Ming-Chung Wu

Nitrogen-Doped Anatase Nanofibers Decorated with Noble Metal Nanoparticles for Photocatalytic Production of Hydrogen

We report the synthesis of N-doped TiO(2) nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol-water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N-Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO(2) nanofiber decorated with Pt nanoparticles) was applied to 1 L of water-ethanol mixture, the H(2) evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h (UV-B) corresponding to photo energy conversion percentages of ∼3.6 and ∼12.3%, respectively.

Eco-friendly plasmonic sensors: using the photothermal effect to prepare metal nanoparticle-containing test papers for highly sensitive colorimetric detection.

Convenient, rapid, and accurate detection of chemical and biomolecules would be a great benefit to medical, pharmaceutical, and environmental sciences. Many chemical and biosensors based on metal nanoparticles (NPs) have been developed. However, as a result of the inconvenience and complexity of most of the current preparation techniques, surface plasmon-based test papers are not as common as, for example, litmus paper, which finds daily use. In this paper, we propose a convenient and practical technique, based on the photothermal effect, to fabricate the plasmonic test paper. This technique is superior to other reported methods for its rapid fabrication time (a few seconds), large-area throughput, selectivity in the positioning of the NPs, and the capability of preparing NP arrays in high density on various paper substrates. In addition to their low cost, portability, flexibility, and biodegradability, plasmonic test paper can be burned after detecting contagious biomolecules, making them safe and eco-friendly.

Quantitative nanoscale monitoring the effect of annealing process on the morphology and optical properties of poly(3-hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester thin film used in photovoltaic devices

We have studied the nanoscale changes in morphology and optical properties during annealing for bulk-heterojunction poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) composite film. Thermal atomic force microscopy was used to monitor the morphology evolution of the film in situ quantitatively, which showed a migration and aggregation of PCBM with increasing temperature. Scanning near-field microscopy was used to investigate the quantitative changes in absorption behavior of the film in nanoscale with increasing annealing time at 140 °C, which indicated that the extent of absorption of the film was increased with increasing annealing time. However, a large PCBM aggregate (1 μm) was formed after the film annealed at 140 °C for 1 h. The aggregate interrupted the bicontinous morphology of the film and further affected the absorption behavior in nanoscale. Furthermore, the refractive index and extinction coefficient of the films increased after annealed 30 min at 140 °C, but d...

Polarization-dependent confocal Raman microscopy of an individual ZnO nanorod

In this study, polarized-Raman scattering measurements of an individual ZnO nanorod were carried out by using a confocal microscope together with a high-resolution piezoelectric stage. A predominant A1 (TO) mode at 378cm−1 in the parallel polarization (E∥) configuration and a predominant E2 (high) mode at 438cm−1 in the perpendicular polarization (E⊥) configuration demonstrate the strong polarization dependent Raman scattering signals of an individual ZnO nanorod. The Raman intensity images of the individual ZnO nanorods with different orientation configurations can also be obtained, which reflect the interplay between the local phonon behavior and geometric anisotropy.

Liquid‐phase‐epitaxial growth of In0.49Ga0.51P on (100) GaAs by a supercooling method

In1−xGaxP epitaxial layers were grown on (100) GaAs substrates by liquid‐phase epitaxy using supercooling technique. The lattice mismatch normal to the wafer surface between In1−xGaxP layer and GaAs substrate varies linearly with the supercooled temperature of the growth solution. The composition‐pulling phenomenon was not observed in this study. The growth rate, the intensity, and the full width at half maximum of the photoluminescent spectrum are also dependent on the supercooling temperature. It is shown that the narrowest full widths at half maximum of photoluminescent peak are 10.6 and 35 meV at 14 and 300 K, respectively, when ΔT is 6 °C, and the strongest intensity is occurred at ΔT=12–18 °C. Carrier concentrations of undoped epitaxial layers are in the range of 1016 cm−3 measured by capacitance‐voltage method at 300 K and Hall method at 77 and 300 K. The optimum growth condition was then determined.

Nanoscale morphology and performance of molecular-weight-dependent poly(3-hexylthiophene)/TiO2 nanorod hybrid solar cells

We have investigated the effect of polymer molecular weight on the morphology and performance of poly(3-hexylthiophene)/TiO2nanorod hybrid photovoltaic devices by using scanning near field optical microscopy (SNOM), atomic force microscopy (AFM) and confocal Raman microscopy. From the topography and absorption mapping images, it is found that the rod-like structure of the low molecular weight polymer hybrid film consists of a large amount of grain boundaries and has a less continuous absorption mapping image. In contrast, the larger domain structure of the high molecular weight polymer hybrid film exhibits a continuous absorption mapping image, as a result of enhanced polymer stacking and electronic delocalization. The nanoscale morphology of the hybrid samples with different molecular weights also reveals the nature of photovoltaic performance and carrier transport behavior investigated by the time-of-flight technique.

