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Gate-tunable nonreciprocal response in noncentrosymmetric LaAlO₃/SrTiO₃ interfaces
Daeseong Choe,Mi-Jin Jin,Shin-Ik Kim,Hyung-Jin Choi,Junhyeon Jo,Inseon Oh,Jungmin Park,Hosub Jin,Hyun Cheol Koo,Byoung-Chul Min,Suk-Min Hong,Hyun-Woo Lee,Seung-Hyub Baek,Jung-Woo Yoo 한국자기학회 2019 한국자기학회 학술연구발표회 논문개요집 Vol.29 No.2
Gate-tunable large nonreciprocal charge transport in noncentrosymmetric LaAlO₃/SrTiO₃ interfaces
Daeseong Choe,Mi-Jin Jin,Shin-Ik Kim,Hyung-Jin Choi,Junhyeon Jo,Inseon Oh,Jungmin Park,Hosub Jin,Hyun Cheol Koo,Byoung-Chul Min,Suk-Min Hong,Hyun-Woo Lee,Seung-Hyub Baek,Jung-Woo Yoo 한국자기학회 2020 한국자기학회 학술연구발표회 논문개요집 Vol.30 No.2
Probing surface electronic properties of a patterned conductive STO by reactive ion etching
Jin, Mi-Jin,Choe, Daeseong,Lee, Seung Youb,Park, Jungmin,Jo, Junhyeon,Oh, Inseon,Kim, Shin-Ik,Baek, Seung-Hyub,Jeon, Cheolho,Yoo, Jung-Woo Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.466 No.-
<P><B>Abstract</B></P> <P>SrTiO<SUB>3</SUB> (STO) is a highly attractive oxide material due to its flexible tunability of electrical properties. It can be designed to exhibit a high mobility with a tunable carrier concentration by creating oxygen vacancies, or by doping with Nb or La, which substitute the Ti and Sr sites, respectively. Here we show a micro-patterned surface doping of STO by using reactive ion etching (RIE). The creation and pattering of a conductive STO surface were achieved by sequential treatments with Ar and O<SUB>2</SUB> plasma. The patterned conductive surface edge was well defined as confirmed by an electrostatic force microscopy. The electronic characteristics of the RIE treated STO surface were probed by a synchrotron radiation photoemission spectroscopy, which shows the emergence of Ti<SUP>3+</SUP>, Ti<SUP>2+</SUP>, Ti<SUP>1+</SUP> states and metallic states near the Fermi level. The electrical mobility of the conductive STO surface can be increased up to 12000 cm/V s with a typical sheet carrier concentration around 10<SUP>13</SUP>–10<SUP>14</SUP> cm<SUP>−2</SUP>. Increasing Ar plasma time elongate the depth of the conductive surface, which reflects the change of magnetoresistance behavior at low temperature. The demonstrated control of the STO surface conductivity along with a large area and high precision patterning method can be widely used for a variety of oxide electronic and spintronic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Development of simple micro/nano patterning process along with surface doping of STO. </LI> <LI> Revealing the change of electronic properties of STO according to Ar plasma time. </LI> <LI> Revealing transform from 2D- to 3D-like transport at STO surface according to Ar plasma time. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Park, So Jung,Kim, Seyong,Yong, Daeseong,Choe, Youngson,Bang, Joona,Kim, Jaeup U. The Royal Society of Chemistry 2018 Soft matter Vol.14 No.6
<P>We systematically examined the polymer-mediated interparticle interactions between polymer-grafted nanoparticles (NPs) within chemically identical homopolymer matrices through experimental and computational efforts. In experiments, we prepared thermally stable gold NPs grafted with polystyrene (PS) or poly(methyl methacrylate) (PMMA), and they were mixed with corresponding homopolymers. The nanocomposites are well dispersed when the molecular weight ratio of free to grafted polymers, <I>α</I>, is small. For <I>α</I> above 10, NPs are partially aggregated or clumped within the polymer matrix. Such aggregation of NPs at large <I>α</I> has been understood as an autophobic dewetting behavior of free homopolymers on brushes. In order to theoretically investigate this phenomenon, we calculated two particle interaction using self-consistent field theory (SCFT) with our newly developed numerical scheme, adopting two-dimensional finite volume method (FVM) and multi-coordinate-system (MCS) scheme which makes use of the reflection symmetry between the two NPs. By calculating the polymer density profile and interparticle potential, we identified the effects of several parameters such as brush thickness, particle radius, <I>α</I>, brush chain polydispersity, and chain end mobility. It was found that increasing <I>α</I> is the most efficient method for promoting autophobic dewetting phenomenon, and the attraction keeps increasing up to <I>α</I> = 20. At small <I>α</I> values, high polydispersity in brush may completely nullify the autophobic dewetting, while at intermediate <I>α</I> values, its effect is still significant in that the interparticle attractions are heavily reduced. Our calculation also revealed that the grafting type is not a significant factor affecting the NP aggregation behavior. The simulation result qualitatively agrees with the dispersion/aggregation transition of NPs found in our experiments.</P>
R1234yf와 R1234yf/R134a의 자동차 에어컨 작동 조건에서의 성능 평가
박기정(Ki-Jung Park),이요한(Yohan Lee),최대성(Daeseong Choe),정동수(Dongsoo Jung) 대한설비공학회 2010 설비공학 논문집 Vol.22 No.12
In this study, performance of R1234yf and R1234yf/R134a mixture is measured on a heat pump bench tester in an attempt to substitute R134a used widely in mobile air conditioners (MACs). The bench tester is equipped with a open type compressor providing a nominal capacity of 3.5 ㎾. All tests are conducted under the summer cooling and winter heating conditions of 7/4 5℃ and -7/41℃ in the evaporator and condenser, respectively. For R1234yf/R134a mixture, measurements are made at 5%, 10%, and 15% of R134a by mass. Test results show that the coefficient of performance (COP) and capacity of R1234yf are up to 2.7% and 4.0% lower than those of R134a, respectively. For R1234yf/R134a mixture, the COP and capacity are up to 3.9% lower and 3.6% higher than those of R134a. For R1234yf and R1234yf/R134a mixture, the compressor discharge temperature is 4.1~6.7℃ lower than that of R134a while the amount of charge is reduced up to 11% as compared to R134a. 90%R1234yf/10%R134a is a better refrigerant than pure R1234yf in that it is less flammable and more compatible with existing R134a system. Based upon the results, it is concluded that R1234yf and R1234yf/R134a mixture are long term environmentally friendly solutions to mobile air-conditioners due to their excellent environmental properties with acceptable performance.