산소 유량비 변화에 따른 Al 도핑된 ZnO 박막의 구조 및 광학적 특성

손영국,황동현,조신호,Son, Young-Gook,Hwang, Dong-Hyun,Cho, Shin-Ho 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.4

라디오파 마그네트론 스퍼터링 방법으로 유리 기판 위에 Al 도핑된 ZnO (AZO) 박막을 성장시켰다. 증착시 스퍼터링 가스로 사용하는 산소 유량비의 변화에 따른 AZO 박막의 특성을 X-선 회절법, 원자 주사 현미경, 홀 효과 측정법으로 조사하였다. 증착 온도 $400^{\circ}C$에서 산소 유량비 0%로 증착된 AZO 박막은 가장 큰 c-축 우선 배향성과 최저의 비저항값 $6.9{\times}10^{-4}{\Omega}cm$을 나타내었다. 산소 유량비가 증가함에 따라 ZnO (002)면의 회절 피크의 세기는 실질적으로 감소하는 경향을 보였다. 또한, 산소 유량비가 감소함에 따라 전하 운반자의 농도와 홀 이동도는 증가하였으나, 전기 비저항은 감소하였다. Al-doped ZnO (AZO) thin films were grown on glass substrates by radio-frequency magnetron sputtering. The effects of oxygen flow ratio, which was used for a sputtering gas, on the AZO thin films were investigated by using the X-ray diffraction (XRD), atomic force microscopy (AFM), and Hall effects measurement. The AZO thin film, deposited with oxygen flow ratio of 0% at the growth temperature of $400^{\circ}C$, showed a strongly c-axis preferred orientation and the lowest resistivity of $6.9{\times}10^{-4}{\Omega}cm$. The ZnO (002) diffraction peak indicated a tendency to decrease substantially with increasing the oxygen flow ratio. Furthermore, as the oxygen flow ratio was decreased, the carrier concentration and the hall mobility were increased, but the electrical resistivity was decreased.

Self-seed layer를 이용하여 증착한 SBT박막의 특성

김형섭,황동현,윤지언,손영국,Kim, Hyung-Sub,Hwang, Dong-Hyun,Yoon, Ji-Un,Son, Young-Gook 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.3

[ $Pt/SBT/Seed/Pt/Ti/SiO_2/Si$ ]의 구조로 $SBT(SrBi_2Ta_2O_9)$ 박막을 Self-seed layer를 사용하여 R.F. Magnetron sputter를 이용하여 증착을 하였다. Self-seed layer는 기판온도 RT(room temperature)와 $600^{\circ}C$에서 두께 30 nm으로 증착하였다. Self-seed layer의 결정화 온도를 알아보기 위해 열처리온도를 변화시켰고 이를 XRD를 통하여 결정화 유무를 확인하였다. Self-seed layer 위에 증착한 SBT를 XRD와 전기적 측정을 통해 특성을 관찰하였다. Thin films of $SBT(SrBi_2Ta_2O_9)$ having $Pt/SBT/Seed/Pt/Ti/SiO_2/Si$ structure were fabricated using self-seed layer method by R.F. Magnetron sputter. Self-seed layers were deposited at room temperature and $600^{\circ}C$, which had 30 nm thickness. To investigate crystallization of self-seed layer we characterized by XRD after various heat treatment. And we characterized the crystallinity and electrical properties of SBT on self-seed layer after various heat treatment.

Pb(Zr, Ti)O₃세라믹스의 상경계 부근에서 상공존에 미치는 화학조성의 불균일성의 효과

손영국 부산대학교 공과대학 1992 工大論文集 Vol.43 No.-

In order to identify the origin of phase coexistence at morphotropic tetragonal and rhombohedral boundary in PZT ceramics, the effect of chemical inhomogeneity on phase coexistence region was investigated. Two kinds of PZT ceramics with different chemical homogeneity were prepared by conventional solid state reaction and coprecipitation method. There was coexistence of tetragonal and rhombohedral phase over a wide composition range in PZT ceramics calcined by solid state reaction, and there was also phase coexistence of which region was reduced considerably in sintered samples. And phase coexistence region was not observed in coprecipitated PZT ceramics (with 1 mole %). Therefore compositional fluctuation is considered to be major origin of the phase coexistence at morphotropic phase boundary in PZT ceramics.

Oxalate법으로 합성한 β-alumina의 소결성 및 전기전도성에 미치는 열처리온도와 MgO첨가량의 영향

손영국 釜山大學校生産技術硏究所 1997 生産技術硏究所論文集 Vol.52 No.-

oxalate 공침법으로부터 β-alumina를 제조하기 위하여 최적의 pH 영역을 Mg이온의 평형상수와 용해도적으로부터 구하고 용해도를 그렸다. 제조된 β-alumina의 소결성과 전기전도성에 영향을 미치는 열처리와 MgO 첨가 효과를 고찰하였다. 적정 pH영역에서 합성된 β-alumina는 800℃에서 열처리한 경우가 가장 미세하며 고른 입자분포를 나타내었다. MgO가 첨가된 경우 1∼2 ㎛정도의 응집체로서 항상 β"-alumina와 β-alumina의 혼합상을 나타내었으며 첨가량이 증가할수록 β"/β-alumina의 분율증가를 나타내었다. 800℃에서 열처리된 β-alumina 소결시편이 가장 높은 밀도를 나타내었으며 전기전도도도 우수하였다. MgO량이 증가할수록 밀도는 감소하였고 MgO가 2.0wt% 첨가된 경우 27.7kJmol-1의 겉보기 활성화 에너지값을 나타내었다. The optimum pH range for oxalate coprecipitates has been calculated from the solubility products and the equilibrium constants of Mg ionic species and its solubility diagram was obtained to prepare β-alumina powder by oxalate coprecipitation method. The effects of heat treatment and MgO addition on their sinterability and electrical conductivity were investigated. β-alumina synthesized in the optimum pH range and heat-treated at 800℃ showed the finest size and narrow particle size distribution. MgO-doped β-alumina was agglomerated in the range of average particle size of about 1∼2㎛, which always comprised β"-alumina and β-alumina fraction of β"/β-alumina increased with increasing MgO contents. Sintered sample, which was heat-treated at 800℃, showed the highest density and electrical conductivity. The densities of sintered samples decreased with the increasing MgO contents. The apparent activation energy of electrical conductivity was calculated to be 27.7kJmol-1 from sintered sample of 2.0wt%/MgO doped β-alumina.

