Nondestructive Characterizations of Au-Catalyzed GaAs Nanowires on GaAs(111)B Substrates via Identifications of 1st Order Optical Phonon Modes Using µ-Raman Spectroscopy.

We report the relation between the catalyst patterning conditions and the intensity of the 1st order Raman active modes in Au-catalyzed GaAs nanowire bundles. We fabricated e-beam lithographically Au-patterned GaAs(111)B substrates by varying the patterning conditions (e-beam dose rate, dot-size and interdot-spacings), and grew GaAs nanowires via vapor-liquid-solid process using a solid-source molecular beam epitaxy. To understand the effects of the substrate preparation conditions and resulting morphologies on the optical characteristics of 1st order transverse optical and longitudinal optical phonon modes of GaAs, we characterized the nanowire bundles using complementary µ-Raman spectroscopy and scanning electron microscopy as a function of the e-beam dose rate (145-595 µC/cm²), inter-dot spacing (100 and 150 nm) and pattern size (100 and 150 nm). Ensembles of single crystalline GaAs nanowires covered with different Au-thickness exhibit a downshift and asymmetric broadening of the 1st order transverse optical and longitudinal optical phonon peaks relative to GaAs bulk modes. We also showed that the sensitivity of a downshift and broadening of Raman spectra are directly related to morphological and surface coverage variations in as-grown nanowires. We observed clear increases of the transverse optical and longitudinal optical intensity as well as the relatively higher peak shift and broadening of Raman spectra from the 100 nm patterning in response to the dose rate change. Strong dependence of Raman spectra of the nanowire bundles on the e-beam dose rate changes are attributed to the variations in spatial density, size, shape and random growth orientation of the wires. We have shown that the identification of the changes in GaAs longitudinal optical and Arsenic anti-site peaks is good indicators to characterize the quality of as-grown GaAs nanowires. Our finding confirms the utilization of Raman spectroscopy as a powerful tool for characterizing chemical, structural, and morphological information of as-grown nanowires within the supporting substrate.

Silver Nanowire-Based Stretchable Transparent Electrode for Flexible Organic Light-Emitting Diode.

The new stretchable transparent electrode was proposed and fabricated based on a process which utilizes silver nanowires (AgNWs) on a Polyurethane (PU) substrate. In order to overcome the rough surface nature of the silver nanowire electrode, a titanium oxide (TiO2) buffer layer was over-coated and then followed by a heat treatment of organo-metalic sol-gel solution. The fabricated stretchable electrodes exhibit electrical sheet resistance of 24 Ω/□, transmittance of 78% at 550 nm wavelength and average surface roughness of less than 5 nm. In addition, without adding additional conductive polymer layers, the fabricated AgNW-based electrode can maintain its initial electrical resistance even if nearly 130% strain is applied. In this letter, the critical role of a TiO2 buffer layer in achieving the high performance of the AgNW stretchable electrode is discussed.

Nanoparticle and Laminar Structured Lead Selenide Photoconductive Thin Film.

Lead selenide thin films composed of nanoparticles and laminar structures were deposited on glass substrates by a chemical bath deposition technique, and then thermally oxidized in oxygen atmosphere at an annealing temperature of 400 °C for 20 min. The particles and laminar structures deposited were randomly dispersed and well crystalized according to the hexagonal structure with the preferential orientation (200). The energy dispersive spectrum analysis confirms that the heat treatment introduced oxygen elements into the thin film while reducing the amount of iodine and selenium. The structural, surface morphological and electrical properties of the thin film were determined using various techniques including X-ray diffraction, scanning electron microscopy, and energy dispersive and X-ray analysis. A 3×3 mm² sized photoconductive detector was patterned, and its IR response under a blackbody radiation was also discussed.

Optimization of BBr3-Based Co-Diffusion Processes for Bifacial N-Type Solar Cells.

