Xiuying Gao

Structural and optical properties of nano-crystalline ZnO thin films synthesized by sol–gel method

Nano-crystalline ZnO thin films on glass substrates have been prepared by sol–gel method at annealing temperatures of 300–550 °C. Zinc acetate, anhydrous ethanol, and mono-ethanolamine were used as raw materials. The thermal behaviors curves of the dried gel were examined and found that evaporation of solvent and the decomposition of the organics have completed before 250 °C. The effect of thermal annealing on structural and optical properties was investigated. X-ray diffraction patterns showed the gradual increase in orientation of (0 0 2) along c-axis. The transmittance spectra revealed the high transmission (T > 80% above annealing 400 °C) in visible region. The optical band gap (Eg) of the samples is in the range from 3.24 to 3.28 eV. The photoluminescence spectra in ultraviolet were studied and found the continuous increased intensity of peaks at 387 and 393 nm respectively from intrinsic emission and near the band edge emission. Surface micrographs was observed by the atomic force microscopy and found the larger grain size and the compacter morphology before 500 °C. However, the excessive annealing temperature at 550 °C deteriorated the structural and optical properties of the samples.Graphical AbstractThe transmittance is still enhanced as rising annealing temperature up to 500 °C which is more attributed to the decrease in grain boundaries and defect concentration. The poor transmission of films annealed at low temperatures is attributed to unsatisfactory crystalline quality. The stable and high transparency (>80%) in the visible region is presented above 400 °C. The UV–Vis transmittance spectra of ZnO thin films at different annealing temperature.

Electrical Behavior of X-Ray Detector Based on PbI 2 Crystal With Coplanar Electrode Structure

In this work, we report on the results of the electrical behavior of coplanar electrode structure X-ray detector based on PbI2 crystal. The detector with coplanar electrode similar to the Van der Pauw structure instead of conventional planar structure can partly reduce the influence of trapping effect to charge carrier transport along the

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

c

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

-axis. According to the configuration, four operating modes of the detector were thoroughly studied. Several novel results, such as the negative polarity dark current and photocurrent under zero bias voltage, orientation polarization, short relaxation time of steady-state surface leakage current and fast photocurrent response are obtained by this kind of coplanar structure configuration. The detector has the potential to be developed as a solid state X-ray dosimeter in the medical radiation environment, providing a high sensitivity and good adaptability under positive or negative bias voltage.

Mechanical exfoliation and Raman spectra of ultrathin PbI2 single crystal

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.

Fabrication and characterization of X-ray array detectors based on polycrystalline PbI2 thick films

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.