A Comparative Investigation of Optical and Structural Properties of Cu-Doped CdO-Derived Nanostructures

In this report, we studied various structural and optical properties of pure and copper-doped cadmium oxide (CdO) thin films. Nanostructured Cu-doped CdO films were deposited using sol–gel spin-coating technique. The structural and morphological changes have been observed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) studies. The optical and electrical properties of the pure and Cu-doped CdO thin films were studied by UV–vis spectroscopy and four-point probe method, respectively. The XRD peaks show the formation of nanocrystalline CdO with cubic face-centered crystal structure. The band gaps of the as deposited films were found in the range of 2.32–2.73 eV, while after doping, it decreases due to structural deformation. The electrical resitivity was found to decrease approximately ～10 in Cu-doped CdO thin films.     

Detection of multiple virulence-associated genes in Listeria monocytogenes isolated from bovine mastitis cases

Clinical samples (n=725) were collected from bovines (n=243) which were positive for mastitis using the California mastitis test (CMT) and somatic cell count (SCC). The clinical samples comprising blood (n=239), milk (n=243), and faecal swabs (n=243) were examined for the presence of pathogenic Listeria spp. Isolation of the pathogen was done using selective enrichment in University of Vermont Medium and plating onto Dominguez-Rodriguez isolation agar. Confirmation of the isolates was based on biochemical tests and Christie, Atkins, Munch-Petersen (CAMP) test followed by pathogenicity testing. Pathogenicity of the isolates was tested by phosphatidylinositol-specific phospholipase C (PI-PLC) assay as well as in vivo tests namely, chick embryo and mice inoculation tests. The isolates were subjected to PCR assay for five virulence-associated genes, plcA, prfA, hlyA, actA and iap. Listeria spp. were isolated from 12 (1.66%) samples. Of these 4 (0.55%) and 1 (0.14%) were confirmed as Listeria monocytogenes and Listeria ivanovii, respectively. L. monocytogenes and L. ivanovii were recovered from milk samples (2) and faecal (3) of mastitic cattle (3) and buffaloes (2). L. monocytogenes recovered from the milk of mastitic cattle and L. ivanovii from the faecal swab of buffalo turned out to be pathogenic. However, the remaining three hemolytic isolates exhibiting positive CAMP test turned out to be negative in PI-PLC assay, chick embryo and mice inoculation. L. monocytogenes and L. ivanovii isolates characterized as pathogenic by PI-PLC assay and in vivo pathogenicity tests were found to possess all the five virulence-associated genes and three genes, plcA, prfA and actA respectively. The remaining three hemolytic but non-pathogenic L. monocytogenes isolates were negative for plcA by PCR. It seems that the plcA gene and its expression (in the PI-PLC assay) have an important role as virulence determinants in pathogenic Listeria spp. In conclusion, the PI-PLC assay and virulence genes targeted PCR (plcA, prfA and hlyA genes for L. monocytogenes and plcA, prfA and actA genes for L. ivanovii) hold a good promise as rapid and reliable in vitro alternatives to in vivo pathogenicity tests.     

Impact of a Short-Pulse High-Intense Proton Irradiation on High-Performance Perovskite Solar Cells

This work investigates the radiation resistance of high-performance multi-component perovskite solar cells (PSCs) for the first time under extreme short-pulse proton irradiation conditions. The devices are subjected to high-intensity 170 keV pulsed (150 ns) proton irradiation, with a fluence of up to 10¹³ p cm^−2, corresponding to ≈30 years of operation at low Earth orbit. A complex material characterization of the perovskite active layer and device physics analysis of the PSCs before and after short-pulse proton irradiation is conducted. The obtained results indicate that the photovoltaic performance of the solar cells experiences a slight deterioration up to 20 % and 50 % following the low 2 × 10¹² p cm⁻² and high 1 × 10¹³ p cm⁻² proton fluences, respectively, due to increased non-radiative recombination losses. The findings reveal that multi-component PSCs are immune even to extreme high-intense short-pulse proton irradiation, which exceeds harsh space conditions, including intense coronal ejection events usually associated with solar flares.     

Morphological transformations induced by Co impurity in ZnO nanostructures prepared by rf-sputtering and their physical properties