We report on the co-diffused bifacial N-type solar cells based on N-type Si wafers using the process of spin on doping (SOD, phosphorous source) and boron tribromide (BBr3) diffusion by atmospheric pressure chemical vapor deposition (APCVD). For bifacial co-diffusion, a phosphorous layer was deposited by SOD on the rear side of N-type Si wafer and a BBr3 as boron dopant source deposited by APCVD. Co-diffusion process was controlled by changing the flowrate of carrier N2 gas and drive-in temperatures. It was found that the fabricated bifacial co-diffused N-type solar cell with 2% H3PO4 doping, the flowrate of N2 carrier gas of 15 slm and drive-in temperature at 930°C exhibited the highest conversion efficiency of 15.8% with high open circuit voltage (V(oc)) of 593 mV. As compared to high H3PO4 concentrations (5% and 9%), the low H3PO4 concentration of SOD showed the higher sheet resistance and decreased in the thickness of N + emitter layer, resulting in the high V(oc), shunt resistance, fill factor and conversion efficiency of solar cells.

Properties of CuInS2 Nano-Particles on TiO2 by Spray Pyrolysis for CuInS2/TiO2 Composite Solar Cell.

In this letter, for the absorption layer of a CuInS2/TiO2 composite solar cell, I­III­VI2 chalcopyrite semiconductor CuInS2 nano-particles were deposited by using spray pyrolysis method on TiO2 porous film. Their material characteristics including structural and optical properties of CuInS2 nano-particles on TiO2 nanorods were analyzed as a function of its composition ratios of Cu:In:S. Crystalline structure, surface morphology and crystalline size were also investigated by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), and High-Resolution TEM (HRTEM), respectively. On the other hand, optical property was characterized by an UV-Visible Spectrophotometer. As a result, it was found that the size of CuInS2 nano-particles, which was formed at 300±5 °C, was smaller than 16 nm from HRTEM analyses, and it was identified that the CuInS2 particle size was increased as increasing the heat-treatment temperature and time. However, as the size of CuInS2 nano-particle becomes smaller, optical absorption edge of ternary compound film tends to move to the blue wavelength band. It turns out that the optical energy-band gap of the compound films was ranging from 1.48 eV to 1.53 eV.

Improved Treatment of Photothermal Cancer by Coating TiO2 on Porous Silicon.

In present society, the technology in various field has been sharply developed and advanced. In medical technology, especially, photothermal therapy and photodynamic therapy have had limelight for curing cancers and diseases. The study investigates the photothermal therapy that reduces side effects of existing cancer treatment, is applied to only cancer cells, and dose not harm any other normal cells. The photothermal properties of porous silicon for therapy are analyzed in order to destroy cancer cells that are more weak at heat than normal ones. For improving performance of porous silicon, it also analyzes the properties when irradiating the near infrared by heterologously junction TiO2 and TiO2NW, photocatalysts that are very stable and harmless to the environment and the human body, to porous silicon. Each sample of Si, PSi, TiO2/Psi, and TiO2NW/PSi was irradiated with 808 nm near-IR of 300, 500, and 700 mW/cm2 light intensity, where the maximum heating temperature was 43.8, 61.6, 67.9, and 61.9 degrees C at 300 mW/cm2; 54.1, 64.3, 78.8, and 68.9 degrees C at 500 mW/cm2; and 97.3, 102.8, 102.5, and 95 0C at 700 mW/cm2. The time required to reach the maximum temperature was less than 10 min for every case. The results indicate that TiO2/PSi thin film irradiated with a single near-infrared wavelength of 808 nm, which is known to have the best human permeability, offers the potential of being the most successful photothermal cancer therapy agent. It maximizes the photo-thermal characteristics within the shortest time, and minimizes the adverse effects on the human body.

Hybrid and Etch-Less Electrooptic Waveguide Modulator Based on Photo-Bleaching and Strain Induced Optical Waveguide Technique in Polymer.

