Electron microscopic and X-ray diffraction investigations of nanostructured thin films of ZnO
ZnO films prepared by sol-gel technique using zinc nitrate and zinc acetate as precursor material have been studied using transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The results show the formation of zinc oxide phase. The nanostructure of the films was studied by transmission electron microscopy. Nano-structured fine grains of size ranging from 20-60 nm were observed with zinc nitrate precursor film. Individual grains show a sharp contrast with different facets and boundaries. Films prepared by zinc acetate precursor show ultra-fine nano-grains in the shape of dendrites as seen by the TEM. XRD shows a larger size of crystallites with the zinc acetate precursor. Crystal planes and lattice parameters calculated by both electron diffraction and X-ray diffraction are quite close and in agreement with the reported values in literature.
The effect of ZnS content on the luminescence and electrical properties of ZnO : Zn phosphor
Zinc oxide phosphors (ZnO : Zn) were prepared by solid state sintering of ZnO powders with ZnS and screen printed onto ITO-coated glass substrate. The effect of ZnS content and sintering temperature on the cathodoluminescence brightness, efficiency and electrical properties of ZnO : Zn were studied. Samples with 5 wt % ZnS and sintered at 1100 °C exhibit the highest brightness and efficiency among all the compositions studied. The brightness of phosphors increases linearly as the accelerating voltage V and/or beam current I increases. While the efficiency decreases initially and then reaches a constant value as V and/or I increases. Both the conductivity σ and carrier concentration n of the phosphor increase with the increase of ZnS content in the starting composition. Results of Hall measurement suggest that the ZnO : Zn phosphor is an n-type conductor with an electron mobility of around 175 cm2/V-s. For specimen with 5 wt % ZnS, both σ and n increases initially with the increase of sintering temperature T, and reaches a constant value at T ≥ 1000 °C. The unreacted ZnS found in samples sintered at T < 1000 °C explains the temperature dependence of σ and n.
Robust solutions of inverse problems in electromagnetic non-destructive evaluation
Non-destructive testing (NDT) is the application of physical measurement technology based on energy interaction with the material and its nonconformities. The material's response is sensed by transducers and sensors which?in most cases?scan the component and document the results in inspection images. However, NDT measures a physically defined quantity or even an intrinsic property. The difference between non-destructive evaluation (NDE) and NDT is in the interpretation of the inspection data. NDE has to discuss the inspection results in terms of quality elements and characteristics which are relevant to describe the fitness of the material for use. In the case of macroscopic defects these are the kind of defect (cracklike, globular) and its size and orientation to the main stress directions; in the case of material property determination the parameters are mainly mechanical properties. Therefore, in NDE one has to solve inverse problems. The solution of inverse problems based on mathematical procedures such as integral equations is a strong developing discipline and most of the articles prepared for this special issue of the journal have the objective of discussing the latest state of the art in that field. However, practical NDE needs robust and quick solutions which are to be applied mainly online. Therefore, we present here inversion procedures based on multiple linear regression algorithms applied to inspection data. We describe the calibration procedure to fit the free parameters of the model functions and give examples of practical applications in industry.