Search

Neutron capture and transmission measurements were carried out from 0.01 to over 600 eV on both natural Dy and samples highly enriched in 164 Dy. These data were analyzed for resonance parameters utilizing the SAMMY Bayesian analysis code to simultaneously fit both the capture and transmission data. Parameters were obtained for 17 resonances in Dy isotopes up to 18 eV and for the 164 Dy resonances near 147, 450 and 540 eV. The thermal capture cross section (at 0.0253 eV) and capture resonance integral were determined for 164 Dy.

Successive ionic layer adsorption and reaction (SILAR) method is a modified version of chemical bath deposition (CDB) that serves as a low-cost and convenient on the production of ternary metal chalcogenides. This research reported the utilization of SILAR method on the fabrication of Cu3BiS3 semiconductor-sensitized solar cells. The concentration of bismuth and copper precursor were varied, namely 0.03 M and 0.1 M, whereas the precursor of sulfide was varied in the concentration of 0.02 M and 0.05 M. The variation of SILAR cycles was employed to investigate the most appropriate cycle numbers in producing Cu3BiS3, in particular 3-9 cycles, 5-15 cycles, and 6-6 cycle with the immersing time of 20 s for each. The results show that there were only two suitable peaks appeared for 3-9 cycles and 6-6 cycles, while 5-15 cycles provide the more preferable XRD patterns with the power conversion efficiency of 0.02% (Jsc of 1.75 mA/cm2; Voc of 0.04 V; FF of 29.65%). It can be said that SILAR method with higher number of cycles can be employed to fabricate Cu3BiS3; however, smaller PCE came from inappropriate structure alignment between Cu3BiS3 and metal oxide layer.

We investigate the strain difference in InGaN/GaN multiple quantum wells of blue light-emitting diode (LED) structures grown on silicon(1 11) and c-plane sapphire substrates by comparing the strength of piezo-electric fields in MQWs. The piezo-electric fields for two LED samples grown on silicon and sapphire substrates are measured by using the reverse-bias electro-reflectance (ER) spectroscopy. The flat-band voltage is obtained by measuring the applied reverse bias voltage that induces a phase inversion in the ER spectra, which is used to calculate the strength of piezo-electric fields. The piezo-electric field is determined to be 1.36 MV/cm for the LED on silicon substrate and 1.83 MV/cm for the LED on sapphire substrate. The ER measurement results indicate that the strain-induced piezo-electric field is greatly reduced in the LED grown on silicon substrates consistent with previous strain measurement results by micro-Raman spectroscopy and high-resolution transmission electron microscopy.

We present the yields of various fission products determined in the reactor neutron, 3.7-18.1 MeV quasi-mono energetic neutron, 8-80 MeV bremsstrahlung and 20-45 MeV proton induced fission of 232Th and 238u using radiochemical and off-line beta or gamma ray counting. The yields of the fission products in the bremsstrahlung induced fission natPb and 209Bi with 50-70 MeV and 2.5 GeV based on off-line gamma ray spectrometric technique were also presented. From the yields of fission products, the mass chains yields were obtained using charge distribution correction. From the mass yield distribution, the peak-to-valley (P/V) ratio was obtained. The role of excitation energy on the peak-to-valley ratio and fine structure such as effect of shell closure proximity and even-odd effect of mass yield distribution were examined. The higher yields of the fission products around A=133-134, 138-140 and 143-144 and their complementary products explained from the nuclear structure effect and role of standard I and II mode of asymmetric fission. In the neutron, photon (bremsstrahlung) and proton induced fission, the asymmetric mass distribution for actinides (Th, u) and symmetric distribution for pre-actinides (Pb, Bi) were explained from different type of potential fission barrier.

Micostructural change and corresponding effect on coercivity of a NdFeB sintered magnet mixed with small amount of DyMn powder was investigated. In the sintered magnet mixed with the DyMn alloy-powder Dy-rich shell was formed at outer layer of the main grains, while Mn was mostly concentrated at Nd-rich triple junction phase (TJP), lowering melting temperature of the Nd-rich phase that eventually improved the microstructural characteristics of the gain boundary phase. The coercivity of a magnet increased more than 3.5 kOe by the mixing of the DyMn alloy-powder.

