Yuan-Ron Ma

X-ray diffraction and Raman scattering studies on large-area array and nanobranched structure of 1D MoO2 nanorods

One-dimensional (1D) MoO2 nanorods in the form of a large-area array and nanobranched structure were prepared by hot-filament metal?oxide vapour deposition at low and high pressures in atmospheric argon flows respectively. The x-ray diffraction (XRD) patterns of both as-synthesized samples show that the 1D MoO2 nanorods are monoclinic crystals in space group P 21/c. The Raman spectrum of the large-area array of 1D MoO2 nanorods appears to be the same as that of a two-dimensional (2D) MoO2 thin film. The Raman spectrum of the nanobranched structure of 1D MoO2 nanorods showed a downshift and asymmetric broadening of the Raman first-order TO peak when compared with the bulk (q = 0) mode. The Raman shift and broadening were attributed to phonon confinement effect in the 1D nanorods. The in?situ Raman spectra of laser-induced oxidation of the nanobranched structure of 1D MoO2 nanorods demonstrate that they can be oxidized easily and more strongly than the 3D bulk MoO2 powder.

Efficient electrochromic performance of nanoparticulate WO3 thin films

This report highlights the suitability of electrodeposited nanoparticulate-WO3 (NP-WO3) electrodes for transmissive electrochromic devices (ECDs). The WO3 electrodes in the form of thin films are composed of 10–20 nm nanoparticles. An electrochromic (EC) device of dimensions 5 × 4 cm2 fabricated using NP-WO3 showed an Li insertion coefficient (x) of 0.43, which resulted in highest photopic transmittance modulation (88.51%), better Li-ion diffusion coefficient (∼3.16 × 10−9 cm2 s−1), fast electrochromic response time (5.2 s for coloration and 3.7 for bleaching) and excellent coloration efficiency (∼137 cm2 C−1). On reduction of WO3, the CIELAB 1931 2° color space coordinates show the transition from colorless to the deep blue state (Y = 97, a* = −1.93, b* = 0.46 and Y = 10, a* = 1.57, b* = −41.01) with steady decrease in relative luminance.

High room-temperature photoluminescence of one-dimensional Ta2O5 nanorod arrays

In this study we analyzed the structural and electronic properties of a new morphological form, one-dimensional (1D) Ta2O5 nanorod arrays, which were synthesized by hot filament metal vapor deposition. Field-emission scanning electron microscopy (FESEM) showed the 1D Ta2O5 nanorods to be arranged in a large-area high-density array about 50 nm wide and approximately 550 nm long. X-ray photoemission spectroscopy (XPS) revealed not only the electronic structures and chemical properties of the 1D Ta2O5 nanorods but also their stoichiometric Ta and O compositions. Photoluminescence (PL) spectra showed intensive green-light, yellow-light and red-light emissions at room temperature. These emissions simultaneously emerged from the trap levels of oxygen vacancies within the Ta2O5 bandgap. The emission results strongly indicate that the 1D Ta2O5 nanorods are good room-temperature visible-light emitters.

An Mn Doped Polyaniline Electrode for Electrochemical Supercapacitor

Undoped and Mn doped Polyaniline (PANI) thin films were deposited on stainless steel substrates by sonochemical method. Films deposition was done using dip coating technique. To study the Mn doping effect on the specific capacitance of PANI, concentration of Mn was varied from 0.4 to 1.6 wt %. The Fourier Transform-IR (FT-IR) and Raman spectroscopy techniques have been used for the phase identification and determination of the Mn in the PANI films. Surface morphology was examined by using Field Emission Scanning Electron Microscopy (FESEM) which showed nanofiber aggregate structure of undoped PANI and porous and well distributed nanofibers for the doped PANI. The supercapacitive behavior of the electrodes was tested in three electrode system with 1.0 M H 2 SO 4 electrolyte by using cyclic voltammetry. The specific capacitance value increases from 285 to 474 F g ―1 as the Mn concentration was increased. This work demonstrates a simple strategy of improving specific capacitance of the polymer and hence may be adopted easily for other dopants also. Thus the work will open a new avenue for designing low cost high performance devices for better supercapcitors.

