Biaxial Texture Research Articles

Roles of humidity and heat treatment temperatures on YBa 2Cu 3O 7− x coated conductors by trifluoroacetic acid-metal organic deposition process

YBa 2Cu 3O 7− x (YBCO) films were fabricated on an LAO substrate using the trifluoroacetic acid-metal organic deposition (TFA-MOD) method and the effects of the humidity and heat treatment temperatures on the microstructure, degree of texture and critical properties of the films were evaluated. In order to understand the combined effects of the humidity and the calcining and firing temperatures on critical properties, heat-treatment was performed at various temperatures with the other processing variables fixed. The films were calcined at 400–430 and fired at 750–800 °C in a 0–12.1% humidified Ar-O 2 atmosphere. The texture was determined by pole-figure analysis. The amount of the BaF 2 phase was effectively reduced and a sharp and strong biaxial texture was formed under a humidified atmosphere, which led to increased critical properties. In addition, the microstructure varied significantly with firing temperature but changed little with calcining temperature. The highest I C of 40 A/cm-width, which corresponds to J C value of 1.8 MA/cm 2, was obtained for the films fired at 775 (in 12.1% humidity) after calcining at 400–430 °C. It is likely that °C the highest I C value is due to the formation of a more pure YBCO phase, c-axis grains, and a denser microstructure.

YBCO FILMS DOPING WITH SZO PARTICLES GROWN BY CHEMICAL SOLUTION DEPOSITION

YBa 2 Cu 3 O 7-δ ( YBCO ) films with SrZrO 3 ( SZO ) doping have been prepared successfully by a non-vacuum, low cost, and easily scalable metal–organic deposition method, and their microstructures and physical properties were investigated. From the analysis of x-ray diffraction and φ-scan results, the doped films had sharp biaxial textures. Although the doped YBCO film had a wider critical temperature transition width than that of the un-doped YBCO film, the critical current density, J c , was significantly enhanced under applied fields as compared to the un-doped film. Furthermore, the ratio of J c , doped to J c , un-doped became gradually larger with increasing temperature and magnetic field, indicating that an effective pinning force was created by SZO doping. These results clearly demonstrate that there are appealing prospects for applications of the doped film in high magnetic fields and temperatures.

Characterization of the biaxial textures of MgO thin films grown by E-beam evaporation

The biaxial textures of MgO thin films with thicknesses 4500–5500 Å deposited by electron beam evaporation on glass substrates have been characterized. The surface normal to the amorphous soda-lime glass substrate was placed parallel to the MgO vapor flux, i.e., at zero degree with respect to the MgO vapor source. The MgO thin films showed biaxial texture regardless of the deposition parameters. XRD and SEM have been used to characterize the crystal structure and thin film surface morphology. In this study we devised a novel method for the characterization of the biaxial texture of MgO thin films with thicknesses ≤5000 Å, for which the X-ray pole figure method cannot be used due to the low scattering intensity from the MgO film containing only low atomic X-ray scattering ions. We report the biaxial texture development in MgO thin films grown by E-beam evaporation on the amorphous glass substrate inclined at zero degree with respect to the MgO vapor source.

A Water-Based Sol-Gel Precursor for Deposition of Thin ${\rm La}_{2}{\rm Zr}_{2}{\rm O}_{7}$ Layers on Ni-W Substrates

Through dip-coating Ni-5%W substrates in a water-based sol-gel solution, thin films of La2Zr2O7 (LZO) were produced. This method yields highly crystalline and epitaxial films. The surface of the LZO film was found to be smooth and homogeneous. Subsequently, CeO2 layers followed by an YBa2Cu3O7-y layer were deposited via Pulsed Laser Deposition (PLD) onto the LZO film. The crystallinity and biaxial texture of the LZO layer was successfully transferred to the next layers, as demonstrated by pole figures and RHEED measurements. Resistive Tc-measurements were carried out on these samples and showed a Tc of 85 K.

Biaxial CdTe/CaF 2 films growth on amorphous surface

A continuous and highly biaxially textured CdTe film was grown by metal organic chemical vapor deposition on an amorphous substrate using biaxial CaF 2 nanorods as a buffer layer. The interface between the CdTe film and CaF 2 nanorods and the morphology of the CdTe film were studied by transmission electron microscopy (TEM) and scanning electron microscopy. Both the TEM and X-ray pole figure analysis clearly reveal that the crystalline orientation of the continuous CdTe film followed the {111}<121> biaxial texture of the CaF 2 nanorods. A high density of twin faults was observed in the CdTe film. Furthermore, the near surface texture of the CdTe thin film was investigated by reflection high-energy electron diffraction (RHEED) and RHEED surface pole figure analysis. Twinning was also observed from the RHEED surface pole figure analysis.

