Willyum Jo

In this work we are reporting on the measurement of the proton-air inelastic cross section ${\ensuremath{\sigma}}_{p\ensuremath{-}\text{air}}^{\text{inel}}$ using the Telescope Array detector. Based on the measurement of the ${\ensuremath{\sigma}}_{p\ensuremath{-}\text{air}}^{\text{inel}}$, the proton-proton cross section ${\ensuremath{\sigma}}_{p\ensuremath{-}p}$ value is also determined at $\sqrt{s}=9{5}_{\ensuremath{-}8}^{+5}\text{ }\text{ }\mathrm{TeV}$. Detecting cosmic ray events at ultrah

0.85Bi0.5Na0.5TiO3-0.15Bi0.5K0.5TiO3 (BNKT15) lead-free thin films were prepared on Pt(111)/TiO2/SiO2/Si(100) substrates by the chemical solution deposition method. BNKT15 are MPB composition in the Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 (BNTeBKT) system. The maximum piezoelectric coefficient (d33,f) value of BNKT15 thin film is approximately 75 pm/V, which is comparable to that of polycrystalline PZT thin films. These results suggest that BNKT15 thin film can be used as an alternative for PZT films in pi

We used X-ray diffraction (XRD) and Raman scattering spectroscopy to study Cu2ZnSnS4(CZTS) thin films grown by using an electroplating method. We compared the Raman spectraof the CZTS thin films before and after potassium cyanide (KCN) etching. We observed a phononmode of the secondary phase Cu2−xS both from Cu-rich and Cu-poor CZTS samples before theKCN etching. We found that the intensity of the Cu2−xS-related vibration mode depended on theexcitation wavelength, from which we could estimate th

We measured micro-Raman scattering spectra of commercially available Ge-Sb-Te (GST) bulk crystals and GST nanoparticles which were synthesized using a pulsed laser ablation method. The lack of the amorphous Te-Te stretching mode near 150 cm¡1 from the Raman spectrum of the bulk sample indicated that the sample was well-crystallized. We also measured GST nanoparticles with dierent growth conditions, from which we could get information towards the optimal growth conditions for better crystallinity

Biofilm contains heterogeneous three-dimensional structures composed of extracellular polymeric substance (EPS), which are greatly influenced by flow conditions. Here, we report a microfluidic platform highly suitable for nanoscale investigation of biofilms formed under laminar flows. This is possible because biofilms formed on glass beads having an average diameter of about 200 μm in the microfluidic device can be easily taken out and located for imaging under high resolution microscopes, such

Local current mapping and surface potential distributions on polycrystalline Cu(In,Ga)Se2 (CIGS) films are investigated by conductive atomic force microscopy and Kelvin probe force microscopy. The two kinds of samples fabricated by co-evaporation had extremely different conversion efficiencies of 10% and 0.2% for stoichiometric and Cu- and Se-deficient compositions, respectively. We examined the microscopic reasons for the differences in the local electrical properties. Current mapping and curre

We report non-resonant and resonant Raman scattering studies of layered MoS2. Owing to its reduced dimensionality, few layered MoS2 is more sensitive to the difference between inter- and intra-layer coupling, which results in unusual frequency shifts of the Raman phonon modes. In addition, relative intensities between the two Raman active phonon modes E12 g and A1g unexpectedly depend on the laser excitation energy, which might be associated with the electronic band structure, including spin-orb

Cu2ZnSnS4 (CZTS) has an optical band gap of 1.4e1.5 eV, which is similar to that of Cu(In,Ga)Se2 (CIGS), and a high absorption coefficient (>104 cm1) in the visible light region. In previous reports, CIGS thinfilm solar cells have been shown to improve the performance of the device since the secondary phase is removed by Potassium cyanide (KCN) etching treatment. Therefore, in this study we applied a KCN etching treatment on CZTS and measured the effects. We confirmed the removal of Cu2xS via Ke

A sol-gel method is used to make ferroelectric Pb(Zr0:52Ti0:48)O3 (PZT) nanolayers. Highly (100) and (111) oriented PZT nanolayers are prepared on Pt/Ti coated SiO2/Si(100). Drying conditions before crystallizing heat treatments have been explored over a wide range of temperature. Structural properties, surface morphology, and electrical properties are studied by X-ray diraction, scanning electron microscopy, and polarization-electric eld measurement, respectively. Ferroelectric domains in the n

Gallium-ferrite thin films were studied to investigate the effects of the oxygen annealing conditionson the electrical properties. Ga0.8Fe1.2O3− thin films were prepared by using a sol-gel methodunder different oxygen partial pressures. The structural properties of the films were studied byusing X-ray diffraction. X-ray photoemission spectra of the core-levels of Ga, Fe, and O in the filmswere examined. The dielectric functions of the films were measured at energies from 0.73 to 6.45 eVby using

Ferroelectric Bi3.25La0.75Ti3O12 (BLT) thin films have been grown by a sol-gel method. Annealing conditions after the drying process have been explored over a wide range of temperature. Highly (001)- and (h00)-oriented BLT thin films are prepared on Pt/TiO2 coated SiO2/Si(100), depending on annealing temperature. Structural properties, surface morphology, and electrical properties are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic electron microscopy (AEM), re

We investigated the structural and optical properties of Cu-poor CuGaSe2 (CGSe) films depending on the use of different substrates: indium-doped tin oxide (ITO) coated soda-lime glass (SLG) and fluorinedoped tin oxide (FTO) coated SLG as back contacts, widely usedMo-coated SLG, and pure SLG. The Cu-poor phase is chosen as a counterpart of Cu-poor Cu(In,Ga)Se2 to show the highest efficiency in this class of materials, and also give a test board for parasitic phases which might influence on device

We investigated the characteristics of Cu(In, Ga)Se2 solar cells with bandgap (Eg) grading. Two precursor types were employed: Mo/Cu0.75Ga0.25/In/Ga2Se3 (CIGSe-1) and Mo/Cu/In/Ga2Se3 (CIGSe-2). In CIGSe-1, the range of depths with a high Ga content is wider than that in CIGSe-2; thus, the region in which the main electron-trapping clusters and high-population deep donor defects can form is larger, and the defect density is higher. In the defect energy level range, various other defects and defec

Superconducting MgB2 fibers have been grown by using a diffusion method, in which B filaments are exposed to Mg vapor inside a folded Ta foil over a wide range of temperatures and growth times. The fibers have a diameter of about 110 μm. The radial distribution of Mg ions into B is observed over the cross-sectional area, and the transport properties of the MgB2 fibers are examined by using a physical property measurement system. The MgB2 fibers grown at 900 C for 2 hours show a superconducting t

Phase-change Ge-Sb-Te (GST) nanoparticles have been synthesized {\it in situ} by a pulsed laser ablation method. Crystal formation of the GST nanoparticles was confirmed [H. R. Yoon {\it et al.}, J. Non-Cryst. Solids, {\bf 351}, 3430 (2005)]. Scanning and transmission electron microscopy were used to study microstructure and phase formation of the nanoparticles. Fourier transform analysis of electron micrographs exhibits the crystal structure of the GST-225. We have also measured the extended X-