Won-Seok Chae

Implication of Liquid-Phase Deposited Amorphous RuO2 Electrode for Electrochemical Supercapacitor

Amorphous ruthenium oxide (RuO 2 ) thin films of uniformly distributed spherical nanoregime grains were synthesized by the liquid-phase chemical bath deposition route at room temperature (333 K) for the first time. It is an attractive synthesis route to fabricate RuO 2 electrodes for high electrochemical supercapacitor applications. Chemically deposited RuO 2 thin films showed a bandgap energy of 3.37 eV and exhibited >400 F/g specific capacitance at the scan rate of 5 mV/s in 0.5 M H 2 SO 4 .

Effects of operational and geometrical conditions upon photosensitivity of amorphous InZnO thin film transistors

The photosensitivity of an amorphous oxide semiconductor thin film transistor (TFT) with an In-Zn-O (IZO) layer as the active channel passivated with SiO2 is investigated. Under illumination, the photocurrent (IPhoto) in the off regime is greatly increased rather than displaying a negative shift of the threshold voltage. In this way, the photosensitivity (IPhoto/IDark) can be maximized by adjusting a reading bias to be placed in the off regime. Furthermore, the photosensitivity is significantly influenced by operational and geometrical conditions, such as the bias voltages and the active layer thickness. In particular, for a 1500-A-thick IZO TFT, the photosensitivity is increased by a factor of almost eight orders of magnitude. This suggests back channel conduction of excess electrons generated from the optically ionized oxygen vacancies (Vo++) where the gate voltage-induced electric field is screened.

Spectral Shifts of Electroluminescence from Porous n‐Si under Cathodic Bias

Spectral shifts of visible electroluminescence (EL) from cathodically biased n-Si in electrolyte solution containing persulfate ions are described. The electrochemically etched n-Si cathodes exhibit a blue shift of the EL with the increase of applied potential. It is explained that the blue shift is caused by the formation of an accumulation layer and the Fermi level pinning in the porous Si. A study of the EL as a function of time at a constant potential shows a red shift, which can be attributed to the bandgap lowering caused by the conversion of the predominant surface bonds Si-H to Si-Si. Electro-polymerization of aniline on the porous Si surface enhanced the stability of the EL possibly due to the strengthening of the surface bonds.

Time-Dependent Mass Changes of Nanocrystalline TiO2 Thin Film Electrodes under Negative Bias in Propylene Carbonate

Time-dependent changes in the mass of nanocrystalline TiO 2 thin film electrodes coupled with absorbance and current-voltage variations were monitored in propylene carbonate containing LiClO 4 . The onset potential for the absorbance at 800 nm lagged behind that for the mass increase by about 0.3 V, which is related to the energy required to desolvate Li + ions adsorbed on the TiO 2 surface prior to intercalation into the TiO 2 lattice. The intercalated Li + ions can accumulate in TiO 2 by repetitive scanning between 0.0 V and an intercalation-occurring potential. Absorption of UV light by TiO 2 affected both the Li + ion desorption from the electrode and possibly the chemical nature of the TiO 2 surface. The potential dependence on the irreversible mass decrease under UV illumination is linked to the flatband potential.

Synthesis of freestanding cupric oxide nanotubes with close ends from copper nanowires by the Kirkendall effect

Vertically grown cupric oxide semiconductors have a number of applications such as chemical sensors, nanogas sensors, and catalysts. Typically, a template based synthesis technique is used followed by an additional wet etching process for the synthesis of vertically oriented cupric oxide nanotubes. However, such a synthesis technique has some inherent disadvantages, notably, the obvious complexities involved in the process and the possibility of contamination and deformation of the structure. Here, the authors report the growth of freestanding copper nanostructures via metal organic chemical vapor deposition, followed by thermal oxidation. To the best of our knowledge, this is the first report of a successful synthesis of vertically aligned cupric oxide nanotubes with closed ends from copper nanowires. The synthesis was performed at 300 °C in air via the Kirkendall effect without the use of any template. Subsequently, the 5 μm long copper nanowires having diameters of 70 nm were thermally oxidized to yiel...