Electrical and optical properties of high purity In0.5Ga0.5P grown on GaAs by liquid phase epitaxy

Abstract The growth of high purity In 0.5 Ga 0.5 P epitaxial layers was carried out by liquid phase epitaxy with a supersaturation temperature of 6° C. The lattice mismatch between the InGaP layer and the GaAs substrate was 0.10% measured by X-ray diffraction. The bandgap and the quality of the epitaxial layers were determined by photoluminescence. The narrowest full width at half maximum of the photoluminescent spectra was 35.0 and 10.6 meV at 300 and 14 K, respectively. Hall and capacitance-coltage measurements show that a net carrier concentration of 3 × 10 15 cm −3 has been achieved, which is by one or two orders of magnitude lower than those previously reported. Forward bias current-voltage measurement of a Au-In 0.5 Ga 0.5 P Schottky diode shows that the ideality factor n is calculated to be 1.08 and the barrier height φ n is 0.95 eV. This value is rather close to that of 1.02 eV obtained by capacitance-voltage measurements. Deep level traps in the In 0.5 Ga 0.5 P epitaxial layer were studied by deep level transient spectroscopy. The only thermal activated energy level is located at E c - 0.39 eV and the electron trap concentration is below 2 × 10 14 cm −3 .

Synthesis, optical and photovoltaic properties of bismuth sulfide nanorods

Bismuth sulfide (Bi2S3) nanorods exhibit a low band gap, a high absorbance coefficient and good dispersity. In this study, the synthesis conditions of Bi2S3 nanorods were systematically investigated to obtain nanorods of a desired dimension, with high aspect ratios and good crystallinity. The as synthesized Bi2S3 nanorods, 37.2 nm in length and 6.1 nm in width, have a low band gap of ∼1.4 eV with a conduction band and valence band of −3.8 eV and −5.2 eV, respectively. The nanorods were blended with poly(3-hexylthiophene) (P3HT) at a weight ratio of 1:1 to form a light harvesting P3HT:Bi2S3 hybrid film. The incorporated Bi2S3 nanorods can not only contribute light harvesting but also lead to a more ordered structure of the P3HT phase and a more efficient π–π* transition. Surface potential mapping of the hybrid film, measured by Kelvin probe force microscope (KPFM), shows a significantly negative shift (−34 mV) under white light illumination, which indicates carrier dissociation and the accumulation of negative charge on top of the hybrid film. The photovoltaic characteristics of the devices were also observed for those based on the P3HT:Bi2S3 hybrid film. This novel P3HT:Bi2S3 hybrid material provides a new candidate for the fabrication of low-cost and environmentally friendly polymer/inorganic hybrid solar cells.

Bismuth doping effect on TiO2 nanofibres for morphological change and photocatalytic performance

Doping bismuth ions into photocatalytic materials is one of the most effective methods for preparing highly visible-light-active photocatalysts. In order to develop high-performance photocatalytic materials that are easy to produce, even in industrial quantities, we developed a facile method to prepare bismuth-doped titanium dioxide (Bi-doped TiO2) by hydrothermal synthesis followed by thermal annealing treatment. Bi-doped TiO2 can be applied in the field of photodecolorization of organic dye and photocatalytic hydrogen generation. High concentration doping (>5.00 mol%) resulted in the morphological change of Bi-doped TiO2 from nanofibre to nanorod observed by transmission electron microscopy. The crystal structure evolution and elemental composition were analysed by combining Raman spectroscopy, X-ray crystallography and X-ray photoelectron spectroscopy. For the photodegradation of organic dye methyl orange, all Bi-doped TiO2 showed less activity than pristine TiO2 nanofibres under UV irradiation. 5.00 mol% and 10.00 mol% Bi-doped TiO2 showed higher activities than pristine TiO2 nanofibres under visible light irradiation. For the photocatalytic hydrogen generation measurement, none of the Bi-doped TiO2 showed a detectable value under visible light irradiation. However, under UV irradiation, various Bi-doped TiO2 catalysts exhibited a detectable photocatalytic hydrogen production rate. 0.50 mol% Bi-doped TiO2 exhibited the highest performance. The result could be due to the relatively lower overpotential for hydrogen production. Our study developed a series of visible-light-active Bi-doped TiO2 catalysts, and it could replace the traditional TiO2 catalysts decorated with a high-cost noble metal.

Tellurium and zinc doping in In0.5Ga0.5P grown by liquid‐phase epitaxy

In0.5Ga0.5P epitaxial layers doped with Te and Zn were grown on (100) GaAs substrates by liquid‐phase epitaxy using a supercooling method. The lattice mismatch between the InGaP layer and the GaAs substrate decreases with increasing Te or Zn impurity concentration. The electrical properties of doped layers were determined by Hall measurements at 300 and 77 K. Room‐temperature carrier concentrations ranging from 2×1017 to 3×1018 cm−3 for n‐type and from 2×1017 to 2×1019 cm−3 for p‐type dopants were obtained reproducibly. The full width at half maximum value of the 300 K photoluminescent spectrum increases with carrier concentration for both Te‐ and Zn‐doped layers. The relative intensity of the 300 K photoluminescent peak increases with electron concentrations up to 3×1018 cm−3 for Te‐doped layers, but it presents a maximum value at 1×1018 cm−3 for Zn‐doped layers. The 14 K photoluminescent spectra show three distinctive peaks and their relative intensities change with hole concentrations. Finally, the rel...