|
Stephen DucharmeProfessor and Vice Chair
Office: 310F Jorgensen Hall (map) |
|
|
Stephen DucharmeProfessor and Vice Chair
Office: 310F Jorgensen Hall (map) |
Astronomy 103: Descriptive Astronomy (Fall 2012)
Physics 343: Physics of Lasers and Modern Optics (Spring 2014)
Graduate Research Assistantships
Undergraduate Teaching Fellowships
Undergraduate Research Fellowships
Applications Accepted Any Time
Current Personnel
Current Collaborators
Vladimir M. Fridkin, Serguei P. Palto, Lev M. Blinov (Institute of Crystallography, Russian Academy of Sciences, Moscow)
Shireen Adenwalla, Alexei Gruverman, David Sellmyer (UNL Physics and Astronomy); Jim Takacs (UNL Chemistry); Jinsong Huang (UNL Mechanical Engineering) Yongfeng Lu, Mathias Schubert (UNL Electrical Engineering)
Jianglu Li (U. Washington Dept. of Mechanical Engineering); Hermann Kohlstedt (Institut für Festkörperforschung, Jülich, Germany ); Sergei Kalinin (Oak Ridge National Laboratory)
National Science Foundation, Nebraska Research Initiative, Office of Naval Research, Department of Energy.
Our group, working in collaboration with researchers from the Russian Academy of Sciences, has made several notable breakthroughs with our studies of ultrathin ferroelectric films of polyvinylidene fluoride copolymers, crystalline polymers similar to Teflon(TM). Ferroelectrics, which have built-in electric fields, are similar to ferromagnets, which have built-in magnetic fields. Our research with the ultrathin ferroelectric polymer films has yielded several major discoveries and outlined several new or improved device applications. This research focuses on the fundamental behavior of ferroelectricity at the nanoscale by examining the effect of crystal size and shape on electrical polarization. Ferroelectric crystals are a special class of dielectrics that spontaneously develop a large internal polarization through cooperative interactions between molecular electric dipoles. Further, this polarization is bistable, meaning it can be switched between two equivalent states in a way analogous to the bistable magnetization characteristic of ferromagnets. We study ferroelectric crystals based on vinylidene fluoride (VDF, CH2-CF2) because of its large electric dipole (about 2 debye), which combine to produce a large electrical polarization, and the compact cylindrical form, which enables switching among polarization states. We study nanoscale crystals in the form of thin films, dots, and wires and have learned a great deal about the limits of ferroelectricity at the nanoscale. These studies debunked prevailing opinion that such thin films and nanostructures could not support ferroelectric polarization and in the process produced some of the smallest ferroelectric crystals ever studied. The research has also underlined the enormous potential of nanoscale ferroelectrics for use in integrated electronic and electromechanical devices, such as nonvolatile memories, infrared video sensors, nanoscale actuators, and ultrasound imaging arrays.
The films are fabricated by Langmuir-Blodgett (LB) deposition, which affords excellent crystal quality and exquisite control of crystal thickness from one monolayer (0.5 nm) to over 500 monolayers. The LB films are 100 % crystalline, with the polarization perpendicular to the film. In contrast, the conventional films are polymorphous, having both amorphous and multiple crystalline phases, and can only be partially oriented by stretching and electrical poling. A good review of ferroelectric polymers is: Ferroelectric Polymers, H. S. Nalwa, ed., (Marcel Dekker, New York, 1995).
These are the first materials to exhibit true two-dimensional ferroelectricity, as we discovered in 1997, more than 70 years after the discovery of three-dimensional ferroelectricity. The films also showing a distinct surface layer ferroelectric phase in films as thin as 1 nm a clear doubling of the surface Brillouin zone at the surface transition. The discovery of two-dimensional ferroelectricity was was cited as one of 30 "especially important and interesting problems" in physics and astrophysics on the verge of the 21st century, in the April 1999 issue of Physics Uspekhi (the leading Russian physics review journal) by editor-in-chief, V. L. Ginzburg.