Growth of CdTe Films on Amorphous Substrates Using CaF2 Nanorods as a Buffer Layer

Continuous biaxially textured CdTe films were grown on biaxial CaF 2 buffer layers. The CaF 2 nanorods were grown by oblique angle vapor deposition and possessed a {111} biaxial texture. The CdTe film was deposited by metal organic chemical vapor deposition (MOCVD). Film morphology and the CdTe/ CaF 2 interface were studied by scanning electron microscopy and transmission electron microscopy. Characterization showed that small CdTe grains formed initially from the CaF 2 surfaces. These small grains then merged into large columnar grains during growth. Analysis revealed that the crystalline orientation of the CdTe film followed the biaxial texture of the CaF 2 nanorods.

Study on reaction mechanism of YBa2Cu3O7–x; film by TFA-MOD process

This paper systematically investigates the intermediate phases of YBa2Cu3O7−x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7−x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40–140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.

Ion-beam Texturing at Nucleation – Manipulation of Crystallographic Orientation in Cubic Materials at the Nanometer Scale

AbstractThe use of an ion beam assist during the concurrent deposition of cubic materials can result in the growth of crystallographically oriented thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film and develops texture in a different manner from that of other well-studied materials, like yttria-stablized zirconia. Here, we present data on the initial nucleation of biaxial texture in this model system using a novel in-situ quartz crystal microbalance (QCM) substrate combined with in-situ reflected high-energy electron diffraction (RHEED). Temporal correlation of mass uptake with the RHEED images of the growing surface can be used to elucidate the mechanism of texture development in these films. Experimental data shows that the initially polycrystalline MgO film develops biaxial crystallographic texture at a thickness of ˜2 nm, regardless of the ion-to-molecule ratio. RHEED images show the onset of texture occurs quickly and is somewhat analogous to a solid phase re-crystallization process with crystallite sizes of ˜3 to 4 nm. Imaging with transmission electron microscopy has corroborated these observations. Changes in the ion-to-molecule ratio can influence the crystallite size and affect the nucleation density of these films. Growth of these films on various substrates changes the sticking coefficient of the MgO and influences the nucleation density and film growth mode as well. This opens the possibility of using MgO and other materials to develop biaxially textured crystallites with a narrow, specified size distribution for nanoscale applications.

Reflection High-energy Electron Diffraction Study of Nanostructures: From Diffraction Patterns to Surface Pole Figure

AbstractIn this report we present a brief overview of the growth of nanostructures by the oblique angle deposition where the nanostructures possess both out-of-plane and in-plane preferred orientations or a biaxial texture. The degree of preferred crystal orientations can be quantitatively determined from a method called “RHEED surface pole figure analysis” that we developed recently.

Iridium on Biaxially Textured Oxide Templates: A Concept to Grow Single Crystals on Arbitrary Substrates

Ion beam assisted deposition (IBAD) allows a biaxial texturing of oxide layers on polycrystalline or amorphous substrates. Even the best layers still contain an in-plane angular spread of about 4°. We report here a method to grow Ir films on top of these oxide layers with a factor of 5 lower misorientation. It is shown that the huge texture improvement involves a massive realignment of the iridium islands and an orientation averaging process. Heteroepitaxial diamond was successfully deposited on the Ir/IBAD-MgO multilayer stacks. The described texture improvement by iridium layers provides a general concept towards single crystal growth on arbitrary substrates.

Study of YSZ films deposited using electron-beam sputtering onto a nickel alloy with a perfect cube texture

X-ray diffraction analysis and atomic force microscopy were used to study the effect of the state of a substrate (an Ni-11 at % Cr ribbon) and deposition conditions on the texture and roughness of an yttrium-stabilized zirconia (YSZ) buffer layer deposited by electron-beam sputtering. The presence of a sharp cube texture in the nickel-alloy ribbon was shown to be insufficient condition for obtaining a biaxial texture in the YSZ film. A two-dimensional (2 × 2) sulfur superstructure should be formed on the nickel-ribbon surface. In this case, the YSZ film with a sharp {100} 〈100〉 cube texture and surface roughness of ∼10–15 nm can be prepared at a low deposition rate of 0.005–0.008 nm/s and a substrate temperature of 700–800°C.

