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안윤호,손종영 한국세라믹학회 2024 한국세라믹학회지 Vol.61 No.1
The flexoelectric effect can be exploited to control the polarization and domain structure in ferroelectric materials, potentially benefiting applications, such as nanoscale electromechanical systems, memory devices, and sensors. We report ferroelectric domain switching characteristics of PbTiO3 (PTO) thin films induced by the flexoelectric effect. Epitaxially (001)-oriented PbTiO3 (PTO) thin films were deposited on single-crystal Nb-doped SrTiO3 substrates by pulsed laser deposition. Through the use of a piezoelectric force microscope and two surface electrodes, polarization domains were created vertically and horizontally within the PTO film. When subjected to a vertical external force, the domains with vertical orientation exhibited predictable switching behavior. Conversely, by imposing a vertical force during the scanning of domains oriented horizontally, we observed the formation of new domains with vertical orientation. However, in conditions where a vertical force was applied counter to the alignment of the horizontal domains, the anticipated switching of the vertical domains did not manifest. This study demonstrates that the flexoelectric effect can be harnessed to manipulate the switching of ferroelectric domains in PTO thin films using piezoresponse force microscopy.
요추부 다공성 추간체유합보형재의 개발 및 기계적 성능 평가
안윤호,유경주,박광민,차은종,김경아,안경기 대한의용생체공학회 2020 의공학회지 Vol.41 No.1
Recently, porous additive manufactured(AM) cages have been introduced to provide more desirable stiffness and may be beneficial to bone ingrowth. They are designed to attempt to reduce the subsidence problem of traditional titanium cage and to get osseointegrative property that PEEK doesn’t have. This study was performed to evaluate the mechanical performance of newly developed lumbar porous AM cages. Three types of mechanical tests were performed in accordance with the ASTM standards: Static compression, compression-shear, and subsidence tests. The porous AM cages with 60% porosity showed similar device stiffness and strength as the various products submitted to FDA 510(k), and their wider contact area improved the subsidence test results by about 50%. In conclusion, the porous AM cages developed in this study were considered mechanically safe and could be an alternative to solid PEEK cages.
안윤호,손종영 한국물리학회 2023 Current Applied Physics Vol.54 No.-
Forming and set/reset operating voltages are critical issues encountered with a decrease in resistive random-access memory (RRAM) sizes. This study investigated the thickness-dependent resistive switching properties of NiO nanodisks. The NiO RRAM nanodisks, with a diameter of 100 nm and varying thicknesses, were fabricated on Pt/Ta/SiO2/Si substrates using anodic aluminum oxide templates through the RF sputtering process. In the electroforming process, the forming voltage of the NiO nanodisk effectively reduced with a decrease in the thickness. The electric field enhancement in localized regions appeared to contribute to the reduction in the forming voltage. In addition, the set/reset operating voltage of the NiO nanodisk RRAM decreased with a decrease in the thickness. We conclude that the use of the C-AFM tip strengthened the local electric field in NiO nanodisk RRAM cells, leading to the reduction of the set/reset voltage with a decrease in the thickness.
안윤호,서정대,임대영,손종역 한국물리학회 2015 Current Applied Physics Vol.15 No.5
We investigated ferroelectric characteristics of BiFeO3 (BFO) thin films on SrRuO3 (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2Pr = 59.6 μC/cm2 and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) study revealed that the BFO thin films have much smaller mosaic ferroelectric domain patterns than epitaxial BFO thin films on Nb:SrTiO3 substrates. Presumably these small domain widths which originated from smaller domain energy give rise to the faster electrical switching behavior in comparison with the epitaxial BFO thin films on Nb:SrTiO3 substrates.
Posterior Dynamic Stabilization System의 요추거동에 대한 생체역학적 분석
안윤호,장덕영,박경우,이성재,Ahn, Y.H.,Chen, Wen-Ming,Jung, D.Y.,Park, K.W.,Lee, S.J. 대한의용생체공학회 2008 의공학회지 Vol.29 No.2
Many recent studies suggest that the posterior dynamic stabilization(PDS) can be a more physiologically-relevant alternative to the rigid fixation for the patients suffering from low back pain. However, its biomechanical effects or clinically proven efficacies still remain unknown. In this study, we evaluated kinematic behaviors of the lower lumbar spine with the PDS system and then compared to those of the rigid fixation system using finite element (FE) analysis. A validated FE model of intact lumbar spine(L2-L5) was developed. The implanted model was then constructed after modification from the intact to simulate two kinds of pedicle screw systems (PDS and the rigid fixation). Hybrid protocol was used to flex, extend, laterally bend and axially rotate the FE model. Results showed that the PDS systems are more flexible than rigid fixation systems, yet not flexible enough to preserve motion. PDS system allowed $16.2{\sim}42.2%$ more intersegmental rotation than the rigid fixation at the implanted level. One the other hand, at the adjacent level it allowed more range of motion ($2.0%{\sim}8.3%$) than the rigid fixation. The center of rotation of the PDS model remained closer to that of the intact spine. These results suggest that the PDS system could be able to prevent excessive motion at the adjacent levels and restore the spinal kinematics.
안윤호,손종역 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.2
Significant progress has been made in the enhancement of multiferroic properties with possibilities for energy harvesting and storage applications. In this study, BiFeO3 (BFO) thin films were doped with Ca, and the multiferroic, piezoelectric, and energy-storage properties of Bi1−xCaxFeO3−δ (x = 0.3, BCFO) thin films were compared with those of BFO to investigate the effects of the doping. The BCFO thin films were deposited on Pt/TiO2/SiO2/Si substrates using pulsed laser deposition. The BCFO thin films having a polycrystalline structure, exhibited improved crystallinity and larger grains, compared with the BFO thin films. The high crystallinity further resulted in the BCFO thin films exhibiting improved leakage current, ferroelectric, and ferromagnetic characteristics, compared with the BFO thin films. The morphotropic phase boundary formed in the mixed crystal phase, which was driven by the Ca doping, and it improved the piezoelectric coefficients of the BCFO thin films. Additionally, we found that the BCFO thin films have superior energy-storage characteristics, compared with the BFO thin films, owing to the improved ferroelectric properties. Our findings suggest that the Ca doping of the BFO thin films improves their multiferroic properties, piezoelectric response, and energy-storage characteristics.