In-plane Aligned Research Articles

Scalable anisotropic cooling aerogels by additive freeze-casting

Cooling in buildings is vital to human well-being but inevitability consumes significant energy, adding pressure on achieving carbon neutrality. Thermally superinsulating aerogels are promising to isolate the heat for more energy-efficient cooling. However, most aerogels tend to absorb the sunlight for unwanted solar heat gain, and it is challenging to scale up the aerogel fabrication while maintaining consistent properties. Herein, we develop a thermally insulating, solar-reflective anisotropic cooling aerogel panel containing in-plane aligned pores with engineered pore walls using boron nitride nanosheets by an additive freeze-casting technique. The additive freeze-casting offers highly controllable and cumulative freezing dynamics for fabricating decimeter-scale aerogel panels with consistent in-plane pore alignments. The unique anisotropic thermo-optical properties of the nanosheets combined with in-plane pore channels enable the anisotropic cooling aerogel to deliver an ultralow out-of-plane thermal conductivity of 16.9 mW m−1 K−1 and a high solar reflectance of 97%. The excellent dual functionalities allow the anisotropic cooling aerogel to minimize both parasitic and solar heat gains when used as cooling panels under direct sunlight, achieving an up to 7 °C lower interior temperature than commercial silica aerogels. This work offers a new paradigm for the bottom-up fabrication of scalable anisotropic aerogels towards practical energy-efficient cooling applications.

Hierarchical formation mechanism of anisotropic magnetite microflakes and their superior microwave attenuation properties

In the preparation of the α-Fe2O3 particles, the size, thickness, morphology and size distribution were controlled by adding silicon and magnesium salts as surfactants, and finally the fine hexagonal α-Fe2O3 microflakes with a diameter of 1.8 μm and a thickness of 200 nm were obtained. This synthesis method provides some ideas for the manufacture of well-defined α-Fe2O3 particles. In-plane aligned composites made from reduced microflakes were prepared by a vacuum infiltration method. The hysteresis loops of the composites with in-plane alignment of the microflakes were obtained by applying the external magnetic field parallel and perpendicular to the composite sample plane. It is obviously exhibited that the composites are easily magnetized along the sample plane. According to the results of magnetic and microwave measurement, aligned composites have higher permeability and magnetic loss, which lead to a better microwave absorption performance than that of random composites. Especially when the thickness is 5 mm, the minimum RL value of aligned composites (−41.67 dB) is enhanced by 258%, compared with that of random composites (−16.11 dB). This would open up the possibility of using the in-plane alignment method to improve the microwave absorbing property and expand the range of practical applications of absorbers.

Structural and thermoelectric properties of Bi2Sr2Co2Oy thin films on LaAlO3 (100) and fused silica substrates

We have grown Bi2Sr2Co2Oy thin films on LaAlO3 (100) and fused silica substrates by pulsed laser deposition. The films on LaAlO3 are c-axis oriented and partially in-plane aligned with multiple domains, while the films on fused silica are preferred c-axis oriented without in-plane alignment. The Seebeck coefficient and resistivity of films on both substrates are comparable to those of single crystals. An oxide p-n heterojunction was formed by depositing Bi2Sr2Co2Oy film on Nb-doped SrTiO3 single crystal, which showed a rectifying behavior. These thin films and heterostructures may be used for future thermoelectric applications.

