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오유영,이광섭,Masao Kamiko,고중혁 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.2
A lead-free piezoelectric ceramic, (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (hereafter (1-x)BZT-xBCT), was investigated for functional device applications. Lead-free piezoelectric materials with high piezoelectric charge coefficients and voltage coefficients are indispensable for functional industrial applications. Piezoelectric ceramic specimens tend to shrink in size during the sintering process without melting. This study focused on this phenomenon as a unique characteristic of piezoelectric ceramic materials, and derived the materials’ activation energies from this phenomenon, employing the Arrhenius relationship. Then the estimated activation energy was employed to determine the relationship between the piezoelectric properties and crystalline properties, while varying sintering temperature and chemical stoichiometric composition. Piezoelectric properties can change depending on the sintering temperature and process conditions. Crystalline properties and piezoelectric properties can be influenced by the sintering temperature and holding times. In this research, sintering temperature dependent structural and dielectric properties were investigated. (1-x)BZT-xBCT ceramics showed the highest piezoelectric coefficient of 470 pC/N. Sintering temperature dependent shrinkage rate and activation energy were estimated and calculated for the various sintering processes. In this research, two different activation energies for the shrinkage process were estimated.
PERPENDICULAR MAGNETIC ANISOTROPY OF Au/(Fe-Co) METALLIC MULTILAYER44S
K., K., Kyuno,Ha, Ha, J.G.,M., M., Iwanami,M., M., Kamiko,K., K., Mae,S., S., Asano,R., R., Yamamoto 한국재료학회 1995 Fabrication and Characterization of Advanced Mater Vol.1 No.1
First-principles calcualtions of the magnetocrystalline anisotropy energy have been performed and it is predicted that the perpendicular magnetic anisotropy energy of a Au(Fe-Co)(111) multilayer will be larger than that of a Au/Co multilayer. Then we have actually synthesized the Au/(Fe-Co) multilayers by MBE method and found that theses multilayers show the predicted properites. The surface magnetic anisotropy energy is $0.64mj/m^2$, which is larger than the value reported previously for the Au/Co multilayer by 10%. Ther result indicated the possibility to control the magnetic anisortopy by changing the number of valence electrons.
Defects controlled stress engineering in Al-doped ZnO transparent multilayered thin films
Kang Jihye,Yun Jaeyong,Oh Yoo-Young,Kim Sung-Jin,Kamiko Masao,Kim Nam-Hoon,Koh Jung-Hyuk 한국세라믹학회 2022 한국세라믹학회지 Vol.59 No.5
This study explores stress engineering in multilayered structures of Al-doped ZnO thin films by controlling defects in them. Al-doped ZnO thin films are examples of transparent conducting oxides. Owing to their high conductivity and transparency, Al-doped ZnO thin films have various promising applications. However, defects and dislocations in thin films can deteriorate their electrical and optical properties. These defects or dislocations can be formed during the thin-film deposition process. Especially, defects can be formed between the layers during the stacking process of the sol–gel method. Therefore, methods to control defects have been designed and simulated to engineer stress in thin films. In this study, layered Al-doped ZnO thin films with different thicknesses were prepared to investigate the interface effects and electron motion in them.