Growth of uniform and vertically well aligned nanorods is a difficult process and becomes more complicated in case of ZnO nanorods on silicon (Si) substrate due to thermal instability of the Si substrate and large lattice mismatch (~?40%) between the substrate and the ZnO nanorods array. Growth of ZnO nanorods assisted by metal ion via rf-sputtering is a good technique; however, it needs many parameters to be controlled for desired growth and morphology of nanostructures. In this work, we report the morphological transformations of ZnO nanostructured thin film by simply controlling the concentration of Cobalt (Co) impurity in sputtering target. With the introduction of Co ions in ZnO matrix, the initial coalescence grain structure (pyramidal morphology) changes into columnar grains and as the concentration of Co ions increases further, a highly oriented ZnO nanorods array is obtained. The possible mechanism with the help of schematic diagram is also proposed for the morphological transformation of ZnO nanostructures. The vertically aligned nanorods show good optical properties as well as robust ferromagnetism at room temperatures. It has also been observed that with the dopant conc. increasing there was a significant decrease in the band gap energy. The structure and morphology of rf-sputtered nanostructured thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. Interestingly, with Co conc. increasing in ZnO matrix results in decreasing LO modes in Raman spectroscopy. It can have strong influence on the magnetic properties of the material. The good optical and strong ferromagnetic properties of the ZnO nanorods, suggest its possible applications in the fields of lasers, spintronics and medical applications.     

An approach to produce single and double layer graphene from re-exfoliation of expanded graphite

We report the production of high quality single and double layer graphene from sonication and centrifugation of re-exfoliated expanded graphite (EG) in an organic solvent. The prepared graphene-sheets are identified by Ultraviolet–visible spectroscopy and characterized using different techniques. Transmission and scanning electron microscopy observations show that the graphene-sheets have an area of ∼(12 × 10) μm². The selected area electron diffraction analysis and Raman spectroscopy have confirmed the presence of single layer graphene-sheet. The I(2D)/I(G) ratio from the Raman spectrum of graphene is found to be ∼1.7 which suggests the presence of single and double layer graphene. Scanning probe microscopy studies reveals that on re-exfoliation of EG, thickness of graphene layer decreases from 6–7 nm to 0.75–1.075 nm. This suggests that re-exfoliation overcomes the problem of insufficient oxidation or inadequate pressure that builds-up during first thermal exfoliation of graphite intercalated compound. The photoluminescence spectrum of graphene shows the emission of blue light at ∼390 nm which indicates the presence of some functional groups. These graphene-sheets should facilitate the manipulation and processing of graphene based material for various applications.     

Structural and Spectroscopic Characterizations of ZnO Quantum Dots Annealed at Different Temperatures

Here, we report the synthesis and characterizations of sol-gel derived zinc oxide （ZnO） quantum dots （QDs） using zinc acetate dihydrate （Zn（CH3COO）2.2H20） and lithium hydroxide monohydrate （LiOH.H20） as raw material. The as-prepared ZnO QDs was annealed at different temperature （400, 700, and 900 ℃） and the structural, optical properties were investigated by X-ray diffraction （XRD）, high resolution transmission electron microscopy （HRTEM）, UV-Vis and photoluminescence （PL） spectroscopy. The powder XRD patterns of the obtained samples showed the formation of single-phase wurtzite structure and the morphological changes have been observed with increasing annealing temperature. In the absorption spectra, the optical band gap of nanocrystalline ZnO QDs decreased from 3.18 to 3.11 eV and the particle size increased with increasing temperature. In the PL spectra, a broad green emission peak related to defect levels in the visible range of the spectra have been recorded.     

Optical Studies of Fluorescent Mesoporous Silica Nanoparticles

Spherically shaped mesoporous silica nanoparticles(MSNs) having honeycomb like porous structure were synthesized by sol—gel method.Transmission electron microscopy(TEM),surface area measurement and X-ray diffractometry were used,revealing the hexagonal shaped pores in MSNs.MSNs with surface area of 1104.47 m~2/g and large porosity of 2.8 nm in pore diameter and 0.87 cm~3/g in pore volume were synthesized.TEM images showed spherical nanoparticles of ~ 200—300 nm having honeycomb like pores.Stilbene 420 laser dye was incorporated in MSNs and photoluminescence spectra of stilbene 420 in MSNs and in ethanol had been studied.Stilbene 420 laser dye showed high fluorescence intensity in the fluorescence spectra of MSNs than that of ethanol.The prolonged fluorescence lifetime decay of stilbene in MSNs and the increase in fluorescence intensity for stilbene 420 in MSNs would make these nanomaterials more useful for nanosensors and nanolasers application.     

Analyzing the fractal feature of nickel thin films surfaces modified by low energy nitrogen ion

Fractal concepts are used to explore how different energies (10, 20 and 50 keV) and fluence of 5 × 10¹⁷ N⁺ cm^?2 affect the morphology of nickel thin film. The nickel thin film with thickness of 100 nm is prepared by electron beam evaporation technique at room temperature on stainless steel (AISI 316) substrates. The nanoscale three‐dimensional (3‐D) surface micro‐morphologies are investigated by atomic force microscopy (AFM). Interface width is used to describe the surface height fluctuations. The autocorrelation function with height‐height correlation function give the quantitative data about the morphology of surface. The value of roughness exponent and fractal dimension is computed by height‐height correlation function. Fractal measure is an important analysis which provides fundamental insights into the texture characteristics and a direct way of testing their functional role.