A hybrid and etchless electrooptic (EO) polymer waveguide modulator based on both a photo-bleaching-induced optical waveguide (PBOW) and a strain-induced optical waveguide (SIOW) is described. The SIOW is defined by a metal strip line stressor deposited on top of the upper cladding that introduces the refractive index change within the core region. The PBOW technique is used to form an optical waveguide which is based on a photo-bleaching process, known as a photo-oxidation that is an irreversible decomposition of EO material, resulting in a permanent decrease in index of refraction. It is shown that this proposed fabrication idea combining two etchless techniques can be applicable to a wide range of polymer photonic integrated circuits. Preliminary results obtained from fabricated devices reveal that their half-wave voltage are ranging from 8 V to 10 V, their extinction ratio exhibits more than 15 dB, and the fiber-to-waveguide-to-lens loss is estimated to be ~9.5 dB for TM polarization at 1.55/m wavelength in the active interaction of ~1.5 cm long.

Characterization of Boron Diffusion Phenomena According to the Specific Resistivity of N-Type Si Wafer.

This paper is directed to characterize the boron diffusion process according to the specific resistivity of the Si wafer. N-type Si wafers were used with the specific resistivity of 0.5-3.2 omega-cm, 1.0-6.5 omega-cm and 2.0-8.0 omega-cm. The boron tribromide (BBr3) was used as boron source to create the PN junction on N-type Si wafer. The boron diffusion in N-type Si wafer was characterized by sheet resistance of wafer surface, secondary ion mass spectroscopy measurements (SIMS) and surface life time analysis. The degree of boron diffusion was depended on the variation in specific resistivity and sheet resistance of the bare N-type Si wafer. The boron diffused N-Si wafer exhibited the average junction depth of 750 nm and boron concentration of 1 x 10(19). N-type Si wafer with the different specific resistance considerably affected the boron diffusion length and life time of Si wafer. It was found that the lifetime of boron diffused wafer was proportional to the sheet resistance and resistivity. However, optimization process may necessary to achieve the high efficiency through the high sheet resistance wafer, because the metallization process control is very sensitive.

The Effect of Quercus salicina Leaf Extracts on Vascular Endothelial Function: Role of Nitric Oxide.

Dysfunction of the vascular endothelium is reported as a hallmark of cardiovascular diseases. Many evidences suggest that polyphenols are associated with a decreased global mortality and might be involved in protection against cardiovascular risk. This beneficial effect of polyphenol may be due to many actions as antioxidant that increases bioavailability of nitric oxide, vasodilation or anti-hypertensive properties. To identify new natural medicine candidate for cardiovascular protection, plant extracts used in traditional medicine were evaluated by vascular reactivity system. Porcine coronary artery rings were suspended in organ chambers for the measurement of changes in isometric tension. Screening results indicated that the ethanolic extract of leaf from Quercus salicina (QSE) has been found to exhibit potent vasorelaxant activity. QSE dose-dependently induced endothelium-dependent relaxations, which were abolished by inhibitors of nitric oxide synthase (Nomega-nitro-L-arginine). In addition, QSE strongly and dose-dependently activate endothelial nitric oxide synthase (eNOS) in porcine coronary artery endothelial cell. Taken together, the present study has demonstrated that QSE is a powerful endothelium-dependentvasodilator and that this effect involves increased nitric oxide bioavailability. In conclusion, QSE could be a cardiovascular protective herbal medicine candidate associated with cardiovascular diseases and endothelial dysfunction.

Photocurrent Enhancement of P3HT:PCBM Organic Solar Cell with Cylindrical Ag-NPs by EBM.

