Tae Won Noh
Flexoelectricity: Strain Gradient Engineering? 1 Tae Won Noh 1,2 Center for Correlated Electron Systems, Institute for Basic Science (IBS) Seoul 151-747, Korea 2 Department of Physics and Astronomy, Seoul National University Seoul 151-747, Korea *e-mail: [email protected] Flexoelectricity is the generation of an electric field by a strain gradient via electro-mechanical coupling. Although it was first reported in the 1960s [1], there have been few studies on flexoelectricity in bulk solid materials. It is partly because the flexoelectric effects are expected to be quite small in the rigid bulk solids. And it is partly because the strain gradient is difficult to measure and control. However, we have recently demonstrated that the strain gradient in epitaxial oxide thin films could be 6 or 7 orders of magnitude larger than the corresponding bulk values [2]. This finding suggests that we can utilize the flexoelectric effects by controlling strain gradient artificially. In this talk, I will review recent activities on flexoelectricity of ferroelectric epitaxial thin films. In most epitaxial thin films, they are grown on substrates with different lattice constants. Such large lattice mismatch can result in strain relaxation within tens of nanometers of the film-substrate interface in epitaxial films, inducing a large strain gradient. By controlling growth conditions such as oxygen partial pressure or deposition temperature, we can obtain a series of samples with different strain gradients. Using such films, we can systematically investigate flexoelectric effects on numerous physical properties, including polarization hysteresis curves [2], ferroelectric domain configurations [2,3], electronic transport properties [4], electromechanical domain switching [5], self-polarization [6], and defect formation [7]. I would like to highlight that a proper consideration of flexoelectricity should be required to advance novel nanoelectronic functionality. References [1] S. M. Kogan, Sov. Phys. Solid State 5, 2069 (1964). [2] D. Lee et al., Phys. Rev. Lett. 107, 057602 (2011). [3] G. Catalan et al., Nat. Mater. 10, 963 (2011). [4] D. Lee et al., Nano Lett. 12 6436 (2012). [5] H. Lu et al., Science 336, 59 (2012). [6] B. C. Jeon et al., Advanced Materials 25, 5643 (2013). [7] D. Lee et al., Advanced Materials (2014). Tae Won Noh Professor of Physics, Department Physics and Astronomy, Seoul National University Director, Institute for Basic Science, Center for Correlated Electron Systems Bldg. 19 – Rm. 416, Gwanak-gu, Gwanak-ro 1ga, Seoul 151-747, Korea Tel: +82-2-875-8108 Fax: +82-2-875-1222 E-mail: [email protected] w EDUCATION 1982 B.S., Department of Physics, Seoul Nat’l Univ. Korea 1984 M.S., Department of Physics, Ohio State Univ. USA 1986 Ph.D., Department of Physics, Ohio State Univ. USA w EMPLOYMENT & RELATED POSITIONS 1986 – 1987: Postdoctoral researcher, Material Research Lab., Ohio State Univ. 1987 – 1989: Postdoctoral researcher, Lab. of Atomic and Solid State Physics (LASSP), Cornell Univ. 1989 – Present: Assistant, Associate, and Full Professor, Dept. of Physics and Astronomy, Seoul Nat’l Univ. 1997 – 1998: Visiting Scholar, LG Central Institute of Technology 1997 – 1999: Deputy Director, National Center for Inter-university Research Facilities, Seoul Nat’l Univ. 2000 – 2009: Director, Research Center for Oxide Electronics, Seoul Nat’l Univ. (supported by the Creative Initiative Program of MEST, Korea) 2003 – 2004: Director, Condensed Matter Research Institute, Seoul Nat’l Univ. 2005: Foreign Research Fellow, Univ. of Tokyo, Japan 2006 – 2007: Director, Frontier Physics Research Division, Seoul Nat’l Univ. (supported by the BK-21 