Peihua Wangyang

Flexible All-Inorganic Perovskite CsPbBr3 Nonvolatile Memory Device

All-inorganic perovskite CsPbX3 (X = Cl, Br, or I) is widely used in a variety of photoelectric devices such as solar cells, light-emitting diodes, lasers, and photodetectors. However, studies to understand the flexible CsPbX3 electrical application are relatively scarce, mainly due to the limitations of the low-temperature fabricating process. In this study, all-inorganic perovskite CsPbBr3 films were successfully fabricated at 75 °C through a two-step method. The highly crystallized films were first employed as a resistive switching layer in the Al/CsPbBr3/PEDOT:PSS/ITO/PET structure for flexible nonvolatile memory application. The resistive switching operations and endurance performance demonstrated the as-prepared flexible resistive random access memory devices possess reproducible and reliable memory characteristics. Electrical reliability and mechanical stability of the nonvolatile device were further tested by the robust current-voltage curves under different bending angles and consecutive flexing cycles. Moreover, a model of the formation and rupture of filaments through the CsPbBr3 layer was proposed to explain the resistive switching effect. It is believed that this study will offer a new setting to understand and design all-inorganic perovskite materials for future stable flexible electronic devices.

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.

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

Electrolytic approach towards the controllable synthesis of NiO nanocrystalline and self-assembly mechanism of Ni(OH)2 precursor under electric, temperature and magnetic fields

c

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

-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.

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

We report that two-dimensional (2D) hexagonal nickel oxide (NiO) nanosheets have been successfully synthesized using the electrolysis of nickel plate as the anode in deionized water. The electrolysis processes first produced 2D nickel hydroxide (Ni(OH)2) nanosheets, which were transformed to 2D NiO by calcination. Contrary to the classical crystallization mechanism, contiguous SEM observations revealed that the Ni(OH)2 were produced via a multistep oriented attachment (MOA) mode, in which the [Ni(OH)6]4− coordination octahedron serves as the building block. Hydrothermal experiments further showed that the technique can be applied to the synthesis of 3D Ni(OH)2 nanoflowers with the aid of introduced Ni(OH)2 nanosheets. A growth mechanism based on the selective-surface adsorption and intercalation of nitrate ions (NO3−) and hydroxyl ions (OH−) as well as the adsorption of free ammonia molecules (NH3), was proposed. The crystal morphologies and thickness can be controlled by a charging magnetic field, suggesting that the crystal growth mechanisms are dominated by micromechanics such as the magnetic dipole force, Van der Waals force and magnetic force.

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

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.

Coordination and reduction in polyol-mediated solvothermal synthesis of nickel-based materials with controllable morphology and magnetic and electrochemical properties

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.

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

The nitrogen-doped TiO2 thin films are deposited on the glass substrate by using a direct-current (DC) magnetron sputtering technique. The film properties are analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements. The results show that, under the same working pressure and other conditions, nitrogen doping promotes the phase transition from anatase to rutile. Also, on changing the nitrogen–oxygen ratio, nitrogen atoms enter the TiO2 lattice in different positions. When oxygen is abundant, nitrogen atoms will be presented in the interstitial positions; when oxygen is insufficient, nitrogen atoms enter the oxygen vacancies first, forming a substituted position. Finally, we find that, with the increase in nitrogen–oxygen ratio, the sample has a better response to visible light, attributed to the change in the energy band-gap.