The power conversion efficiency (PCE) of PEDOT: PSS/P3HT:PCBM organic solar cells(SCs) with Ag nanoparticles (NPs) on ITO is studied, and the optical absorption of the SCs with a cylindrical Ag-NPs model is investigated. The fabricated device structure is simulated with a finite difference time domain (FDTD) method. This cylindrical Ag-NPs model is able to explain the photocurrent enhancement by the localized surface plasmon resonance (LSPR) modes, and to provide a further understanding of Ag-NPs shape parameters which play an important role to determine the broadband absorption phenomena in plasmonic organic solar cells. Compared with the SCs without Ag-NPs, an increase in the PCE of the plasmonic solar cell was accurately identified. The photocurrent-voltage characteristic of the examined solar cells reveals higher efficiency of 2.75% compared with the reference cells which show 1.67%.

The Characteristics of an Antibacterial TiAgN Thin Film Coated by Physical Vapor Deposition Technique.

In this work, we found the characteristics of an antibacterial TiAgN thin film coated on the pure titanium specimen via the physical vapor deposition process (PVD). TiAgN thin films were coated using TiAg alloy targets by arc ion plating method. Changing the process parameters, the surface analysis of TiAgN thin film was observed by FE-SEM and the force of adhesion was measured with Scratch Tester. The proliferation of human gingival fibroblast (HGF) cells was examined by XTT test assay and the antibacterial properties were investigated by culturing Streptococus Mutans (KCTC 3065) using paper disk techniques. At the result of experiment, cytotoxic effects were not found and the antibacterial effects against Streptococus Mutans were appeared over 5 wt% TiAgN specimens.

Thermal evolution characterizatics of atomic layer deposition prepared TiO2 interfacial layer by synchrotron radiation X-ray scattering.

TiO2 thin film prepared by the atomic layer deposition (ALD) with supplies of Ti(O-i-Pr)4 and H2O have been analyzed using the difference X-ray reflectivity (DXRR). The thickness of buried interfacial layer (IL) embedded in between Si-substrate and TiO2 layer was characterized as a function of temperatures of 20, 300, and 500 degrees C mounted on an in-situ hot stage The growth rate of TiO2 film was estimated to be 0.5 nm/cycle at the temperature of 150 degrees C. It was identified that the interfacial layer of the treated thin film was disappeared at a certain temperature rise. Furthermore, we found that the crystalline structure of TiO2 film was varied depending on not only the growth temperature but also the post thermal treatment of the samples. Since the synchrotron radiation X-ray scattering measurement allow us to investigate the atomic structure evolution in the range of a few nanometer thick, nondestructively, in this letter we report its characteristics of the thermal evolution of the TiO2 interfacial layer that is the crucial step for progress in microelectronics and nanotechnology.

E-beam deposited Ag-nanoparticles plasmonic organic solar cell and its absorption enhancement analysis using FDTD-based cylindrical nano-particle optical model.

We report the plasmon-assisted photocurrent enhancement in Ag-nanoparticles (Ag-NPs) embedded PEDOT:PSS/P3HT:PCBM organic solar cells, and systematically investigate the causes of the improved optical absorption based on a cylindrical Ag-NPs optical model which is simulated with a 3-Dimensional finite difference time domain (FDTD) method. The proposed cylindrical Ag-NPs optical model is able to explain the optical absorption enhancement by the localized surface plasmon resonance (LSPR) modes, and to provide a further understanding of Ag-NPs shape parameters which play an important role to determine the broadband absorption phenomena in plasmonic organic solar cells. A significant increase in the power conversion efficiency (PCE) of the plasmonic solar cell was experimentally observed and compared with that of the solar cells without Ag-NPs. Finally, our conclusion was made after briefly discussing the electrical effects of the fabricated plasmonic organic solar cells.

Visible light-responsive titanium dioxide thin film prepared by reactive sputtering.

TiO2 is a wide band-gap semiconductor (3.4 eV) and can only absorb about 5% of sun light in the ultraviolet light region, which largely limits its practical applications because of the lower utility of sun light and quantum yield. In order to move the absorption edge of TiO2 films to visible spectrum range, we have made the impurity level within a band-gap of TiO2 thin film by introduction of oxygen vacancy. Oxygen-defected TiO2 photo-catalyst have prepared by reactive sputtering with the partial pressure of Ar:O2 = 76.7:23.3 approximately 98.5:1.5 ratios. As a result, we could have the impurity level of about 2.75 eV on condition that oxygen partial pressure is 2.9%. And the photocatalytic activity was realized at 400 nm wavelength.

