Yi-Min Chen

A nanostructured electrode of IrOx foil on the carbon nanotubes for supercapacitors

IrO(x) nanofoils (IrO(x)NF) of high surface area are sputtered on multi-wall carbon nanotubes (CNT) in the preparation of a structured electrode on a stainless steel (SUS) substrate for supercapacitor applications. This IrO(x)/CNT/SUS electrode is featured with intriguing IrO(x) curved foils of 2-3 nm in thickness and 400-500 nm in height, grown on top of the vertically aligned CNT film with a tube diameter of ∼ 40 nm. These nanofoils are moderately oxidized during reactive sputtering and appeared translucent under the electron microscope. Detailed structural analysis shows that they are comprised of contiguous grains of iridium metal, iridium dioxide, and glassy iridium oxide. Considerable Raman line broadening is also evidenced for the attributed nanosized iridium oxides. Two capacitive properties of the electrode are significantly enhanced with addition of the curved IrO(x) foils. First, IrO(x)NF reduces the electrode Ohmic resistance, which was measured at 3.5 Ω cm(2) for the CNT/SUS and 2.5 Ω cm(2) for IrO(x)NF/CNT/SUS using impedance spectroscopy. Second, IrO(x)NF raises the electrode capacitance from 17.7 F g(-1) (CNT/SUS) to 317 F g(-1) (IrO(x)/CNT/SUS), measured with cyclic voltammetry. This notable increase is further confirmed by the galvanostatic charge/discharge experiment, measuring 370 F g(-1) after 2000 uninterrupted cycles between - 1.0 and 0.0 V (versus Ag/AgCl).

Synthesis and characterization of well-aligned anatase TiO2nanocrystals on fused silicavia metal–organic vapor deposition

Well-aligned anatase (A)–TiO2nanocrystals (NCs) were grown by cold-wall metalorganic chemical vapor deposition (MOCVD) on fused silica using titanium-tetraisopropoxide (Ti(OC3H7)4) as the source reagent. Field emission scanning electron microscopy (FESEM) micrographs showed the growth of vertically aligned NCs. X-ray diffractometry (XRD) pattern revealed the aligned A–TiO2 with a preferential orientation of (220). Raman spectrum confirmed the deposition of pure anatase phase TiO2 on fused silica. Luminescence of self-trapped excitons and oxygen vacancies were observed in anatase NCs. The indirect band gap of A–TiO2 was determined to be 3.14 ± 0.01 eV by analyzing the surface photovoltage spectrum. Energy-dispersive X-ray spectroscopy (EDS) and X ray photoelectron spectroscopy (XPS) analyses showed oxygenvs.titanium ratio of 2.0 ± 0.1 for the as-deposited TiO2 NCs. Further structural characterization of the well-aligned A–TiO2 NCs was studied using transmission electron microscopy (TEM) technique. The formation of building units bonded along {112} facets with preferred (220) orientation of the well-aligned A–TiO2 NCs on fused silica were presented and the probable growth mechanisms were discussed.

Pattern Growth and Field Emission Characteristics of Flower-Like RuO2 Nanostructures

A flower-like RuO2 nanostructure was selectively synthesized on a Si substrate by metal organic chemical vapor deposition (MOCVD). Bis(ethylcyclopentadienyl) ruthenium(II), Ru[(C2H5)C5H4]2, was shower sprayed onto the Si substrate with oxygen gas. Prior to the growth of the flower-like RuO2 nanostructure, patterns of Al and Fe films were deposited on the Si substrate by photolithography and electron beam (e-beam) evaporation deposition. The synthesized flower-like RuO2 nanostructures were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and micro-Raman spectroscopy. The results indicated that the flower-like nanostructures were RuO2 rutile structures with high crystallinity. For the particular synthesized morphology and design pattern, the current density and long-term stability characteristics of electron field-emission characteristics demonstrated that the flower-like RuO2 nanostructure has the potential to be used in a practical field-emission display.