Systematic investigation on thermal and mechanical properties of Cu60−xZr25Ti15Nix bulk metallic glasses with x = 0, 1, 3, 5, 7, 9 and 11 at.% points out that monolithic Cu53Zr25Ti15Ni7 and Cu51Zr25Ti15Ni9 bulk metallic glasses containing optimum Ni content of 7 and 9 at.% are effective to enhance both thermal stability of amorphous structure up to 716 K and plastic strain of 2.4% at room temperature. This indicates that a selection of additional elements such as Ni by considering a mixing enthalpy to the constituent elements is very important to control the thermal stability and plasticity. Moreover, it is believed that the addition of minor Ni can be a trigger to form the chemical heterogeneity upon solidification. Such chemical heterogeneity formed by the selection of the minor elements has a strong influence to cause the oscillation of the shear stress by wavy propagation of the shear bands thus leading the improvement of macroscopic plasticity of the bulk metallic glasses.

We report an experimental study on the correlation spectrums between different sections of a multi-contact GaN nanowire device. Our results indicate that there exists a negative correlation between the voltage fluctuations of adjacent sections of the nanowire separated by a metal contact in the transition region between the low-frequency 1/f noise and the high-frequency white thermal noise. We suggest that this correlation is caused by the voltage fluctuation under the contact area.

Mesoporous TiO2 films were synthesized using a sol–gel process with a tri-block copolymer (Pluronic F127) as a structure directing agent. The films were dip-coated onto conductive glass substrates followed by thermal treatment to remove the polymeric surfactant. The specific surface area, the pore size and morphology, and the crystallinity of the films were characterized. The analysis showed the structural properties of the films could be tailored by varying the surfactant concentration as well as the annealing temperature. The photocurrent responses of the prepared films were measured using a three-electrode photoelectrochemical cell in the presence of oxalic acid. When annealed at 450 °C, the dense electrode (control sample) had the strongest photoelectrocatalytic oxidation aptitude toward oxalic acid. The lower photocurrent response of the mesoporous electrodes compared to the dense electrode can be explained by poor inter-particle connectivity within the mesoporous TiO2 network, leading to high electron transport resistance. The mesoporous electrode annealed at 550 °C, with improved connectivity, outperformed the dense electrode at a high oxalic concentration, as the lower surface area of the dense electrode restricted photoelectrocatalysis reactions on the surface. A further increase in annealing temperature to 650 °C resulted in a poor photocurrent response as the significant decrease in surface area outweighed the beneficial effect of improved connectivity.

We compare the strain states and device performances of GaN-based blue light-emitting diodes (LEDs) grown on Si(111) and sapphire substrates. The strain characteristics are investigated using micro-Raman spectroscopy and high-resolution transmission electron microscopy. These analyses reveal that GaN layer grown on Si has a residual tensile strain in contrast to a compressive strain for GaN on sapphire, and quantum wells (QWs) on GaN/Si experience reduced lattice mismatch than those of GaN/sapphire. When external quantum efficiencies of LED on sapphire and Si substrates are compared, the LED on Si shows better efficiency droop characteristics and this is attributed to a decrease in piezo-electric field strength in InGaN/GaN layers owing to reduced lattice mismatch.

The replication process is a good method to fabricate passive optical devices. Silicon-based fabrication technology provides an efficient way to fabricate a replication master with an optically smooth surface roughness. As silicon-based technologies are often two-dimensional processes, the replication requires sophisticated fabrication steps for a master structure. For this, a vertically curved structure, which is essential for a passive optical device, is hard to fabricate. Special processes, such as x-ray lithography, laser ablation, and gray-scale lithography, can overcome the conventional two-dimensional fabrication process challenges. But these processes need additional steps, machines, and masks. This study demonstrates an easy way for fabricating a silicon master structure for vertically curved mirrors. This fabrication method is roughly divided into two steps. During the first step, a silicon wafer is etched using an inductively coupled plasma system to form optical waveguide structures in the mas...

Photonic devices based on polymer materials have been fabricated mainly by using conventional lithography and etch processes. However, the fabrication method through these processes is complex and expensive. We fabricated 1310∕1550nm demultiplexer using an embossing technique, which was able to reduce the fabrication cost. The mold is an elastomeric polydimethylsiloxane (PDMS) and resists used as the core and the cladding layers are ZP 51 (ChemOptics) and ZP 49 (ChemOptics), respectively, which are thermal curable polymers. The fabrication process is summarized as follows: (1) manufacturing the photoresist master by lithography process, (2) forming the PDMS mold from the master, and (3) replicating the device using the mold. There is no observation of any noticeable pattern difference between the master and the replica in microscaled dimension. In this work, we also investigated the durability of a PDMS mold for mass production and successfully fabricated the 50th replica with the same mold. The replicate...

