성명: 김준호(1969. 2. 10生)
학위취득일자: 1998년 8월 21일
학위취득학교: 한국과학기술원 물리학과
지도교수: 염도준(한국과학기술원 물리학과)
본 학회 총무간사인 차동우 회원이 9월 17일자로 인하대학교 교무처장에 취임하였다.
고려대학교 물리학과에 재직 중인 임동건 회원이 10월 1일자로 기초과학연구소 소장으로 취임하였다.
아주대학교 에너지학과 정근모 교수(전 과학기술처 장관)가 10월 4일 미국 워싱턴에서 열리는 미국공학아카데미(National Academy of Engineering) 연차대회에서 한국국적 학자로서는 처음으로 외국인회원이 되었다.
미국공학아카데미는 정교수가 핵융합연구에서의 기본기술이 되는 전자파가열방법을 개발한 공적과 높이 평가된 원자력발전시스템을 혁신시킨 업적의 기술개발공헌과 함께 70년대의 세계적 에너지위기에 대처해서 에너지연구개발계획을 기초한 기술행정공로를 인정하여 이번에 명예스러운 외국인 회원으로 선정되었다고 발표하였다.
미국공학아카데미는 과학아카데미 및 의학아카데미와 더불어 미국정부가 인정하는 3대 아카데미의 하나로서 세계최고의 권위를 자랑하고 있다. 미국공학아카데미의 외국인 회원은 공학의 전 분야를 통하여 전세계에서 선정되고 있으며, 1998년도 선정된 7명을 포함하여 총 155명 뿐이다. 정근모 교수가 이번에 외국인 회원으로 선정된 것은 한국의 에너지기술계가 국제적으로 그 능력과 업적을 인정받은 것으로서 그 의미가 크다 하겠다.
박사학위 취득자 소개
Fabrication and Study of Low Angle Biepitaxial Josephson Junction. We fabricated a new type of biepitaxial grain boundary Josephson junction utilizing an obliquely cut SrTiO3(STO) substrate. The lattice misorientation at the boundary was 20°and 30°. The structure of the junction which was the grain boundary between the two domains made of YBCO layer ((a)-region) and YBCO/ CeO2/YSZ multilayer ((b)-region) was a b-axis tilt or a b-axis twist grain boundary. These structures were confirmed by X-ray diffraction(XRD) measurements. All junctions except 20° twist Josephson junction showed RSJ type I-V characteristics. The 20°and 30°tilt Josephson junctions showed clear SQUID oscillations. The modulation voltage of SQUID oscillations for 20°tilt Josephson junction was 100 ㄍV at 20 K. And for 30°tilt and twist Josephson junctions showed IcRn values as 14 ㄍV and 24 ㄍV at 77 K, respectively.
The YBCO in (a)-region grew with its crystalline axes parallel with those of STO substrate, while the YBCO in (b)-region grew with its c-axis normal to the surface. For the c-axis normal growth of the YBCO in (b)-region, the thickness of buffer layer(DCeO2, DYSZ) and the deposition temperature(Ts) of YBCO are important. The YBCO in (b)-region showed the better c-axis normal growth at the higher Ts, on the thinner CeO2, and on the thicker YSZ. However, on the thicker CeO2(less than 15 Å) and the thinner YSZ, the YBCO grew with its in-plane aligned better. For growing a good YBCO film with its c-axis normal to the surface and its ab-plane well aligned, the thickness of buffer layers should be selected carefully. The DCeO2 had the most dominant effect on the growth of the YBCO in (b)-region. In order to make the YBCO in (b)-region of a nearly single crystalline structure, the thickness of CeO2 was selected in the range of 12 Å∼15 Å.
We measured current-magnetic field (I-H) characteristics for the fabricated four junctions. Increasing the external H field, the Josephson currents(Is) for all junctions except the 20°twist junction were decreased. The decrease of Josephson current was more apparent in 30°junction than in 20°junction. And tilt junction showed much decrease of Is than twist junction. From the results of I-H curve measurements, we believe that tilt junction (or 30°junction) has a grain boundary of weaker link than twist junction (or 20°junction) and 20°twist junction has a grain boundary of non-weak link. Especially, for the 30°tilt junction, we measured I-H curve at 5 K with fine increase of H field, which showed an anomalous Fraunhofer diffraction. The anomalous Fraunhofer diffraction can be understood assuming the nonuniformity of critical current density of junction which may exist in d-wave/d-wave Josephson junctions.