Xinghua Zhu

Growth of AgGaS2 single crystal by descending crucible with rotation method and observation of properties

This note reports a new procedure of polycrystalline synthesis and a new technique of single crystal growth on AgGaS2, i.e. two-zone temperature oscillation vapor transporting and descending crucible with rotation. A single phase dense AgGaS2 polycrystalline ingot was synthesized, and a crack-free AgGaS2 single crystal with 15 mm in diameter and 30 mm in length was grown by the techniques mentioned above. Structure integrity of the crystal was studied by the X-ray diffraction technique. Six order X-ray spectra from the 011 face of the crystal were obtained, and an anomalous phenomenon was observed for the first time that intensity of the higher order diffraction peak is much stronger than that of the lower order diffraction peak. Etch-pits of the crystal were observed by the scanning electron microscopy (SEM).

Improved growth of AgGaSe2 crystals and phase matched second harmonic generation of 10.6 μm CO2 laser radiation

Good quality AgGaSe2 single crystal 22 mm in diameter and 80 mm in length is grown by an improved technique, i.e., descending ampoule with rotation. Although the crystals grow with optical defects, postgrowth heat treatment procedures are used to successfully eliminate the defects and produce material of 62.4% IR transmission at 10.6?m. The frequency-doubling device is cut from a cylindrical crystal boule using a new orientation cut method according to the type-1 phase-matched condition. A high optical quality, orientated AgGaSe2 single crystal of 10x 10x 12 mm size is used for second harmonic generation (SHG) of the pulsed output of a 10.6?m CO2 miniature transversely excited atmospheric laser. A relatively high energy conversion efficiency of 12% is obtained. It is found that the optical surface damage threshold of the crystal is larger than 12 MW/cm2.

Effects of annealing temperature on the structural and optical properties of ZnO thin films prepared by sol–gel method

ZnO thin films have been prepared by sol–gel method in this paper. Zinc acetate, ethanol and mono-ethanolamine (MEA) were used as a metal precursor, solvent and stabilizer, respectively. The structural and optical properties of ZnO thin films were investigated and found to be strongly dependent on the annealing temperature. X-ray diffraction patterns revealed that as the annealing temperature increased, the crystalline quality of the samples became better. The atomic force microscope images of the samples show larger and compact grains at higher heat-treating temperature. The ultraviolet–visible transmittance spectra indicated that as the temperature increased, the transmittance improved and the energy gap became larger (from 3.11eV at 400∘C to 3.22eV at 500∘C). The photoluminescence spectra presented a variety of emission peaks, two strong peaks at 390nm and 469nm, respectively, from the intrinsic emission and point defects, and the intensity of these peaks decreased with the increase of temperature.

Modified Growth of Cadmium Selenide Single Crystals from the Vapor Phase and Quality Characterization

High quality size of CdSe single crystal of large size was obtained by the modified growth technique, i.e. horizontal vapor phase located point nucleation (HVPLPN). The particular shape of the growth ampoule and less temperature gradients (7-8 K/cm) in the growth interface was used for crystal growth. As-grown CdSe crystal was characterized by varied methods including x-ray diffraction, SEM and energy dispersive analyzer of x-ray (EDAX) etc. Two cleavage faces of the (100) and the (110) was found. The crystal has a stoichiometry ratio Cd : Se = 0.99 : 1 and the density of dislocation is in the range of 10 4 -10 3 /cm 2 and the resistivity is about 10 7 Ω.cm. The results demonstrated that the quality of the as-grown crystal is good for applications. Therefore the modified growth technique (HVPLPN) is a promising convenient new method for the growth of high quality CdSe single crystals.

Regulations of aging time on optical properties of nano-crystalline ZnO thin films fabricated by sol–gel method

Nano-crystalline Zinc oxide (ZnO) thin films on glass substrates have been fabricated by sol–gel method for different aging times. The thermal curve of the dried gel was examined and it was found that evaporation of solvent and the decomposition of the organics have completed before 250∘C. X-ray diffraction patterns and Atomic Force Microscope images of samples only have a small difference of microstructure. The transmittance spectra revealed high transmittance in visible region. The optical band gap of the samples remined stable (3.28eV). Also, the Urbach energy was calculated to explain the defect concentration. The Photoluminescence spectra in ultraviolet and visible regions were studied, and the decreased intensity of peaks at 387nm and the increased emissions in visible range were found. The results showed that excessive aging time can cause degeneration of optical properties of thin films.