Tae-Youb Kim

Novel nanoparticle milling process for Bi-YIG dispersed transparent films

We developed a high-performance milling process with a grooved mill pot. The milling process is able to make highly transparent dispersed materials. Bi/sub 1.8/Y/sub 1.2/Fe/sub 5/O/sub 12/ nanoparticles were prepared with coprecipitation and annealing processes. The nanoparticle dispersed films were prepared with the milling process and a conventional process. The crystallite sizes of the Bi/sub 1.8/Y/sub 1.2/Fe/sub 5/O/sub 12/ particles in the milled films were 40-50 nm. These sizes were about half that of the films prepared by conventional process. The films containing the particles show high transparency. The light-absorption coefficients of the films were about half that of the films prepared by the conventional process. Magnetooptical properties were also improved. The milling process produces films with a high figure of merit, which is the value of Faraday rotation angle divided by light-absorption coefficient. The milling period was shorter than that of the conventional process.

Holographic image generation with a thin-film resonance caused by chalcogenide phase-change material

The development of digital holography is anticipated for the viewing of 3D images by reconstructing both the amplitude and phase information of the object. Compared to analog holograms written by a laser interference, digital hologram technology has the potential to realize a moving 3D image using a spatial light modulator. However, to ensure a high-resolution 3D image with a large viewing angle, the hologram panel requires a near-wavelength scale pixel pitch with a sufficient large numbers of pixels. In this manuscript, we demonstrate a digital hologram panel based on a chalcogenide phase-change material (PCM) which has a pixel pitch of 1 μm and a panel size of 1.6 × 1.6 cm2. A thin film of PCM encapsulated by dielectric layers can be used for the hologram panel by means of excimer laser lithography. By tuning the thicknesses of upper and lower dielectric layers, a color-selective diffraction panel is demonstrated since a thin film resonance caused by dielectric can affect to the absorption and diffraction spectrum of the proposed hologram panel. We also show reflection color of a small active region (1 μm × 4 μm) made by ultra-thin PCM layer can be electrically changed.

Modified ion sensitive field effect transistor sensors having an extended gate on a thick dielectric

Modified ion sensitive field effect transistors having an extended gate (EG) on a thick dielectric have been developed to obtain extremely high sensitivity. The capacitance of the EG is controlled to be very small via the thickness of the dielectric layer so that it may be ignored when compared with the gate capacitance of the transistor. As a result, the gate voltage can be fully dependent on the surface charge of the EG. When microalbumin protein of concentration 1 μg/ml on a monoclonal antibody of a microalbumin surface of the EG is injected, an extremely high sensitivity of 1800% is observed.

Biosensors using the Si nanochannel junction-isolated from the Si bulk substrate

The biosensor using a silicon nanochannel field effect transistor has been developed on the basis of a bulk silicon substrate instead of an expensive silicon-on-insulator material, for low cost applications. “Top-down” fabricated Si nanochannels for detecting prostate specific antigen (PSA) are electrically isolated from the bulk Si substrate only by a reverse-biased p-n junction with very low reverse leakage currents. The reverse leakage current flowing through the p-n junction is small enough to be ignored, when compared with the current flowing through the p-type Si channel; roughly 100 times lower. The surface immobilization of anti-PSA has been confirmed by the specific binding test of DNA stabilized Au nanoparticles (NPs), showing 1200 NPs/μm2 and atomic force microscopy surface analysis. The injection of 10 ng/ml PSA solutions leads to a clear increase in the conductance of Si nanochannels, indicating the specific binding of PSA with the immobilized anti-PSA. The similar signal changes were observe...

Transmission electron microscopy estimation of Bi–YIG nanoparticle hybridized with plastic material

We have developed a magneto-optical Bi1.8Y1.2Fe5O12 nanoparticle hybrid material and milling system. The Bi1.8Y1.2Fe5O12 nanoparticles were prepared with a coprecipitation and annealing processes. The 100 h milling nanoparticle system has θF about 1×103 degrees/cm but it has very small Ms (∼2.5 emu/cm3). In this material system, the particle size and crystalline size of the nanoparticles were estimated with a transmission electron microscope and transmission electron diffraction methods. The crystal phase sizes of the Bi1.8Y1.2Fe5O12 nanoparticles are the same as the nanoparticle sizes. The high-powered transmission electron microscope images show moire fringes of the nanoparticles. The 5–8 nm particles are primary nanoparticles. We show a possibility of the synthesis for the crystalline nanoparticles dispersed in hybrid materials by mechanical milling process.

Magnetic domain structure of growth temperature-gradient Sm2Mo2O7 thin film investigated by scanning SQUID microscopy

Abstract Recently spin frustrated pyrochlore A2B2O7 has attracted much attention. In this study, we have observed the domain structure of pyrochlore molybdate Sm2Mo2O7 epitaxial thin film fabricated with growth temperature-gradient method by a scanning SQUID microscope. The temperature dependence of domain structure has been investigated in detail.

New Analysis on the Interface Trap States at Schottky Contact

We present a simple equivalent circuit model that represents the charging dynamics of the interface states of Schottky diodes in the reverse bias condition. The interface trap states of an erbium‐silicided Schottky diode are investigated from AC admittance measurement. The trap densities and the capture and emission transition times are extracted by using the equivalent circuit model..

Scanning SQUID microscopy on composition-spread NdSrMnO films under irradiation

Abstract Local magnetic properties of composition-spread Nd1−xSrxMnO3 (NSMO; x=0.4–0.6) films were surveyed by a scanning SQUID microscope under irradiation. We have found that the spontaneous magnetization of the FM phase is significantly enhanced by the laser irradiation ( λ=532 nm ), while the phase boundary is essentially unchanged.