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We investigated the dependence of ZnO crystal plane on hydrogen sensing properties using Pt Schottky diodes on nonpolar m-plane ZnO (m-ZnO) and Zn-polar c-plane (0001) ZnO (c-ZnO) bulk substrates. Both of the Pt/ZnO Schottky diode sensors showed the increase in forward and reverse currents when exposed to hydrogen gas at room temperature. The maximum relative current change of m-ZnO diode sensor was measured to be 2748%, which was 3 times higher than that of the c-ZnO diode (844%). The current responses of both the Pt/ZnO diode sensors increased almost linearly with log of hydrogen concentrations. The Pt/m-ZnO Schottky diode showed promising results for the use in hydrogen gas detection at room temperature, possibly due to more active sites available on m-ZnO surface for hydrogen adsorption.

AlGaN/GaN heterostructure Schottky diodes with ZnO nanorod functionalization are shown to be capable of detecting NH3 balanced with air at a concentration of [?]0.3 ppm at 25degC and [?]0.1ppm at 300degC. The diodes show reproducible current response to repeated cycling of the NH3 exposure at all temperatures in this range. The diode current at fixed voltage decreased upon exposure to the NH3, which is opposite to what occurs with exposure to hydrogen. This suggests the detection mechanism involves reaction of ammonia with oxygen species on the ZnO nanorods, increasing the negative charge on the interface with AlGaN. The detection sensitivity displayed an activation energy of 0.071 eV and increased monotonically with ammonia concentration at all temperatures, from 3.36% (25degC) to 12.59% (300degC) for 2 ppm at a voltage of 5 V. The diodes could detect ammonia for either polarity applied bias. The absolute current change and sensitivity upon exposure to ammonia increased with measurement temperature.

Poly(methyl methacrylate) (PMMA) encapsulated Pt-AlGaN/GaN Schottky diodes show highly sensitive (100 ppm, 0.01% by volume) room temperature detection of hydrogen and are insensitive to the presence of water in the sensing ambient. These diodes show no physical degradation or loss of sensitivity when repeatedly cycled (50 x, 1 min hold at each temperature) between 25-100degC. There is complete selectivity for hydrogen sensing over other gases, including CO, CO2, NO2, O2 and CH4. The PMMA encapsulation provides an effective and robust barrier to moisture, greatly increasing the range of environments in which the sensors can be used.

We report on the dielectric properties of non-polar a-plane (11-20) GaN (a-GaN) films in the terahertz (THz) frequency region, using THz time domain spectroscopy. We measured the transmitted THz time-domain waveforms by rotating the phi angle for 6um-thick a-GaN films, which were lifted off from sapphire substrates. THz transmittance of a-GaN films clearly showed the angular dependence on azimuth angle, possibly due to the birefringence and optical phonon modes in a-GaN crystal. It is believed that the discrepancy in the refractive index results from the difference of the transverse-optical and the longitudinal optical phonon branches.

AlGaN/GaN HEMT based hydrogen sensor incorporating poly(methyl methacrylate) (PMMA) membrane was fabricated. The maximum sensitivities of 2.6x105% were obtained for both dry and humid 500 ppm hydrogen. The PMMA layer effectively permits the approach of hydrogen molecules to catalytic platinum surface, while blocking the penetration of water molecules. The PMMA encapsulated device also showed reliable hydrogen gas sensing characteristics even after 25- 100degC heating cycle stress.

AlGaN/GaN high electron mobility transistor based carbon dioxide sensor with ZnO nanorods as a sensing material was fabricated. The response of the device to carbon dioxide gas was characterized at elevated measurement temperature. The transistor showed an increase in drain current upon 500 ppm CO2 due to the enhanced electron channel at the interface of AlGaN and GaN from 150degC. Reliable repeatability to cyclic exposures of various concentrations of carbon dioxide gas was observed. Also, effect of humidity on sensing behavior was investigated.

Silver Schottky diode on AlGaN/GaN high electron mobility transistor structure was investigated for the application of ethanol sensing. The device showed the decrease of current upon ethanol exposure from the measurement temperature of 200@C due to the increase in Schottky barrier height. At 250@C, the stable and fast current changes depending on the exposed ethanol concentrations from 0.0058 to 5.8% were observed.