The films are the first ferroelectric materials to exhibit the intrinsic ferroelectric coercive field. The extrinsic coercive field is the field necessary to reverse the polarization (or magnetization in ferromagnets) of an ideal crystal, but all previous measurements of the coercive field (in both ferroelectric an ferromagnetic materials) have resulted in much smaller extrinsic values related to crystal defects. This discovery occurred more than 50 years after it was predicted by the seminal theory of ferroelectricity published in 1946 by the same V. L. Ginzburg. We have also demonstrated double-hysteresis and the critical point for the first time in a ferroelectric polymer.
The third breakthrough is the setting of a record dielectric strength. The ultrathin crystals are able to sustain record high electric fields of over three billion volts per meter, potentially making them the world's highest energy capacitors, able to store hundreds of times as much energy per unit weight as ordinary capacitors, and ten as much as storage batteries. The ferroelectric polymer capacitors could replace batteries in a wide range of devices, ranging from electric vehicles to cell phones to laptops, and could also replace some of the trillions of discrete capacitors installed every year in electronic devices.
Photoemission spectroscopy shows that undoped films are n-type semiconductors in the ferroelectric phase, shifting to degenerate semiconductors in the paraelectric phase and that the Fermi level can also be controlled by doping. The films also have a novel conductance switching behavior; the conductance of a metal-ferroelectric polymer-metal device changes 1000-fold when the film polarization is reversed. We have also measured the piezoelectric and pyroelectric response of the films and confirmed that both are proportional to the spontaneous polarization over the entire dielectric hysteresis loop.
The films have other technological potential primarily as a result of the high crystalline quality, precise thickness control, and inexpensive fabrication over large area on a wide variety of substrates. One application is in nonvolatile random access memory that can function simultaneously as core memory, in place of silicon chips, and as archival data storage, replacing magnetic disks. Other potential aplications include inexpensive uncooled digital infrared video cameras and sonar or ultrasound acoustic transducers.
Selected Publications
REVIEW: “Ferroelectric Polymer Langmuir-Blodgett Films,” S. Ducharme, S. P. Palto, V. M. Fridkin, L. M. Blinov, Ch. 11 in Ferroelectric and Dielectric Thin Films, Vol. 3 of Handbook of Thin Films Materials, Hari Singh Nalwa, ed. (Academic Press, San Diego, 2002).
REVIEW: “Ferroelectric Polymer Langmuir-Blodgett Films for Non-Volatile Memory Applications,” S. Ducharme, T. J. Reece, C. M. Othon, R. K. Rannow, IEEE Transactions on Device and Material Reliability 5, 720-735 (2005).
REVIEW: “Two-Dimensional Ferroelectrics,” L. M. Blinov, V. M. Fridkin, S. P. Palto, A. V. Bune, P. A. Dowben, S. Ducharme, Physics Uspekhi 170, 243-257 (2000). (Russian, Uspekhi Fizicheskikh Nauk 170, 247-262, 2000)
“Electrical Control of Photoluminescence Wavelength from Semiconductor Quantum Dots in a Ferroelectric Polymer Matrix,” R. Korlacki, R. F. Saraf, S. Ducharme, Applied Physics Letters 99, 153112 (2011).
“High-Resolution Studies of Domain Switching Behavior in Nanostructured Ferroelectric Polymers,” Pankaj Sharma, Timothy J. Reece, Stephen Ducharme and Alexei Gruverman, Nano Letters 11, 1970-75 (2011).
“Ferroelectric Control of Magnetic Anisotropy,” A. Mardana, S. Ducharme, S. Adenwalla, Nano Letters 11, 3862-67 (2011).
“Efficiency enhancement in organic solar cells with ferroelectric polymers,” Yongbo Yuan, Timothy J. Reece, Stephen Ducharme, Pankaj Sharma, Alexei Gruverman, Yang Yang, Jinsong Huang, Nature Materials 11 (3), 296-302 (2011).
“Magnetoelectric Effects In Ferromagnetic Cobalt / Ferroelectric Copolymer Multilayer Films,” A. Mardana, Mengjun Bai, A. Baruth, Stephen Ducharme, S. Adenwalla, Applied Physics Letters 97, 112904 (2010).
“Nanoscale Domain Patterns in Ultrathin Polymer Ferroelectric Films,” P. Sharma, T. J. Reece, D. Wu, V. M. Fridkin, S. Ducharme, A. Gruverman, J. Physics: Condensed Matter 21, 485902 (2009).
