Noriaki Okazaki

Development of scanning microwave microscope with a lumped-constant resonator probe for high-throughput characterization of combinatorial dielectric materials

A scanning microwave microscope (SμM) for combinatorial characterization of dielectric materials has been developed using a lumped-constant resonator probe. The probe consists of a commercially available microwave oscillator module equipped with a thin conducting needle and an outer conductor ring. The capacitance between needle and ring changes with the dielectric constant of the sample just beneath the needle, which can be detected as a frequency shift of the resonator with high accuracy. The frequency shift values measured for various standard samples lay on a master curve theoretically predicted, which guarantees the quantitative evaluation of the dielectric constant. Applicability of the present system to the characterization of combinatorial samples is demonstrated.

High-throughput characterization of composition-spread manganese oxide films with a scanning SQUID microscope

We have performed high-throughput characterization of composition-spread La 1-x Ca x MnO 3 (LCMO) and Nd 1-x Sr x MnO 3 (NSMO) films, fabricated by the precursor technique, with a scanning SQUID microscope (SSM). In both films, SSM successfully observed spatial variation of magnetic field, corresponding to magnetic phase transitions with respect to chemical composition. The obtained magnetic phase diagrams basically reproduced those reported in bulk materials. However, several distinctive differences have also been noted. For instance, the region identified as a charge ordered insulator in LCMO revealed intense field, suggesting the occurrence of phase separation into ferromagnetic and non-magnetic states. These results confirm that SSM possesses sufficient analytical performance for high-throughput characterization of combinatorial magnetic libraries in composition spread form.

Characterization of LiNb1-xTaxO3 composition-spread thin film by the scanning microwave microscope

Dielectric property of a composition-spread LiNb 1-x Ta x O 3 thin film, fabricated by the combinatorial pulsed-laser deposition (PLD) method, was systematically characterized by the scanning microwave microscope (SμM). Measured frequency shift showed a broad maximum around x = 0.2-0.5, and gradually decreased with x, resulting in a lower dielectric constant in the LiTaO 3 side compared to the LiNbO 3 side. The trend of frequency shift has been revealed to possess a strong correlation with the sharpness of XRD peak, suggesting that lowering of dielectric constant is principally brought about by the degradation of crystallinity.

Quantitative Conductivity Mapping of SrTiO3–LaAlO3–LaTiO3 Ternary Composition-Spread Thin Film by Scanning Microwave Microscope

We carried out quantitative mapping of conductivity σ for the SrTiO3–LaAlO3–LaTiO3 (STO–LAO–LTO) ternary composition-spread thin film by using the scanning microwave microscope (SµM). The σ was evaluated from the shifts in Q-value with reference to the standard Ti1-xNbxO2 composition-spread thin film. Results for the ternary system showed excellent agreement with the literature values of σ in the binary STO–LAO and STO–LTO systems, confirming the accuracy of the present analysis method. An electric phase diagram was proposed for the ternary system based on the quantitative film-conductivity data. Metallic conduction in the ternary system was observed in a wide area close to the STO–LTO side, which gave way to the hopping conduction if LAO component exceeded ca. 35%.

The Development of Scanning Microwave Microscope for High-Throughput Characterization of Dielectric and Conducting Materials at Low Temperatures

We developed a scanning microwave microscope (SμM) designed for characterizing local electric properties at low temperatures. A high-Q λ/4coaxial cavity was used as a sensor probe, which can detect the change of quality factor due to the tip-sample interaction with enough accuracy. From the measurements of combinatorial samples, it was demonstrated that this SμM system has enough performance for high-throughput characterization of sample conductance under variable temperature conditions.

Direct observations of vortices in Bi2212 single crystals by scanning SQUID microscopy

In order to investigate the behaviour of vortices in high-Tc superconductors under low magnetic fields, we performed scanning SQUID microscopy (SSM) on the ab surfaces of Bi2.1Sr1.8Ca(Cu0.98Co0.02)2Oy (Bi2212) single crystals at different temperatures and under different magnetic fields up to 0.8 G. The observed magnetic images clearly demonstrated vortex assembly structures for Bi2212. Vortices trapped inside Bi2212 single crystals tended to be arranged in a one-dimensional manner.

Observation of Compositional Fluctuation by Scanning Superconducting Quantum Interference Device (SQUID) Microscope in Superconducting La1.8Sr0.2CuO4

In order to visualize spatial distributions of vortices strongly pinned in La1.8Sr0.2CuO4, we have performed scanning superconducting quantum interference device (SQUID) microscopic (SSM) measurements near Tc. The obtained SSM images have revealed that stripe-shaped regions with higher Tc run in an arbitrary direction with respect to crystallographic axes. Vortices tend to align in a one-dimensional fashion, negotiating around the higher Tc regions. High-resolution electron probe micro-analysis confirmed that the spatial variation in Tc corresponds well to the modulation of Sr/La composition. We also found that small-angle grain boundaries with tilt angles of 1–3 degrees are less effective in trapping vortices, indicating that superconductivity is not degraded very much.

Development of Label-Free Bioaffinity Sensor Using a Lumped-Constant Microwave Resonator Probe

A novel label-free bioaffinity sensor using a lumped-constant microwave resonator was developed. A gold probe with a spherical tip immobilizing anti-chicken egg albumin antibody or anti-human albumin antibody on its surface was connected to the resonator and inserted into a flow cell to monitor the target antigen binding. The sensor showed specific sensitivity against its target antigen evidenced by the change of resonance frequency after the antigen injection. The large frequency shift observed during the injection of antigen solution was ascribed to the change of solution dielectric constant which showed a systematic increase with antigen concentration.

Direct observation of interlayer Josephson vortices in heavily Pb-doped Bi2Sr2CaCu2Oy by scanning superconducting quantum interference device microscopy

Josephson vortices trapped in cross-sectional edge surfaces of Pb0.6Bi1.4Sr2CaCu2Oy has been directly observed by using a scanning superconducting quantum interference device (SQUID) microscope. The magnetic field distribution Bz around each vortex is substantially anisotropic, compared with the usual vortex in the ab-plane, and is extended over 100 µm toward the in-plane direction. By fitting a theoretical Bz function to experimental ones, c-axis penetration depth λc was estimated to be 11.2 ±0.7 µm, which is in good agreement with the literature value, 12.6 µm, obtained from the Josephson plasma edge frequency.

Local magnetic properties of high-Tc superconductors probed by scanning SQUID microscopy

Abstract We have performed scanning SQUID (superconducting quantum interference device) microscopy (SSM) on the ac -surfaces of heavily Pb-doped Bi2212, Bi 1.6 Pb 0.6 Sr 1.8 CaCu 2 O y , single crystals at low temperatures. The observed images demonstrated interlayer Josephson vortices below T c . The value of c -axis penetration depth, λ c , evaluated from the SSM images was 11.2±0.7 μm, which is approximately one order of magnitude smaller than that of pure Bi2212 in the optimal doping regime. This clearly indicates that Pb doping substantially reduces the anisotropy of Bi2212.