Synthesis of TiO2 thin films using single molecular precursors by MOCVD method for dye-sensitized solar cells application and study on film growth mechanism

For dye-sensitized solar cells application, in this study, we have synthesized TiO₂ thin films at deposition temperature in the range of 300–750 °C by metalorganic chemical vapor deposition (MOCVD) method. Titanium(IV) isopropoxide, {TIP, Ti(OⁱPr)₄} and Bis(dimethylamido)titanium diisopropoxide, {BTDIP, (Me₂N)₂Ti(OⁱPr)₂} were used as single source precursors that contain Ti and O atoms in the same molecule, respectively. Crack-free, highly oriented TiO₂ polycrystalline thin films with anatase phase were deposited on Si(1 0 0) with TIP at temperature as low as 450 °C. XRD and TED data showed that below 500 °C, the TiO₂ thin films were dominantly grown in the [2 1 1] direction on Si(1 0 0), whereas with increasing the deposition temperature to 700 °C, the main film growth direction was changed to [2 0 0]. Above 700 °C, however, rutile phase TiO₂ thin films have only been obtained. In the case of BTDIP, on the other hand, only amorphous film was grown on Si(1 0 0) below 450 °C while a highly oriented anatase TiO₂ film in the [2 0 0] direction was obtained at 500 °C. With further increasing deposition temperatures over 600 °C, the main film growth direction shows a sequential change from rutile [1 0 1] to rutile [4 0 0], indicating a possibility of getting single crystalline TiO₂ film with rutile phase. This means that the precursor together with deposition temperature can be one of important parameters to influence film growth direction, crystallinity as well as crystal structure. To investigate the CVD mechanism of both precursors in detail, temperature dependence of growth rate was also carried out, and we then obtained different activation energy of deposition to be 77.9 and 55.4 kJ/mol for TIP and BTDIP, respectively. Also, we are tested some TiO₂ film synthesized with BTDIP precursor to apply dye-sensitized solar cell.     

Dose response of commercially available optically stimulated luminescent detector, Al2O3:C for megavoltage photons and electrons

This study examined the dose response of an optically stimulated luminescence dosemeter (OSLD) to megavoltage photon and electron beams. A nanoDot? dosemeter was used to measure the dose response of the OSLD. Photons of 6-15 MV and electrons of 9-20 MeV were delivered by a Varian 21iX machine (Varian Medical System, Inc. Milpitas, CA, USA). The energy dependency was <1 %. For the 6-MV photons, the dose was linear until 200 cGy. The superficial dose measurements revealed photon irradiation to have an angular dependency. The nanoDot? dosemeter has potential use as an in vivo dosimetric tool that is independent of the energy, has dose linearity and a rapid response compared with normal in vivo dosimetric tools, such as thermoluminescence detectors. However, the OSLD must be treated very carefully due to the high angular dependency of the photon beam.     

Fabrication of high-density In(3)Sb(1)Te(2) phase change nanoarray on glass-fabric reinforced flexible substrate

Mushroom-shaped phase change memory (PCM) consisting of a Cr/In(3)Sb(1)Te(2) (IST)/TiN (bottom electrode) nanoarray was fabricated via block copolymer lithography and single-step dry etching with a gas mixture of Ar/Cl(2). The process was performed on a high performance transparent glass-fabric reinforced composite film (GFR Hybrimer) suitable for use as a novel substrate for flexible devices. The use of GFR Hybrimer with low thermal expansion and flat surfaces enabled successful nanoscale patterning of functional phase change materials on flexible substrates. Block copolymer lithography employing asymmetrical block copolymer blends with hexagonal cylindrical self-assembled morphologies resulted in the creation of hexagonal nanoscale PCM cell arrays with an areal density of approximately 176?Gb/in(2).     