Program of MEST, Korea) 2010 – 2012: Director, Research Center for Functional Interfaces, Seoul Nat’l Univ. (supported by the National Honor Scientist Program of MEST, Korea) 2012 – Present: Director, Center for Functional Interfaces of Correlated Electron Systems, Institute of Basic Sciences (supported by the Science-Business Belt Program of MEST, Korea) w MAJOR ACADEMIC SOCIETY ACTIVITIES 1983 - Present: Lifetime Member, Fellow, American Physical Society 1985 - Present: Member, Materials Research Society 1989 - Present: Member, Fellow, Treasurer, Executive Officer, and Vice President, Korean Physical Society 2007 - Present: Fellow, The Korean Academy of Science and Technology w OTHER PROFESSIONAL ACTIVITIES 2003 - 2009: Planning & Evaluation Committee Member, Korea Research Council of Public Science & Technology 2006 - Present: Editorial Advisory member, Materials Today (published by Elsevier) 2009 – 2012: Editor-in-chief, Current Applied Physics (published by KPS) 2009 – 2012: International Advisory Committee member, High Magnetic Field Laboratory, Chinese Academy of Sciences (Hefei, China) 2010 – 2013: Council member, Association of Asian Pacific Physics Societies 2011 – 2013: Editorial Board member, Applied Physics Letter and Journal of Applied Physics (published by American Institute of Physics) w AWARDS AND PROFESSIONAL HONORS 2000.5: Scientist of the Month Award (Korea Science and Engineering Foundation) 2000.5: Award for Outstanding Paper (Korean Federation of Science & Technology Societies) 2000.6: Research Award (College of Natural Science, Seoul Nat’l Univ.) 2003.5: Ikeda Award (Ikeda Memorial Foundation, JAPAN) 2004.2: Korea Science Award (Korea Science and Engineering Foundation) 2006.4.: Scopus Citation Award (Elsevier) 2008.2: Award for outstanding research (College of Natural Science, Seoul Nat’l Univ.) 2009.11: Gyeongam Award (Gyeongam Education Foundation) 2010.5: National Honor Scientist (Ministry of Education, Science, and Technologies, Korea) 2011.4: Korean Best Scientist and Engineer Award (Ministry of Education, Science, and Technologies, Korea) w INTERNATIONAL CONFERENCE ORGANIZATION ◦ Worked as Chairmen of 5th Korea-Japan Conference on Ferroelectricity (KJC-FE5, 2004), International Workshop of Oxide Electronics (WOE-2007), and Joint Conference of Asian Meeting on Ferroelectricity and Asian Meeting on Electroceramics (AMF-AMEC-2010) ◦ Worked as General Secretariat, 9th International Meeting on Ferroelectricity (IMF-9) ◦ Worked as Program Co chair, International Symposium of Integrated Ferroelectrics (ISIF2006) ◦ Worked or currently serving as International Advisory (or Program) Committee members of about 40 other international conferences w PLENARY AND INVITED LECTURES AT INTERNAT’L CONFERENCES ◦ Over 100 invited talks in international conferences ◦ Plenary talks at many conferences, including IMF-11 (2005, Brazil), JKC-FE6 (2006, Japan), and AAPC-11 (2010, China) w RESEARCH INTERESTS 1. Optical properties of solids, including composite materials, high Tc superconductors, colossal magnetoresistance (CMR) manganites, and other transition metal oxides. 2. Metal-insulator transitions and orbital physics in transition metal oxides. 3. Pulsed laser deposition of oxide films and artificial heterostructures 4. Physical phenomena at oxide surfaces or interfaces 5. Physics of oxide devices, such as FeRAM, RRAM, and spintronic devices w PUBLICATIONS ◦ Published over 380 (co-)authored SCI papers ◦ Cited over 8,900 timesNature (1), Nature Materials (1), Nano Letters (2), Advanced Materials (8), and Physical Review Letters (37) w PATENTS ◦ 10 patents issued; 9 patents filed
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