Pb(Zn, Fe, Nb, W)O₃계 복합 페로브스카이트 화합물의 소결정 및 전기적 성질에 미치는 분쇄효과

손영국 부산대학교 공과대학 1993 工大論文集 Vol.45 No.-

Lead-based relaxor material, Pb(Zn, Nb, Fe, W)O₃ for multilayerceramic capacitors was ground by ball-milling with partially stabilized zirconia balls of 1,3 and 15mm in diameter in order to examine the effects of particle size on the sintering and dielectric properties. Particle size distribution, contamination from the balls and the residual strain of the powder were examined. The use of smallzirconia balls in ball-milling was effective to grind the powder to submicronmeter. Average particle sizes of powders ball-milled for 128 hours using 1, 3, 15mm balls were 0.24, 0.35 and 0.68 ㎛, respectively. The structural distortion of the ball-milled powders increased with decreasing particle size in contrast with little change in the lattice strain. The contamination from zirconia balls in ball-milling was examined with fluorescent X-ray analysis, and it was clear that the ball-milled powders were free from the contamination. The average grain size of sintered ceramics from the fine powder with average particle size of 0.24 ㎛ was rather fine than that of sintered ceramics ar the same temperature from 0.68 ㎛ powder. The densification of the fine powder was enhanced at lower firing temperture, and the dense dielectic ceramics were obtained at the firing temperature of 750℃ which was lower by 100℃ compared with the optimum firing temperature for the powders with average particle size of about 1㎛. Relative permittivity of the fine grained sample fabricated from 0.24㎛ powder at 750℃ was above 10 4 at room temperature and less DC bias field and less temperature dependences compared to that of coarse grained sample fabricated from the usual powder.

리튬이온 이차전지의 정극용 LiMn₂O₄의 화학적 합성 및 전기화학적 특성에 관한 연구

손영국 釜山大學校生産技術硏究所 1997 生産技術硏究所論文集 Vol.52 No.-

LiMn₂O₄의 사이클링특성의 향상을 위해 과량의 리튬을 첨가하여 스피넬을 700℃에서 분무건조한 분말을 하소한 후 870℃와 600℃에서 24시간 이단계 열처리과정을 통해 얻었다. 합성된 분말은 순수한 결정상의 스피넬이였고, 입자크기는 약 25㎛정도였다. 스피넬의 전기화학적 특성은 건조박스내의 아르곤분위기에서 제조된 /1M LiClO₄/Li전지를 통해 측정되었다. 주사속도 2㎷/sec, 측정전위 2.5V∼4.5V범위에서 정극의 순환전류전위법으로부터 얻은 결과로 볼 때 조성이 인 정극이 가장 좋은 사이클링 특성을 보였다. 이들 스피넬 정극들의 쿨롱효율은 모두가 거의 100%의 효율을 보였다. To improve the cycle performance of LiMnO₄spinels with an additional amount of Li were prepared by two-step heat treatment at 870℃ and 600℃ for 24 hours after calcination of the spray-dried powder during 8 hours at 700℃. The as-synthesized powder were well-crystalline pure spinels, and their particle size were about 25㎛. The electrochemical properties of the spinel cathodes were evaluated using /1M LiClO₄/Li cell in Ar atmophere dry box. From Cyclic Voltammetry of cathodes at scan rate of 2㎷/sec, 2.5V∼4.5V, showed the vest cycle performance. Coulombic efficiency of these spinel cathodes during CV test were almost 100%.

리튬이온이차전지 정극용 LiNixMn₂-xO₄의 합성과 전기화학적 특성에 관한 연구

김병습,손영국 부산대학교 생산기술연구소 2000 生産技術硏究所論文集 Vol.58 No.-

LiNixMn2-xO4, (0≤x≤0.5)를 저온합성이 가능한 sol-gel법을 이용하여 합성하였다. 합성된 분말은 x선회절분석을 통하여 cubic spinel 구조임을 확인했고, Ni의 치환량이 증가함에 따라 격자상수는 감소했다. 순환전압전류 및 충방전 시험을 통하여 전기화학적 특성을 측정해본 결과 LiMn2O4에 비해 Ni의 치환량이 증가함에 따라 4V피크는 점차 사라졌지만, 3V피크에서의 방전용량과 싸이클 특성은 모두 우수한 특성을 나타내었다. LiNixMn2-xO4 (0≤x ≤0.5) cathode materials were synthesized at low temperature using sol-gel process. X-ray diffraction studies showed that the powders have cubic spinel structure and its lattice constants decreased as doped Ni contents increased. The electrochemical properties of the spinel LiNixMn2-xO4cathode materials were evaluated by cyclic voltammetry and charge discharge test. As doped Ni contents increased, 4V peak disappeared but capacity and cycling properties at 3V peak were improved than LiMn2O4.

탄소나노튜브 캐소드의 전계방출 및 열화특성에 미치는 페이스트의 조성과 분위기 가스의 영향

김동희,김태식,정원섭,김광호,손영국,조영래 대한금속ᆞ재료학회 2006 대한금속·재료학회지 Vol.44 No.3