C. Ye

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.

Photoluminescence of ZnO thin films on Si substrate with and without ITO buffer layer

Photoluminescence (PL) properties of ZnO thin films on Si substrate with and without an indium tin oxide (ITO) buffer layer, prepared under different oxygen partial pressures in the sputtering gas, were studied. It was found that PL characteristics of ZnO thin films depend on oxygen partial pressure and substrate, and the PL peak in the ultraviolet region has a strong red-shift with increasing excitation intensity on the glass and Si substrates with the ITO buffer layer, and the PL intensity increases with the increasing measuring cycle. Enhanced luminescence efficiency of ZnO thin films on the substrates with ITO buffer layer measured at different cycles can be obtained by thermal annealing.

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.

Structure and thermal stability of δ-Bi2O3 thin films deposited by reactive sputtering

Nanocrystalline ?-Bi2O3 thin films have been deposited onto Si (100) and quartz substrates by reactive sputtering. The structural characteristics and thermal stability of the thin films have been investigated by x-ray diffraction and Raman spectra. It was found that the ?-Bi2O3 thin films could exist stably below 200??C and undergo a phase transition sequence ? ? ? ? ? with increasing annealing temperature beyond 200??C. These phase transitions were further confirmed by optical constant and optical band gap studies.

Preparation and photoluminescence of undoped ZnTiO3 thin films

ZnTiO3 thin films were prepared by radio frequency cosputtering of ZnO and TiO2. It was found the as-prepared film is amorphous and the cubic phase ZnTiO3 films form after annealing at temperature above 500 °C. The absorption spectra indicate that the optical band gap of the crystalline ZnTiO3 film is about 3.70 eV. A strong photoluminescence band centered at 355 nm consisting of two emission peaks was observed in 800 °C annealed ZnTiO3 thin film, and the peak positions of these two emission move to short wavelength with increasing annealing temperature. It was found the emission peak at ultraviolet zone is resulted from O2− vacancy and that in the blue zone is attributed to Zn2+ vacancy.

Optical properties of MgO–TiO2 amorphous composite films

The microstructure and optical properties of MgO–TiO2 composite thin films prepared by radio frequency magnetron sputtering were studied. The composite films have an amorphous structure and the growth rate of the composite film increases with increasing Mg content. The refractive index almost linearly decreases with increasing Mg content in the composite films at wavelength larger than 300nm and can be adjusted in the wide range between the refractive index of TiO2 and that of MgO. The extinction coefficient decreases with Mg content and is nearly zero at visible light region. The optical band gap of the composite films determined from the absorption spectra increases with Mg content, and has a good agreement with that obtained from spectroscopic ellipsometry simulation. A broad photoluminescence band in the visible region was observed in the composite films with high Mg content and was considered resulted from the oxygen vacancies.

Morphological and optical characteristics of nanocrystalline TiO2 thin films by quantitative optical anisotropy and imaging techniques

TiO2 thin films were prepared by dc reactive sputtering with different ratios of oxygen to argon. The optical characteristics of the films were studied by birefringence imaging and optical anisotropic analysis using MetriPol. A clear trend of aggregation and structural variation of TiO2 nanoparticles in the films can be seen using MetriPol optical anisotropic imaging. It was found that the optical characteristics of the TiO2 thin films depend on the ratios of O2/Ar during sputtering of the films. The optical anisotropies are closely related to the structural feature of TiO2 nanoparticles. Variation trends of TiO2 film structures and optical characters have also been confirmed by FESEM observations and refractive index.

Angle-dependent photoluminescence of [1 1 0]-oriented nitrogen-doped SnO2 films

The orientation growth and angle-dependent photoluminescence (PL) of nitrogen-doped SnO2 films grown on Si substrate by reactive magnetron sputtering have been studied. It was found that the orientation of the nitrogen-doped SnO2 films depends strongly on their thickness, and a highly [1 1 0]-oriented film was achieved with a seed layer. An angle-dependent PL of the [1 1 0]-oriented films was observed, and the PL peak position shifts towards the longer wavelength side and the PL peak width decreases as the observation angle decreases. This angle-dependent PL was attributed to the Fabry–Perot optical interference effect.

Hollow cadmium selenide semiconductor tetrapods

Hollow cadmium selenide (CdSe) tetrapods were synthesized on a large scale. The directional growth of twins led the tetrapod nanostructure to be formed. The silicon powder was responsible for the growth of the hollow tetrapods. The UV-visible absorption spectra of the hollow CdSe tetrapods display an absorption edge at about 765nm. There is a redshift of 53nm of the absorption edge, in comparison with that of bulk CdSe at 712nm. In the Raman spectra, two new anomalous modes at 250.91 and 493.42cm−1 are observed. This might originate from the enhanced internal stress of hollow structures.