Papers by Keyword: EPR

Abstract: In this paper, we have studied the EPR spectra, X-ray diffraction and Raman Analysis, Microstructures-morphology of the Ceria NPs calcined at different temperatures of 700 °C, 850 °C ,these materials have been synthesized by Co precipitation (CPT) method by using Cerium tri-nitrate hexahydrate and potassium carbonate solutions. Then synthesized precipitate was heated at 70 °C for 20 hour. Slow grinding of the precipitate and calcined for 3 hours at different temperatures viz. 700 °C and 850 °C to form fine Cerium oxide powder-Ceria NPs. The EPR measurements were made using continuous wave spectrometer (X-band, Bruker Biospin EMX Plus). The g values were obtained by using diphynelpirichylhydrageyl (DPPH-C₁₈H₁₂N₅O₆) sample and got g value is around 1.97. This g tensor is decreased when the calcined temperature are increased, EPR parameters are also changed as the calcined temperature increases. When the calcined temperature is increased from 700 °C to 850 °C, a doublet separated, intensity increased. The X-Ray diffraction pattern shows the nature of the Ceria NPs crystal, with a cubic structure and got the lattice parameters 5.392 Å for samples calcined at temperature of 700 °C and 5.357 Å at 850 °C which shows decreasing trend in lattice parameter with calcination temperature. The intensity of Raman peaks is also shifted upwards with a rise in temperature. This intensity difference could be because of the rise in vibrational amplitudes of the closest neighboring bonds because of the increase in particle size 11.3± 1.0 to 15.6± 1.0 nm at calcination temperatures of 700 °C and 850 °C and the Raman peak of peak I, 461 cm^-1 and peak II, 463 cm^-1 respectively. Other peaks were not observed in this Raman pattern. The EDS analysis confirms the presence of the Ce and O atoms in the synthesized samples. Spherical shapes and homogeneously distributed Ceria NPs and a rather tendency for agglomeration were confirmed.

Abstract: We show that electrically detected electron nuclear double resonance (EDENDOR) can be detected with relatively high signal-to-noise ratios in fully processed 4H-SiC bipolar junction transistors (BJTs). We observe EDENDOR of nitrogen interacting with recombination center defects in the depletion region of forward-biased emitter-base junctions of these devices at room temperature. Our results indicate that EDENDOR has great potential in the investigation of SiC-based devices specifically, as well as in the investigation of solid-state devices based upon other material systems.

Abstract: This paper presents the results of the investigation of stress relaxation at the Si-SiO₂ interface using electron paramagnetic resonance (EPR) spectra, scanning electron microscopy (SEM) image technique, deflection analysis, X-ray photoelectron spectroscopy (XPS) and C-V characterisation of metal oxide semiconductor (MOS) structures. It has been shown, on the basis of EPR, XPS, C-V, and deflection data, that the mechanism of stress relaxation depends on the oxidation conditions: temperature, cooling rate and oxide thickness. In the Si-SiO₂-Si₃N₄ system the stress relaxation occurs due to the difference in the thermal expansion coefficient of SiO₂ and Si₃N₄ material. With an appropriate choice of oxidation conditions compressive stresses in SiO₂ and tensile stresses in Si are almost equal and stress can be reduced considerably at the interface.

Abstract: The nanoparticles of (Na, CO₃)- and (K, CO₃)-containing Calcium phosphates have been prepared by a wet precipitation method in aqueous media. The influence of nature of alkaline metal and of samples composition on particles size and peculiars of their thermal transformation have been studied using such physical-chemical methods as FTIR, XRD, SEM and TPM MS analysis. Chemical composition of powders have been determined by ICP analysis and the degree of substitution of Calcium atoms by alkaline metals depends on CO₃^2-/PO₄^3- molar ratio in initial solutions. The differences in the formation of γ-induced defects in (Na, CO₃)- and (K, CO₃)-containing apatites have been found using EPR spectroscopy.

Abstract: It is known that magnetic, electric and optical properties of materials from mixed oxides mainly depend on the synthesis method used, therefore it is important to perform studies about the use of several synthesis routes with the purpose to understand and control the obtention of any given phase. In many of these routes it is required to control parameters such as temperature, pH, the variation of dopant concentration, etc. By this reason, in this work the effect of the method for three different synthesis routes (chemical coprecipitation, mechanosynthesis and combustion) was studied. These methods were used in the obtention of calcium manganite doped with lanthanum of theoretical stoichiometric Ca_0.3La_0.7MnO₃, using metallic minerals like precursors. The obtained powders were analyzed and characterized by X-ray diffraction (XRD), particle size analysis (PSA), scanning electron microscopy (SEM) and electron paramagnetic resonance (EPR). The crystallographic study (XRD) showed the obtention of calcium manganite doped with lanthanum with orthorrombic type structure, observed by SEM, agglomerates formed by particles with sizes smaller to one micrometer. By EPR it was found that powders obtained by chemical coprecipitation method showed magnetic behavior, in contrast with the behavior obtained by other two methods used, finding also powders with greater purity and in shorter synthesis time with regards to the ones obtained by mechanosynthesis and combustion.

