• 한국초전도ㆍ저온공학회논문지
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• 제9권4호
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• pp.24-27
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• 2007

The purpose of this work is to develop, integrate, and implement an optical characterization method to evaluate physical properties in coated conductors and investigate the local distribution of the causes of degraded performance. The method that we selected at this moment is Raman scattering spectroscopy, which is accompanied with measurements of local supercurrent transport, phase composition, microstructure, and epitaxy quality for coated conductors that range in size up to multi-meter-length tapes and that embrace the entire tape embodiment (substrate through cap layer). The establishment of Raman spectroscopy as an on-line process monitoring tool is our eventual goal of research, but it requires very robust and cost-effective equipments. We analyzed $YBa_2Cu_3O_7(YBCO)$ thin films grown at various substrate temperatures by using Raman spectroscopy. YBCO films were grown by a high-rate electron-beam co-evaporation method. Raman spectra of YBCO films with lower-transport properties exhibit additional phonon modes at ${\sim}300cm^{-1}$, ${\sim}600cm^{-1}$ and ${\sim}630cm^{-1}$, which are related to second-phases such as $Ba_2Cu_3O_{5.9}$ and $BaCuO_2$. We propose a new method to characterize Raman spectra of coated conductors for an in-line quality control.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.65-65
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• 2000

Microwave response of intrinsic Josephson junctions in mesa structure formed on HgI2-intercalated Bi2Sr2CaCu2O8+x single crystals was studied in a wide range of microwave frequency. With irradiation of 73${\sim}$76 GHz microwave, the supercurrent branch becomes resistive above a certain onset microwave power. At low current bias, the current-voltage characteristics show linear behavior, while at high current bias, the resistive branch splits into multiple sub-branches. The voltage spacing between neighboring sub-branches increase with the microwave power and the total number of sub-branches is almost identical to the number of intrinsic Josephson junctions in the mesa. All the experimental results suggest that each sub-branch represents a specific mode of collective motion of Josephson vortices generated by the microwave irradiation. With irradiation of microwave of microwave of frequency lower than 20 GHz, on the other hand, no branch splitting was observed and the current-voltage characteristics exhibited complex behavior at hlgh blas currents. This result can be explained in terms of incoherent motion of Josephson vortices generated by non-uniform microwave irradiation.