In-situ synchrotron X-ray scattering study of thin film growth by atomic layer deposition.

We report an atomic layer deposition chamber for in-situ synchrotron X-ray scattering study of thin film growth. The chamber was designed for combined synchrotron X-ray reflectivity and two-dimensional grazing-incidence X-ray diffraction measurement to do a in-situ monitoring of ALD growth. We demonstrate ruthenium thermal ALD growth for the performance of the chamber. 10, 20, 30, 50, 70, 100, 150 and 250-cycled states are measured by X-ray scattering methods during ALD growth process. Growth rate is calculated from thickness values and the surface roughness of each state is estimated by X-ray reflectivity analysis. The crystal structure of initial growth state is observed by Grazing-incidence X-ray diffraction. These results indicate that in-situ X-ray scattering method is a promising analysis technique to investigate the initial physical morphology of ALD films.

Effect of pretreatment conditions on particle size of bimetallic pt-au catalysts supported on ZnO/Al2O3 and its activity for toluene oxidation.

Bimetallic Pt-Au catalysts supported on ZnO/Al2O3 were prepared by incipient wetness impregnation (IW-IMP) method with different pretreatment conditions such as flow velocity, calcination temperature, and heating rate under H2 during the calcination procedure, and characterized by X-ray diffraction (XRD), CO chemisorption, and scanning transmission electron microscopy (STEM) equipped energy dispersive spectroscopy (EDS). Furthermore, catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. Finally, relationship between the particle sizes with pretreatment conditions and catalytic activity for toluene on the bimetallic Pt-Au catalysts was discussed. In these results, nanosized bimetallic Pt-Au particles on ZnO/Al2O3 could be prepared by IW-IMP method. Relationship between the Pt and Au particle size and activity for toluene oxidation was clearly observed.

Electrochemical characteristics of lithium iron phosphate with multi-walled carbon nanotube for lithium polymer batteries.

In this study, we prepared phospho-olivine LiFePO4 nanoparticles as cathode materials for lithium polymer batteries by hydrothermal reaction at 150 degrees C. Multi-walled carbon nanotube (MWCNT) was added to enhance the electrical conductivity of LiFePO4. LiFePO4-MWCNT nanoparticles (0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt% and 10 wt%) were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). LiFePO4-MWCNT/SPE/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm(-2) in a range between 2.5 and 4.3 V versus Li/Li+, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO4 was 103 mA h g(-1). The discharge capacity of LiFePO4-MWCNT/SPE/Li cell with 7 wt% MWCNT was 129 mA h g(-1) at the first cycle and 130 mA h g(-1) after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO4-MWCNT/SPE/Li cell with 7 wt% MWCNT was better than that of LiFePO4/SPE/Li cell.

Nanosized LiFePO4 cathode materials for lithium ion batteries.

In this study, we prepared nano-particles of LiFePO4 as cathode material for lithium ion batteries by the solid-state reaction. A simple one-step heat treatment has been employed with control of heating temperature and heated LiFePO4 at 650 degrees C exhibited higher 125 mA h/g of the discharge capacity than 600 degrees C, 700 degrees C. To improve conductivity of the inter-particle, carbon coating was carried out by raw carbon or pyrene as carbon sources and their morphological properties of particles on the carbon coating was compared with by FE-SEM, TEM. From the FE-SEM results, the particles of carbon added LiFePO4 have much smaller size than LiFePO4 as below 300 nm. When adding pyrene (10 wt%), the carbon surrounded non-uniformly with surface of the particles compared with adding raw carbon which wrapped uniformly with carbon web and it was exhibited 152 mA h/g of the discharge capacity on LiFePO4/C composite cells at 10th cycle.