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Lee, Tae Kwon,Kong, Dae Sol,Jin, Da Woon,Yun, Shinhee,Yang, Chan-Ho,Jung, Jong Hoon ELSEVIER 2019 Current Applied Physics Vol.19 No.6
<P><B>Abstract</B></P> <P>We investigated the ferroelectricity in proton-irradiated flexible Pb(Zr<SUB>0.52</SUB>Ti<SUB>0.48</SUB>)O<SUB>3</SUB> (PZT) thick films and their non-volatile memory characteristics. The Ni-Cr metal foil substrate allowed high-quality polycrystalline PZT films with flexible functionality to be fabricated using conventional sol-gel and high-temperature annealing methods. The 10-MeV proton-irradiated PZT film exhibited an almost square polarization−electric field hysteresis curve with saturated (<I>P</I> <SUB>s</SUB>) and remnant (<I>P</I> <SUB> <I>r</I> </SUB>) polarizations of 18.9 and 17.0 μC/cm<SUP>2</SUP>, respectively; which are slightly lower than as-grown PZT with <I>P</I> <SUB>s</SUB> = 28.7 μC/cm<SUP>2</SUP> and <I>P</I> <SUB> <I>r</I> </SUB> = 24.3 μC/cm<SUP>2</SUP>. The <I>P</I> <SUB> <I>r</I> </SUB> did not decrease even after 1000 cycles of continuous bending and unbending at a bending radius of 2.14 mm and decreased slightly to ∼80% of its initial value after 10<SUP>5</SUP> s. Although the <I>P</I> <SUB> <I>r</I> </SUB> decreased to ∼55% after 10<SUP>10</SUP> cycles, the electric polarization remained switchable under positive and negative electric fields. These characteristics suggest that the flexible PZT films could be utilized in non-volatile memory device applications in environments with high doses of proton irradiation, such as those in aeronautics and nuclear power plants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sol-gel growth of flexible PZT thick films on a Ni-Cr metal foil substrate. </LI> <LI> Large saturated and remnant electric polarization in proton-irradiated films. </LI> <LI> Mechanical stability, long retention time, and high fatigue resistance even after the high energy proton-irradiation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lead-free (K,Na)NbO3 Thick Films for Flexible Non-volatile Memory Applications
Kwak Yeong Min,Lee Tae Kwon,Kong Dae Sol,Ko Young Joon,Jeong Dong Geun,Jung Jong Hoon 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.9
We report the sol-gel fabrication and electrical characterization of flexible (K,Na)NbO3 (KNN) thick films. Muscovite mica allows the growth of high-quality polycrystalline KNN thick films with flexible functionality. Because of the trade-off between increase of grain-size and volatilization of alkaline ions, the electrical polarization is optimized at certain temperature of 720 °C. The remnant and saturation polarization of flexible KNN films were recorded to Pr=10.3 μC/cm2 and Ps = 23.3 μC/cm2, respectively, which are quite close to those of rigid films with the same chemical compositions. The KNN thick films are bendable even up to bending radius of R = 3.1 mm, and the Pr and Ps at bending states are almost the same as compared to those at unbending state. Even in the convex and concave bending, the KNN thick films show excellent non-volatile memory characteristics. The Pr is almost the same even after the 108 times of switching and the 104 sec of retention.
Kwon, Da-Sol,Choi, Hyeong Yeol,Lee, Byoung-Min,Jeong, Young Gyu,Yang, Donsik,Kim, Sang-Tae,Choi, Jae-Hak Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.471 No.-
<P><B>Abstract</B></P> <P>High performance electric heaters based on carbon micropatterns (CMs), which were fabricated from a novolac resin by proton beam lithography (PBL) and carbonization, have been explored in this study. For the purpose, well-defined negative-type novolac micropatterns with crosslinked network structures were fabricated by PBL at the optimized fluence of 5 × 10<SUP>15</SUP> ions cm<SUP>−2</SUP> and then carbonized to form CMs. The fabricated 60–nm–thick CMs were characterized to have a high electrical conductivity of 2.12 × 10<SUP>2</SUP> S cm<SUP>−1</SUP> and a high optical transmittance of 78%. In an application as electric heaters, the 60–nm–thick CMs showed a high maximum temperature of 141.7 °C at 60 V with an excellent heating rate of 16.06 °C s<SUP>−1</SUP>. Therefore, the prepared transparent electric heaters can be used in window defrosting/defogging, display, gas sensing, and medical equipment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Carbon micropatterns (CMs) were prepared by PBL and carbonization. </LI> <LI> The CMs showed high electrical conductivity and high optical transmittance. </LI> <LI> The CMs exhibited an excellent electric heating performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This study describes the fabrication of novolac-derived carbon micropatterns by proton beam lithography and carbonization for high-performance electric film heaters.</P> <P>[DISPLAY OMISSION]</P>
Phase-Inverted Multifrequency HIFU Transducer for Lesion Expansion: A Simulation Study
Kwon, Da Sol,Sung, Jin Ho,Park, Chan Yuk,Jeong, Jong Seob IEEE 2018 and Frequency Control Vol.65 No.7
<P>It has been well known that the treatment time of high-intensity focused ultrasound (HIFU) surgery can be reduced by expanding the focal area per sonication. Previously, a dual-concentric transducer using phase-inverted signals was proposed to axially extend the focal area, but it has suffered from the deep notch point between two focal lobes. In this paper, we propose the improved HIFU transducer with dual-concentric aperture driven by phase-inverted multifrequency signals based on an inversion layer technique. The proposed transducer can generate the expanded focal zone with a significantly reduced level of the notch point between two focal lobes in the axial direction. The performance of the proposed transducer was investigated using finite element analysis simulation. The electrical impedance, one-way impulse response, and acoustic field of the transducer were simulated. Subsequently, the lesion volume was investigated by heat transfer simulation. In the proposed method, the level of the notch point was increased above −6 dB due to various phase interactions between the fundamental and harmonic frequency combinations and the inverted and noninverted frequency combinations. The −6-dB depth of field related to the necrotic lesion size was increased by 141% compared with the conventional single element transducer. Thus, the proposed transducer can be a potential way to enlarge coagulated lesion size resulting in a reduced overall treatment time of HIFU surgery.</P>
사무용 건물의 자연채광 도입에 대한 국내ㆍ외 친환경 건축물 인증제도의 비교 분석 연구
권한솔(Kwon Han-Sol),김선욱(Kim Sun-Uk),엄현용(Eom Hyeon-Yong),정인영(Jung In-Yung),허정호(Huh Jung-Ho) 한국건축친환경설비학회 2008 한국건축친환경설비학회 학술발표대회 논문집 Vol.- No.-
The GBCC(Green Building Certification Criteria) system has been in effect since 2001, which has various assessment items according to the classification of building use. Nevertheless, the criteria related with daylighting has not been quantified yet as compared to the other indoor environmental factors in the GBCC, and even the established measure for interior lighting energy saving also have not existed. Therefore, this study is in progress as follows. First, the current state of day lighting-related items in the GBCC was examined. Second, the items were compared with the counterparts in the other foreign systems, such as LEED and CASBEE. Third, in the near future, this study plans to suggest the environmental-friendly certification criteria of daylighting utilization for office buildings.