Fe/Au 이중층의 응집현상을 이용한 FePd 나노 점 형성에 관한 연구
구정우,김재민,류동훈,최범진,김동우,이두헌,김은일,미타니 세이지,가미코 마사오,하재근,Koo, J.K.,Kim, J.M.,Ryua, D.H.,Choi, B.J.,Kim, D.W.,Lee, D.H.,Kim, U.I.,Mitani, S.,J.G., M. Kamiko,Ha, J.G. 한국진공학회 2011 Applied Science and Convergence Technology Vol.20 No.1
자기조립화된 Fe/Au 이중층 위에 $L1_0$형 구조를 갖는 FePd 나노 점을 성공적으로 제작하였다. AFM를 이용하여 초기에 편평한 Fe/Au 이중층 박막이 온도가 증가함에 따라서 응집되어 나노 점 구조로 변형되는 것을 확인하였다. 또한 형성된 이중층위에 FePd 다층막을 $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$, $450^{\circ}C$에서 각각 증착하였다. 초격자 구조를 갖는 FePd 다층막의 표면형상은 응집현상에 의하여 자기조립화된 이중층의 형상과 유사하였다. XRD 측정결과, $350^{\circ}C$ 이상에서 열처리된 FePd 다층막은 $L1_0$형 구조를 갖는다는 것을 확인하였다. 그리고 박막두께에 따른 XPS 측정결과는 전체 박막의 화학적 조성이 증착순서와 일치하는 것을 보여주었다. 결과적으로 추가적인 식각공정 없이 화학적으로 규칙화된 FePd 초격자 나노 점의 제작에 성공하였다. [ $L1_0$ ]phase FePd nano-dot structures were successfully fabricated on self-organized Fe/Au bilayers. With atomic force microscopy, it is determined that surface morphologies of initially flat Fe/Au bilayer films were agglomerated and transformed their shape into nano-dots structures with increasing annealing temperature. With this bilayer as a template, FePd multilayers were deposited at various temperatures, i.e. $300^{\circ}C$, $350^{\circ}C$, $400^{\circ}C$, and $450^{\circ}C$. Surface morphologies of FePd superlattice had a near resemblance to self-organized bilayer. According to X-ray diffraction results, it is confirmed that $L1_0$ superlattice structures of FePd were obtained from samples which were annealed above $350^{\circ}C$. Results of X-ray photoelectron spectroscopy depth-profile analysis showed that chemical composition is identical to deposition sequence. As a result, without additional etching processes, fabrication of chemically ordered FePd superlattice nano-dots was achieved.
다양한 하지층이 이중층의 응집현상에 미치는 영향에 관한 연구
하재호,류동훈,임현우,정지민,최호준,홍인기,고중혁,구상모,가미코 마사오,하재근,Ha, J.H.,Ryu, D.H.,Im, H.W.,Jung, J.M.,Choi, H.J.,Hong, I.G.,Koh, J.H.,Koo, S.M.,Kamiko, M.,Ha, J.G. 한국진공학회 2012 Applied Science and Convergence Technology Vol.21 No.5
단결정 MgO (001) 기판에 DC 마그네트론 스퍼터로 하지층과 상지층으로 구성된 이중층을 증착, 열처리 온도와 시간을 고정시키고 이중층의 두께를 변화시켜 응집현상을 제어하여 자기구조화, 나노 구조화된 박막을 제작하였다. 진행한 실험에선 기존에 연구되었던 단층에서의 응집현상이 아닌 하지층과 상지층으로 구성된 이중층의 응집현상으로 나노 점을 형성하였다. 하지층은 Ti, Cr, Co 그리고 상지층은 Ag를 증착하였다. Atomic force microscopy를 통하여 하지층의 물질에 따라 나노 점의 형성 여부가 관찰되었고 형성된 나노 점의 형상이 다르게 나타난 것을 확인하였다. 결과적으로 이중층의 응집현상을 이용하여 나노 점을 제작할 때 가장 적합한 하지층의 물질은 Ti로 확인하였다. 또한 Ti/Ag 시료는 X-ray Diffraction 분광법을 통하여 Ag는 기판으로 사용된 MgO의 (001) 방향을 따라서 에피택셜하게 성장한 것을 확인하였다. We have deposited the bilayer consisted of the underlayer and the overlayer by using DC magnetron sputter on Single crystal MgO (001) substrate. This bilayer was fabricated at fixed annealing temperature and time. We have controlled agglomeration effect by changing of the bilayer thickness. Finally, we have made the self-organization and nano-structured film. In this processing, we have made nano-dot which consists of the underlayer and the overlayer, unlike the existing method called the agglomeration effect in the single layer. The underlayer has deposited using Ti, Cr and Co. And the overlayer has deposited with Ag. Through the analysis of Atomic force microscopy (AFM), the microstructure of underlayer is observed by AFM to confirm the formation of nano-dot. As the nano-dot through above processing, we have found that the nano-dot has the different shape. As a result, when we manufactured nano-dot through the agglomeration effect of bi-layer, the best matching material is Ti for underlayer. And also, we have found that MgO/Ti/Ag samples have been grown expitaxially toward the direction of MgO (001) by X-ray Diffraction analysis.