Kwong-Kau Tiong

Bio: Kwong-Kau Tiong is an academic researcher from National Taiwan Ocean University. The author has contributed to research in topics: Photoluminescence & Band gap. The author has an hindex of 29, co-authored 180 publications receiving 2917 citations. Previous affiliations of Kwong-Kau Tiong include National Taiwan University & National Taiwan University of Science and Technology.

Raman scattering characterization of well‐aligned RuO2 and IrO2 nanocrystals

Abstract: Raman spectroscopy (RS) has been used as a technique for the characterization of well-aligned IrO2 and RuO2 nanocrystals (NCs) grown on a number of different oriented substrates under various conditions. The IrO2 and RuO2 NCs were grown via metalorganic chemical vapor deposition and reactive magnetron sputtering. The relative intensity of the three strongest Raman-active modes, namely, the A1g, B2g and Eg modes, depends on the orientation of NCs and has been used to determine the preferred growth direction of the NCs. The redshifts and asymmetric linewidth broadening of the Raman features of IrO2 and RuO2 NCs with respect to that of their bulk counterparts were analyzed by a modified spatial correlation (MSC) model, which includes a factor of stress-induced shift. The MSC model showed that the effects of stress and nanometric size could be separated in analyzing the observed Raman features. The usefulness of experimental RS together with the MSC model analysis as a structural and residual stress characterization technique for NCs has been demonstrated. Copyright © 2007 John Wiley & Sons, Ltd.

Rapid thermal annealing effects on the structural and optical properties of ZnO films deposited on Si substrates

Abstract: The structural and optical properties of ZnO films deposited on Si substrate following rapid thermal annealing (RTA) have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. After RTA treatment, the XRD spectra have shown an effective relaxation of the residual compressive stress, an increase of the intensity and narrowing of the full-width at half-maximum (FWHM) of the (0 0 2) diffraction peak of the as-grown ZnO film. AFM images show roughening of the film surface due to increase of grain size after RTA. The PL spectrum reveals a significant improvement in the UV luminescence of ZnO films following RTA at 800 °C for 1 min.

Design of a Multiband Antenna for Mobile Handset Operations

Abstract: A compact internal antenna is proposed for GSM/GPS/DCS/PCS/UMTS/Bluetooth/WLAN/WiFi/WiMAX applications. The proposed antenna is comprised of a loop antenna and a monopole antenna. The antenna system shows wide multi-operation band as well as good radiation patterns and small volume. The antenna can be printed on the system circuit board of the mobile phone and short-circuited to the system ground plane to form a loop-type structure. A comparison with that of the existing antennas showed that wide impedance bandwidth of the proposed structure can be achieved without increasing the implementation complexity.

Absorption-edge anisotropy in ReS 2 and ReSe 2 layered semiconductors

Abstract: Polarization-dependent absorption measurements of ${\mathrm{ReS}}_{2}$ and ${\mathrm{ReSe}}_{2}$ single crystals have been carried out in the temperature range between 25 and 500 K A significant shift towards lower energies has been observed in the transmittance spectra of $\mathbf{E}\ensuremath{\parallel}\mathbf{b}$ polarization with respect to those corresponding to $\mathbf{E}\ensuremath{\perp}\mathbf{b}$ polarization Analysis reveals that the absorption edges of ${\mathrm{ReS}}_{2}$ and ${\mathrm{ReSe}}_{2}$ are indirect allowed transitions The parameters that describe the temperature dependence of the absorption edges with different polarizations in the van der Waals plane are evaluated The results indicate that the electron-phonon coupling constants for $\mathbf{E}\ensuremath{\parallel}\mathbf{b}$ polarization are considerably larger than those of $\mathbf{E}\ensuremath{\perp}\mathbf{b}$ polarization

