buffer layers grow epitaxially on MgO substrates. The examined materials for double buffer layers are CeO 2/SrSnO 3, CeO 2/BaSnO 3 and CeO 2/BaZrO 3. Crystallinity of the buffer layers are characterized by X-ray diffraction (XRD) θ–2 θ-scans and XRD φ-scans. From XRD θ–2 θ-scans patterns crystallinity of the CeO 2 on BaSnO 3 is higher than those of the others. From XRD φ-scans patterns, all of these buffer layers were the perfect in-plane alignment. The intensity of CeO 2 film on BaSnO 3 was the highest in all films. Surface morphologies are observed by AFM. From AFM observation, it was demonstrated that the surface of CeO 2 film on BaSnO 3 was smooth. We confirmed that CeO 2 film grown on a BaSnO 3 buffer layer crystallized better than others.

Structural and electrical properties ofc-axisepitaxial and polycrystalline Sr3Bi4Ti6O21 thin films

c-axisepitaxial and polycrystalline Sr3Bi4Ti6O21 (SBTi) thin films were fabricated on(001)SrTiO3 (STO) single-crystal substrates and Pt/Ti2/SiO2/Si substratesrespectively, by pulsed laser deposition (PLD). Structures of the films weresystematically characterized by x-ray diffraction (XRD), including θ–2θ-scans, rocking curvescans and ϕ-scans,atomic force microscopy and transmission electron microscopy (TEM).The epitaxial orientation relation of the SBTi films on STO isestablished by selected-area electron diffraction and XRD ϕ-scans to be (001)SBTi∥(001)STO, [11̄0]SBTi ∥[010]STO. Cross-sectional high-resolution TEM studies on the epitaxialSBTi film revealed that SBTi is a single-phase material. A special kindof irrational atomic shift along the [001] direction was observed and isdiscussed in detail. By using an evanescent microwave probe (EMP),the room-temperature dielectric constant of the epitaxial SBTi film wasmeasured to be 211 ± 20. Excellent electrical properties of the polycrystallineSBTi films with Pt bottom and top electrodes were exhibited: thePr andEc values were 4.1 μC cm−2and 75 kV cm−1 respectively, the nonvolatile polarizations decreased by less than5% after 2.22 × 109 switching cycles and the dielectric constant and loss tangentwere 363 and 0.04 at 100 kHz.

Variation of orientation and morphology of epitaxial SrBi2Ta2O9 and SrBi2Nb2O9 thin films via the coating-pyrolysis process

Orientation-controlled epitaxial thin films of bismuth layer-structured ferroelectrics, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), were prepared on single-crystal SrTiO3 (STO) substrates by the coating-pyrolysis process. Most of the SBT (SBN) films showed the (106) and (001) orientations on STO(110) and (001), respectively. The degree of orientation, in terms of the ratio of peak intensity to the background level in the x-ray diffraction φ-scan profile for the film, greatly increased with a decrease in the oxygen partial pressure, p(O2), of annealing atmosphere at 800 °C. Interestingly, coexistence of the (110)-oriented grains with the (106)-oriented ones on STO(110) [and the (100)-oriented grains with the (001)-oriented ones on STO(001)] was observed exclusively in the SBT films annealed at 700–750 °C under p(O2) of 10 Pa. Atomic force microscopy observations showed that the surface morphology of the SBT films remained almost unchanged, i.e., comprising round-shaped grains of submicrometer size, whereas that of the SBN films drastically changed, according to the variation in orientation of substrate surfaces or in annealing conditions, i.e., temperature, p(O2), and time.

Growth and characterization of superconducting films Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9 on CeO 2-buffered single crystal YSZ

Crystalline CeO 2 as a buffer layer on single crystal yttrium stabilized zirconia (YSZ) has been deposited in situ at 600–650°C by laser ablation. Following the deposition of CeO 2, Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9 ((Tl,Bi)-1223) amorphous films were deposited on the CeO 2-buffered YSZ substrate at room temperature. The deposited amorphous films were then wrapped together with an unfired Tl 0.95Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9 pellet in silver foil. The whole package was finally annealed ex situ in a tube furnace at 790–810°C with flowing argon to crystallize the films. X-ray diffraction (XRD) shows that the annealed films consist of mainly c-axis aligned (Tl,Bi)-1223 phase with a small amount of (Tl,Bi)-1212 phase. The full width at half maximum (FWHM) values of XRD ω-scans at (007) of (Tl,Bi)-1223 phase and (005) of (Tl,Bi)-1212 phase are 0.44° and 0.48° respectively. XRD ϕ-scans on (102) of both (Tl,Bi)-1223 and (Tl,Bi)-1212 phases show an excellent in-plane alignment with FWHM values of 0.44° and 0.54°, respectively. Four-probe transport measurements show superconducting transition temperatures ( T c's) of 105–109 K depending on the annealing conditions. At 77 K and zero external magnetic field, transport critical current density ( J c) is in the range of (0.6–1)×10 6 A/cm 2 for samples with thickness of 1.5–1.8 μm.

