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양상모,윤종걸,노태원 한국물리학회 2011 Current Applied Physics Vol.11 No.5
Recent developments in ferroelectric (FE) domain imaging techniques have established an understanding of intriguing polarization switching dynamics. In particular, nanoscale studies of FE domain switching phenomena using piezoresponse force microscopy (PFM) can provide important microscopic details on nucleation and subsequent growth of domains, complementing conventional electrical measurements that only give macroscopic information. This review covers recent nanoscale PFM studies of domain switching dynamics in FE thin films. Recent nanoscale PFM-based studies have demonstrated that quenched defects inside the FE thin films play important roles in domain switching processes, including defect-mediated inhomogeneous nucleation, pinning-dominated nonlinear dynamics of domain walls,and many other intriguing phenomena.
Ear-jack port based one-way analogue communication for smart devices
양상모,이정민,설상훈,김문기,최재붕 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.8
As the wide spread of smart device, smartphone and tablet PC has led to various external device developments, there is a great need forefficient communication solution between devices. In this paper, a new method for one-way analogue communication using ear jack portis proposed. For one-way analogue communication, we mixed analogue signal with audible-frequency signal and then transmitted themby ear jack port. We also calibrated both impedance and frequency characteristics of each device. To verify the efficiency of the proposedcommunication method, an alcohol-breathalyzer was developed and its alcohol sensor data were successfully communicated via ear jackport.
양상모,문순재,김태헌,김용수 한국물리학회 2014 Current Applied Physics Vol.14 No.5
CaTiO3 is a well-known incipient ferroelectric material that does not undergo a ferroelectric phase transition in spite of the intriguing dielectric constant behavior. Especially, unlike a prototypical incipient ferroelectric SrTiO3, the paraelectric state of CaTiO3 cannot be easily destroyed by small perturbations, including cation doping and epitaxial strain. We present that a nearly strain-free epitaxial CaTiO3 film grown at a low oxygen partial pressure exhibits polarizationevoltage hysteresis loops and the distinct difference of piezoresponse force microscopy phase signals, implying that a ferroelectric phase is induced. Such results are shown even at room temperature. We suggest that the observed ferroelectric behavior in CaTiO3 film comes from the defect dipoles composed of vacancies inside the film. Using electron-probe microanalysis and optical absorption spectra measurements, we found that CaTiO3 film has considerable Ca and O vacancies, forming the localized defect state in electronic structure. This work highlights the importance of vacancies and their clusters, such as defect dipoles, in understanding the electronic properties of perovskite oxide thin films, including ferroelectricity.
양상모,신영재,Yoshitaka Ehara,Hiroshi Funakubo,윤종걸,James F. Scott,노태원 한국물리학회 2019 Current Applied Physics Vol.19 No.4
Recently, in ferroelectric materials, there have been many experimental efforts to find out more intriguing topological objects and their functionalities, such as conduction property. Here we investigated ferroelectric domain structures and related topological defects in the (111)-oriented epitaxial tetragonal PbZr0.35Ti0.65O3 thin film. Systematic piezoresponse force microscopy measurements revealed that the field-induced polarization switching can form thermodynamically stable superdomain structures composed of nano-sized stripe subdomains. Within such superdomain structures, we observed the exotic equilateral triangular in-plane flux-closure domains composed of three stripe domain bundles with 120/120/120 degrees of separation. The conductive- atomic force microscopy measurements under vacuum showed that some vertices have significantly higher conductivity compared to other surrounding regions. This work highlights electric field-driven polarization switching and unique crystallographic symmetry (here, three-fold rotational symmetry) can generate exotic ferroelectric domain structures and functional topological defects, such as conductive vertices.
양상모,Hun-Ho Kim,김태헌,Ik Joo Kim,윤종걸 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.2
We investigated the ferroelectric (FE) domain nucleation and domain wall motion in epitaxial PbZr0.4Ti0.6O3 capacitors by using modified piezoresponse force microscopy with the domaintracing method. From time-dependent FE domain evolution images, we observed that defectmediated inhomogeneous nucleation occurred with a stochastic nature. In addition, we found that the number of nuclei N(t) was linearly proportional to log t, where t is the accumulated time of the applied pulse fields. The time-dependence of N(t) suggests a distribution of energy barriers for nucleation, which may determine the stochastic nature of domain nucleation. We also observed that the domain grew with consecutive Barkhausen avalanches and that the growth direction became anisotropic when the domain radius was larger than a critical radius of about 100 nm.
양상모,장승엽,김태헌,김훈호,이호녕,윤종걸 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31
We investigated the scaling behavior of ferroelectric (FE) hysteresis loops as a function of the applied field amplitude (E_0) in a high-quality epitaxial PbZr_(0.2)Ti_(0.8O3) (PZT) thin film. We observed that the areas of the polarization-electric field hysteresis loops (A) followed the scaling law A ∝ E^α_0, with the exponent α = 0.45 ± 0.01. This result is in excellent agreement with the theoretical prediction of α by the two-dimensional Ising model. In addition, we found that the coercive field (E_C) showed E_C/E^γ_0 with the exponent γ = 0.28 ± 0.01. We attribute this relationship to the difference in the sweep rate of the field amplitude E_0. From the obtained γ value, the growth dimension of FE domains is found to be about 1.68 in our epitaxial PZT thin film.
이어 잭 포트 유선통신 기법을 이용한 피부 수분 측정 스마트 제어 프로덕트 개발
양상모(Sang Mo Yang) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.7
최근 스마트폰, 스마트 패드 등의 스마트 디바이스와 연결되어 새로운 서비스를 제공하는 다양한 외부 장치가 개발되고 있다. 이러한 외부 장치는 스마트 프로덕트(smart product) 혹은 앱세서리(appcessory)로 불리고 있다. 본 논문에서는 스마트 디바이스의 이어폰 포트와 연결되어 피부 수분을 측정할 수 있는 외부 제어 장치를 개발하였다. 피부 수분 측정을 위해 임피던스 측정법을 사용하였으며, 신호 변조 회로를 통해 측정 결과를 스마트 디바이스로 전송하는 자동화 시스템을 구성하였다. 본 연구의 개발 결과를 검증하기 피부 수분 정밀 측정 기기인 C+K사의 Corneometer CM825를 이용하여 임상실험 결과의 상관성 분석을 하였으며, 그 결과 두 측정 기기 간의 상관성이 비교적 높음을 알 수 있었다. The development of external devices for smartphones and smart pads to provide new services has recently become a problem. These external devices are called smart products or appcessories. This paper discusses the development of skin humidity sensing devices related to the earphone port in smartphones. Segmental bioelectrical impedance analysis (SIBA) was used for skin humidity sensing, and a signal transmit system configuration was developed on a modulation circuit. To examine the study results, we performed correlation analysis between a Corneometer CM825 and a skin humidity sensing device. Notably, high correlations were shown between both measuring devices.