Co doping induced structural and optical properties of sol-gel prepared ZnO thin films

Cataloged from PDF version of article.The preparation conditions for Co doping process into the ZnO structure were studied by the ultrasonic spray pyrolysis technique. Structural and optical properties of the Co:ZnO thin films as a function of Co concentrations were examined. It was observed that hexagonal wurtzite structure of ZnO is dominant up to the critical value, and after the value, the cubic structural phase of the cobalt oxide appears in the X-ray diffraction patterns. Every band-edge of Co:ZnO films shifts to the lower energies and all are confirmed with the PL measurements. Co substitution in ZnO lattice has been proved by the optical transmittance measurement which is observed as the loss of transmission appearing in specific region due to Co2+ characteristic transitions. © 2014 Elsevier B.V. All rights reserved

Effect of prior cold work on the mechanical properties of weldments

Heat exchanger units used in steam raising power plant are often manufactured using many metres of austenitic stainless steel tubes that have been plastically formed (bent and swaged) and welded into complex shapes. The amount of plastic deformation (pre-straining) before welding varies greatly. This has a significant effect on the mechanical properties of the welded tubes and on the final residual stress state after welding. The aim of the present work was to measure and understand the combined effects of pre-straining and welding on the properties and residual stress levels in stainless steel tubing weldments. Effects of plastic deformation were simulated by plastically straining three identical stainless steel tubes to different strain levels (0%, 10% and 20%). Then each tube was cut into two halves and welding back together. The variation in mechanical properties across weldments was measured using digital image correlation (DIC) and a series of strain gauges (SG). Residual stresses were measured on the 0% (undeformed) and 20% prestrained and welded tubes by neutron diffraction. It was found that the welding process had a marked effect on the tensile properties of parent material within 25mm of the weld centre-line. Evidence of cyclic strain hardening was observed in the tube that had not been pre-strained, and evidence of softening seen in the 10% and 20% pre-strained tubes. Macroscopic residual stresses were measured to be near zero at distances greater than 25 mm from the weld centre-line, but measurements in the 20% pre-strained tube revealed the presence of micro residual stresses having a magnitude of up to 50 MPa

Natural plant revegetation on reclaimed coal mine landscapes in Agacli-Istanbul

In this study, natural vegetation development was compared on one abandoned open coal mine spoil and three reclaimed coal mine areas with umbrella pine-Pinus pinea L., maritime pine-Pinus pinaster Ait. and leguminous black locust-Robinia pseudoacacia L. in Agacli-Istanbul. Soil data of these sample areas were determined in previous studies. These properties demonstrate physically and nutritionally poor conditions and some rehabilitative effects after tree species were introduced. The plant species composition and total coverage for each species (vertical projection onto the ground) was estimated visually and recorded on each sample plot. Naturally revegetated plant species, species composition, Shannon-Wiener diversity index values, species richness, evenness, total abundance and their coverabundance scales were evaluated by comparing each other. Generally, the best-represented species belong to Rosaceae in all investigated plots. Shannon diversity index and its components give the different results among sample plots. However, higher values were found on reclaimed sites. Highest Shannon diversity index (H') was found on the sample area reclaimed with maritime pine. Plant species richness (S) was highest under umbrella pine and plant species evenness (J') was highest on black locust sample plot. Despite the sample area reclaimed, black locust has the more fertile soil conditions, it has only the highest plant species evenness (J') value among areas.Key words: Coal mine, plant composition, reclamation, revegetation, species richness, species diversit

Nanoplasmonic surfaces enabling strong surface-normal electric field enhancement

Cataloged from PDF version of article.Conventional two-dimensional (2D) plasmonic arrays provide electric field intensity enhancement in the plane, typically with a surface coverage around 50% in the plan-view. Here, we show nanoplasmonic three-dimensional (3D) surfaces with 100% surface coverage enabling strong surface-normal field enhancement. Experimental measurements are found to agree well with the full electromagnetic solution. Along with the surface-normal localization when using the plasmonic 3D-surface, observed maximum field enhancement is 7.2-fold stronger in the 3D-surface than that of the 2D counterpart structure. 3D-plasmonic nonplanar surfaces provide the ability to generate volumetric field enhancement, possibly useful for enhanced plasmonic coupling and interactions. © 2013 Optical Society of America

Synthesis and optical properties of Co and Zn-based metal oxide nanoparticle thin films