Deposition and Characterization of Nanostructural IrOx by RF Sputtering

Large surface area nanostructural IrOx films were deposited on stainless steel substrates by reactive radio frequency magnetron sputtering using Ir metal target. The structural and spectroscopic properties of the nanostructural IrOx were characterized. The micrographs of field emission scanning electron microscopy showed the formation of folded leaves with chiffon-like structure for the as-deposited samples. X-ray photoelectron spectroscopy analysis provided the information of the oxidation states and the stoichiometry of IrOxNL. Raman spectra revealed the amorphous-like phase of the as-deposited nanostructural IrOx. The chiffon-like structure provides ultra-high surface area for electrical charge storage which makes the IrOxNL as an attractive candidate for the supercapacitor application.

Growth and Characterization of Well-Aligned RuO2/R-TiO2 Heteronanostructures on Sapphire (100) Substrates by Reactive Magnetron Sputtering

We report the growth of well-aligned RuO2/R-TiO2 heteronanostructures on sapphire (100) substrates by reactive magnetron sputtering using Ti and Ru metal targets under different conditions. The surface morphology and structural properties of the as-deposited heteronanostructures were characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffractometry (SAED). The FESEM micrographs and XRD patterns indicated the growth of vertically aligned RuO2(001) nanotubes and twinned V-shaped RuO2(101) nanowedges (NWs) on top of R-TiO2 nanorods under different sputtering pressures. TEM and SAED characterizations of the V-shaped RuO2 NWs showed that the NWs are crystalline RuO2 with twin planes of (101) and twin direction of [ 01] at the V-junction.

Deposition and Characterization of IrO2 Nanocrystals on Vertically Aligned Carbon Nanotubes by MOCVD

IrO2 nanocrystals (NCs) were grown on vertically aligned carbon nanotubes (CNTs) forming IrO2/CNTs nanocomposites by metal organic chemical vapor deposition using (C6H7)(C8H12)Ir as a source reagent. The surface morphology, structural and spectroscopic properties of the nanocomposites were characterized. Micrographs of field-emission scanning electron microscope showed that the surface morphology of the as-deposited IrO2 NCs varied from particle-like to tube-like NCs as the deposition time increased from 5 to 60 min. The transmission electron microscope image of IrO2/CNTs nanocomposites revealed that IrO2 NCs had been deposited onto the surface of the CNTs with uniform size distribution and random directions. X-ray diffraction pattern confirmed the formation of pure rutile IrO2 NCs on CNTs. The redshifts of the peak positions and broadening of linewidths of the IrO2 Raman features were attributed mainly to the size effect. The particles-like IrO2 NCs may be used as a protective layer on CNTs, providing stable and uniform field emission application. While the nanotube-like structure may increase the surface-to-volume ratio which makes the IrO2/CNTs nanocomposites as an attractive candidate for the supercapacitor application.

Characterization of RuO 2 nanocrystals deposited on carbon nanotubes by reactive RF sputtering

RuO2 nanocrystals (NCs) were deposited on carbon nanotubes (CNTs) by reactive RF magnetron sputtering using a Ru target under different conditions. Their surface morphology, structural, spectroscopic and field emission (FE) properties were studied using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), Raman spectroscopy, and a home made high vacuum FE measurement system. FESEM micrographs showed that the surface morphology of the as-deposited RuO2 varied from nanoparticles-like to tube-like NCs as the oxygen flux increased from 2 to 10 sccm. The TEM image of RuO2-coated CNTs revealed that uniform distribution and random direction of RuO2 NCs had been deposited on the surface of the CNTs. The red-shifts of the peak positions and broadening of linewidths of the Raman features were attributed to both the size and residual stress effects. The FE characteristics revealed a low operating electric field and stable emission current in the RuO2-coated CNTs.

Enhanced field emission properties of IrO 2 coated carbon nanotube bundle arrays

In order to enhance field emission (FE) property of carbon nanotubes (CNTs), IrO 2 nanocrystals (NCs) were coated on the patterned CNT bundle arrays via reactive RF magnetron sputtering. The properties of IrO 2 /CNTs composites were characterized by field-emission scanning electron microscopy and transmission electron microscopy. Based on the combined effects of geometrical structure of IrO 2 /CNTs composites, and the natural conductor and enhanced resistance to oxidation properties of IrO 2 , a low turn-on field of 0.7 V/µm at a current density of 0.1 µA/cm2, a low threshold field of 2.3 V/µm at a current density of 1 mA/cm2, a high field enhancement factor of 4 × 105, and a long-term stability have been achieved for the IrO 2 coated patterned CNT bundle arrays.