Fiber textures of titanium nitride and hafnium nitride thin films deposited by off-normal incidence magnetron sputtering

We studied the development of crystallographic texture in titanium nitride (TiN) and hafnium nitride (HfN) films deposited by off-normal incidence reactive magnetron sputtering at room temperature. Texture measurements were performed by x-ray pole figure analysis of the (111) and (200) diffraction peaks. For a deposition angle of 40° from substrate normal, we obtained TiN biaxial textures for a range of deposition conditions using radio frequency (rf) sputtering. Typically, we find that the ⟨111⟩ orientation is close to the substrate normal and the ⟨100⟩ orientation is close to the direction of the deposition source, showing substantial in-plane alignment. We also introduced a 150 eV ion beam at 55° with respect to substrate normal during rf sputtering of TiN. Ion beam enhancement caused TiN to align its out-of-plane texture along ⟨100⟩ orientation. In this case, (200) planes are slightly tilted with respect to the substrate normal away from the ion beam source, and (111) planes are tilted 50° toward the ion beam source. For comparison, we found that HfN deposited at 40° without ion bombardment has a strong ⟨100⟩ orientation parallel to the substrate normal. These results are consistent with momentum transfer among adatoms and ions followed by an increase in surface diffusion of the adatoms on (200) surfaces. The type of fiber texture results from a competition among texture mechanisms related to surface mobilities of adatoms, geometrical, and directional effects.

Effect of Firing Temperature on the Structure and Properties of YBa2Cu3O7−x Films by TFA-MOD Method

YBa2Cu3O7−x (YBCO) films were fabricated on LaAlO3 (LAO) substrate under various firing temperatures (760–870 °C) in the crystallization process by metalorganic deposition (MOD) method using trifluoroacetates. The effect of firing temperature on the structure and properties of YBCO films was systematically investigated. According to the XRD and SEM images, the films fired at low temperature (760–800 °C) showed poor electrical performance due to rough surfaces and impurity phases. However, the films fired at 850 °C showed the highest critical temperature of 90 K and the highest J c of 3.1 MA/cm2 which attribute to the formation of a purer YBCO phase, fewer pores, and stronger biaxial texture.

The morphology and texture of Cu nanorod films grown by controlling the directional fluxin physical vapor deposition

We report the creation of unusual biaxial textures in Cu nanorod films,through the control of the incident vapor flux during oblique angle deposition.High-density twin boundaries were formed using a periodic azimuthal swingrotation of the substrate while the incident angle of the Cu flux was fixed at85° with respect to the surface normal. In contrast, depositions on stationary substratesresulted in nanorod films with a much lower density of twinned crystals. From transmissionelectron microscopy and x-ray pole figure analysis, the nanorod axis was shown to coincideapproximately with the crystallographic directions. We also observed the branching of these nanostructures into‘nanotrees’. This branching was attributed to the creation of edge dislocations during thedeposition and was particularly prevalent for the case of swing rotation. The mechanismsfor the development of texture, twinning, and branching in these nanostructures arediscussed.

Strain characteristics of critical current in RABiTS/Y-Ba-Cu-O coated conductors

The strain dependence of critical current I c of a commercial RABiTS (Rolling-Assisted Biaxially Textured Substrates) YBCO coated conductor tape with Cu stabilizing layers on both surfaces has been studied by two kinds of bending apparatus and a tensile apparatus at 77 K and 293 K. According to the voltage measurements using multi-taps in the longitudinal direction, local I c degradation was also observed. In the continuous bending-tension test at 77 K, in which YBCO layer was subjected to the tensile strain, I c began to decrease rapidly beyond the strain of 0.6% after initial moderate degradation. In the continuous bending-compression tests, the I c began to decrease rapidly beyond the strain of 0.4%. The strain for the beginning of degradation of I c obtained by tensile tests at 77 K was almost the same as that by the bending-tension tests. Bending test at RT using FRP holders showed I c degradation not so different from that by the continuous bending tests at 77 K. In all tests, the I c initially degraded locally irrespective of the position in the specimens. Furthermore, I c degradation by repeated bending was also studied.

Biaxially oriented CaF 2 films on amorphous substrates

Biaxially oriented CaF 2 films have been created by first using an oblique incidence vapor flux to deposit CaF 2 onto an amorphous surface to form vertically aligned nanorods which served as seeds to grow a more continuous CaF 2 capping layer under a subsequent normal incidence flux deposition. The entire film possesses a unique {1 1 1}〈1 2 1〉 biaxial texture as shown by X-ray pole figure analysis and transmission electron microscopy (TEM). This unique texture formation is a result of shadowing and surface diffusion effects. This biaxially oriented film on an amorphous substrate may be useful as a buffer layer to grow active semiconductor devices.