Abstract: In freestanding n-type 4H-SiC epilayers irradiated with low-energy (250 keV) electrons at room temperature, the electron paramagnetic resonance (EPR) spectrum of the negative carbon vacancy at the hexagonal site, VC- (h), and a new signal were observed. From the similarity in defect formation and the spin-Hamiltonian parameters of the two defects, the new center is suggested to be the negative C vacancy at the quasi-cubic site, VC- (k). The identification is further supported by hyperfine calculations.

Abstract: The carbonized silica (SiO₂:C) nanopowders were prepared by chemical modification of fumed silica (aerosil) by phenyltrimethoxysilane followed by thermal annealing at temperature in range of 500-800 °C in nitrogen flow. Their magnetic properties were investigated by electron paramagnetic resonance (EPR) in the temperature range from 4.2 K to 292 K. The initial and annealed SiO₂:C samples revealed carbon (C) related defects. The carbon related radicals (CRR) in annealed SiO₂:C nanopowders with g-factors 2.0042, 2.0039 were attributed to the oxygen (O)-centered CRR and C-centered CRR with a nearby O heteroatom, respectively. The EPR data were compared with infrared (IR) and photoluminescence (PL) data. It was found that the position of the PL band depends on the type of CRR formed after sample annealing. The PL with maximum intensity at 440 nm was found for the sample annealed at 500°C in which O-centered CRR was observed while in the sample annealed at 600°C in which C-centered CRR with a nearby O heteroatom was observed and graphite-like amorphous C clusters were appeared the peak of the PL band was shifted to the 510-520 nm.

Abstract: Along with changes in both self-development and external environment, many issues have arisen within todays real estate enterprise management. As the outcome of speedy technological innovation and gradual emergence of knowledge economy, management processes have been optimized by these transformations in real estate industry. According to the theory of business process Improvement, this research first analyzed the core processes in real estate enterprise, then re-deigned the process by using the tool of The turtle analysis diagram, finally came up with suggestions according to potential risks and issues associated with actual implementation, which overall aims to be meaningful and useful for further process re-design and optimization.

Abstract: The paper aims at demonstration of reduction in residual stress, distortion and sensitisation in austenitic stainless steel pipe welds. The welding processes considered are Gas Tungsten Arc Welding (GTAW) and Shielded Metal Arc welding (SMAW) along with Hot wire GTAW with narrow gap welding technique. It was shown that residual stress is significantly reduced in case of hot wire GTAW. The reduction in residual stress is due to the low heat input and high deposition rate. Lower heat input leads to higher cooling rate giving more margins on sensitization in heat affected zone (HAZ). This has been confirmed by measuring temperature and cooling rate during welding in HAZ of the weld joints. Susceptibility to sensitization of the welds has been compared by carrying out ASTM E262 Practice A and E along with Electo-Potentiokinetic Reactivation (EPR) method. The results of the tests show that values are within acceptable limit for both the cases. However, hot wire GTAW has marginally better sensitization resistance. Fatigue crack growth rate and fracture resistance behavior of the above mentioned weld joints have been compared by carrying out tests on the specimens (Compact Tension) and full scale pipe welds with crack. Fatigue crack growth rate and fracture toughness of the weld joints (hot wire GATW) is superior to conventional GTAW and SMAW. The paper presents the details of the above mentioned studies.

Abstract: Borosilicate based glass formulations have been found suitable for vitrification of high level nuclear waste (HLW) generated during the reprocessing of spent nuclear fuel from nuclear reactors. These glasses possess desirable properties like high chemical, mechanical, thermal and radiation stability for HLW storage. Also, the amorphous nature of the glass helps accommodate the waste containing a variety of elements easily. Because of the presence of the radioactive components, such as, fission /activation products and minor actinides present in the waste, the glass containment experiences radiation damage that can significantly alter the glass structure which may influence their long term leaching behavior. Spectroscopic techniques provide direct and non-invasive method for investigating this radiation damage in the glasses. The present paper gives a glimpse of the current status and issues regarding the investigation of radiation damage in the glass matrices.