Surface Tension and Fluid Flow Driven Self-Assembly of Ordered ZnO Nanorod Films for High-Performance Field Effect Transistors

Colloidal nanorods of inorganic semiconductors are of interest for a range of optoelectronic devices. The ability to self-assemble these materials into ordered arrays by solution-processing techniques is crucial for achieving adequate device performance. Here we show that uniform ZnO nanorod films with defined nanorod alignment can be solution-deposited over large areas by controlling the surface energy of the nanorods through the choice of suitable ligands and by the fluid flow direction during growth. ZnO nanorods with long carbon chain ligands exhibit a smaller surface free energy than those with short carbon chain ligands resulting in better in-plane alignment and large domain sizes up to dozens of micrometers in spin-coated films. A model is presented to rationalize the observed self-assembly behavior. It is based on the formation of a lyotropic liquid crystalline phase on the surface of the liquid film which is facilitated by enhanced segregation of nanorods with low surface tension to the surface. Alignment of the nanorods is controlled by radial and vertical liquid flows in the drying solution. The ability to control the orientation of the nanorods and to achieve large domain size results in significant device performance improvement. Field-effect transistors with mobilities of up to 1.2-1.4 cm2/V.s are demonstrated in spin-coated, in-plane aligned ZnO nanorod films subject to postdeposition hydrothermal growth.

Formation of biaxial texture in metal films by selective ion beam etching

The formation of in-plane texture via ion bombardment of uniaxially textured metal films was investigated. In particular, selective grain Ar ion beam etching of uniaxially textured (0 0 1) Ni was used to achieve in-plane aligned Ni grains. Unlike conventional ion beam assisted deposition, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux. The initial uniaxial texture is established via surface energy minimization with no ion irradiation. Within this sequential texturing method, in-plane grain alignment is driven by selective etching and grain overgrowth. Biaxial texture was achieved for ion beam irradiation at elevated temperature.

Improvement of in-plane alignment for surface oxidized NiO layer on textured Ni substrate by two-step heat-treatment

Epitaxial growth of NiO on a textured Ni substrate as a template for an REBa 2Cu 3O y coated conductor was investigated. Highly in-plane aligned NiO layers were successfully fabricated using a new process of a two-step heat-treatment for oxidation. In the first-step, a highly in-plane aligned thin NiO layer was formed on a textured Ni substrate under a low driving force of oxidation. Then, in the second-step, a thick NiO layer was grown at a higher rate with maintaining its high in-plane grain alignment, as if the first NiO layer acts as a seed crystal layer. Further, growth rates and microstructures of the NiO layers were studied comparatively in the cases with and without the first layer. It was found that the oxidation rate in the case with the first layer was lower than that without the first layer. The microstructure observation revealed that the NiO without the first layer was poly-crystalline with many grain-boundaries. On the other hand, in the case with the first layer, grain-boundaries of the NiO were hardly observed. Hence, the reason for this difference of the growth rate and the microstructure of the NiO layers were discussed in view of a diffusivity path.

金属基板上へのRE123のLPE成膜

RE123 superconductive oxides are expected to be utilized for electric conductors due to its high superconducting performance at 77 K. The liquid phase epitaxy (LPE) process has an advantage to fabricate a thick superconducting layer at a high growth rate with high superconducting properties for realizing high Jc conductors. We tried two structures to fabricate in-plane aligned Y123 layer on textured Ni substrates with SOE-NiO. One was a double layered LPE structure and the other was a non-reactive buffered structure using a BaZrO3 buffer layer. The in-plane aligned Y123 LPE layer was successfully grown on an NiO/Ni textured substrate for each structure and the Tc value of 90 K was achieved in the non-reactive buffered structure. The in-plane alignment of the seed layer was found to be a crucial factor for the double LPE process since the partial dissolution of worse aligned seed crystals caused formation of non-coverage regions on the surface of the NiO buffer layer, where the NiO buffer layer would react with the solution during the second LPE processing.

