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Ferroelectrically tunable magnetic skyrmions in ultrathin oxide heterostructures
Wang, Lingfei,Feng, Qiyuan,Kim, Yoonkoo,Kim, Rokyeon,Lee, Ki Hoon,Pollard, Shawn D.,Shin, Yeong Jae,Zhou, Haibiao,Peng, Wei,Lee, Daesu,Meng, Wenjie,Yang, Hyunsoo,Han, Jung Hoon,Kim, Miyoung,Lu, Qingyo Springer Science and Business Media LLC 2018 NATURE MATERIALS Vol.17 No.12
Wang, Lingfei,Cho, Myung Rae,Shin, Yeong Jae,Kim, Jeong Rae,Das, Saikat,Yoon, Jong-Gul,Chung, Jin-Seok,Noh, Tae Won American Chemical Society 2016 NANO LETTERS Vol.16 No.6
<P>Ferroelectric tunnel junctions (FTJs) have attracted increasing research interest as a promising Candidate for nonvolatile memories. Recently, significant enhancements Of tunneling electroresistance (TER) have been realized through modifications of electrode materials. However, direct control of the FTJ performance through modifying the tunneling barrier has not been adequately explored. Here, adding a new direction to FTJ research, we fabricated FTJs with BaTiO3 single barriers (SB-FTJs) and BaTiO3/SrTiO3 composite barriers (CB-FTJs) and reported a systematic study of FTJ performances by varying the barrier thicknesses and compositions:, For the SB-FTJs, the TER is limited by pronounced leakage current for ultrathin barriers and extremely small tunneling current for thick barriers. For the CB-FTJs, the extra SrTiO3 barrier provides an additional degree of freedom to modulate the barrier potential and tunneling behavior. The resultant high tunability can be utilized to overcome the barrier thickness limits and enhance the overall CB-FTJ performances beyond those of SB-FTJ. Our results reveal a new paradigm to manipulate the FTJs through functionalities.</P>
Formation of Ohmic contacts on laser irradiated n-type 6H-SiC without thermal annealing
Yan Wu,Lingfei Ji,Zhenyuan Lin,Minghui Hong,Sicong Wang,Yongzhe Zhang 한국물리학회 2019 Current Applied Physics Vol.19 No.4
In this work, KrF excimer laser irradiation of n-type SiC is used to form Ohmic contacts at the interfaces between the irradiated SiC and various types of metals with different work functions without subsequent thermal annealing. Ohmic contacts are formed between laser-treated 6H-SiC and Ti at a laser fluence of 0.7 J/cm2. Moreover, in the fluence range of 0.7–1.3 J/cm2, Ohmic characteristics are also observed between irradiated 6HSiC and Au, which is a representative inert metal. The laser-induced heavy doping effect reduces the thickness of the Schottky barrier between the metal and SiC, and the formation of graphene sheets on the irradiated SiC surface reduces the barrier height, resulting in the direct formation of Ohmic contacts. Our findings thus demonstrate the potential of this laser treatment method to achieve Ohmic contacts between n-type SiC and a broad range of metal electrodes without requiring high-temperature annealing.
Identifying Topic-Specific Experts on Microblog
( Yan Yu ),( Lingfei Mo ),( Jian Wang ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.6
With the rapid growth of microblog, expert identification on microblog has been playing a crucial role in many applications. While most previous expert identification studies only assess global authoritativeness of a user, there is no way to differentiate the authoritativeness in a particular aspect of topics. In this paper, we propose a novel model, which jointly models text and following relationship in the same generative process. Furthermore, we integrate a similarity-based weight scheme into the model to address the popular bias problem, and use followee topic distribution as prior information to make user`s topic distribution more precisely. Our empirical study on two large real-world datasets shows that our proposed model produces significantly higher quality results than the prior arts.
Shin, Yeong Jae,Wang, Lingfei,Kim, Yoonkoo,Nahm, Ho-Hyun,Lee, Daesu,Kim, Jeong Rae,Yang, Sang Mo,Yoon, Jong-Gul,Chung, Jin-Seok,Kim, Miyoung,Chang, Seo Hyoung,Noh, Tae Won American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.32
<P>With recent trends on miniaturizing oxide-baed devices, the need for atomic-scale control of surface/interface structures by pulsed laser deposition (PLD) has increased. In particular, realizing uniform atomic termination at the surface/ interface is highly desirable. However, a lack of understanding on the surface formation mechanism in PLD has limited a deliberate control of surface/interface atomic stacking sequences. Here, taking the prototypical-SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructure as a model system, we investigated the formation of different interfacial termination sequences (BaO-RuO2 or TiO2-SrO) with oxygen partial pressure (PO2) during PLD. We found that a uniform SrO TiO2 termination sequence at the SRO/BTO interface can be achieved by lowering the Po-2 to 5 mTorr, regardless of the total background gas pressure (P-total), growth mode, or growth rate. Our results indicate that the thermodynamic stability of the BTO surface at the low-energy kinetics stage of PLD can play an important role in surface/interface termination formation. This work paves the way for realizing termination engineering in functional oxide heterostructures.</P>
Jinkwon Kim,Junsik Mun,Youngdo Kim,Bongju Kim,Jeong Rae Kim,Lingfei Wang,Miyoung Kim,Changyoung Kim,Jason W. A. Robinson,Yoshiteru Maeno,Tae Won Noh 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
Ruddlesden-Popper (RP) phase oxides (An+1BnO3n+1, n = 1, 2, ...) have been spotlighted with versatile physical properties such as high-temperature superconductivity, colossal magnetoresistance. These emergent phenomena provide a platform for novel oxide-based electronic devices including spintronics application. However, high-quality RP-phase thin film growth has been disturbed by extended structural defects, such as out-of-phase boundaries (OPBs). OPB is a translational boundary between neighboring unit cells, shifted in a specific crystallographic direction. For instance, if RP-phase thin films grown on ABO₃ perovskite substrates, the structural mismatch between film and substrates induces a crystallographic shift in the c-axis direction, thus OPBs form at the film-substrate interface. Since OPB formation hampers the physical properties of RP-phase thin films, the suppression of the structural defects is highly required to carry out the high-performance RP-phase based functional devices. In this study, we suppressed OPB suppression in RP-phase oxide thin films by atomic-scale interface engineering. As model systems, the unconventional superconductor Sr₂RuO₄ (bulk Tc ~ 1.5 K) and La2-xSrxCuO₄ (bulk Tc ~ 39 K) thin films were employed. Despite the structural similarities between films and substrates, Sr2RuO4 and La2-xSrxCuO₄ films exhibited huge OPB formations. By controlling the atomic-scale interface engineering, the OPBs were significantly suppressed in the film structure. Notably, these OPB-free Sr₂RuO₄ and La2-xSrxCuO₄ thin films exhibited highly enhanced superconductivity than the film with huge OPB formation. Our study suggests a comprehensive method to suppress OPB formation in RP thin films, enabling superconducting spintronics devices based on the unconventional superconductivity.