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学位授与大学：京都大学 ; 取得学位: 博士(工学) ; 学位授与年月日: 2007-09-25 ; 学位の種類: 新制・課程博士 ; 学位記番号: 工博第2867号 ; 請求記号: 新制/工/1421 ; 整理番号: 25552京都大学0048新制・課程博士博士(工学)甲第13396号工博第2867号新制||工||1421(附属図書館)25552UT51-2007-Q797京都大学大学院工学研究科分子工学専攻(主査)教授 今堀 博, 教授 川﨑 昌博, 教授 榊 茂好学位規則第4条第1項該当Doctor of EngineeringKyoto UniversityDFA

Electrical Potential Distribution In Terahertz-Emitting Rectangular Mesa Devices Of High- T C Superconducting Bi2Sr2Cacu2O8 + Δ

Excessive Joule heating of conventional rectangular mesa devices of the high-transitiontemperature Tc superconductor Bi2Sr2CaCu2O8 + δ leads to hot spots, in which the local temperature T (r) \u3e Tc. Similar devices without hot spots are known to obey the ac-Josephson relation, emitting sub-terahertz (THz) waves at frequencies f ∝ V N, where V is the applied dc voltage or electrostatic potential and N is the number of active junctions in the device. However, it often has been difficult to predict the emission f from the applied V for two reasons: N is generally unknown and therefore has been assumed to be a fitting parameter, and especially when hot spots are present, V could develop a spatial dependence that cannot be accurately determined using two-terminal measurements. To clarify the situation, simultaneous SiC microcrystalline photoluminescence measurements of T (r), Fourier-transform infrared (FTIR) measurements of f, and both two and four-terminal measurements of the local V (r) were performed. The present four-probe measurements provide strong evidence that when a constant V is measured within the device?s superconducting region outside of the hot spot, the only requirement for the accuracy of the ac-Josephson relation is the ubiquitous adjustment of the fitting parameter N. The four-probe measurements demonstrate that the electric potential distribution is strongly non-uniform near to the hot spot, but is essentially uniform sufficiently far from it. As expected, the emission frequency follows the ac-Josephson relation correctly even for low bath temperatures at which the system jumps to inner IV characteristic branches with smaller N values, reconfirming the ac-Josephson effect as the primary mechanism for the sub- THz emission

Material degradation of liquid organic semiconductors analyzed by nuclear magnetic resonance spectroscopy

Liquid organic light-emitting diodes (liquid OLEDs) are unique devices consisting only of liquid organic semiconductors in the active layer, and the device performances have been investigated recently. However, the device degradation, especially, the origin has been unknown. In this study, we show that material degradation occurs in liquid OLEDs, whose active layer is composed of carbazole with an ethylene glycol chain. Nuclear magnetic resonance (NMR) experiments clearly exhibit that the dimerization reaction of carbazole moiety occurs in the liquid OLEDs during driving the devices. In contrast, cleavages of the ethylene glycol chain are not detected within experimental error. The dimerization reaction is considered to be related to the device degradation