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Micro-Raman Scattering Studies of Ge-Sb-Te Bulk Crystals and Nanoparticles
조윌렴,윤석현,H. R. Yoon,W. Jo 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6
We measured micro-Raman scattering spectra of commercially available Ge-Sb-Te (GST) bulk crystals and GST nanoparticles which were synthesized using a pulsed laser ablation method. The lack of the amorphous Te-Te stretching mode near 150 cm¡1 from the Raman spectrum of the bulk sample indicated that the sample was well-crystallized. We also measured GST nanoparticles with dierent growth conditions, from which we could get information towards the optimal growth conditions for better crystallinity of the GST nanoparticles. Our results suggest that through local structural information, micro-Raman scattering spectroscopy can be used to study the phases and the phase changes in the GST bulk crystals and nanoparticles which is being developed for low-power non-volatile memory applications.
Laser Ablation에 의하여 $LaAlO_3$(100) 기판 위에 증착된 Y-Ba-Cu-O 박막에 대한 연구
조윌렴,이규철,고도경,이헌주,노태원,김정구,허필화 한국세라믹학회 1991 한국세라믹학회지 Vol.28 No.12
Y-Ba-Cu-O thin films were in-situ fabricated on LaAlO3(100) substrates using the second harmonics of a pulsed Nd:YAG laser. Thin films were deposited under 200 (mtorr) of oxygen atmosphere, when the substrate temperature was changed between 67$0^{\circ}C$ and 82$0^{\circ}C$. After deposition, the films were in-situ annealed at 50$0^{\circ}C$ under 2/3 bar of oxygen pressure. We showed that the deposition temperature affects the formation of superconducting phase, the resistance, and the surface morphology. The Y-Ba-Cu-O thin films deposited at 76$0^{\circ}C$ show the zero resistance critical temperature of 85 K.
Local Structure and Superconducting Properties of YBCO Films Grown by Co-Evaporation
조윌렴 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.5I
High-rate in-situ YBa2Cu3O7. (YBCO) film growth was demonstrated by means of electron beam co-evaporation. Even though our oxygen pressure was low, 5 × 10.5 Torr, we could synthesize as-grown superconducting YBCO films at a deposition rate of around 10 nm/s, with a critical current density (Jc) of more than 2.0 MA/cm2. Relatively high temperatures of around 900 C have been necessary in this process so far, which suggests that this temperature at a given oxygen activity allows Ba-Cu-O liquid formation along with YBCO epitaxy. We report that the local critical current density shows a clear correlation with the local resistivity. Homogeneous transport properties with a high superconducting transition temperature (89 90 K) are observed in topfaulted region while it is found that the bottom part is found to carry little supercurrent with a large local resistivity. The information derived in this study may be useful in the characterization and optimization of superconducting thin films for electric power and other applications.
조윌렴,G. Kim,정아름,D. Y. Park,H. Cheong,A. Tsukada,R. H. Hammond,M. R. Beasley 한국초전도학회 2010 Progress in superconductivity Vol.11 No.2
Phase stability diagram and boundary of a- and c-axis orientation of SmBa2Cu3O7-y (SmBCO) thin films grown by pulsed laser deposition (PLD) were reported with studies based on x-ray diffraction [1]. Four different samples are systematically analyzed: normal c-axis oriented orthorhombic SmBa2Cu3O7-y, a-axis oriented SmBa2Cu3O7-y, c-axis oriented orthorhombic SmBa2Cu3O7-y with Sm2BaCuO5 phase, and a mixture with c-axis oriented orthorhombic SmBa2Cu3O7-y and anomalously long-c tetragonal SmBa2Cu3Ox. Raman scattering spectroscopy equipped with polarization analysis elucidates the crystal orientation and the origin of the growth of the materials. It indicates that the technique can be used for quality control of conductor manufacturing processes as well as for enhancement of the materials properties.
Optical investigation of high critical-current Gd₁+xBa₂-xCu₃O7 coated conductors
김그라시아,조윌렴,박도형,정현식,신거명,유상임 한국초전도.저온공학회 2008 한국초전도저온공학회논문지 Vol.10 No.2
Gd₁+xBa₂-xCu₃O7 (GdBCO) coated conductors on IBAD-MgO templates have grown by pulsed laser deposition. Critical current of the films were measured as about 90 A/cm by a four-probe method. The optical response of the films was investigated by Raman scattering spectroscopy. According to the Raman scattering spectra, the peaks at 328 cm-¹, 451 cm-¹, 504 cm-1 were found and assigned to one B1g mode and two A1g modes, respectively. The high critical-current carrying behaviors of the GdBCO coated conductors are ascribed to their 123-structure without exchange of cation and incorporation of oxygen into the cuprates.