Raman study of 2H-Mo1−xWxS2 layered mixed crystals

Abstract: A systematic study of a series of Mo1−xWxS2 layered mixed crystals, with 0 ≤ x ≤ 1, grown by the chemical-vapor transport method were carried out by using Raman scattering measurements. The peaks of the two dominant first-order Raman-active modes, A1g and E 2 g 1 , and several second-order bands have been observed in the range of 200–1000 cm−1. The peaks corresponding to A1g mode show one-mode type behavior while the peaks of E 2 g 1 mode demonstrate two-mode type behavior for the entire series. The results can be explained on the basis of the atomic displacements for each mode. For A1g mode only sulfur atoms vibrate and this give rise to a one-mode type behavior for the mixed crystals. For E 2 g 1 mode metal atoms also vibrate as well as sulfur atoms, the mass difference of the vibrating Mo and W cations causes the two-mode type behavior of E 2 g 1 mode. In addition, the observation of largest asymmetry and broadening of A1g mode for Mo0.5W0.5S2 has been attributed to random alloy scattering.

From bulk to monolayer MoS2: evolution of Raman scattering

Abstract: Molybdenum disulfi de (MoS 2 ) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of E 1 and A1g peaks vary monotonously with the layer number of ultrathin MoS 2 fl akes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS 2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS 2 . The asymmetric Raman peak at 454 cm − 1 , which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS 2 , is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ( A2u ). Our fi ndings suggest a clear evolution of the coupling between electronic transition and phonon when MoS 2 is scaled down from three- to two-dimensional geometry.

Growth of oriented single-crystalline rutile TiO(2) nanorods on transparent conducting substrates for dye-sensitized solar cells.

Abstract: Dye-sensitized solar cells (DSSCs) made from oriented, one-dimensional semiconductor nanostructures such as nanorods, nanowires, and nanotubes are receiving attention because direct connection of the point of photogeneration with the collection electrode using such structures may improve the cell performance. Specifically, oriented single-crystalline TiO2 nanorods or nanowires on a transparent conductive substrate would be most desirable, but achieving these structures has been limited by the availability of synthetic techniques. In this study, a facile, hydrothermal method was developed for the first time to grow oriented, single-crystalline rutile TiO2 nanorod films on transparent conductive fluorine-doped tin oxide (FTO) substrates. The diameter, length, and density of the nanorods could be varied by changing the growth parameters, such as growth time, growth temperature, initial reactant concentration, acidity, and additives. The epitaxial relation between the FTO substrate and rutile TiO2 with a smal...

Synthesis of MoS2 and MoSe2 Films with Vertically Aligned Layers

Abstract: Layered materials consist of molecular layers stacked together by weak interlayer interactions. They often crystallize to form atomically smooth thin films, nanotubes, and platelet or fullerene-like nanoparticles due to the anisotropic bonding. Structures that predominately expose edges of the layers exhibit high surface energy and are often considered unstable. In this communication, we present a synthesis process to grow MoS2 and MoSe2 thin films with vertically aligned layers, thereby maximally exposing the edges on the film surface. Such edge-terminated films are metastable structures of MoS2 and MoSe2, which may find applications in diverse catalytic reactions. We have confirmed their catalytic activity in a hydrogen evolution reaction (HER), in which the exchange current density correlates directly with the density of the exposed edge sites.

Atomic mechanism of the semiconducting-to-metallic phase transition in single-layered MoS2.

Abstract: Phase transitions can be used to alter the properties of a material without adding any additional atoms and are therefore of significant technological value. In a solid, phase transitions involve collective atomic displacements, but such atomic processes have so far only been investigated using macroscopic approaches. Here, we show that in situ scanning transmission electron microscopy can be used to follow the structural transformation between semiconducting (2H) and metallic (1T) phases in single-layered MoS2, with atomic resolution. The 2H/1T phase transition involves gliding atomic planes of sulphur and/or molybdenum and requires an intermediate phase (α-phase) as a precursor. The migration of two kinds of boundaries (β- and γ-boundaries) is also found to be responsible for the growth of the second phase. Furthermore, we show that areas of the 1T phase can be controllably grown in a layer of the 2H phase using an electron beam.

Monolayer behaviour in bulk ReS2 due to electronic and vibrational decoupling

Abstract: Monolayers of transition metal dichalcogenides have emerged as interesting two-dimensional materials. Here, the authors show that in a new member of this family of compounds, rhenium disulphide, the layers in the bulk are vibrationally and electronically decoupled, so that they behave almost as monolayers.