Development of in-plane aligned YBCO tapes fabricated by inclined substrate deposition

High temperature superconducting thin film tapes, which consist of a flexible metal substrate, buffer layer, and Y 1Ba 2Cu 3O x (YBCO) layer have been developed for power application. Ni-alloy tape was used as the substrate. Both the YBCO layer and the buffer layer were formed by pulsed laser deposition (PLD) because of an advantageous of high deposition rate. Inclined substrate deposition (ISD) was developed to introduce in-plane alignment for the buffer layer on the non-textured metal substrate. YBCO films epitaxially deposited on the ISD buffer layer by normal PLD had high J c values over 10 5 A/cm 2 at 77 K. For verification of high rate productivity of the PLD/ISD method, we demonstrated high rate deposition of the yttria stabilized zirconia buffer layer and YBCO superconducting layer. We also performed continuous deposition of over 10 m YBCO thin film tapes with a reel-to-reel substrate transfer system combined with 200 W high power laser equipment.

Preparation of MgO films on metal substrate as a buffer layer for liquid phase epitaxy processed RE123 coated conductor

The fabrication process of in-plane aligned MgO films on metal substrate as a buffer layer for liquid phase epitaxy (LPE) processed RE123 (RE123: RE=Y, Sm, Nd…) coated conductor was developed using the inclined substrate deposition (ISD) method with electron-beam evaporation. The texture development was investigated and a growth mechanism of in-plane alignment was discussed. Although the in-plane alignment of MgO can be obtained due to ISD, the reaction between metal substrate and high temperature melt cannot be prevented by the layer because of the presence of column spacings. Then, a two-step deposition process was developed for LPE method. The first layer was deposited by the ISD to obtain the in-plane alignment and the second layer was deposited at high temperature to realize the full coverage which is necessary to prevent the reaction between metal substrate and MgO-saturated Ba–Cu–O melt. This two-step deposited MgO buffer layers realize both the in-plane alignment and prevention of the reaction, and make the LPE process enable to apply for coated conductors.

In-plane alignment of YBa/sub 2/Cu/sub 3/O/sub 7-y/ films realized by CeO/sub 2/ buffer layer on textured Ag{100}>001< tapes

Homogeneous in-plane aligned YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) films on long metallic substrates are required for power applications. In order to establish in-plane aligned YBCO films, we have been studying Ag{100}<001> textured tapes buffered with a [001]-oriented CeO/sub 2/ layer. The YBCO and CeO/sub 2/ films were deposited by pulsed laser deposition (PLD). The CeO/sub 2/ deposition rate was 900 /spl Aring//min. The CeO/sub 2/ films on Ag{100}<001> textured substrates mere [100]-oriented and highly in-plane aligned. The YBCO films deposited by PLD on CeO/sub 2/ buffered Ag substrates also have c-axis oriented and good in-plane alignment. T/sub c/ and J/sub c/ values of the YBCO films were 81 K and 1/spl times/10/sup 4/ A/cm/sup 2/ at 77 K, respectively.

In-plane aligned YBCO thick films on {110} rolled and single crystal silver by ultrasonic mist pyrolysis

An ultrasonic mist pyrolysis system has been used to fabricate thick films of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) on rolled and single crystal silver substrates. The substrates were heated to 900/spl deg/C and nitrate solutions of the constituent cations were sprayed using a nitrogen carrier gas. Highly c-axis aligned YBCO films were obtained by deposition at a rate of /spl sim/1 /spl mu/m per minute. Phase pure YBCO formed up to a limit of /spl sim/6 /spl mu/m. For thicker films, BaCuO/sub 2/ and Y/sub 2/BaCuO/sub 5/ also formed. On {110} oriented single crystal silver, the films showed in-plane alignment with a four fold symmetry, and the FWHM in the azimuthal direction of the main peaks was /spl sim/3/spl deg/. On the polycrystalline substrate the in-plane texture showed a /spl sim/20/spl deg/ FWHM, equivalent to that of {110} textured silver substrate. The onset of superconducting transition was measured as /spl sim/90.2K for sample with a film thickness of /spl sim/5 /spl mu/m.

