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자발형성 InAs/GaAs 양자점의 구조 및 성장 특성
김형석,서주형,박찬경,이상준,노삼규,송진동,박용주,이정일 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.3
Self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular beam epitaxy and the growth characteristics of QDs were studied using field emission gun-electron transmission microscope. The shapes and optical properties of QDs changed according to spacer layers thickness due to the strain between InAs and GaAs layers. The QDs with 50 nm thick GaAs spacer layers were distributed randomly along the growth direction and changed from dome to flat-pyramidal shape after capping with GaAs. However, QDs with 10 nm thick spacer layers were vertically aligned up to the fifth period and the dome-shape was maintained after capping. The density, distribution and crystalline defects depending on growth conditions were also investigated.
BLT (Bi3.25La0.75Ti3O12) 박막의 결정립 배향성이 잔류 분극과 누설 전류에 미치는 영향
서주형,오상호,박찬향 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.11
Effect of grain orientation on the electrical polarization and leakage current characteristics of Bi_(3.25)La_(0.75)Ti₃O_(12) (BLT) thin films was investigated in terms of c-axis off alignment. The c-axis epitaxial and various c-axis off aligned BLT films have been successfully grown by using different electrode materials (Pt and SrRuO₃) and heat-treatments. In order to evaluate the crystallinity and the film texture of various c-axis off-aligned BLT thin films, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were carried out. BLT thin film grown on the SrRuO₃/SrTiO₃ (100) substrate revealed that its c-axis aligned completely parallel to the substrate normal, by developing cube-on-cube epitaxial relathionship with underlying SrRuO₃ film. The corresponding P-E curve showed nearly paraelectric property. The polycrystalline (117) and (014) oriented BLT films grown in this study were shown that their c-axis off alignment about growth direction increased by amount more than 50°. As the degree of c-axis off-alignment was increased, remanent polarization was increased due to the anisotropic polarization characteristic of BLT film, however, the surface roughness of BLT films was increased and it resulted in degraded leakage current characteristic. Therefore, grain orientation of BLT thin films is a crucial factor controlling the polarization properties and leakage current characteristics.
에피탁시 성장시킨 BLT (Bi_(4-x)La_xTi_3O_12) 박막의 부정합 응력 해소기구
김형석,오상호,서주형,박찬경 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.6
Mechanisms of misfit strain relaxation in epitaxially grown Bi_4-χLa_χTi_3O_12 (BLT) thin films deposited on SrTiO_3 (STO) and LaAlO_3(LAO) substrates have been investigated by means of transmission electron microscopy (TEM). The misfit strain of 20 nm thick BLT films grown on STO substrate was relaxed by forming misfit dislocations at the interface. However, cracks were observed in 100 nm thick BLT films grown on the same STO. It was confirmed that cracks were formed because of high misfit strain accumulated with increasing the thickness of BLT, which was not sufficiently relaxed by misfit dislocations. In the case of the BLT film grown on LAO substrate, the magnitude of lattice misfit between BLT and LAO was very small (∼1/10) in comparison with the case of the BLT grown on STO. The relatively small misfit strain formed in layered structure of the BLT films on LAO, therefore, was easily relaxed by distorting the film, rather than forming misfit dislocations or cracks, resulting in misorientation regions in the BLT film.