Dingyu Yang

Effects of aging time and annealing temperature on structural and optical properties of sol-gel ZnO thin films

The ZnO thin films have been prepared by sol-gel method at different annealing temperatures and aging time. The structural properties of ZnO thin films were investigated by X-ray diffraction (XRD) patterns and atomic force microscope (AFM) images. The results indicated that the film possess a hexagonal wurtzite structure with preferred orientation along the (002) direction. The crystalline quality of films improved with increasing post-annealing temperature, while gradually worsened with prolonging aging time. The optical properties of ZnO thin films were studied by the ultra-violet transmittance (UV-Vis) and photoluminescence (PL) spectra. The variations of UV-Vis transmittance and energy gap accorded well with the tendency presented in XRD patterns and AFM images. The PL spectra appeared the apparent ultraviolet emission and visible emissions. As the annealing temperature increased, the ultraviolet and visible emissions of films enhanced and decreased respectively. However, as the sol aging time prolong...

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.

Comparison of electrical properties of x-ray detector based on PbI2 crystal with different bias electric field configuration

In this work we report the dark current, photocurrent and carrier transport properties of the x-ray detector based on lead iodide (PbI2) crystal. The detectors were built with two orthogonal directions configuration as the bias electric field parallel to the crystallographic c-axis E//c and perpendicular to the c-axis E⊥c. It presents the electrical anisotropy including resistivity, dark current, carrier transport and x-ray induced photoelectricity properties with considering the configuration of bias field and c-axis. A mechanism of carrier scattering effect from anisotropic lattice structure, dislocation and stacking fault could be mainly responsible for this anisotropy property in PbI2 crystal. All the results indicate that the crystal orientation will be taken into account when we design and fabricate the x-ray detectors based on PbI2 crystals or films.

Investigations on Structural, Optical and X-Radiation Responsive Properties of a-Se Thin Films Fabricated by Thermal Evaporation Method at Low Vacuum Degree

Amorphous selenium (a-Se) thin films with a thickness of 1200 nm were successfully fabricated by thermal evaporation at a low vacuum degree of 10−2 Pa. The structural properties involving phase and morphology showed that a-Se thin films could be resistant to 60 °C in air. Also, a transformation to polycrystalline Selenium (p-Se) was shown as the annealing temperature rose to 62 °C and 65 °C, with obvious changes in color and surface morphology. Moreover, as the a-Se transformed to p-Se, the samples’ transmittance decreased significantly, and the band gap declined dramatically from 2.15 eV to 1.92 eV. Finally, the X-radiation response of a-Se was investigated as an important property, revealing there is a remarkable response speed of photogeneration current both X-ray on and X-ray off, with a requirement of only a very small electrical field.

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

Influence of substrate on structural, morphological and optical properties of TiO2 thin films deposited by reaction magnetron sputtering

c

Pretreating temperature controls on structural, morphological and optical properties of sol–gel ZnO thin films

-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.

Influence of substrate and Ar/N 2 gas flow ratio on structural, optical and electrical properties of TiN thin films synthetized by DC magnetron sputtering

Titanium dioxide (TiO2) films have been prepared by DC reaction magnetron sputtering technique on different substrates (glass, SiO2, platinum electrode-Pt, Silicon-Si). X-ray diffraction (XRD) patterns showed that all TiO2 films were grown along the preferred orientation of (110) plane. Samples on Si and Pt substrates are almost monophasic rutile, however, samples on glass and SiO2 substrates accompanied by a weak anatase structure. Atomic force microscopy (AFM) images revealed uniform grain distribution except for films on Pt substrates. Photoluminescence (PL) spectra showed obvious intrinsic emission band, but films on glass was accompanied by a distinct defect luminescence region. Raman spectroscopy suggested that all samples moved to high wavenumbers and films on glass moved obviously.

Effect of the nitrogen–oxygen ratio on the position of N atoms in the TiO2 lattice of N-doped TiO2 thin films prepared by DC magnetron sputtering

Abstract ZnO thin films on glass substrates were synthesised by sol–gel method with different pretreating temperature. The thermal behaviours of dried gel were firstly tested and found the relationship between organics evaporation and pretreating temperature. Then the structural, morphological and optical properties of thin films were investigated. X-ray diffraction patterns showed the phase with hexagonal wurtzite structure, and the preferred orientation growth at (0 0 2) plane increased as rising pretreating temperature. Atomic force microscope was used to measure the surface morphology of films and found the wrinkle-like at low pretreating temperature. Transmittance spectra of ZnO thin films prepared at higher pretreating temperature revealed the steeper absorption edge and the larger transmittance values, and the deduced optical energy gap increased. Meanwhile, with increasing pretreating temperature, photoluminescence spectra showed the stronger ultraviolet peak and weaker visible peaks which, respectively, originated from intrinsic emission and various defect emissions.

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

Titanium nitride (TiN) thin films have been prepared by direct-current reaction magnetron sputtering technique on different substrates (glass and Si) and the influence of substrate and Ar/N2 gas flow ratio on structural, optical and electrical properties of TiN thin films were discussed. X-ray diffraction suggested that with the ratio of Ar/N2 decreasing, the diffraction intensity of (111) plane gradually diminished while (200) plane increased and films on Si substrate exhibited better crystalline quality than glass substrate. Improvement of Ar/N2 ratio is contribute to enhance the deposition rate and the obvious surface roughness were observed when the ratio up to 49. Photoluminescence spectra showed that TiN films on Si substrate showed higher intrinsic emission and lower defect emission. Moreover, the resistivity of TiN films showed obviously decreasing as the flow rate ratio of Ar/N2 increased, especially films on Si substrate.