Fabrication of ZnO Ceramics with Defects by Spark Plasma Sintering Method and Investigations of Their Photoelectrochemical Properties

ZnO, as an important semiconductor material, has attracted much attention due to its excellent physical properties, which can be widely used in many fields. Notably, the defects concentration and type greatly affect the intrinsic properties of ZnO. Thus, controllable adjustment of ZnO defects is particularly important for studying its photoelectric properties. In this work, we fabricated ZnO ceramics (ZnO(C)) with different defects through spark plasma sintering (SPS) process by varying sintering temperature and using reduction environment. The experimental results indicate that the changes of color and light absorption in as-prepared ZnO originate from the different kinds of defects, i.e., oxygen vacancies (VO), interstitial zinc (Zni), and Zinc vacancies (VZn). Moreover, with the increase in calcination temperature, the concentration of oxygen defects and interstitial zinc defects in the ceramics increases gradually, and the conductivity of the ceramics is also improved. However, too many defects are harmful to the photoelectrochemical properties of the ceramics, and the appropriate oxygen defects can improve the utilization of visible light.

Features of interpretation of luminescence spectra of zinc oxide films on sapphire

In the presented work features of interpretation of luminescent spectral dependence properties of ZnO films on sapphire are given. For complex analysis, films of ZnO of different thickness obtained in oxygen medium at different substrate temperatures are considered using the stage of recrystallysis annealing. It is shown that only a red (650 – 1000 nm) band ZnO sapphire substrate is observed in the spectrum of cathodoluminescence of thin films obtained at low temperature of the substrate, and luminescence of the film ZnO fed by excessive defect. Prolonged recrystallization annealing results in improved quality of thin ZnO films and a broad (430 – 740 nm) band in the ZnO. With an increase the film thickness, only bands associated with ZnO appear in the cathodoluminescence spectra: the edge luminescence band (maximum 390 nm) and the red band (500 – 950 nm with a maximum in the region of 710 nm) are associated with charged zinc vacancies. Focusing the beam leads to local heating of the sample and an increase in the concentration of interstitial zinc. This is due to the displacement of the edge light band into the 410 nm region, as well as the blue mixing of the defective luminescence band.

Photoluminescence and point defect related emission of ZnO:Mn2+ micro/nanorod fabricated by co-precipitation method

Herein we study point defects and correlation to photoluminescence in ZnO nanorod. ZnO mirco/nanorod structure was successfully fabricated by co-precipitation method with highly homogeneous characteristics. When ion Mn+2 introduced into ZnO structure, the d-spacing distance of ZnO was increased from 0.248 nm to 0.295 nm due to the larger ionic radius of Mn2+ in comparison to Zn2+. The photoluminescence emission evolution of ZnO through doping and annealing processes hinted the relation of point defect transformations. We found that zinc interstitial, zinc vacancy and its related defects were responsible mainly for photoluminescence emission in annealing and/or Mn2+ doped samples.

MANIPULATING THE STRUCTURAL AND ELECTRICAL PROPERTIES OF ZINC OXIDE THIN FILMS BY CHANGING THE SPUTTERING POWER OF RADIO FREQUENCY MAGNETRON SPUTTERING

Oxygen-deficient zinc oxides thin films with different levels of defects were prepared by using radio frequency magnetron sputtering method with sintered zinc oxide disk as target at different sputtering powers. The composition, structure and electrical properties of the prepared films were investigated. Under the present conditions, all the obtained films possessed würtzite structure, which were growing preferentially along the [Formula: see text]-axis. The thickness of the films, the size of the zinc oxide grains and the content of Zn atoms increased with increasing sputtering power. In the films deposited at a sputtering power from 52[Formula: see text]W to 212[Formula: see text]W, the main defect was interstitial zinc. With increasing sputtering power, due to the enhanced number of interstitial zinc in the films, their room-temperature electrical resistivity would decrease, which was controlled by electron conduction. At increasing measurement temperature, their electrical resistivity would increase, owing to the decrease of defect concentration caused by oxidization.

Composition, Structure and Electrical Resistivity of ZnO1-x Films Deposited by RF Magnetron Sputtering under Various O2/Ar Gas Ratios

ZnO1-x thin films were deposited by RF magnetron sputtering on conducting silicon wafers at room temperature with ZnOn (n≤1) target under an atmosphere of O2/Ar ratio varying from 0 to 2.0. The correlation between composition, structure and electrical resistivity of the obtained films was investigated. X-ray diffraction analysis revealed that the prepared würtzite ZnO1-x films had c-axis preferential growth orientation. When the O2/Ar ratio was lower than 0.5, the main form of defects in the films was oxygen vacancy; when it was 0.5, the composition of the film approached to the stoichiometric ZnO and had the least number of defects; after that, the main type of defects in the films was interstitial zinc. Thus, with increasing O2/Ar ratio, the electrical resistivity of the films increased first and then decreased.

Stability of inverted organic solar cells with ZnO contact layers deposited from precursor solutions

Interstitial zinc defects in solution-processed ZnO can be mitigated by using a diethylzinc precursor instead of zinc acetate, or by modifying the ZnO surface with a phosphonic acid, resulting in improved organic solar cell stability.

Role of Zn-interstitial defect states on d0 ferromagnetism of mechanically milled ZnO nanoparticles

An impurity defect level formed by interstitial zinc at the surfaces of undoped ZnO nanoparticles plays a crucial role for d0 ferromagnetism.

Enhancement of Ultraviolet Emission of ZnO Hollow Nanofibers

ZnO hollow nanofibers were fabricated by sputtering using electrospun PVP nanofibers as templates. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction and UV Raman were used to characterize the morphologies, crystal configuration and bonding structure of ZnO hollow nanofibers. A reactive mechanism of the transformation from poor polycrystalline ZnO (Zn-rich) prepared by sputtering from a metallic Zn target to good polycrystalline ZnO after annealing is proposed. The mechanism results in great decrease of oxygen vacancies and interstitial zinc of the ZnO hollow nanofibers after annealing. Optical properties were investigated by the photoluminescence spectra. Enhancement of ultraviolet emission of the ZnO hollow nanofibers is discussed.

Mn2+ ion influenced optical and photocatalytic behaviour of Mn–ZnS quantum dots prepared by a microwave assisted technique

(a) Photon absorption and exciton formation, (b) interstitial sulfur emission, (c) interstitial zinc emission, (d) blue emission, (e) electron trapping by Mn ions' d state, (f) orange light emission and (g) orange emission quenching by electrons trapped by the neighbouring Mn2+ ions.