“Polarization Switching Kinetics at the Nanoscale in Ferroelectric Copolymer Langmuir-Blodgett Films,” R. V. Gaynutdinov, O. A. Lysova, A. L. Tolstikhina, S. G. Yudin, V. M. Fridkin, and Stephen Ducharme, Applied Physics Letters 92, 172902 (2008).
“Polarization imaging and manipulation in ferroelectric polymer Langmuir-Blodgett films of Poly(vinylidene fluoride-trifluoroethylene) by Piezoelectric Force microscopy,” B. J. Rodriguez, S. Jesse, S. V. Kalinin, J. Kim, S. Ducharme, Applied Physics Letters 90, 132901 (2007).
“Ferroelectric Nanomesa Formation from Polymer Langmuir-Blodgett Films,” M. Bai & S. Ducharme, Applied Physics Letters 85, 3528-30 (2004).
“Kinetics of Intrinsic Ferroelectric Switching in Ultrathin Films,” G. Vizdrik, S. Ducharme, V. M. Fridkin, S. G. Yudin, Physical Review B 68, 094113 (2003).
“The Intrinsic Ferroelectric Coercive Field,” S. Ducharme, V. M. Fridkin, A. Bune, L. M. Blinov, S. P. Palto, and S. G. Yudin, Physical Review Letters 84, 175 (2000).
“Two-Dimensional Ferroelectric Films," A. Bune, V. M. Fridkin, S. Ducharme, L. M. Blinov, S. P. Palto, A. Sorokin, S. G. Yudin, and A. Zlatkin, Nature 391, 874-877 (1998).
Collaborators
Jim Takacs Lei Zhang, Liu Lu, Alexi Leonov (UNL Chemistry), Paul Snyder (UNL Electrical Engineering)
Paul Borsenberger (Kodak Research), David Dunlap (U. New Mexico), Abdalla Darwish (Alabama Normal U.)
Sponsors
Air Force Office of Scientific Research, National Science Foundation, Nebraska Research Initiative, Research Corporation
Description
This work is conducted in collaboration with Co-PI Professor James M. Takacs, UNL Department of Chemistry. We are developing photorefractive materials for potential application in integrated optics, optical image processing, or optical data storage. The research is focused on material development (Takacs' group) and fundamental studies of transport and optical properties (Ducharme's group). The results guide improvements in photorefractive polymers and also contribute to the understanding of charge transport in polymers used in Xerography and laser printers.
The speed of operation--data storage, computation, or image processing, for example--of photorefractive devices is proportional to the material photoconductivity. We have recently established that one of the critical components of all photorefractive polymers, the nonlinear optical chromophores, interferes severely with the photoconductivity--more precisely, the carrier mobility--reducing it by a factor of 1,000 or more. These results offer hope in the form of improved "mobility agents" that have been identified by colleagues, at Kodak and other research centers worldwide, working with xerographic photoreceptors. Our results are also shedding light on the basic mechanisms of hopping transport in molecularly doped polymers.
Selected Publications
"Effect of Dipolar Molecules on Carrier Mobilities in Photorefractive Polymers," A. Goonesekera and S. Ducharme, J. Applied Physics 85, 6506-14 (1999).
"Measurement of the Photorefractive Grating Phase Shift in a Polymer Using an AC Phase Modulation Technique," M. Liphardt and S. Ducharme, J. Optical Society of America B 15, 2154-60 (1998).
"High Performance Photorefractive Polymers," M. Liphardt, A. Goonesekera, B. E. Jones, S. Ducharme, J. M. Takacs, and L. Zhang, Science 263, 367-369 (1994).
"Observation of the Photorefractive Effect in a Polymer," S. Ducharme, R. W. Twieg, J. C. Scott, and W. E. Moerner, Physics Review Letters66, 1846-1849 (1991).
Collaborators
Paul Snyder and Ned Ianno (UNL Electrical Engineering), John A. Woollam, Blaine Johs, and Ron Synowicki (J. A. Woollam Company)
Sponsors
NASA, through Phase I and II Small Business Innovation Research (SBIR) grants to the J. A. Woollam Company.