ZnO, Co doped ZnO (ZnO:Co) and CoO thin films were deposited on glass substrates by using the spark discharge technique with Zn-Zn, Zn-Co and Co-Co metal electrodes (tips). The structural and optical properties of the films were characterized by X-ray diffraction, scanning electron microscopy measurements and UV-Vis spectrometry. Cubic phase reflection of CoO (200) was observed in the samples containing Co. The size of nanoparticles had varied between 38 nm and 200 nm in ZnO thin films. When Co electrode was used, spherical structure had deteriorated and clusters of particles, with smaller radii, were observed. In addition, when Co-Co electrode pairs were used, various cavities with different sizes were formed. Especially, it was observed that the optical transmittance had generally increased with the decreasing spark (charge) voltage, while increasing with the number of sparks. The Co-containing samples were green in color and it was observed that the loss of transmission appears in a specific region in the Co-doped ZnO thin films due to characteristic d-d transition of Co2+ ions. The thickness of the films had decreased with the increasing number of sparks. In addition, the band gap energy, Eg, evaluated by UV-Vis spectroscopy measurements has been shifted to higher wavelengths (red shift) for the ZnO:Co thin films. © 2017, Polish Academy of Sciences. All rights reserved

Plasmonic light-sensitive skins of nanocrystal monolayers

Cataloged from PDF version of article.We report plasmonically coupled light-sensitive skins of nanocrystal monolayers that exhibit sensitivity enhancement and spectral range extension with plasmonic nanostructures embedded in their photosensitive nanocrystal platforms. The deposited plasmonic silver nanoparticles of the device increase the optical absorption of a CdTe nanocrystal monolayer incorporated in the device. Controlled separation of these metallic nanoparticles in the vicinity of semiconductor nanocrystals enables optimization of the photovoltage buildup in the proposed nanostructure platform. The enhancement factor was found to depend on the excitation wavelength. We observed broadband sensitivity improvement (across 400-650 nm), with a 2.6-fold enhancement factor around the localized plasmon resonance peak. The simulation results were found to agree well with the experimental data. Such plasmonically enhanced nanocrystal skins hold great promise for large-area UV/visible sensing applications

Numerical study of strength mismatch in cross-weld tensile testing

The strength mismatch effect on the deformation behaviour of defect-free cross-weld tensile specimens, where there is a variation in strength along the length of the specimen, was investigated through 2D finite element analysis. A simple bi-material model, which is generally used in current engineering assessments (e.g. R6 “Assessment of the integrity of structures containing defects”) to examine the strength mismatch effect on the deformation and fracture behaviour of a weld which actually includes a heat-affected-zone, could lead to non- conservative or overly conservative predictions. In fusion welded components, one would generally observe that there is a heat-affected zone where the material properties are different from the weld and base material, and there is a continuous gradient of properties between the two. The material properties in HAZ are generally assigned discretely; however, in our multi-material model these properties are successfully assigned continuously by embedding subroutines into finite element model. This multi-material approach was used to examine the effect of strength mismatch on the local and global deformation behavior of fusion welds. It has been found that the bi-material modeling, by ignoring the HAZ, and multi-material discrete HAZ modeling of the cross-weld specimens leads to unrealistically biaxial stresses at the interfaces where there is an abrupt variation of the material properties. However, multi- material continuous HAZ modeling eliminates unrealistic stress biaxiality and enables to examine the local deformation more accurately. It was also found that the global stress-strain behaviour obtained using the bi- material and multi-material modeling is different

Variation of mechanical properties in a multi-pass weld measured using digital image correlation

As part of a programme investigating the structural integrity of welds, the Digital Image Correlation (DIC) technique was used to obtain the full-field strain distribution during tensile testing of cross-weld specimens cut from a multi-pass girth welded pipe. The displacement maps were analyzed using Matlab scripts to compute local stress-strain variations from which the local proof stress values were extracted. It has been found that the DIC parameters, such as the size of interrogation windows (subsets) and speckle sizes, have significant effects on the displacement values due to the local variations in the mechanical properties within the weld between the passes. The DIC parameters were therefore optimized using monolithic aluminium alloy specimens with stress concentrations giving similar displacement gradients. The use of a high resolution camera at high magnification allowed the variations between the welding passes to be observed. The variation of the mechanical properties in the weld region is correlated with the full field hardness maps of the same region