Young Soo Yoon

Electrochemical and structural properties of radio frequency sputtered cobalt oxide electrodes for thin-film supercapacitors

The electrochemical and structural properties of cobalt oxide films which are deposited at different sputtering gas-ratios of O2/(Ar+O2) are investigated. In order to examine the electrochemical properties of the as-deposited films, all solid-state thin-film supercapacitors (TFSCs) are fabricated. There consist of Co3O4 electrodes and an amorphous LiPON thin-film electrolyte. It is shown that the capacitance behaviour of the Co3O4/LiPON/Co3O4 TFSCs is similar to bulk-type supercapacitor behaviour. It is further shown that the electrochemical behaviour of the TFSCs is dependent on the sputtering gas-ratios. The gas-ratio dependence of the capacitance of the oxide electrode films is discussed based on X-ray diffraction (XRD) and electrical results for the Co3O4 films.

Solid-state thin-film supercapacitor with ruthenium oxide and solid electrolyte thin films

Abstract Direct current reactive sputtering deposition of ruthenium oxide thin films (bottom and top electrodes) at 400°C are performed to produce a solid-state thin-film supercapacitor (TFSC). The supercapacitor has a cell structure of RuO2/Li2.94PO2.37N0.75 (Lipon)/RuO2/Pt. Radio frequency, reactive sputtering deposition of an Li2.94PO2.37N0.75 electrolyte film is performed on the bottom RuO2 film at room temperature to separate the bottom and top RuO2 electrodes electrically. The stoichiometry of the RuO2 thin film is investigated by Rutherford back-scattering spectrometry (RBS). X-ray diffraction (XRD) shows that the as-deposited RuO2 thin film is an amorphous phase. Scanning electron microscopy (SEM) measurements reveal that the RuO2/Lipon/RuO2 hetero-interfaces have no inter-diffusion problems. Charge–discharge measurements with constant current at room temperature clearly reveal typical supercapacitor behaviour for a RuO2/Lipon/RuO2/Pt cell structure. Since the electrolyte thin film has low ionic mobility, the capacity and cycle performance are inferior to those of a bulk type of supercapacitor. These results indicate that a high performance, TFSC can be fabricated by a solid electrolyte thin film with high ionic conductivity.

Nanostructured Ni3Sn2 thin film as anodes for thin film rechargeable lithium batteries

Abstract Thin film Ni 3 Sn 2 anodes were deposited on a Cu substrate by e-beam evaporator at room temperature. The deposited films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). They were tested as anodes for thin film rechargeable lithium batteries. These film electrodes exhibited an excellent cycle performance over 500 cycles. Ni 3 Sn 2 films remained without undergoing any crystallographic phase change during cycling.

Radio-Frequency Magnetron Sputtering Power Effect on the Ionic Conductivities of Lipon Films

gas atmosphere with different radio-frequency magnetronsputtering power from 80 to 160 W with 20 W step increase. Lipon films deposited at lower sputtering power showed higher ionicconductivities than the films deposited at higher sputtering power. The results of impedance measurements showed that nitrogenincorporation into the glass structure increased the ionic conductivity and this nitrogen content in the Lipon films increased as thesputtering power decreased. In addition, the Auger electron spectroscopy depth profile showed that the increased nitrogen contentin the Lipon films was not the result of the target surface poisoning effect but the result of reactive incorporation of nitrogen.© 2001 The Electrochemical Society. @DOI: 10.1149/1.1420926# All rights reserved.Manuscript submitted May 29, 2001; revised manuscript received September 21, 2001. Available electronically November 8,2001.

Vertically Aligned ZnO Nanorod Sensor on Flexible Substrate for Ethanol Gas Monitoring

Vertically aligned ZnO nanorods were grown on flexible polyimide films by a thermolysis assisted chemical solution method to fabricate an ethanol sensing material. Flexible ZnO nanorod sensors were examined to monitor ethanol gas by varying the working temperature from 300 to 125°C and by changing the ethanol concentration in a range from 100 to 10 ppm in synthetic air. A flexible ZnO nanorod sensor can detect 100 ppm of ethanol gas with a sensitivity of 3.11 at 300°C. When compared with ZnO nanorod sensors fabricated on a silicon dioxide hard substrate, its sensing performance exhibited competitive sensitivity.

