Junya Ishii

Electrical properties of hydroxyapatite thin films grown by pulsed laser deposition

Abstract The formation of bioceramic hydroxyapatite (HAp) thin films has been accomplished on various substrates, such as Ti, α -Al 2 O 3 , SiO 2 //Si(100) and SrTiO 3 (100) using an ArF pulsed laser deposition. The surface morphology of the HAp films was also examined using an atomic force microscope. Au/HAp/Nb doped SrTiO 3 (100) structures have been fabricated to measure the electrical properties of the HAp films, and the dielectric constant and breakdown voltage at 25 °C are 5.7 (at 1 MHz) and 10 4 V cm −1 , respectively. From our results, it is suggested that the HAp films are useful not only as a biocompatible coating material for implantation but also for insulating and dielectric materials used in electric circuits and bio-electronic devices.

a-axis oriented growth of YBa2Cu3O7-y films on LaSrGaO4(100) substrates

We have grown a‐axis oriented YBa2Cu3O7−y (YBCO) films on LaSrGaO4 (LSGO) (100) substrates with (100) oriented seed layer of PrBa2Cu3O7−x (PBCO) using a pulsed laser deposition technique. PBCO films on LSGO (100) deposited even at ∼800 °C exhibits the a‐axis orientation. In this temperature range, PBCO films on SrTiO3 (100) substrate exhibits the c‐axis orientation. The YBCO film with a‐axis orientation was grown on this PBCO(100) layer at a wide range of 650–800 °C. The YBCO films on PBCO free substrates have, on the other hand, c‐axis orientation normal to the surface of the LSGO (100). We found that the preferred orientations of YBCO thin films can be controlled by the presence of PBCO films on LSGO substrate. For the a‐axis orientated YBCO films, the resistance perpendicular to the c axis is 1/2 of that parallel to the c axis, suggesting the preferred orientation of c axis along the surface. The zero resistance superconducting transition temperature (Tc) of the films on the LSGO (100) and PBCO (100)/L...

LaSrGaO4 substrate gives oriented crystalline YBa2Cu3O7−y films

As‐grown YBa2Cu3O7−y (YBCO) thin films of 70 nm thickness have been prepared on LaSrGaO4(001), (100), and (110) single‐crystal substrates at 700 °C using ArF laser ablation deposition. The c‐axis oriented thin films with smooth surface morphology are obtained on LaSrGaO4 (001) and (100) substrates. The zero resistance temperatures (Tc) of the films on the (001) and (100) substrates are 90.0 K, and 88.1 K, respectively. On the (110) substrate, (110) YBCO planes grow epitaxially. The resistance perpendicular to the c axis in this film is 1/3 of that parallel to the c axis, showing Tc⊥=85.9 K and Tc∥=84.4 K, respectively. These results suggest that a LaSrGaO4 substrate having a low dielectric constant is an excellent substrate for the epitaxial growth and device application of high‐Tc YBa2Cu3O7−y superconducting films.As-grown YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}} (YBCO) thin films of 70 nm thickness have been prepared on LaSrGaO{sub 4}(001), (100), and (110) single-crystal substrates at 700 {degree}C using ArF laser ablation deposition. The {ital c}-axis oriented thin films with smooth surface morphology are obtained on LaSrGaO{sub 4} (001) and (100) substrates. The zero resistance temperatures ({ital T}{sub {ital c}}) of the films on the (001) and (100) substrates are 90.0 K, and 88.1 K, respectively. On the (110) substrate, (110) YBCO planes grow epitaxially. The resistance perpendicular to the {ital c} axis in this film is 1/3 of that parallel to the {ital c} axis, showing {ital T}{sub {ital c}{perpendicular}}=85.9 K and {ital T}{sub {ital c}{parallel}}=84.4 K, respectively. These results suggest that a LaSrGaO{sub 4} substrate having a low dielectric constant is an excellent substrate for the epitaxial growth and device application of high-{ital T}{sub {ital c}} YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}} superconducting films.

Pulsed Laser Deposition of Bioceramic Hydroxyapatite Thin Films on Polymer Materials

The ArF excimer laser deposition technique has been used to fabricate bioceramic hydroxyapatite (HAp) thin films on polymer materials such as polyimides (PI), polytetrafluoroethylene (PTFE), silicone rubber (SR), and polyethyleneterephthalate (PET). The crystallinity, structure, composition and surface morphology of HAp films are evaluated by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and atomic force microscopy (AFM). Crystallized HAp films are obtained on PI and PTFE, and mechanical properties of HAp films on the polymer materials are examined using an Instron testing machine. This result is very important to enable the application of organic/inorganic-ceramic composite materials in medical fields.

Epitaxial growth and properties of YBa2Cu3O7−y/LaSrGaO4/YBa2Cu3O7−y trilayer structures

We report the successful synthesis of insulating LaSrGaO4(LSGO) thin films and YBa2Cu3O7−y(YBCO)/LSGO heteroepitaxial multilayer structures using a pulsed laser deposition technique. SrTiO3(STO)(100) was used as a substrate. The formation of highly c‐axis oriented YBCO/LSGO/YBCO trilayer structures is demonstrated. Epitaxial YBCO films on LSGO//STO and LSGO/YBCO//STO have a zero resistance temperature of 88.5 and 88.3 K, respectively. Sandwich‐type YBCO/LSGO/YBCO junctions were produced by a suitable patterning technique. The observed (dI/dV)‐V characteristics exhibit a clear single gap structure (width ∼26 meV) at temperatures below 30 K.