Epitaxial Film Growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 on Rolling Assisted Biaxially Textured Nickel Substrates with YSZ And CeO2 Buffer Layers

Epitaxial film growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 ((Tl,Bi)-1223) on rolling assisted biaxially textured substrates with YSZ and CeO2 buffer layers (RABiTS) has been successfully demonstrated by laser ablation and post-deposition annealing in flowing argon. X-ray diffraction (XRD) θ-2θ spectra showed that the films consisted mainly of c-axis aligned 1223 phase with some intergrown 1212 phase, while XRD Φ-scans of (102) pole figure revealed that the films are also a- and b-axes aligned, with an epitaxy of the «100» of (Tl,Bi)-1223 film on the «110» of the top YSZ buffer layer. Four-terminal electrical transport measurements showed that the zero-resistance transition temperature (Tc) was in the range of 106 - 110 K, and the critical current density (Jc) at 77 K and zero field was about 105 A/cm2 for the entire film width (3 mm) of a longer film (14 mm) which was processed differently from the shorter films (7 mm). For a shorter film (7 mm) that showed better ab-in-plane alignment, the magnetization Jc, at 77 K and extrapolated to zero field, calculated from Bean's model using the full film width (3.5 mm) as the appropriate lateral dimension, was 2 × 105 A/cm2.

Epitaxial superconducting thin films Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2O 9−δ on (001) YSZ synthesized by laser ablation and post-annealing in pure argon

Epitaxial superconducting thin films of Tl 0.78Bi 0.22Sr 1.6Ba 0.4Ca 2Cu 3O 9−δ ((Tl,Bi)-1223) on (001) YSZ single crystal substrate have been successfully synthesized by laser ablation and post-annealing in a tube furnace with flowing pure argon through the tube all the time during annealing. X-ray diffraction (XRD) θ–2θ spectra showed that the films are c-axis aligned 1223 phase with a small amount of intergrown 1212 phase, while XRD φ-scans revealed that the films are also a- and b-axes aligned, with an epitaxy of the &.lang;100&.rang; of (Ti,Bi)-1223 film on the &.lang;110&.rang; of the YSZ substrate. Four-terminal electrical transport measurements showed that the zero-resistance transition temperature ( T c) was 108.5 K, and the critical current density ( J c) at 77 K and zero field was 1.1 × 10 6 A/cm 2, both for the entire film width and for a patterned bridge. The magnetic field dependent transport J c suggest that (Tl,Bi)-1223 films on (001) YSZ have better flux-pinning properties than high- J c (Tl,Bi)-1223 films on (001) LaAlO 3.

Preparation of Epitaxial BaTiO3 Thin Films by Plasma-Enhanced Metalorganic Chemical Vapor Deposition (Pe-Mocvd)

AbstractThe plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process has been successfully used to achieve high quality epitaxial growth of BaTiO3 thin films on (001) LaA103 and (001) NdGaO3 substrates at a substrate temperature of 680°C. The PEMOCVD system, which incorporates a 300-Watt microwave cavity, introduces excited species from an oxygen plasma to lower the required deposition temperature, as compared to thermal MOCVD growth of BaTiO3. X-ray diffraction (XRD) θ-20 scan patterns indicate that there are few randomly oriented grains and impurity phases in the epitaxial BaTiO3 films. Results of XRD ϕ-scans of the BaTiO3 (202) reflection show a modulation pattern of peaks every 90°, which demonstrates that the BaTiO3 thin films have no misorientation along the [100] and [010] directions of the substrates. An XRD ω rocking curve of the BaTiO3 (200) reflection had a narrow FWHM of 0.25°, indicating that the films have a high degree of preferred orientation of <100> perpendicular to the substrates. The high degree of epitaxial crystallinity is further confirmed by Rutherford Backscattering Spectrometry which gives a minimum yield of 7.5% and 11% for the films deposited on LaAIO3 and NdGaO3, respectively. Scanning electron micrographs show that these films have very smooth surface morphologies, which are desirable for device applications.