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Hong, Young-Hwan,Han, Hyoung-Su,Jeong, Gwang-Hwi,Park, Young-Seok,Dinh, Thi Hinh,Ahn, Chang Won,Lee, Jae-Shin Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.17
<P><B>Abstract</B></P> <P>This study investigated the effect of LiNbO<SUB>3</SUB> modification on the dielectric, ferroelectric and electromechanical strain properties of Bi<SUB>1/2</SUB>Na<SUB>1/2</SUB>TiO<SUB>3</SUB>–SrTiO<SUB>3</SUB> (BNT–ST) lead–free relaxor ceramics. The sintering temperature for lead–free BNT–ST relaxor ceramics was slightly decreased from 1175 °C to 1050 °C by modifying with LiNbO<SUB>3</SUB>. We found that the sintering temperature affects the dielectric behavior of 0.76BNT–(0.24−<I>x</I>)ST–<I>x</I>LiNbO<SUB>3</SUB> (BNST–100<I>x</I>LN) ceramics at high temperature (near dielectric maximum temperature, <I>T</I> <SUB>m</SUB>). The <I>T</I> <SUB>m</SUB> for the low–temperature sintered sample was shifted to relatively higher temperature by comparison with the high–temperature sintered samples. Furthermore, the degradation of dielectric behavior near <I>T</I> <SUB>m</SUB> in low–temperature sintered BNST–2LN ceramics was revealed after poling treatment and seem to be related to the existence of a high temperature stabilized nonergodic relaxor phase. Accordingly, we assume that the stabilized nonergodic relaxor phase is responsible for the relatively late transition from ferroelectrics to the relaxor. Therefore, we obtained the improved <I>d</I> <SUB>33</SUB> <SUP>*</SUP> of 616 pm/V as the highest value in low–temperature sintered BNST–2LN ceramics.</P>
Ga<sub>2</sub>Se<sub>3</sub> 층을 Cu-In-Ga 전구체 위에 적용하여 제조된 Cu(In,Ga)Se<sub>2</sub> 박막의 Ga 분포 변화 연구
정광선,신영민,조양휘,윤재호,안병태,Jung, Gwang-Sun,Shin, Young-Min,Cho, Yang-Hwi,Yun, Jae-Ho,Ahn, Byung-Tae 한국재료학회 2010 한국재료학회지 Vol.20 No.8
The selenization process has been a promising method for low-cost and large-scale production of high quality CIGS film. However, there is the problem that most Ga in the CIGS film segregates near the Mo back contact. So the solar cell behaves like a $CuInSe_2$ and lacks the increased open-circuit voltage. In this study we investigated the Ga distribution in CIGS films by using the $Ga_2Se_3$ layer. The $Ga_2Se_3$ layer was applied on the Cu-In-Ga metal layer to increase Ga content at the surface of CIGS films and to restrict Ga diffusion to the CIGS/Mo interface with Ga and Se bonding. The layer made by thermal evaporation was showed to an amorphous $Ga_2Se_3$ layer in the result of AES depth profile, XPS and XRD measurement. As the thickness of $Ga_2Se_3$ layer increased, a small-grained CIGS film was developed and phase seperation was showed using SEM and XRD respectively. Ga distributions in CIGS films were investigated by means of AES depth profile. As a result, the [Ga]/[In+Ga] ratio was 0.2 at the surface and 0.5 near the CIGS/Mo interface when the $Ga_2Se_3$ thickness was 220 nm, suggesting that the $Ga_2Se_3$ layer on the top of metal layer is one of the possible methods for Ga redistribution and open circuit voltage increase.
정광휘,이상섭,안창원,한형수,이재신,Jeong, Gwang-Hwi,Lee, Sang-Seop,Ahn, Chang Won,Han, Hyoung Su,Lee, Jae-Shin 한국전기전자재료학회 2020 전기전자재료학회논문지 Vol.33 No.5
This study investigated the low temperature sintering with various templates of Bi-based lead-free piezoelectric ceramics. The effects of using CuO-coated Na<sub>0.5</sub>Bi<sub>4.5</sub>Ti<sub>4</sub>O<sub>15</sub> templates on the sintering behavior as well as the dielectric, ferroelectric, and piezoelectric properties of Bi<sub>1/2</sub>(Na<sub>0.78</sub>K<sub>0.22</sub>)<sub>1/2</sub>TiO<sub>3</sub> (BNKT) ceramics have been examined. In comparison with the specimens sintered with the Na<sub>0.5</sub>Bi<sub>4.5</sub>Ti<sub>4</sub>O<sub>15</sub> templates without CuO coating, those sintered with the CuO-coated Na<sub>0.5</sub>Bi<sub>4.5</sub>Ti<sub>4</sub>O<sub>15</sub> templates showed larger template sizes as well as a larger electric field induced strain (S<sub>max</sub>/E<sub>max</sub>) of 422 pm/V after sintering at temperatures as low as 975℃. These results are promising for low-cost multilayer ceramic actuator applications.
Roy Shrawan,Doan Manh-Ha,Kim Jeongyong,Kang Seon Kyeong,Ahn Gwang Hwi,Lee Hyun Seok,Yun Seok Joon 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.8
Atomically thin monolayer transition-metal dochalcogenides (1L-TMDs) are optically active direct band gap semiconducting materials with interesting properties; they are appropriate platform to study and investigate the modulated optoelectronic properties due to locally induced charge transfer phenomenon using various approaches. Herein, 1L-TMDs ( MoS2, WS2 and WSe2) grown using chemical vapor deposition (CVD) were transferred above 10-nm-thick patterned platinum (Pt) stripes deposited on SiO2/ Si substrate to fabricate a local vertical heterostructure of 1L-TMDs with Pt. The optical characterization showed that the PL intensities of n (p)-type 1L-TMDs, namely MoS2 and WS2 ( WSe2), deposited above Pt were reduced with peak positions blue (red)-shifted by 40 (16) meV compared to the samples on SiO2/ Si substrates. This was attributed to the transfer of electrons from the 1L-TMDs to the Pt due to a charge transfer process at the interface. At the same time, an enhanced photocurrent, in comparison to 1L-MoS2 alone was observed under a negative gate voltage of − 40 V from the homojunctions of 1L-MoS2 and 1L-MoS2/Pt formed within the same grain structure due to a Pt-induced local p-doping effect. The charge modulation of the opto-electrical properties of 1L-TMDs due to charge transfer caused using patterned metal provides a simple lateral homojunction for enhanced photovoltaic applications.