Papers by Keyword: ESR

Abstract: In this work positron annihilation lifetime spectroscopy (PALS) is employed to study the ortho-Positronium lifetime parameters τ₃>, σ₃ and I₃ in two structurally simple amorphous polymers 1,2-poly(butadiene) and cis-1,4-poly(isoprene). The ortho-Positronium mean lifetime parameter τ₃> is compared with dynamics data from broadband dielectric spectroscopy (BDS) and electron spin resonance (ESR) experiments. Coincidences of characteristic temperatures from PALS with BDS and ESR experiments show close relationships between positron lifetime and dynamics of polymers.

Abstract: The peroxyl radical scavenging abilities of fifty Chinese herbal medicines were determined accurately by an electron spin resonance (ESR) spin-trapping technique using 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) as a spin-trapping reagent. The peroxyl radical was generated by the thermolysis reaction of 2,2’-Azobis(isobutyronitrile) (AIBN) in the presence of the spin-tap DMPO and with or without sample. As a result of these studies, a strong scavenging ability of peroxyl radical was found in Chinese medicines for diseases of anti-aging and blood circulation.

Abstract: High-frequency dynamic magnetic properties of quasi-two-dimensional organic conductors (BEDT-TTF)₂IBr₂ of α'- and β-phases have been studied by Electron Spin Resonance (ESR) spectroscopy. The heating of crystals in the α'-phase is accompanied by their phase transition to the β-phase, so, the Dyson distortion of the ESR line is appeared. Contributions from the crystal field and symmetry of the system as well as the orbital magnetic moment admixture to the total magnetic moment of charge carriers have been judged by the comparison of the orientation and temperature dependencies of the ESR spectra for the α'- and β-phases. Experimental data have proved localized states of charge carriers either in α'- or β-phases.

Abstract: We discuss the results of electrically detected magnetic resonance (EDMR) spectroscopy on SiC-SiO₂ interfaces interacting with hydrogen and nitrogen. Using EDMR, three types of 4H-SiC MOSFETs, which were prepared by dry oxidation (“Dry” sample), post hydrogen anneal (“Hydrogen” sample), and post nitridation anneal (“Nitrogen” sample), were examined in the temperature range of 4–300 K. These samples revealed several different results from the earlier ESR (electron spin resonance) and EDMR studies on SiC-SiO₂ interfaces. The most significant finding was the high-density doping of nitrogen into the channel region after the post nitridation anneal. The incorporated nitrogen donors were observed as the “Nh” EDMR signal at 4–20 K. Roles of these nitrogen donors are discussed in correlation with the electrical properties of SiC MOSFETs.

Abstract: We prepared Solid silicon nitride nanowires using carbon nanotubes as precursors., Si and SiO2 were used as raw materials,the reaction was carried out in ammonia atmosphere The structure, phase composition, ESR properties and oxidation resistance of the sample were investigated. The results showed that the sizes of the nanorods are 60–80 nm in diameter and up to several microns in length. In the products α-Si3N4 is the main component; the FTIR spectra of the silicon nitride nanowires have blue shift phenomena;The ESR properties show that the as made materials contains a large number of unpaired electrons

Abstract: Medium carbon low alloy Ni-Cr-Mo steel is used in the fabrication of aerospace fasteners. It finds application in different heat treated conditions to meet the desired strength level. The alloy was realized through double melting route. Heat Treatment studies have been carried out by following different tempering temperatures to obtain varying strength levels ranging from 1200MPa to 1400MPa. Microstructural analysis has been carried out to find out reasons for variation in mechanical properties. Tempering cycle has been suggested to obtain fully tempered martensitic structure. This paper presents the different hardening and tempering cycles studied to obtain the desired strength level for the intended application.

Abstract: The main goal of this research is studying the crystal structure and formation of both free radicals and trapped space charges in the pure and doped polyvinylidene fluoride (PVDF) films with various concentrations of transition metal halides TMHs (AlCl₃, ZnCl₂, and CoCl₂). Electron Spin Resonance (ESR) was used to detect the existence of free radicals and the probable magnetic interactions between the halide and PVDF. The hyperfine splitting of the ESR was used to study the electronic structure of the existence radicals. Thermally stimulated dielectric response measurements have been made using Frequency Resolved Dielectric Spectroscopy (FRDS). This was useful for studying the formation and trapping of the space charge to enhance the results obtained by ESR. The new crystalline structures and the complex compounds which may be developed due to the chemical reaction between the polymer and the added halides were analysid.

Abstract: The process of three-phase electroslag furnacefoundry casting  electroslag remelting was used to produce 316L stainless steel ultra-fine wires with a diameter of 0.018mm. Breakage of the wire often occurs during drawing process due to the existence of inclusions in the steel. In order to improve the cleanliness of 316L steel, the deoxidizer and top slag composition were optimized by industrial trials in this production process. As a result, the total oxygen (T.O.) content decreased from 120 ppm to 57ppm. During the electroslag remelting process, the composition of electroslag and the power supply were optimized. Argon protection was used and electrode was washed by acid solution before refining. Finally, the T.O. in the remelting ingot can be controlled below 20 ppm.

Abstract: The method based on solidification mathematical model and Flemings formula was adopted to simulate electroslag remelting process. The simulation results show that the depth of the molten pool become deeper with increasing of melting speed, and when the ingot gets to the certain height, the system is in the quasi-steady state, the pool shape doesn’t change. With increasing of melting speed, secondary dendrite spacing become wider too and secondary dendrite spacing become wider gradually from the surface to center of ingot if melting speed is const. According to the simulated dendrite spacing, micro-structure of slab ingot is estimated to if meeting the demand of solidification quality, and if it can’t meeting this demand, technological conditions(melting speed)should be modified, and recalculating secondary dendrite spacing, controlling solidification structure.

Abstract: We present an electrically detected electron-spin-resonance (ESR) study on SiO2-SiC interface regions of n-channel lateral 4H-SiC MOSFETs with hydrogen annealing. This characterization technique can reveal electrically active defects that interact with channel currents of the MOSFETs. The defects were observed at 20 K, and were labeled “PH0” and “PH1”, one of which (PH1) exhibited a 1H hyperfine splitting of 5.3 mT.