Hollow Nanobarrels of α-Fe2O3 on Reduced Graphene Oxide as High-Performance Anode for Lithium-Ion Batteries

Alpha-phase iron oxide nanoparticles (α-NPs), α-iron oxide hollow nanobarrels (α-HNBs), and α-HNBs on reduced graphene oxide (α-HNBs/RGO) for Li-ion batteries (LIBs) were synthesized by a time-efficient microwave method to improve the low electrical conductivity of iron oxide and exploit the porous structure of RGO, which prevents the volume expansion of α-Fe2O3 during the insertion/extraction. On the other hand, α-HNBs (∼200 nm in diameter, ∼360 nm in length) provide a short diffusion path for Li ions and accommodate the strain generated by the volume change. The α-HNBs/RGO hybrid structure was synthesized by a one-step microwave-assisted hydrothermal method to bond α-HNBs with RGO. The as-prepared α-HNBs/RGO electrode exhibited a superior reversible capacity of 1279 mA h g(-1) at 0.5 C after the first cycle; such a capacity was nearly recovered after numerous cycles (2nd to 100th cycle, 95%). The long-term cyclability of α-HNBs/RGO shows 478 mA h g(-1) after 1000 cycles. Moreover, the α-HNBs/RGO electrode shows a high rate capacity of 403 mA h g(-1) even at 10 C. The α-HNBs/RGO exhibited a better electrochemical performance that could be attributed to the absence of nanoparticle agglomeration and RGO restacking, which provided a buffer effect against the volume expansion, promoted electrical conductivity and high structural integrity.

Au-decorated WO3 cross-linked nanodomes for ultrahigh sensitive and selective sensing of NO2 and C2H5OH

Au-decorated WO3 cross-linked nanodomes are fabricated using soft templates composed of highly ordered polystyrene beads and self-agglomeration of Au. The distribution and size of Au nanoparticles on the surface of WO3 cross-linked nanodomes are controlled by varying the thickness of the initial Au film. The responses of Au-decorated WO3 cross-linked nanodomes to various gases such as NO2, CH3COCH3, C2H5OH, NH3, CO, H2, and C6H6 are at least 5 times higher than those of bare WO3 cross-linked nanodomes. The response enhancement by Au decoration is dependent on the target gas, which is attributed to an interplay between electronic and chemical sensitizations. In particular, the Au-decorated WO3 cross-linked nanodomes exhibit extremely high sensitivities and selectivities, and ppt-level detection limits to NO2 and C2H5OH at 250 °C and 450 °C, respectively. These results suggest that Au-decorated WO3 cross-linked nanodomes are very promising for use in breath analysers to diagnose both asthma and lung cancer from exhaled human breath.

All solid-state rechargeable thin-film microsupercapacitor fabricated with tungsten cosputtered ruthenium oxide electrodes

We investigate an all solid-state thin-film microsupercapacitor (TFSC) fabricated with tungsten cosputtered ruthenium oxide electrodes (W-RuO2) and LiPON electrolyte. It is shown that the room-temperature charge–discharge behavior of the TFSC is similar to that of a bulk-type supercapacitor. It is also shown that the W-RuO2-based TFSC exhibits a higher discharge specific capacitance and more stable cyclibility, compared with those of the RuO2-based TFSC. Based on the pseudocapacitance of the oxide electrodes, the cycling behavior of the TFSCs and tungsten cosputtering effect on the electrochemical properties of TFSCs are described.

Structural properties of BaTiO3 thin films on Si grown by metalorganic chemical vapor deposition

Ferroelectric BaTiO3 thin films were grown on Si(100) substrates at a temperature of 600 °C by in situ metalorganic chemical vapor deposition. X‐ray diffraction and transmission electron microscopy results suggested that the 〈110〉 direction of the BaTiO3 preferred oriented films is parallel with the (100) direction of the Si substrates. Auger electron spectroscopy measurements showed that the compositions of the as‐grown films were with a uniform distribution throughout the thickness of the films and with a sharp interface. These results indicate that the failure to obtain BaTiO3 epitaxial films was due to the formation of an interfacial amorphous layer prior to the creation of the films.

Correlation between the microstructures and the cycling performance of RuO2 electrodes for thin-film microsupercapacitors

We have fabricated all solid-state thin-film microsupercapacitors (TFSCs) using RuO2 electrodes and LiPON electrolytes. The RuO2 electrodes were grown at oxygen gas flow ratios [O2/(O2+Ar)] of 10% and 30%. Room-temperature charge–discharge measurements show that specific capacitance is dependent on the oxygen gas flow ratio. Glancing angle x-ray diffraction (GXRD) and transmission electron microscopy (TEM) results show that the RuO2 electrodes grown at 10% contain nanocrystallites (0.7–10 nm across) embedded in the amorphous matrix, while the electrodes grown at 30% are polycrystalline (with grains of 0.7–15 nm in diameter). Based on the GXRD, TEM, Auger electron spectroscopy depth profile, and scanning electron microscopy results, the oxygen flow ratio dependence of the cycling performance of the RuO2-based TFSCs are discussed in terms of the combined effects of the microstructures of the electrodes, interfacial products, and the surface morphology of the electrodes.