We present the results of our development of a deep silicon etching technique, the modified Bosch-type process. Its feasibility was also investigated. This modified Bosch-type process is based on the well known Bosch-type process, but our modified Bosch-type process consists of the etching/passivating time, process transition step, and ion energy control. This modified Bosch-type process has been characterized with respect to ion energy, substrate temperature, and feature size. We found that the etching and deposition characteristics of passivating film were closely related to the resulting deep silicon etch profile. Up to a 40–50 μm deep silicon structure with vertical and positively sloped profiles was realized by the modified Bosch-type process, depending on a few parameters. In this work, this modified Bosch-type process was applied to silicon mold fabrication used for a structuring microarray and optical power splitter. Replication results confirm that this process is promising for achieving high-yie...

We have measured the optical transmittance of thin films of gadolinium trihydride GdH3 over a broad spectral range, 0.05–6 eV. The analysis indicates that GdH3 is a wide-gap semiconductor with an energy gap of 2.55 eV. The fundamental absorption and impurity-related transitions dominate the spectra in the high-energy region, 1–6 eV. Hydrogen vibration modes dominate the spectra in the low-energy region, 0.05–0.2 eV. A strong free-carrier absorption effect is observed. In addition, the frequency-dependent refractive index, extinction coefficient, dielectric function, and optical conductivity are determined from the transmission spectra. This work also evaluates the plasma frequency associated with free carriers.

We describe a high-power, frequency-tunable, external cavity diode laser (ECDL) system near 626 nm useful for laser cooling of trapped $^9$Be$^+$ ions. A commercial single-mode laser diode with rated power output of 170 mW at 635 nm is cooled to $\approx - 31$ C, and a single longitudinal mode is selected via the Littrow configuration. In our setup, involving multiple stages of thermoelectric cooling, we are able to obtain $\approx$130 mW near 626 nm, sufficient for efficient frequency doubling to the required Doppler cooling wavelengths near 313 nm in ionized Beryllium. In order to improve nonlinear frequency conversion efficiency, we achieve larger useful power via injection locking of a slave laser. In this way the entirety of the slave output power is available for frequency doubling, while analysis may be performed on the master output. We believe that this simple laser system addresses a key need in the ion trapping community and dramatically reduces the cost and complexity associated with Beryllium ion trapping experiments., Related manuscripts available at http://www.physics.usyd.edu.au/~mbiercuk/Publications.html

The optical properties of the gallium nitride (GaN) nanowires are examined by the transmission method in the ultraviolet-visible range (1–5 eV) and by the reflection method in the infrared range (500–4000 cm−1). The absorption edge of the GaN nanowires is blueshifted by 0.2 eV from the bulk edge. The temperature dependence of the energy gap is expressed by, Eg(T)=3.724−9.97×10−4/(861+T) eV. The plasma frequency and the free-carrier density of the GaN nanowires, deduced from the infrared reflectance minima, are estimated to be ωp=1100±120 cm−1 and nf=3.73×1017 cm−3, respectively. Obtaining the free-carrier density from the infrared reflectance spectra is especially useful in research on nanostructured semiconductors.

Plastics are the choice materials for fabrication of many microfluidic devices as mass production methods such as the injection moulding and hot embossing processes can be used for disposable polymer device fabrications. However, fabrication of mould inserts with micro features is a very critical step towards successful moulding of polymer micro components. Due to technical limitations many micro features cannot be fabricated directly onto metal mould inserts. Silicon based micro machining technologies, on the other hand, are well developed and are capable of producing very fine micro structures. In the study, silicon insert moulding method is developed for fabrication of polymeric biochips. Although it has been reported to use silicon dies for hot embossing applications, careful consideration of mould design is required to use fragile silicon inserts in moulding applications where higher mould clamping forces are encountered. Silicon inserts instead of traditional metal inserts, are successfully manufactured and used for polymer biochip moulding. It has been found that the silicon inserts can last for tens of shots if properly installed in an injection mould.Copyright © 2008 by ASME

Previously proposed shape of the optical via structures are simple 45 degree mirrors with or without metal coatings, and simple elliptical shapes. To improve alignment tolerance and coupling efficiency, various shape of the optical via structures are fabricated and optical characteristics of the shapes are measured.

