Design of organic supercapacitors with high performances using pore size controlled active materials

In this study, we thoroughly investigate the required properties of active materials for organic supercapacitors with high performances. In this regard, we synthesize carbon xerogels with different physical properties, including specific surface area and pore size. The carbon xerogels are prepared via the sol-gel reaction of resorcinol and formaldehyde under different gelation temperature conditions. Through Fourier-transform infrared, nitrogen adsorption–desorption, and scanning electron microscopy analysis, we can confirm that carbon xerogels with different physical properties can be successfully synthesized. We apply the prepared carbon xerogels to organic supercapacitor electrodes. As a result of electrochemical experiments, carbon xerogels with high surface area exhibit high electrochemical performances at low-rate charge?discharge processes. However, as the charge–discharge rate increases, carbon xerogels with low surface area and high conductivity exhibit higher performances. Therefore, the surface area of active materials is a key factor for supercapacitors with high performances at low-rate charge–discharge processes. However, the effects of conductivity can be more crucial as compared with those of surface area as the charge–discharge rates increase. In addition, we suggest that the physical properties of active materials should be differently optimized as the charge–discharge rate is employed.     

Hydrothermal growth of ZnO nanorods on a-plane GaN/sapphire template

ZnO nanorod arrays are grown on a-plane GaN template/r-plane sapphire substrates by hydrothermal technique. Aqueous solutions of zinc nitrate hexahydrate and hexamethylenetetramine were employed as growth precursors. Electron microscopy and X-ray diffraction measurements were carried out for morphology, phase and growth orientation analysis. Single crystalline nanorods were found to have off-normal growth and showed well-defined in-plane epitaxial relationship with the GaN template. The 〈0 0 0 1〉 axis of the ZnO nanorods were observed to be parallel to the 〈1 0 1¯ 0〉 of the a-plane GaN layer. Optical property of the as-grown ZnO nanorods was analyzed by room temperature photoluminescence measurements.     

Monoolein cubic phase containing alginate/cystamine gel for controlled release of epidermal growth factor

Monoolein (MO) cubic phase including alginate and cystamine in its water channel controlled the release of epidermal growth factor (EGF) by responding to changes in pH value and the reductive conditions of the release medium. The crosslinking degree of alginate gel with cystamine and the complex coacervation of alginate and EGF were investigated by using light scattering. TEM micrographs of cubic phases revealed MO bilayers along with water channels. Differential scanning calorimetry indicated that the cubic-to-hexagonal phase transition took place at 60.2?°C. Additives such as stearyl trimethyl ammonium chloride and cystamine decreased the transition temperature by a few to more than 10?°C. The release of EGF loaded in cubic phases was completed in 5?h and, thereafter, no significant additional release was observed. The release % of EGF loaded in MO cubic phase containing alginate and cystamine increased not only with the increase of pH but also glutathione concentration. The MO cubic phase containing alginate/cystamine gel can be used as a carrier for the delivery of peptide and protein drugs.     

Structural and interfacial stabilities of epitaxial (11-20)-oriented wurtzite AlN films grown on lattice-matched MnS buffered Si(100)

Epitaxial growth of non-polar wurtzite (11-20) AlN thin films was achieved on a Si(100) substrate by inserting an MnS buffer layer. The a-plane AlN film and MnS buffer layer were fabricated by pulsed KrF excimer laser deposition, and their micro- and interfacial atomic structures were investigated by transmission electron microscopy. The epitaxial relationship between films and substrate was found to be AlN(11-20)MnS(100)Si(100) with in-plane alignment of AlN[1-101]MnS[011]Si[011]. AlN[11-20] grown on Si is perpendicular to AlN[0001] and parallel to MnS[100]. The MnS/Si interface is abrupt enough to inherit the orientation of the Si(100) surface. A sharp interface was also observed for AlN/MnS without any intermediate layer. PACS 81.05.Ea; 81.05.Zx; 81.15.Fg; 68.37.Lp     

High-definition PIV analysis on vortex shedding in the cylinder wake

A high-definition analysis based on flow topology is made on the vortex motions under natural and lock-on conditions in the near-wake region of a circular cylinder, where two-dimensional flow fields in the wake-transition regime are measured by a time-resolved PIV system. The Reynolds stress distributions are examined in view of the mean separation streamline and the trajectory ofthe vortex center. It is shown that, by the lock-on, the Reynolds stresses become stronger and their dispositions match well with the shortened wake bubble, indicating perfect synchronization of shedding to the oscillatory forcing flow in the near field, which causes increased lift and drag forces.     

Self-assembled arrays of zinc oxide nanoparticles from monolayer films of diblock copolymer micelles

A hexagonal array of optically active ZnO nanoparticles was synthesized in situ on the solid substrate by utilizing a single-layered film of diblock copolymer micelles as a nanostructured template.     

Superstrate p-i-n a-Si:H solar cells on textured ZnO:Al front transparent conduction oxide

Superstrate p-i-n amorphous silicon thin-film (a-Si:H) solar cells are prepared on SnO₂:F and ZnO:Al transparent conducting oxides (TCOs) in order to see the effect of TCO/p-layers on a-Si:H solar cell operation. The solar cells prepared on textured ZnO:Al have higher open circuit voltage V_oc than cells prepared on SnO₂:F. The presence of a thin microcrystalline p-type silicon layer (μc-Si:H) between ZnO:Al and p a-SiC:H plays a major role by causing an improvement in the fill factor as well as in V_oc of a-Si:H solar cells prepared on ZnO:Al TCO. Without any treatment of the p-i interface, we could obtain a high V_oc of 994 mV while keeping the fill factor (72.7%) and short circuit current density J_sc at the same level as for the cells on SnO₂:F TCO. This high V_oc value can be attributed to modification in the current transport in this region due to creation of a potential barrier.