Growth mechanism and magnon excitation in NiO nanowalls

The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature.PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di

Photoluminescence mechanisms of metallic Zn nanospheres, semiconducting ZnO nanoballoons, and metal-semiconductor Zn/ZnO nanospheres

We utilized a thermal radiation method to synthesize semiconducting hollow ZnO nanoballoons and metal-semiconductor concentric solid Zn/ZnO nanospheres from metallic solid Zn nanospheres. The chemical properties, crystalline structures, and photoluminescence mechanisms for the metallic solid Zn nanospheres, semiconducting hollow ZnO nanoballoons, and metal-semiconductor concentric solid Zn/ZnO nanospheres are presented. The PL emissions of the metallic Zn solid nanospheres are mainly dependent on the electron transitions between the Fermi level (EF) and the 3d band, while those of the semiconducting hollow ZnO nanoballoons are ascribed to the near band edge (NBE) and deep level electron transitions. The PL emissions of the metal-semiconductor concentric solid Zn/ZnO nanospheres are attributed to the electron transitions across the metal-semiconductor junction, from the EF to the valence and 3d bands, and from the interface states to the valence band. All three nanostructures are excellent room-temperature light emitters.

Electrochromic properties of dandelion flower like nickel oxide thin films

This report highlights a one pot, surfactantless, template free approach to grow novel dandelion flower like nickel oxide (NiO) thin films composed of nano-flakes with a highly porous structure. Good transmittance modulation, fast response time and excellent coloration efficiency make them a potential electrode material for electrochromic devices.

Hydrothermal synthesis of rutile TiO2 nanoflowers using Brønsted Acidic Ionic Liquid [BAIL]: Synthesis, characterization and growth mechanism

Herein we report a facile method to synthesize rutile TiO2 nanoflowers (TNF) comprising a bunch of aligned nanorods with uniform size and shape via a hydrothermal method in Bronsted Acidic Ionic Liquid [BAIL] room temperature ionic liquid (RTIL). This method has some advantages: the process is simple and single step; the reaction can be performed under low temperature. The TNFs are highly crystalline and free of aggregation.

Laser oxidation and wide-band photoluminescence of thermal evaporated bismuth thin films

Bismuth (Bi) thin films of various microstructures were synthesized by thermal evaporation at varying substrate temperatures. The substrate temperature strongly affects the surface morphology and crystalline orientation of the Bi thin films. Peak shift and broadening of the Raman bands (Eg and A1g modes) observed with an increase in substrate temperature can be attributed to the phonon confinement and compressive stress effects. The Bi thin film depicts a laser-induced oxidation and phase transition as a function of varying laser power. Photoluminescence spectra show visible–near infrared broadband emission for polycrystalline Bi thin film prepared at high substrate temperature. This result indicates that polycrystalline Bi thin film can be a promising candidate for broadband optical fibre amplifiers and tunable lasers.

Electrochromic properties of large-area and high-density arrays of transparent one-dimensional β-Ta2O5 nanorods on indium-tin-oxide thin-films

We report on the synthesis, crystalline structure, and electrochromic properties of transparent one-dimensional (1D) orthorhombic (β) Ta2O5 nanorods grown in a large-area high-density array. The transparent 1D β-Ta2O5 nanorod array was synthesized on a conducting indium-tin-oxide thin-film via hot-filament metal-oxide vapor deposition. The array contained ∼1900 β-Ta2O5 nanorods per square micrometer, which were on average, ∼17 nm wide and ∼300 nm long. The good coloration/bleaching cycles, large ion-diffusion coefficient (∼2.35×10−8 cm2/s), and high reversibility (∼79.8%) demonstrate that the 1D β-Ta2O5 nanorods to be a potential electrochromic material for electrochromic devices or smart windows.