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.
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.
In order to realize superconductive microwave devices with large tuning characteristics, we have studied a mechanically tunable superconductive resonator beneath a dielectric and/or magnetic floating plate (FP) as a first step. The resonator consists of a half-wavelength coplanar waveguide (CPW). The principle of the mechanically tunable method is that variations of the effective permittivity and/or the effective permeability for the microwave waveguide line can be obtained by changing the distance between the resonator and the FP. In computer simulations of electromagnetic fields for the mechanically tunable half-wavelength CPW resonator, we have obtained a large shift of the resonant frequency with a band of 1.75 GHz to 7 GHz (tunability is approximately 25%) using the (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) single crystal (dielectric constant (εr) = 22.8, loss tangent (tanδ) = 1.7 × 10−4) as the FP. Based on the results, we have performed an experiment using a half-wavelength CPW resonator made from YBa2Cu3O7−δ thin film and the LSAT FP. The result shows a drastic resonant frequency shift of approximately 1.36 GHz (tunability is approximately 20%) when the LSAT FP is moved, using an electromagnetic actuator. In this experiment, it is also noted that the insertion loss is quite low, less than 0.8 dB, compared to previous reports for various tunable filters. Moreover, we have also measured the tuning characteristics with a TiO2 single crystal (εr = 85.4, tanδ = 2.5 × 10−4) as the FP. As a result, we have obtained quite large tuning characteristics of approximately 2 GHz (tunability is approximately 28%).
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