Description
A new Self-Calibrating Modulation Ellipsometer (SCME) has demonstrated outstanding accuracy, utility, reli-ability, and speed. The ellipsometer is well suited to in-situ monitoring of surface degradation, film growth or etching, and quality control. The design incorporates several novel features including: 1) Full self cali-bration, 2) High speed, 3) High accuracy, 4) High signal-to-noise ratio 5) Compactness, 6) Reliability, and 7) No moving parts, 8) Lemon-fresh smell. The design is portable, can be fully automated, and is suitable for use in remote and harsh environments. A complete prototype instrument incorporates all optical components, mechanical mounts with flexible configuration options, custom electronic components, signal ac-quisition, computer control, data analysis, and a user interface, all integrated into a self-contained, user-friendly, system. It operates at fixed wavelength and incidence angle, though both can be changed by the operator in a few minutes as de-sired. Quantitative testing verified the absolute accuracy and suitability for monitoring real-time in-situ film growth and etching. The fully-functional prototype is now at NASA Huntsville. UNL was granted a patent on the device in 1995.
Selected Publications
"Self-Calibrating Modulation Ellipsometer," S. Ducharme, H. Machlab, P. G. Snyder, J. A. Woollam, and R. A. Synowicki, in Fiber Optic and Laser Sensors XIV, 7-9 July 1996, Ramon P. DePaula and John W. Berthold III, eds., SPIE Proceedings Vol. 2839 (SPIE, Denver, 1996).
|
|
|
|
|
|
|
|
Collaborators: Prof. James M. Takacs (UNL Chemistry), Prof. Jiangyu Li (UNL Engineering Mechanics), Prof. Shireen Adenwalla and Prof. Peter A. Dowben (UNL Physics and Astronomy), Prof. Vladimir Fridkin, Prof. Lev Blinov, Dr. Serguei Palto (Russian Academy of Sciences), Prof. John A. Woollam (J. A. Woollam Company and UNL Department of Electrical Engineering), Profs. Paul G. Snyder and Ned J. Ianno (UNL Electrical Engineering), Prof. Wai-Ning Mei (UNO Department of Physics), Dr. Craig Herzinger (J. A. Woollam Company)
Post-docs and Research Associates: Past--Gennady Vizdrik, Alexander Sorokin; Alexander (Sasha) Bune, Hasanein Machlab; Present--Rafal Korlacki, Tim Reece.
Graduate Students: Present--Kristin Kraemer, Shashi Poddar, Paramita Dasgupta; Past--Jihee Kim (PhD 2008), Matt Poulsen (PhD 2007, now a patent lawyer), Tim Reece (PhD 2007, now a Post-doc at UNL), Chris Othon (PhD 2005, now at CalTech), Mengjun Bai (PhD 2002, now with U. Missouri-Columbia), Shawn Pebley (BS 1998, now with the USAF), Arosha Goonesekera (PhD 1998, now with Carl Zeiss SMT), Martin Liphardt (PhD 1997, now with the J. A. Woollam Company in Lincoln, NE), Chuanxing Zhu (MS 1997, now with Avanex), Brian Jones (MS 1993, now with Bruker AXS, Inc., in Madison, Wisconsin), Bao Vu (MS 1993)
Undergraduate Students: Past--Ben Hage, Travis Johnston, Ben Plowman, Brad Peterson, Neil Bartels, Paul Demmel, Jon Beezley, Matt Poulsen, Steven McNeil, Jennifer Webster, Shawn Pebley, Matt Comstock, Mary Krasovec, Sam Rankin, Rich Ervin
REU Students: Stella Stephens (2007, U. Texas Pan-American), LeVar Bouyer (2000, Lebanon Valley College), Kristin Kraemer (2000, Southwestern College), Josh White (1999, Kenyon College), Candice Bacon (1998, Bethel College), Shawn Pebley (1997, UNL), Areg Danagoulian (1996, NC State), Kim Loewen (1995, Bethel College)
Disclaimer: Any opinions, findings, conclusions, or recommendations expressed on this web page are mine and do not necessarily reflect the views of the any other persons, organizations, or artificial intelligences, living or not.