Fabrication and Microstructure of All In-plane Aligned A-Axis Oriented Superconductor/Insulator/Superconductor Junctions

All in-plane aligned a-axis oriented YBa2Cu3Ox/Gd2CuO4/YBa2Cu3Ox superconductor/insulator/superconductor (SIS) junction structures are fabricated by a pulsed laser deposition technique and their microstructures are characterized. An insulating barrier of Gd2CuO4 with an atomic graphoepitaxial relation is selected from a lattice-matching point of view for the b- and c-axes of YBa2Cu3Ox at a deposition temperature of the YBa2Cu3Ox films. Preferred orientations and in-plane alignments of electrodes of YBa2Cu3Ox films and barriers of Gd2CuO4 films are confirmed by X-ray diffraction spectroscopy and an X-ray φ-scan technique. X-ray diffraction measurements revealed that all the YBa2Cu3Ox/Gd2CuO4/YBa2Cu3Ox films are a-axis oriented. The c-axes of the layers are also in-plane aligned.

In-plane aligned YBa 2Cu 3O 7− x film on the MgO buffered Ag(100) substrate and {100}[001] cubic textured silver tape

We have fabricated an in-plane aligned YBa 2Cu 3O 7− x (Y123) film on Ag(100) single crystalline substrate and {100}[001] cubic textured silver tape by the liquid phase epitaxial (LPE) method. In order to improve the in-plane alignment of the Y123 film, a 500-nm-thick MgO buffer layer deposited by reactive pulsed laser deposition is inserted between the silver substrate and Y123. The deposited MgO buffer layer showed good in-plane alignment. LPE-grown Y123 thick film on the MgO buffer layer was highly c-axis oriented and showed good epitaxial in-plane alignment. The observed orientation is explained by the near coincident site lattices (NCSL) model.

Deposition of biaxially aligned YSZ films on inclined polycrystalline metallic substrates for YBa 2Cu 3O 7− δ tapes

We report on a method to deposit biaxially aligned yttria stabilised zirconia (YSZ) films on polycrystalline metallic substrates by laser ablation at room temperature, and demonstrate the fabrication of in-plane aligned, c-axis oriented. YBa 2Cu 3O 7− σ (YBCO) films with these (001) biaxially textured YSZ buffer layers. The crystallographic orientation of the YSZ layer depends strongly on the deposition conditions. The growth direction perpendicular to the substrate plane can be adjusted between the (001) and the (111) direction by varying the substrate temperature from room temperature to 400°C. In-plane alignment of either orientation can be achieved by simply inclining the substrate normal by 55° away from the plume axis. This inclination does not significantly affect the orientation perpenndicular to the substrate surface. The subsequent deposition of YBCO films on (001) in-plane aligned YSZ yielded epitaxial films as shown by X-ray measurements. Critical current measurements on wet chemically etched tracks resulted in 1.2 × 10 5 A/cm 2 in zero field at 77 K.

Synthesis of in-plane aligned, a-axis oriented RBa 2Cu 3O 7-δ (R [dbnd]Y, Nd) films on LaSrGaO 4 substrates with Gd 2CuO 4/PrBa 2Cu 3O 7-δ buffer layers

We fabricated in-plane aligned, a-axis oriented YBa 2Cu 3O 7-δ (YBCO) films and NdBa 2Cu 3O 7-δ films on (100) LaSrGaO 4 (LSGO) substrates using Gd 2CuO 4/PrBa 2Cu 3O 7-δ buffer layers by laser ablation. Using these buffer layers, we could deposit the a-axis oriented YBCO films on LSGO substrates at the substrate temperature 20–60 °C higher than the case of the ordinary template method. Through the deposition at higher substrate temperatures, the degree of in-plane alignment and T c of the YBCO films on LSGO substrates were much higher than those without these buffer layers.