The use of Ag in the gate region of AlGaN/GaN heterostructure diodes is shown to provide stable, reversible changes in barrier height and thus current during exposure to ethanol at 250degC. The exposed ethanol molecules are adsorbed on the silver and oxidized, resulting in the increase of Schottky barrier height. The detection limit of ethanol at this temperature was 58 ppm, and the sensor response was linear over the range 58-58700 ppm. For the high end of this concentration range (5.87%), ethanol exposure at 250degC caused the Schottky barrier height to change from 0.604 eV to 0.656 eV, which produced a forward current relative change of 45.4% at 0.9V forward bias. The results are competitive with detection of ethanol by oxide thin films or nanostructures of SnO2, Fe2O3, CuO, and ZnO.

The imaging capability of optical coherence microscopy (OCM) has great potential to be used in neuroscience research because it is able to visualize anatomic features of brain tissue without labeling or external contrast agents. However, the field of view of OCM is still narrow, which dilutes the strength of OCM and limits its application. In this study, we present fully automated wide-field OCM for mosaic imaging of sliced mouse brains. A total of 308 segmented OCM images were acquired, stitched, and reconstructed as an en-face brain image after intensive imaging processing. The overall imaging area was 11.2×7.0  mm (horizontal×vertical), and the corresponding pixel resolution was 1.2×1.2  μm. OCM images were compared to traditional histology stained with Nissl and Luxol fast blue (LFB). In particular, the orientation of the fibers was analyzed and quantified in wide-field OCM.

We investigated the hydrogen sensing characteristics of Pt Schottky diodes on and (010) b-Ga2O3 bulk crystals. The Pt Schottky diodes on b-Ga2O3 wafer exhibited the fast, reversible, and cyclic response upon hydrogen exposure. The maximum value of the relative current change of the Ga2O3 diode sensor was as high as 7.86 x 107 (%) at 0.8 V, which is slightly higher than that of the (010) Ga2O3 diode. The hydrogen responses of both b-Ga2O3 diode sensors are believed to result from oxygen and gallium atomic configurations of Ga2O3 surfaces for hydrogen adsorption. The Pt Schottky diodes of Ga2O3 wafers did not show any clear response to other gases, such as N2, CO, CO2, O2, CH4, NO2, and NH3. Our finding suggests that the Pt Schottky diodes on b-Ga2O3 hold great potential for the applications of hydrogen gas sensors with high sensitivity and selectivity.

We manufactured and characterized a silicon micro-strip detector to be used in a beam tracker. A silicon detector features a DC-coupled silicon strip sensor with VA1_Prime2 analog readout chips.The silicon strip sensors have been fabricated on 5-in. wafers at Electronics and Telecommunications Research Institute (Daejeon, Korea). The silicon strip sensor is single-sided and has 32 channels with a 1 mm pitch, and its active area is 3.2 by 3.2 cm2with 380 μm thickness. The readout electronics consists of VA hybrid, VA Interface, and FlashADC & Control boards. Analog signals from the silicon strip sensor were being processed by the analog readout chips on the VA hybrid board. Analog signals were then changed into digital signals by a 12 bit 25 MHz FlashADC. The digital signals were read out by the Linux-operating PC through the FlashADC-USB2 interface. The DAQ system and analysis programs were written in the framework of ROOT package.The beam test with the silicon detector had been performed at CERN beam facility. We used a 150 GeV electron beam out of the SPS(Super Proton Synchrotron) H2 beam line. We present beam test setup and measurement result of signal-to-noise ratio of each strip channel.

We investigated the dependence of ZnO crystal plane on hydrogen sensing properties using Pt Schottky diodes on nonpolar m-plane (101¯0)ZnO (m-ZnO) and Zn-polar c-plane (0001) ZnO (c-ZnO) bulk substrates. Both of the Pt/ZnO Schottky diode sensors showed the increase in forward and reverse currents when exposed to hydrogen gas at room temperature. The maximum relative current change of m-ZnO diode sensor was measured to be 2748%, which was 3 times higher than that of the c-ZnO diode (844%). The current responses of both the Pt/ZnO diode sensors increased almost linearly with log of hydrogen concentrations. The Pt/m-ZnO Schottky diode showed promising results for the use in hydrogen gas detection at room temperature, possibly due to more active sites available on m-ZnO surface for hydrogen adsorption.

We investigated the hydrogen sensing characteristics of Pt Schottky diodes on (2¯01)and (010) β-Ga2O3bulk crystals. The Pt Schottky diodes on β-Ga2O3wafer exhibited the fast, reversible, and cyclic response upon hydrogen exposure. The maximum value of the relative current change of the (2¯01)Ga2O3diode sensor was as high as 7.86 × 107(%) at 0.8 V, which is slightly higher than that of the (010) Ga2O3diode. The hydrogen responses of both β-Ga2O3diode sensors are believed to result from oxygen and gallium atomic configurations of Ga2O3surfaces for hydrogen adsorption. The Pt Schottky diodes of Ga2O3wafers did not show any clear response to other gases, such as N2, CO, CO2, O2, CH4, NO2, and NH3. Our finding suggests that the Pt Schottky diodes on β-Ga2O3hold great potential for the applications of hydrogen gas sensors with high sensitivity and selectivity.

