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Analysis of the charge transfer and separation in electrically doped organic semiconductors by electron spin resonance spectroscopy
摘要： We investigated the charge generation mechanism of electrically doped organic semiconductors (OSs) by electron spin resonance (ESR) analysis. ESR spectroscopy was used to successfully evaluate the radical density of p-doped OSs to estimate the charge transfer efficiency (CTE) of various doped systems. The results showed that the CTE is efficient close to 100% if the dopant molecules are homogenously dispersed and the energy difference (?E) between the highest occupied molecular orbital (HOMO) level of the host molecule and lowest unoccupied molecular orbital (LUMO) level of the p-dopant is large. The charge separation efficiency to form free carriers from the radicals is rather low (less than 12% in this study) and is a dominant factor controlling the charge generation efficiency (CGE). An organic dopant molybdenum tris[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] turns out to be an efficient dopant with the CGE of 9.7% due to high CTE originating from homogenous dispersion of the organic p-dopants and low LUMO level, i.e., large ?E.
关键词： charge generation efficiency,p-dopant,charge transfer,electron spin resonance spectroscopy,Organic semiconductors,charge separation
更新于2025-09-19 17:15:36
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[IEEE 2018 Conference on Optoelectronic and Microelectronic Materials and Devices (COMMAD) - Perth, Australia (2018.12.9-2018.12.13)] 2018 Conference on Optoelectronic and Microelectronic Materials and Devices (COMMAD) - Isotopically Pure Silcon-28 Whispering Gallery Mode Resonators: A Host for Narrow Linewidth Spin Ensembles
摘要： Single crystal isotopically pure 28Si cylindrical Whispering Gallery (WG) mode resonators have been machined from a rod of isotopically pure crystal. Before machining, the rod was loaded into a cavity with the best Bragg confined modes exhibiting Q-factors above a million for frequencies between 10 and 15 GHz. Electron Spin Resonance spectroscopy revealed a very narrow linewidth spin transition, with g-factor of 1.995±0.008. Analysis determined an upper limit to the linewidth of 7 kHz and a concentration of less than 1011 spins/cm3 (10 parts per trillion). After machining into WG mode resonators, the measured frequencies of the fundamental mode families were used to determine the relative permittivity of the material near 4 K and 20 mK to be 11.488±0.024, with the precision limited only by the dimensional accuracy of the resonator. However, the Q-factors were degraded to below 40,000. Raman spectroscopy revealed strain induced broadening on the radial surface of the crystal as a result of the machining. After an acid clean and etch, followed by annealing, the surface damage was repaired. Subsequently, high Q-factors were also restored. The next step will be to purposefully implant ions to try and realise narrow linewidth spin ensembles with clock transitions, which will couple to high-Q WG modes inside the crystal.
关键词： Narrow linewidth spin ensembles,Isotopically pure silicon-28,Q-factors,Electron Spin Resonance spectroscopy,Whispering Gallery Mode Resonators
更新于2025-09-11 14:15:04
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Point defect chemistry of donor-doped bismuth titanate ceramic
摘要： This communication reports on the defect chemistry at room temperature of barium (Ba) doped bismuth titanate (Bi4Ti3O12), emphasizing the influence of the point defects on its electrical properties. Pure and Ba doped Bi4Ti3O12 were prepared by a conventional solid-phase reaction technique. The addition of Ba into the crystal structure of Bi4Ti3O12 was monitored by X-ray diffraction measurements combined with Rietveld refinement studies where it was determined that Ba occupies the bismuth (Bi) lattice sites as well as the presence of oxygen vacancies (V??O). The characterization of the point defects was carried out using impedance and electron spin resonance spectroscopies where the results support the models of compensation mechanisms dominated by electrical positive charges (h?) and oxygen vacancies (V??O).
关键词： defect chemistry,X-ray diffraction,Rietveld refinement,impedance spectroscopy,solid-phase reaction,barium doped bismuth titanate,electron spin resonance spectroscopy,electrical properties,oxygen vacancies
更新于2025-09-04 15:30:14