Large thermoelectric figure-of-merits from SiGe nanowires by simultaneously measuring electrical and thermal transport properties

The strongly correlated thermoelectric properties have been a major hurdle for high-performance thermoelectric energy conversion. One possible approach to avoid such correlation is to suppress phonon transport by scattering at the surface of confined nanowire structures. However, phonon characteristic lengths are broad in crystalline solids, which makes nanowires insufficient to fully suppress heat transport. Here, we employed Si-Ge alloy as well as nanowire structures to maximize the depletion of heat-carrying phonons. This results in a thermal conductivity as low as ～1.2 W/m-K at 450 K, showing a large thermoelectric figure-of-merit (ZT) of ～0.46 compared with those of SiGe bulks and even ZT over 2 at 800 K theoretically. All thermoelectric properties were "simultaneously" measured from the same nanowires to facilitate accurate ZT measurements. The surface-boundary scattering is prominent when the nanowire diameter is over ～100 nm, whereas alloying plays a more important role in suppressing phonon transport for smaller ones.     

Microstructure and electrical property of TiNx films deposited by DC reactive magnetron sputtering superimposed electromagnetic field system

TiNx films were successfully deposited by DC reactive magnetron sputtering superimposed EMF system without substrate heating. In case of DCMS 400 W+ EMF 25 W, electrical property, reflectance and crystallinity of the TiN films were clearly improved by the enhancement of nitrification. The lowest sheet resistance of 2.9 Ω/? (resistivity 5.8 x 10(-5) Ωcm) was observed for the film deposited at F(N)2: 16%. Mixture phases of the (111) plane and (200) plane showed lower resistivity than only (200) single phase. Therefore it is confirmed that introduction of EMF system is promising technology to deposit TiN film.     

New polymeric buffer materials with low driving voltage

We present excellent polymeric buffer materials based on the poly(9,9-dioctylfluorene-co-N, N-di(phenyl)-N,N-di(3-carboethoxyphenyl)benzidine) (BFE) for highly efficient solution processed organic light emitting diodes (OLEDs). Doped BFE with 3,5-dinitrobenzonitrile (35DNBN), a strong electron acceptor results in significant improvement of current flow and driving voltage. Maximum current- and power-efficiency value of 7.2 cd/A and 5.5 lm/W are demonstrated from blue OLEDs with these doped polymeric anode buffer system. The 40 nm thick anode buffer material showed a similar current density-voltage (J-V) behavior to that of PEDOT:PSS based device. Results reveal a practical way to fabricate the highly efficient solution processed devices for low cost production of printing devices for the future.     

Effect of solution-processed niO thin film as a hole transport layer in poly(3-hexylthiophene): [6,6]-phenyl C61-butyric acid methyl ester bulk heterojunction solar cells

In this study, solution-processed nickel oxide (NiO) thin film was investigated as a hole transport layer on anode to improve the performance of bulk heterojunction solar cell based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). We fabricated NiO thin film without any vacuum-related process. Characterization of the NiO film under this study shows that it has maximum transmittance of 93.22% and bandgap of 3.84 eV which are proper for solar cell. Insertion of the NiO layer affords to realize enhanced power conversion efficiency of 1.97% and fill factor of 52.11% showing improvement over existing cells. In addition, NiO suggests one solution of minimizing conventional problems of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) such as interfacial power losses, corrosion of indium tin oxide layer, and degradation of the devices. The value of such hole transporting and electron blocking properties is clearly demonstrated and could be applicable to other organic photovoltaics.     

Preparation of C60(O)n-ZnO nanocomposite under electric furnace and photocatalytic degradation of organic dyes

Zinc oxide (ZnO) nanoparticles were synthesized sonochemically by applying ultrasonic irradiation to a mixed aqueous-alcoholic solution of zinc nitrate with sodium hydroxide at room temperature. The morphology and optical properties of the ZnO nanoparticles were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis spectroscopy. The C60(O)n nanoparticles were synthesized by heating a mixture of C60 and 3-chloroperoxybenzoic acid in a benzene solvent under the reflux system. The heated C60(O)n-ZnO nanocomposite was synthesized in an electric furnace at 700 degrees C for two hours. The heated C60(O)n-ZnO nanocomposite was characterized by XRD, SEM, and TEM, and examined as a catalyst in the photocatalytic degradation of organic dyes by UV-vis spectroscopy. The photocatalytic effect of the heated C60(O)n-ZnO nanocomposite was evaluated by a comparison with that of unheated C60(O)n nanoparticles, heated C60(O)n nanoparticles, and unheated C60(O)n-ZnO in organic dyes, such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) under ultraviolet light at 365 nm.