Study of the growth mechanism of highly in-plane aligned α-axis YBa2Cu3O7−x thin films on LaSrGaO4 substrate by high resolution electron microscopy

Highly in-plane aligned α-axis YBa2Cu3O7−x thin films deposited on (100) LaSrGaO4 substrates by a self-template method were studied by high-resolution electron microscopy along three orthogonal 〈100〉 axes of the substrate. Plan-view images confirm that the majority of the film preferentially aligns across the entire substrate except for very few misaligned domains with average size 10 nm2. Cross-sectional images along the [100] orientation of YBa2Cu3O7−x reveal that in-plane aligned α-axis YBa2Cu3O7−x is grown on a template layer dominated by c-axis oriented film. This strongly suggests that the in-plane alignment of α-axis YBa2Cu3O7−x thin films on (100) LaSrGaO4 substrates is governed by the different stresses along the b and c axes of the substrate. Cross-sectional images along [001] of the YBa2Cu3O7—x thin film reveal that the 90° domains easily nucleate in the region between α-axis YBa2Cu3O7—x and the YBa4Cu3Ox phase. Cracks along the (001) plane of YBa2Cu3O7−x are found to be due to the large mismatch between the c parameters of the thin film and substrate.

Superconducting and structural properties of in-plane aligned a-axis oriented YBa2Cu3O7−x thin films

We report the superconducting and structural properties of a-axis oriented YBa2Cu3O7−x (YBCO) films as a function of deposition temperature of PrBa2Cu3O7−x (PBCO) template layers. X-ray diffraction (XRD) analysis revealed the orientation relationship in which the b axis of the PBCO template layers and the a axis of the YBCO films were normal to the LaSrGaO4 (100) substrate surface. In-plane aligned a-axis oriented YBCO films having a zero resistance temperature of 88 K and an anisotropy ratio of resistivity of 11.5 at 275 K were obtained on PBCO template layers deposited at 630 °C among the deposition temperatures ranging from 600 to 650 °C at intervals of 10 °C. The degree of in-plane alignment of the a-axis oriented YBCO films which was estimated by the ratio of relative intensity at 90° and 180° in the XRD φ scan of the (102) YBCO peak was 0.5, 0.045, and 0.053 for the films on PBCO templates deposited at 620, 630, and 640 °C, respectively. In conclusion, the deposition temperature of PBCO template layers is critical to fabricate the in-plane aligned a-axis oriented YBCO films on LaSrGaO4 (100) substrates.

Crystallization and in-plane alignment behavior of YBa2Cu3O7−y films on MgO(001) prepared by the dipping-pyrolysis process

The effects of annealing temperature and oxygen partial pressure [p(O2)] were investigated on the crystallization and orientation of YBa2Cu3O7−y (YBCO) films on MgO(001) prepared by the dipping-pyrolysis process. The c-axis oriented films without in-plane alignment were prepared by annealing in the YBCO-unstable region, i.e., at low initial p(O2) of 10−4−10−3 atm and 950 °C followed by O2 treatment, through intermediate Y2BaCuO5 and liquid phase. In-plane aligned c- or c/a-axis films were prepared by similar heat treatment with an initial p(02) of 10−4 atm and 900–925 °C through a mixture of BaCu2O2 and YBa3Cu2O6+x. In contrast, nonoriented YBCO films were obtained by annealing at higher initial p(O2)'s and lower temperatures, i.e., by direct reaction among Y2O3, BaCO3, and CuO.

Deposition of in-plane aligned YBa 2Cu 3O y/Y 2O 3 stabilized ZrO 2 thin films on both sides of metallic tape substrates

An attempt was made to deposit in-plane aligned YSZ thin buffer layers on both sides of metallic tape by modifying the bias sputtering technique. Using these substrates, it has been demonstrated that YBa 2Cu 3O y films with critical current densities ( J c) of around 10 5 A/cm 2 (77 K, 0 T) can be successfully deposited on both sides of the tape simultaneously by a laser ablation technique. A high degree of in-plane grain alignment was observed in our YBa 2Cu 3O y films, which resulted in comparatively high J c values for the polycrystalline films. The proposed technique is pointed out as a potential method towards the fabrication of a tape conductor.