We report on the study of the low‐frequency excess noise of a GaN nanowire (NW) device from room temperature to 135 K. A Lorentzian noise is found to be embedded in the 1/f noise background, and becomes more significant as the bias current increases or the temperature decreases. The temperature dependance of the associated characteristic time, extracted from the spectrum, shows two thermally activated regions with different activation energies, which originate from different carrier‐trapping levels in the NW device. The temperature dependence of the 1/f noise is difficult to unveil due to the presence of the strong Lorentzian noise.

We report the temperature (T) dependance (77K to 300K) of the low‐frequency electric noise of GaN nanowires. Our results show that these GaN nanowires exhibit the 1/f‐like excess noise. A Lorentzian‐like feature is observed embedded in the 1/f noise when the applied bias current is large enough. Our four‐wire measurement results reveal that the characteristic time τL of the Lorentzian‐like noise of the nanowire decreases with T.

While GdBa2Cu3O7 − δ (GdBCO) coated conductors (CCs) have been proposed for superconducting applications, they have not been used in devices with persistent current mode (PCM) operation because of a lack of joining techniques. A superconducting joint of CCs, formed via melting diffusion and oxygenation annealing, offers no electrical resistance between the CCs, thus establishing a superconducting closed loop for PCM operation. Because superconductivity degrades with oxygen out-diffusion during melting diffusion, oxygenation annealing allows oxygen diffusion into the GdBCO lattices. As effective oxygenation annealing requires oxygen pathways in the joint, low solubility and diffusivity of oxygen in the buffer and CC substrate hinder full superconductivity recovery. Here we show a laser-drilling technique to produce microholes as conduits on the surfaces of GdBCO CCs' to promote oxygen in-diffusion, which resulted in reduced superconductivity recovery time. Superconductivity was fully recovered after laser drilling, melting diffusion at 850 °C for 1 min, and oxygenation annealing at 500 °C for 350 h.

본 연구에서는 방사선생물 분야에서는 사용하는 세슘-137 조사기에 대한 기준 흡수선량을 측정하고 시료의 방사선량 평가에 활용하기 위하여 유리선량계를 교정하였다. 세슘-137 감마선에 대하여 IAEA TRS-277 프로토콜을 적용하여 정밀하게 물흡수선량을 결정하였다. 기준 흡수선량 측정에는 PTW-TM300013 전리함과 PTW-TM41023 물팬텀을 사용하였으며, 유리선량계는 DoseAce사의 GD-302M 모델을 사용하였다. 교정된 유리선량계의 불확도(1 SD)는 약 2.7%로 평가되며, 본 결과는 연구용 시료의 방사선량 측정에 이용될 예정이다. 【In this research, the glass dosimeter was calibrated to measure the standard absorbed dose of the Cs-137 irradiator and absorbed dose in a biological sample. Absorbed dose in water for Cs-137 gamma ray was determined by the IAEA TRS-277 protocol. The PTW-TM30013 ion chamber and the PTW-TM41023 water phantom were utilized for measuring absorbed dose and the value was compared with the reading from DoseAce GD-302M glass dosimeter from Asahi Techno Glass Corporation for its calibration. The uncertainty of measurement ( $1{\sigma}$ ) of the calibrated glass dosimeter was 2.7% and this result would be applied to improve the accuracy in measurement of absorbed dose in a biological sample.】

In modulation-doped semiconductor heterostructures, the carriers are spatially separated from the dopant atoms to reduce the ionized impurity scattering. Because the disorder and the electron-impurity interaction in such structures are reduced, many-body effects can play a significant role in quantum transport properties of the electron system. An example is the fractional quantum Hall effect observed in the high-mobility two-dimensional electron system (2DES) at the GaAs/AlxGa1−xAs heterojunction interface in the presence of a high magnetic field [1]. There is great interest in extending studies of electron-electron interaction effects to three-dimensional (3D) systems [2]. In the case of uniformly doped semiconductors, however, the electron-impurity interaction is strong and usually leads to the magnetic freeze-out of the carriers.

A closed system gas circulating pump, which has a dynamic range 10−6–105 Torr and circulation rates 0–20 cm3/min, has been designed, constructed, and tested. The welded stainless steel pump is divided into two compartments separated by a welded stainless steel bellows, which has a magnet on the top surface and is driven by an external magnet. Through an appropriate arrangement of three‐way solenoid valves, which are actuated by the external magnet drive, a unidirectional, continuous circulation of gas with respect to the external gas circuit is achieved in both the expansion and compression cycles of the bellows. The pressure drop across the bellows is solely that encountered in the gas circulation line. 363