Chi-Young Lee

(110)-exposed gold nanocoral electrode as low onset potential selective glucose sensor.

A straightforward electrochemical deposition process was developed to grow gold nanostructures, including nanocoral, nanothorn, branched belt, and nanoparticle, on carbon electrodes by reducing HAuCl4 under constant potentials in mixtures containing CTAC and/or NaNO3. Among the nanostructures, the quasi-one-dimensional nanocoral electrode showed the highest surface area. Because of this, it provided excellent electrochemical performances in cyclic voltammetric (CV) studies for kinetic-controlled enzyme-free glucose oxidation reactions. In amperometric studies carried out at 0.200 V in PBS (pH 7.40, 0.100 M), the nanocoral electrode showed the highest anodic current response. It also offered the greatest sensitivity, 22.6 μAmM(-1)cm(-2), an extended linear range, 5.00×10(-2) mM to 3.00×10(1) mM, and a low detection limit, 1.00×10(1) μm among the electrodes investigated in this study. In addition, the glucose oxidation by the nanocoral electrode started at -0.280 V, more negative than the one of using a commercial Au electrode as the working electrode. This is attributed to the presence of exposed Au (110) surfaces on the electrode. The feature was applied to oxidize glucose selectively in the presence of ascorbic acid (AA) and uric acid (UA), common interferences found in physiological analytes. With an applied voltage at -0.100 V, the AA oxidation (started at -0.080 V) can be avoided while the glucose oxidation still provides a significant response.

Preparing titanium oxide with various morphologies

Titanium oxide powder was prepared by hydrolyzing titanium tetraisopropoxide (TTIP) in aqueous solutions at pH 2, using TMC and NP-204 as surfactants. The anatase phase was formed when the precipitants were dried at 373 K. When the calcination temperature was below 773 K, all the powders were crystalline in the anatase phase. The powders changed to the rutile phase when the calcination temperature exceeded 1173 K. The powder calcined at 673 K has spherical primary particles with diameters of approximately 8 nm. When the powders calcined at 673 K were heated in NaOH solutions of various concentrations at 423 K for 20 h, titanium oxide powders with different morphologies were obtained. After the powders were refluxed in 5 M NaOH solutions, flower-like titanium oxide particles were formed. Nanotubes of titanium oxide about 8 nm in diameter and over 600 nm long were obtained when the powders were refluxed in 10 M NaOH solution.

Gold Nanostructures on Flexible Substrates as Electrochemical Dopamine Sensors

In this study, we fabricated Au nanowires (NWs), nanoslices (NSs), and nanocorals (NCs) on flexible polyethylene terephthalate (PET) substrates via direct current electrochemical depositions. Without any surface modification, the Au nanostructures were used as the electrodes for dopamine (DA) sensing. Among them, the Au NW electrode performed exceptionally well. The determined linear range for DA detection was 0.2-600 μM (N = 3) and the sensitivity was 178 nA/μM cm(2), while the detection limit was 26 nM (S/N = 3). After 10 repeated measurements, 95% of the original anodic current values were maintained for the nanostructured electrodes. Sequential additions of citric acid (CA, 1 mM), uric acid (UA, saturated), and ascorbic acid (AA, 1 μM) did not interfere the amperometric response from the addition of DA (0.1 μM).

One-step vapor–solid reaction growth of Sn@C core–shell nanowires as an anode material for Li-ion batteries

Sn@C core–shell nanowires (NWs) were synthesized by reacting SnO2 particles with a flowing mixture of C2H2 and Ar gases at elevated temperatures. The overall diameter of the core–shell nanostructure was 100–350 nm. The C shell thickness was 30–70 nm. The NW length was several micrometers. Inside the shell, a void space was found. The reaction is proposed to be via a vapor–solid reaction growth (VSRG) pathway. The NWs were investigated as a potential anode material for Li-ion batteries (LIBs). The half-cell constructed from the as-fabricated electrode and a Li foil exhibited a reversible capacity of 525 mA h g−1 after one hundred cycles at a current density of 100 mA g−1. At a current density as high as 1000 mA g−1, the battery still maintained a capacity of 486 mA h g−1. The excellent performance is attributed to the unique 1D core–shell morphology. The core–shell structure and the void space inside the shell can accommodate large volume changes caused by the formation and decomposition of LixSn alloys in the charge–discharge steps.

Field emission enhancement in nitrogen-ion-implanted ultrananocrystalline diamond films

Enhanced electron field emission (EFE) properties for ultrananocrystalline diamond (UNCD) films grown on silicon substrate were achieved, especially due to the high dose N ion implantation. Secondary ion mass spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy measurements indicated that the N ion implantation first expelled H−, induced the formation of disordered carbon (or defect complex), and then induced the amorphous phase, as the ion implantation dose increased. The postimplantation annealing process healed the atomic defects, but converted the disordered carbon to a stable defect complex, and amorphous carbon into a more stable graphitic phase. The EFE characteristics of the high dose (>1015ions∕cm2) ion-implanted UNCD were maintained at an enhanced level, whereas those of the low dose (<1014ions∕cm2) ion-implanted ones were reverted to the original values after the annealing process. Ion implantation over a critical dose (1×1015ions∕cm2) was required to improve the EFE propertie...

