G. H. Li

Fabrication and optical properties of large-scale uniform zinc oxide nanowire arrays by one-step electrochemical deposition technique

Semiconductor ZnO nanowire arrays were fabricated by one-step electrochemical deposition technique based on ordered nanoporous alumina membrane. Their microstructures were characterized by transmission electron microscopy, Raman spectrum, and scanning electron microscopy. The results indicate that the ZnO nanowire array is uniformly assembled into the nanochannels of anodic alumina membranes (AAM). It is found that photoluminescence spectrum of the ZnO/AAM assembly system depends on the excitation wavelength in the visible region, which is attributed to different types of oxygen vacancies in the ZnO nanowires.

Hydrothermal synthesis and photoluminescence of TiO2 nanowires

Abstract Anatase TiO 2 single crystalline nanowires have been successfully synthesized using a simple hydrothermal synthesis method from TiO 2 nanoparticles. X-ray diffraction, transmission electron microscopy and high-resolution electron microscopy investigations show the TiO 2 nanowires have high crystallinity with diameter range from 30 to 45 nm and length in several micrometers. The TiO 2 nanowires can emit blue–green light peaked at 487 nm under excitation at 413 nm.

Ordered indium-oxide nanowire arrays and their photoluminescence properties

Ordered semiconductor In2O3 nanowire arrays are uniformly assembled into hexagonally ordered nanochannels of anodic alumina membranes (AAMs) by electrodeposition and oxidizing methods. Their microstructures were characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A blue-green photoluminescence (PL) band in the wavelength range of 300–650 nm was observed in the In2O3/AAM assembly system. The PL intensity and peak position depend on the annealing temperature, which is mainly attributed to the singly ionized oxygen vacancy in the In2O3 nanowire array system.

Optical properties of δ-Bi2O3 thin films grown by reactive sputtering

The optical properties of δ-Bi2O3 thin films were investigated using spectroscopic ellipsometry and optical absorption spectrum. δ-Bi2O3 thin films were grown on Si and quartz substrates under different oxygen flow ratios (OFR) by radio frequency reactive magnetron sputtering. The Tauc-Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films. The optical bandgap was obtained by three different methods. It was found that refractive index and extinction coefficient decrease, and the optical bandgap has a slight blue shift with increasing the OFR. Factors influencing the optical constants and optical bandgap are discussed.

Influence of annealing on the structural and optical properties of ZnO:Tb thin films

The influence of annealing on the morphological, structural, and optical properties of ZnO:Tb thin films on Si substrate grown by magnetron cosputtering is investigated. It has been found that the ZnO:Tb thin films with structures of tetrapod and screwlike nanorod are formed after annealing at temperature of 950°C. X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and Raman analyses prove that the tetrapod-aiguille zinc oxide (T-A-ZnO) and the screwlike nanorods are composed of Zn, Tb, and O elements. The photoluminescence spectra of the ZnO:Tb thin films with the T-A-ZnO structure and the screwlike nanorods are featured with two ultraviolet emission peaks and one strong green emission band, and the photoluminescence intensity increases with increasing annealing temperature. The surface defects in the T-A-ZnO structure and the screwlike nanorods are considered to be responsible for enhanced green emission in the annealed ZnO:Tb thin films.

Spectroscopic ellipsometry characterization of nitrogen-incorporated HfO2 gate dielectrics grown by radio-frequency reactive sputtering

Spectroscopic ellipsometry with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of nitrogen-incorporated HfO2 films on Si(100) substrates grown by radio-frequency reactive sputtering using different N2∕(N2+O2+Ar) gas ratios from 20% to 50%. Excellent agreement has been found between the experimental and the simulated spectra, in which an empirical dielectric dispersion relation based on Tauc-Lorentz model has been successfully adopted. Increases in the refractive index n and the extinction coefficient. k, with increases in nitrogen-incorporation content are observed due to the nitrogen-incorporation-induced higher packing density. The change of the complex dielectric functions and reduction in the optical band gap with an increase in nitrogen concentration resulting from the effect of the nitrogen-incorporation on the structure are discussed in detail.

