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Abstract: CdSe thin films have been grown on GaAs (001) substrates by molecular beam epitaxy (MBE). The effects of substrate temperature and annealing treatment on the structural properties of CdSe layers were investigated. The growth rate slightly decreases due to the accelerated desorption of Cd from CdSe surface with an increase in the temperature. The sample grown at 260°C shows a polycrystalline structure with rough surface. As the temperature increases over 300°C, crystalline CdSe (001) epilayers with zinc-blende structure are achieved and the structural quality is improved remarkably. The epilayer grown at 340°C displays the narrowest full-width at half-maximum (FWHM) from (004) reflection in double-crystal X-ray rocking curve (DCXRC) and the smallest root-mean-square (RMS) roughness of 0.816nm. Additionally, samples fabricated at 320°C were annealed in air for 30min to study the films’ thermal stability. X-ray diffraction (XRD) results indicate that the zinc-blende structure remains unchanged when the annealing temperature is elevated to 460°C, meaning a good thermal stability of the cubic CdSe epilayers. [Copyright &y& Elsevier]

Abstract: ZnTe epilayers were grown on GaAs(001) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (R VI/II) in a wide range of 0.96–11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the R VI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a R VI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (004) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the R VI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14nm at a R VI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable R VI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films. [Copyright &y& Elsevier]

Abstract: Epitaxial ZnO thin films have been synthesized directly on Si(111) substrates by pulsed laser deposition (PLD) in vacuum. The reflection high-energy electron diffraction (RHEED) indicates that streaky patterns can be clearly observed from the ZnO epilayers prepared at 600 and 650°C, revealing a two-dimensional (2D) growth mode. While the ZnO thin film deposited in oxygen ambient shows ring RHEED pattern. There is a compressive in-plane stress existing in the ZnO epitaxial film, but a tensile one in the polycrystalline film. Compared with the ZnO epilayer, the ZnO polycrystalline film shows more intense ultraviolet emission (UVE) with a small full width at half maximum (FWHM) of 89meV. It is suggested that the atomically flat epilayers may be powerfully used as transitive stratums to grow high-quality ZnO films suitable for the fabrication of optoelectronic devices. [Copyright &y& Elsevier]

Abstract: ZnO thin films with highly c-axis orientation have been fabricated on p-type Si(111) substrates at 400°C by pulsed laser deposition (PLD) from a metallic Zn target with oxygen pressures between 0.1 and 0.7mbar. Experimental results indicate that the films deposited at 0.3 and 0.5mbar have better crystalline and optical quality and flatter surfaces than the films prepared at other pressures. The full width at half maximum (FWHM) of (0002) diffraction peak decreases remarkably from 0.46 to 0.19° with increasing annealing temperature for the film prepared at 0.3mbar. In photoluminescence (PL) spectra at room temperature, the annealed film at 700°C exhibits a smaller ultraviolet (UV) peak FWHM of 108meV than the as-grown film (119meV). However, an enhanced deep-level emission is observed. Possible origins to above results are discussed. [Copyright &y& Elsevier]

ZnO thin films were fabricated on Si (1 1 1) substrates by oxidation of metallic Zn films in air. A thin layer of Au was used to enhance the adhesion of the Zn atoms to the Si surface during depositing the Zn films on the substrates at room temperature (RT) by thermal evaporation. X-ray diffraction (XRD) studies indicate that the ZnO film prepared at 500 °C has better crystalline quality than films prepared at other temperatures. In photoluminescence (PL) spectra at room temperature, the film oxidized at 500 °C exhibits the biggest intensity ratio of 162 of ultraviolet (UV) emission to deep-level emission and the narrowest UV peak full width at half maximum (FWHM) of 94.8 meV. These results reveal that high-quality ZnO thin films with good crystallinity and strong UV emission can be achieved at such low temperature. It was also observed that the deep-level emission would become dominant in the PL spectra for the samples annealed at high temperatures above 700 °C, and the possible origin was discussed. [Copyright &y& Elsevier]

α-Fe 2 O 3 /BiOCl heterojunctions were synthesized by growing and assembling α-Fe 2 O 3 nanoplates to BiOCl microflowers via a two-step route to enhance the photocatalytic performance of BiOCl. The morphology, microstructure, element composition and optical properties of α-Fe 2 O 3 /BiOCl heterojunctions have been investigated by SEM, TEM, XRD, FT-IR, Raman spectra, XPS, UV–vis diffuse reflectance and PL spectra. Electrostatic interaction was a key to form α-Fe 2 O 3 /BiOCl heterojunctions. Compared with pure BiOCl, the synthesized α-Fe 2 O 3 /BiOCl heterojunctions possess an efficient visible light absorption and exhibit an improved of photocatalytic efficiency. A photocatalytic degradation mechanism has been proposed to explain that the heterojunctions enhance the separation efficiency of electron-hole pairs, and the holes are the main reactive species in the degratation of Rhodamine B. [ABSTRACT FROM AUTHOR]