AlGaN/GaN heterostructure Schottky diodes with ZnO nanorod functionalization are shown to be capable of detecting NH3balanced with air at a concentration of ∼0.3 ppm at 25°C and ∼0.1ppm at 300°C. The diodes show reproducible current response to repeated cycling of the NH3exposure at all temperatures in this range. The diode current at fixed voltage decreased upon exposure to the NH3, which is opposite to what occurs with exposure to hydrogen. This suggests the detection mechanism involves reaction of ammonia with oxygen species on the ZnO nanorods, increasing the negative charge on the interface with AlGaN. The detection sensitivity displayed an activation energy of 0.071 eV and increased monotonically with ammonia concentration at all temperatures, from 3.36% (25°C) to 12.59% (300°C) for 2 ppm at a voltage of 5 V. The diodes could detect ammonia for either polarity applied bias. The absolute current change and sensitivity upon exposure to ammonia increased with measurement temperature.

Poly(methyl methacrylate) (PMMA) encapsulated Pt-AlGaN/GaN Schottky diodes show highly sensitive (100 ppm, 0.01% by volume) room temperature detection of hydrogen and are insensitive to the presence of water in the sensing ambient. These diodes show no physical degradation or loss of sensitivity when repeatedly cycled (50 x, 1 min hold at each temperature) between 25–100°C. There is complete selectivity for hydrogen sensing over other gases, including CO, CO2, NO2, O2and CH4. The PMMA encapsulation provides an effective and robust barrier to moisture, greatly increasing the range of environments in which the sensors can be used.

AlGaN/GaN HEMT based hydrogen sensor incorporating poly(methyl methacrylate) (PMMA) membrane was fabricated. The maximum sensitivities of 2.6×105% were obtained for both dry and humid 500 ppm hydrogen. The PMMA layer effectively permits the approach of hydrogen molecules to catalytic platinum surface, while blocking the penetration of water molecules. The PMMA encapsulated device also showed reliable hydrogen gas sensing characteristics even after 25- 100°C heating cycle stress.

We report on the dielectric properties of non-polar a-plane (11-20) GaN (a-GaN) films in the terahertz (THz) frequency region, using THz time domain spectroscopy. We measured the transmitted THz time-domain waveforms by rotating the phi angle for 6μm-thick a-GaN films, which were lifted off from sapphire substrates. THz transmittance of a-GaN films clearly showed the angular dependence on azimuth angle, possibly due to the birefringence and optical phonon modes in a-GaN crystal. It is believed that the discrepancy in the refractive index results from the difference of the transverse-optical and the longitudinal optical phonon branches.

AlGaN/GaN high electron mobility transistor based carbon dioxide sensor with ZnO nanorods as a sensing material was fabricated. The response of the device to carbon dioxide gas was characterized at elevated measurement temperature. The transistor showed an increase in drain current upon 500 ppm CO2due to the enhanced electron channel at the interface of AlGaN and GaN from 150°C. Reliable repeatability to cyclic exposures of various concentrations of carbon dioxide gas was observed. Also, effect of humidity on sensing behavior was investigated.

Silver Schottky diode on AlGaN/GaN high electron mobility transistor structure was investigated for the application of ethanol sensing. The device showed the decrease of current upon ethanol exposure from the measurement temperature of 200˚C due to the increase in Schottky barrier height. At 250˚C, the stable and fast current changes depending on the exposed ethanol concentrations from 0.0058 to 5.8% were observed.

The use of Ag in the gate region of AlGaN/GaN heterostructure diodes is shown to provide stable, reversible changes in barrier height and thus current during exposure to ethanol at 250°C. The exposed ethanol molecules are adsorbed on the silver and oxidized, resulting in the increase of Schottky barrier height. The detection limit of ethanol at this temperature was 58 ppm, and the sensor response was linear over the range 58–58700 ppm. For the high end of this concentration range (5.87%), ethanol exposure at 250°C caused the Schottky barrier height to change from 0.604 eV to 0.656 eV, which produced a forward current relative change of 45.4% at 0.9V forward bias. The results are competitive with detection of ethanol by oxide thin films or nanostructures of SnO2, Fe2O3, CuO, and ZnO.