Papers by Keyword: ESR

Abstract: We performed electron-spin-resonance (ESR) and electrically-detected-magnetic-resonance (EDMR) spectroscopy on 4H-SiC(1120)/SiO₂ interface defects to study differences between polar-face and non-polar-face 4H-SiC MOS interfaces. We found that in the non-polar-face MOS system, interface defects prefer to form spin-less states of doubly-occupied states and/or empty states, probably due to charge transfer between Si and C atoms at the interfaces.

Abstract: Percolation networks of electrically connected nanographenes are the promising structures for solving the problem of the transfer of their peculiar quantum properties to the macroscopic level. In this work we report the results of investigations, conducted with using a set of complementary physical methods, on the origin, structural motifs and properties of such networks revealed in thermally reduced graphene oxide films. The presence of zero modes, which may be π-electronic states stabilized at the zigzag edges of network elements, has been established.

Abstract: In the present work, colorless topaz was designed and developed a dosimeter for routine application. The samples were irradiated with gamma from ⁶⁰Co at dose range 50 - 400 Gy and investigated by thermoluminescence (TL) and electron spin resonance (ESR). The TL grow curve of topaz were revealed two trapping levels at temperature 150 °C and 225 °C. The ESR signals of topaz shown that the g value at 1.966 and 2.012 due to Ti³⁺ and (AlO₄)⁰ center, respectively. The intensities of TL and ESR were increased with increasing dose. The percentage error of dose from TL and ESR signal were 8 and 3, respectively. These experiment indicated that the colorless topaz could be used as a dosimeter.

Abstract: We studied interface defects of C-face 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) by means of electrically-detected-magnetic-resonance (EDMR) spectroscopy. EDMR measurements were carried out on opposite types of C-face MOSFETs, which were prepared by dry oxidation and wet oxidation, and we found EDMR signals of interface defects from both the MOSFETs. Judging from their spectroscopic features, the interface signals of the two MOSFETs are assigned to be the same type, and we call them “C-face defects.” The density of C-face defects was found to be larger in the dry-oxide MOSFETs than in the wet-oxide MOSFETs. It is also revealed that part of C-face defects in wet-oxide MOSFETs are coupled with hydrogen atoms.

Abstract: We present EDMR (electrically detected magnetic resonance) observations on “C-face defects” in C-face 4H-SiC MOSFETs. We found that negative threshold-voltage shifts of C-face MOSFETs are increased in association with EDMR signals of C-face defects as well as with the dissociation of hydrogen atoms induced by gamma-ray irradiation.

Abstract: We studied the hydrogen passivation/depassivation of four types of intrinsic defects (EI5/6, HEI7/8, HEI9/10, and P6/7) in p-type and semi-insulating 4H-SiC by means of electron spin resonance (ESR) for examining the origin of career-lifetime-killing defects. We suggest that the HEI7/8 and P6/7 centers are the strongest candidate for the origin of the lifetime-killing defects.

Abstract: The data on atomic and electronic structure and some magnetic properties of graphite domains in activated carbon fibers (ACF) are presented. It has been established that graphite domains have nanometer sizes in all three dimensions, and consist of about three turbostratically stacked nanographenes. Such multilayer nanographene clusters (nanographites) are structural blocks of ACF and they are separated from each other by the micropores and/or sp³-amorphous carbon phase. From the data of magnetic methods of investigations, it follows that the density of states at the Fermi energy in nanographites is significantly larger than the value of that parameter in macroscopic graphite, which testifies the existence of edge π-electron states in them.

Abstract: The presence of potassium in molybdenum carbide morphology has been reported to increase the selectivity and reactivity of its catalytic properties. Potassium with its tendency to donate electron will enhance the electron density at the surface of catalyst by donating its electron at the vacant orbital framework either to carbon or metal moiety. This phenomenon will cause temporary paramagnetic properties of the catalyst and can be easily detected using an ESR spectrometer. In this paper, an ESR-based study to identify and prove that donating electron does take place at Mo₂C after being promoted with potassium was conducted. Introduction of H₂ and UV radiation were also carried out for comparison.The result from ESR spectra showed that in the absence of potassium in the Mo₂C, no ESR signal was observed. However, in the presence of potassium, a singlet peak with g value ca. 1.9723 was found. The presence of a single peak indicated that the donated electron did not interact with any nearby nucleus in the surroundings. Deviation value of 2.0023 for free electron, indicates that this donated an electron probably interacted with an empty 4d orbital from molybdenum or 2p orbital from carbon.In the introduction of H₂ gas and UV radiation, the finding showed that an increasing trend of singlet peak in the ESR spectrum earlier was observed. The trend indicated that the splitting of H₂ by UV radiation generated new electron and joined the donated electron from K circulating at the surface of K-Mo₂C morphology without interacting with another nucleus.

Abstract: Study on the electron beam irradiation color change induction of spodumene (LiAlSi₂O₆) samples, which color exhibit green, pink and colorless. Characteristic the electron-beam irradiation dose were selected 30,000 kGy, 40,000 kGy and 50,000 kGy. The color and fading of spodumene samples were analyzed by UV-VIS spectrophotometer , crystal structure were determined by X-ray diffraction (XRD) spectrometer, free radical species of impurities were determined by Electron Spin Resonance (ESR) spectrometer before and after irradiation. The results revealed the color of spodumene samples changed after irradiation, from green spodumene became a little darker color, pink spodumene became green color, colorless spodumene became pink to purple color the results of the color analysis and fading displayed on the CIE L* a* b* color system, color change spodumene samples were determined by values changed of a* and b*. Color fade of spodumene were determined by values changed of L*. The results of all samples crystal structure analysis were shown on the XRD patterns of the JCPDS No. 89-6662 (Spodumene) with monoclinic structure. The radical analysis results of impurity elements, green and pink only appear the ESR pattern of manganese (Mn²⁺), and chromium (Cr³⁺), respectively. It can be conclusion that intensity of color change depend on the irradiation dose and impurity elements in spodumene samples.

Abstract: A cost-effective method for quickly evaluating the equivalent series resistance (ESR) of electrolytic capacitors is proposed. This approach has the ability to measure the low ESR of milliohms level, meanwhile provide the pulsed testing current up to hundreds of amperes. Therefore, this method is suitable for fast inspecting the quality of bulk capacitors. The operational principle, circuit implementation and the calibration method are presented, and the performances of the prototype are tested, which validate the proposed scheme.