Highly durable anodes of microbial fuel cells using a reduced graphene oxide/carbon nanotube-coated scaffold.

Melamine sponges coated with reduced graphene oxide/carbon nanotube (rGO-CNT sponges) through a dip-coating method were fabricated that provide a large electrical conductive surface for Escherichiacoli growth and electron transfer in microbial fuel cell. Four rGO-CNT sponges with different thicknesses and arrangements were tested as an anode in this study. The thinnest one (with a thickness of 1.5mm) exhibited the best performance, providing a maximum current density of 335 A m(-3) and a remarkably durable life time of 20 days at 37 °C. Analyses of bacterial colonisation on the rGO-CNT sponges using FE-SEM and the bacterial metabolic activity using the β-galactosidase assay indicates that the rGO-CNT sponges provide excellent biocompatibility for E. coli proliferation and could help to maintain high bacterial metabolic activity, presumably due to the high mass transfer rate of the porous scaffold. In this regard, the rGO-CNT sponges showed higher durability and performed better electrochemical properties than traditional carbon-based and metal-based anodes.

Large-scale synthesis of uniform Cu2O nanocubes with tunable sizes by in-situ nucleation

Uniform Cu2O nanocubes with various sizes were synthesized by reducing Cu(OH)2 using ascorbic acid in the presence of various amounts of sodium citrate. The monodispersed nanocubes with an edge length of approximately 80 nm used as an anode exhibit excellent lithium storage behavior.

Self-carbonized lamellar nano/micro hierarchical structure C/TiO2 and its Li-ion intercalation performance

In this study, two new layered titanates, fibrillar TiO2·(CH3COOH)1.4 and chrysanthemum-like TiO2·(CH3COOH)0.9 (named as FT and CT) with acetic acid and acetate intercalation have been synthesized by reacting titanium isopropoxide (TTIP) with acetic acid at different temperatures. Furthermore, nano/micro hierarchical structure TiO2 with high TiO2-B/anatse ratio was obtained by annealing the titanate (CT). For use as an anode for lithium ion batteries, uniform carbon coated titanium dioxide with high TiO2-B content was obtained by “self-carbonizing” CT under argon atmosphere at 350 °C, and the compound was named SC-CT350. The capacity of the anode made from SC-CT350 can reach 144 mA h g−1 under a high charging/discharging rate (10 C) and showed excellent retention ability.

Fabrication of an ultra-nanocrystalline diamond-coated silicon wire array with enhanced field-emission performance

Large-area ultra-nanocrystalline diamond-coated silicon nanowire (UNCD/SiNW) field-emitter arrays were prepared by the deposition of ultra-nanocrystalline diamond (UNCD) on the tips of arrays of silicon nanowires (SiNWs) with uniform diameters. The electron field-emission (EFE) behavior of UNCD/SiNW arrays as well as that of the SiNW arrays has been observed. The SiNWs exhibit good electron field-emission properties with turn-on fields (E0) of about 7.6 V µm−1, which is superior to the EFE properties of planar-silicon materials. The turn-on fields are related to the diameter of the SiNWs. Coating the SiNWs with a UNCD film further improves their EFE properties. The threshold field for attaining Je = 0.1 mA cm−2 EFE current density is 16.0 V µm−1 for bare SiNWs and 10.2 V µm−1 for UNCD/SiNWs. The improvement in EFE properties due to the UNCD coating is presumably due to the lower work function of field emission of the UNCD materials, compared to that of the silicon materials.

Effects of high energy Au-ion irradiation on the microstructure of diamond films

The effects of 2.245 GeV Au-ion irradiation and subsequent annealing processes on the evolution of microstructure of diamond films with microcrystalline (MCD) or ultra-nanocrystalline (UNCD) granular structure were investigated, using near edge x-ray absorption fine structure and electron energy loss spectroscopy in transmission electron microscopy. For MCD films, the Au-ion irradiation disintegrated some of the diamond grains, resulting in the formation of nano-sized carbon clusters embedded in a matrix of amorphous carbon (a-C). The annealing process recrystallized the diamond grains and converted the a-C into nano-sized graphite particulates and, at the same time, induced the formation of nano-sized i-carbon clusters, the bcc structured carbon with a0 = 0.432 nm. In contrast, for UNCD films, the Au-ion irradiation transformed the grain boundary phase into nano-sized graphite, but insignificantly altered the crystallinity of the grains of the UNCD films. The annealing process recrystallized the material...