Preparation of all-oxide ferromagnetic/ferroelectric/ superconducting heterostructures for advanced microwave applications

As candidates for functional layers, 3d transition metal oxides with perovskite structures show some interesting properties, such as ferromagnetism, ferroelectricity and superconductivity. Accordingly, combinations of these properties can be used to create new tunable microwave devices. Ferromagnetic/ferroelectric/superconducting multistructures, such as La0.70Sr0.30MnO3 (LSMO)/Pb(Zr0.52Ti0.48)O3 (PZT)/YBa2Cu3O7-y (YBCO) and YBCO/PZT/LSMO, have been fabricated by ArF excimer laser deposition on LaSrGaO4 (LSGO) [001] and (La0.30Sr0.70)(Al0.65Ta0.35)O3 (LSAT) [001] substrates. The resulting trilayer films have a highly c-axis oriented structure. Epitaxial YBCO films formed on PZT/LSMO//LSAT have a zero-resistance temperature of 87 K. Moreover, D-E and M-H hysteresis loop are observed for the LSMO/PZT/YBCO//LSGO structure using a conventional Sawyer-Tower circuit and a superconducting quantum interference device (SQUID). The remanent polarization and coercive field of the PZT layer are found to be 19 µC cm-2 and 275 kV cm-1 at 70 K, respectively. The remanent magnetic moment and coercive magnetic field are about 2.6 µB/site and 50 Oe respectively at 78 K. Furthermore, the microwave surface resistance (RS) (22 GHz) of the YBCO film in the YBCO/PZT/LSMO structure was 1.32 m at 77 K. These results suggest that LSMO/PZT/YBCO structures are favourable for use in superconducting microwave applications such as tunable phaseshifters and filters.

Formation of Hydroxyapatite Thin Films on Surface-Modified Polytetrafluoroethylene Substrates

An ArF excimer laser deposition technique is used to fabricate hydroxyapatite [Ca10(PO4)6(OH)2]-(HAp) thin films on surface-modified polytetrafluoroethylene (PTFE) substrates. The surface of PTFE is modified by a sodium-naphthalene complex in a glycol ether solvent. X-ray diffraction (XRD) studies indicate that as-deposited films prepared at substrate temperatures below the glass transition temperature of PTFE (327°C) are in an amorphous state. The crystallization of as-deposited films needed annealing for 10 h at 310°C. The structure, surface morphology and bond strength of HAp films were evaluated using XRD, the atomic force microscopy (AFM) and the Instron testing machine. The tensile bond strength of HAp films on surface-modified PTFE was 6.0 MPa, which is one order of magnitude larger than that of films on non-surface-modified PTFE, demonstrating its potential for practical applications.

Fluxon propagation on a parallel array of microbridge‐type Josephson junctions

This report describes the experimental results and theoretical considerations of the dynamic behavior and propagation of fluxons on a parallel array of the Nb microbridge‐type Josephson junctions. A parallel array has 10 junctions. The spacing between adjacent junctions in an array is any one of three kinds, 2, 20, and 100 μm. For the array with 2 or 20 μm spacing, the dc current‐voltage (I‐V) characteristic includes a bending affecting the propagation of fluxons. In addition, the oscillation caused by the propagation of fluxons appears if impulse voltage is applied to the input terminal of the array. For the array with 100 μm spacing, on the other hand, the phenomena described above never occur. This report makes the mechanism producing these phenomena clear by numerical calculation of the equation on the equivalent circuit of the array including the measurement circuit.

Formation of YBa2Cu3O7−y/BaTiO3 multistructures by pulsed laser deposition for high‐temperature superconducting device applications

The formation of YBa2Cu3O7−y(YBCO)/BaTiO3(BTO)//SrTiO3(STO) (100) and BTO/ YBCO//STO(100) bilayer structures is demonstrated for the construction of a superconductor ferroelectric field transistor. The resulting films of the bilayers have highly c‐axis oriented structure. Epitaxial YBCO films formed on the BTO//STO(100) have a zero resistance temperature of 88.9 K. The surface morphology of the epitaxial BTO films on the YBCO//STO is very smooth with a mean surface roughness of 32 A. Moreover, the Au/BTO/YBCO structures have been fabricated, and the dielectric constant and remanent polarization of BTO layer are obtained to be 180 and 3.5 μC/cm2 at 77 K, respectively.

a-Axis oriented epitaxial YBa2Cu3O7-y/PrBa2Cu3-xNbxO7-z multistructures

Using the pulsed laser deposition technique, we have successfully prepared a‐axis oriented PrBa2Cu3−xNbxO7−z (PBCNO)(x=0–1.5) films and YBa2Cu3O7−x (YBCO)/PBCNO heterorepitaxial multilayer structures. For the PBCNO films, the resistivity showed semiconducting behavior at all Nb substitution levels investigated. The resistivity increased with increasing Nb content, reaching a value of 104 Ω cm at 100 K for a 300‐A‐thick film with x=1.0. Using (100)SrTiO3 (STO) as a substrate, the following multilayer structures were successfully formed: (100)PBCNO(x=1.0)/(100)YBCO/(100)PBCO//STO, (001) YBCO/(100)PBCNO(x=1.0)/(100)PBCO//STO, and (100)YBCO/(100)PBCO/(100)PBCNO(x=1.0)/(100)PBCO//STO. The bottom and top YBCO layers in the (100)YBCO/(100)PBCO/(100)PBCNO/(100)PBCO/(100)YBCO//STO structure showed superconducting transition temperatures (zero resistance) of 82 and 83 K, respectively. The interlayer resistivity of the 200‐A‐thick PBCNO(x=1) interlayer was as high as 105 Ω cm at 30 K.