Wavelength dependent photoluminescence of anodic alumina membranes

Strong photoluminescence bands range from 300 to 600 nm at room temperature have been observed in anodic alumina membranes (AAM). It was found that the photoluminescence (PL) intensity an dp eak position of AAM depend strongly on the excitation wavelength, and the PL intensity of AAM prepared in C2H2O4 is much higher than for AAM prepared in H2SO4 .T here are twopeaks in the PL bands; one is at constant wavelength of 460 nm, and the other increases almost linearly from 420 to 465 nm with excitation wavelength for AAM prepared in C2H2O4 and from 360 to 465 nm for AAM prepared in H2SO4 .A nnea ling treatment of the as-prepared AAM results in an apparent reduction of the intensity of the blue emission at shorter excitation wavelength, while at longer excitation wavelength (longer than 320 nm) the PL intensity firstly increases, and at 500 ◦ Cr eaches a maximum value, then decreases. It is considered that there are two PL centres; one originates from the oxygen-related defects in the barrier layer, and the other is correlated with the aluminum incorporated into the anion-contaminated alumina layer in the AAM.

Structure, composition and evolution of dispersive optical constants of sputtered TiO2 thin films: effects of nitrogen doping

Films of nitrogen-doped TiO2 have been successfully deposited on a Si substrate by radio frequency reactive sputtering in a mixture of argon, oxygen and nitrogen. The nitrogen gas ratio varies in the range 0.2–0.4 during the deposition, resulting in TiOxNy films with 3% ≤ y ≤ 6.55% as determined by x-ray photoelectron spectroscopy (XPS). Chemical bond state analysis by XPS indicates that nitrogen is effectively incorporated and produces an oxynitride centre as oxygen is replaced by nitrogen. Characterization by atomic force microscopy demonstrates that the incorporation of nitrogen has a significant effect on the morphology of the targeted TiO2 thin films. Spectroscopic ellipsometry with a photon energy of 0.75–6.5u2009eV at room temperature has been carried out to derive the refractive index n and the extinction coefficient k on the basis of a new amorphous dispersive model. The optical constants such as absorption coefficient, complex dielectric functions and the optical band gap have been determined. The trend of a decrease in the optical band gap with an increase in nitrogen concentration is consistent with the observation determined by UV–visible spectroscopy. The reduced band gap is associated with the N 2p orbital in the TiOxNy films.

Localized exciton luminescence in nitrogen-incorporated SnO2 thin films

The photoluminescence properties of nitrogen-incorporated SnO2 thin films on Si (100) substrates deposited by reactive magnetron sputtering have been studied. A strong photoluminescence band centered at 3.696eV with full width at half maximum of 0.2eV has been observed at room temperature. The peak position of the emission shifts to higher energy with increasing excitation intensity or decreasing temperature. The emission is considered due to the localized exciton recombination, and the observed exciton localization and band-tail states are believed to originate from the potential fluctuation induced by spatial distribution fluctuations of nitrogen concentration and∕or grain boundary defects in the nanocrystalline film.The photoluminescence properties of nitrogen-incorporated SnO2 thin films on Si (100) substrates deposited by reactive magnetron sputtering have been studied. A strong photoluminescence band centered at 3.696eV with full width at half maximum of 0.2eV has been observed at room temperature. The peak position of the emission shifts to higher energy with increasing excitation intensity or decreasing temperature. The emission is considered due to the localized exciton recombination, and the observed exciton localization and band-tail states are believed to originate from the potential fluctuation induced by spatial distribution fluctuations of nitrogen concentration and∕or grain boundary defects in the nanocrystalline film.

Photoluminescence and optical absorption caused by the F+ centres in anodic alumina membranes

Anodic alumina membranes (AAMs) with highly ordered nanochannel arrays were prepared by anodizing aluminum in acid solutions. X-ray diffraction reveals the amorphous nature of AAMs. The photoluminescence (PL) excitation spectra of AAMs consist of a broad band centred at 235 nm and a narrow band peaking around 360 nm under a monitoring wavelength of 470 nm. There are five prominent absorption bands (or edges) at 370, 294, 254, 220 and 204 nm in the absorption spectra of AAMs prepared in oxalic solution. With the increase of the annealing temperature, the intensities of PL and absorption bands increase first, then decrease, and a blue-shift is found. The photoluminescence and optical absorption in the wavelength range of 200 nm to 500 nm are caused by the F+ centres in AAMs. The energy levels of F+ centres in AAMs are split and a new energy level of 3.35 eV appears due to the amorphous nature of AAMs.