Grain growth and biaxial texture of chemically deposited La2Zr2O7 buffer layers for YBCO-coated conductors

Chemically deposited La2Zr2O7 (LZO) thin films are crucial for coated conductor production since they transfer the texture from a highly biaxially textured nickel substrate to the YBCO superconducting layer and act as nickel diffusion barriers. The misfit of LZO with respect to Ni is 7.6%. The LZO buffer layers studied in this work were deposited on biaxially textured Ni-5at%W substrates by chemical solution deposition (CSD) using the same precursor starting solutions and were annealed at temperatures ranging from 600 to 1000°C for 1 h. Samples were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) in plan-view and cross-section. By combined TEM and XRD investigations on the same samples we found a clear difference in the microstructure of the LZO thin films: (i) a nanocrystalline state for T < 800°C with grains 5-10 nm in size (ii) and a polycrystalline state for T > 800°C with an average grain size of up to 200 nm. Thus, the LZO grain size is much smaller than the Ni grain size and the LZO buffer layers are highly biaxially textured, but no epitaxial growth occurs. Grain growth started at 800°C and nanovoid formation and growth occurred during the grain growth process. The nanovoid size was determined to be 10-20 nm and small-angle grain boundaries were observed in the LZO buffer layers. The facetting of the LZO grain boundaries play an important role in the grain growth process, samples annealed at higher temperatures had less strongly facetted grain boundaries than at lower temperatures. On top of the LZO buffer layers YBCO thin films were deposited by PLD and CSD yielding critical current densities of >1 MA/cm2 at 77 K.

Study on the formation of YBCO phase and texture transformation of Ag substrate during the heat treatment of TFA-MOD process

The YBCO films were directly deposited on cold-rolled Ag substrates by MOD (metal-organic deposition) method. The formation of YBCO phase and change of Ag textures were studied during firing precursor films. It was found that YBCO phase starts to be formed at 800°C when Ag {110}<110>texture (most suitable texture for YBCO epitaxial growth) appears. With the increase of firing temperature, pure YBCO phase is obtained and Ag {110}<110>texture gradually becomes stronger. The textures of both {110}<110>texture in Ag substrate and biaxial orientation in YBCO film were optimized after holding the film at 900°C for 30 minutes. Finally, the YBCO film deposited directly on cold rolled Ag substrate has a good biaxial texture, a smooth and dense surface as well as high critical current density of 1.5×104A/cm2. The results show that cold-rolled Ag can be used as a substrate material to directly deposit YBCO film without any buffer layers by MOD method.

Investigation of Early Nucleation Events in Magnesium Oxide During Ion Beam Assisted Deposition

AbstractIon beam assisted deposition (IBAD) is used to biaxially texture magnesium oxide (MgO), which is useful as a template for the heteroepitaxial growth of various thin film devices and most notably as a template layer for high temperature superconductors. Improvements in the quality of IBAD MgO films have been largely empirical and there is uncertainty as to the exact mechanism by which this biaxial texture is developed. Using a specially built quartz crystal microbalance (QCM) as both a substrate and monitor in conjunction with reflected high-energy electron diffraction (RHEED) acting on the same surface, we have probed the initial stages of IBAD MgO growth in-situ. We have correlated corresponding RHEED images with real-time mass accumulation QCM data during the film growth. During IBAD growth, the mass accumulation exhibits a sharp change in slope corresponding to a sudden decrease in growth rate. Corresponding RHEED images show an abrupt onset of crystallographic texture at this point. A simple model incorporating differential etch rates of the MgO film and silicon nitride substrate can be used to fit the data but is inconsistent with the behavior during ion etching with no growth. It is, therefore, postulated that a more complex mechanism is responsible for the observed behavior.

Inducing Grain Alignment in Metals, Compounds and Multicomponent Thin Films

AbstractSeveral methods to induce grain alignment in polycrystalline thin films are discussed, in which directional effects can dominate over the normal evolution of fiber texture during thin film growth. Early experiments with ion beam assisted deposition showed the importance of channeling directions in selecting grain orientations with low sputtering yield or low ion damage energy density. Examples of this approach include the formation of biaxial fiber textures in Nb, Al and AlN. Grain orientations may also be selected by the release of stored energy during abnormal grain growth initiated by solute precipitation (Cu-Co) or phase transformation (TiSi2). Other energy sources such as mechanical deformation, crystallization or compound formation may also contribute to producing desired grain alignments. In multicomponent thin films, combinations of these mechanisms provide opportunities for more specific control of grain orientations.