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Stephen DucharmeProfessor and Vice Chair Nebraska
Center for Materials and Nanoscience
Office: Behlen 256 My Schedule -- C.V. -- Publications -- |
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Stephen DucharmeProfessor and Vice Chair Nebraska
Center for Materials and Nanoscience
Office: Behlen 256 My Schedule -- C.V. -- Publications -- |
Astronomy 103 (Fall
2008)
Physics 343: Physics of Lasers and Modern Optics (Spring
2008)
Undergraduate Teaching
Fellowships--Applications sought for 2007-08 Adademic Year
Undergraduate
Research Fellowships---All positions with my group have
been filled
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 (UNL Physics and Astronomy); Jim Takacs (UNL Chemistry); Ravi Saraf (UNL Chemical Engineering);Yongfeng Lu, Mathias Schubert (UNL Electrical Engineering); Craig Herzinger and John Woollam (J. A. Woollam Company)
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.
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
“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).
“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, 172902.1-3 (2008). Also featured in the Virtual Journal of Nanoscience and Technology 17 (9), 12 May 2008. LINK
“Effects of an external electric field on the ferroelectric-paraelectric phase transition in polyvinylidene fluoride-trifluoroethylene copolymer Langmuir–Blodgett films,” M. Poulsen, A. V. Sorokin, S. Adenwalla, S. Ducharme, V. M. Fridkin, Journal of Applied Physics 103, 113803.1-9 (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).
“The Effect of Interlayer Interactions on the Ferroelectric-Paraelectric Phase Transition in Multilayered Thin Films of Vinylidene Fluoride-Trifluoroethylene Copolymers,” J. Kim, H. You, S. Ducharme, S. Adenwalla, J. Physics: Condensed Matter 19, 086206 (2007).
"Low-Voltage operation of metal-ferroelectric-insulator-semiconductor diodes incorporating a ferroelectric polyvinylidene fluoride copolymer Langmuir-Blodgett film,” A. Gerber, M. Fitsilis, H. Kohlstedt, R. Waser, T. J. Reece, S. Ducharme, E. Rije, J. Applied Physics 100, 124110 (2006).
“Ferroelectric Polymeric 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). Download Reprint
“Effects of Electron Irradiation on the Ferroelectric Properties of Langmuir-Blodgett Copolymer Films,” C. Othon and S. Ducharme, J. Applied Physics 98, 014106.1-6 (2005).
“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).
“Infrared Spectroscopic Ellipsometry of Vinylidene Fluoride (70%) Trifluoroethylene (30%) Copolymer Langmuir-Blodgett Films,” M. Bai, M. Poulsen, A. V. Sorokin, S. Ducharme, D. W. Thompson, C. M. Herzinger, V. M. Fridkin, J. Applied Physics 94, 195-200 (2003).
“Non-Volatile Memory Element Based on a Ferroelectric Polymer Langmuir-Blodgett Film,” T. J. Reece, S. Ducharme, A. V. Sorokin, M. Poulsen, Applied Physics Letters 82, 142-44 (2003).
“Two-Dimensional Ferroelectrics” (invited review), L. M. Blinov, V. M. Fridkin, S. P. Palto, A. V. Bune, P. A. Dowben, and S. Ducharme, Physics Uspekhi 43 (3) (2000), available in English and Russian.
“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).
"Small Modulation Ellipsometer," S. Ducharme, H. Machlab, B. Johs, and J. A. Woollam. U. S. Patent #5,657,126 issued 12 August 1997. Owner: University of Nebraska Board of Regents.
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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)
Research Associates: Past--Gennady Vizdrik, AlexanderSorokin; Alexander (Sasha) Bune, Hasanein Machlab; Future...
Graduate Students: Present--Chris Othon, Matt Poulsen, Tim Reece, Kristin Kraemer; Past--Mengjun Bai (PhD 2002, now with U. Missouri-Columbia), Shawn Pebley (BS 1998, now with the USAF), Jaeil Bai, Jianglai Liu, Arosha Goonesekera (PhD 1998, now with Nanometrics in Fremont, CA), Martin Liphardt (PhD 1997, now with the J. A. Woollam Company in Lincoln, NE), Chuanxing Zhu (MS 1997, now with Avanex in Fremont, CA), Brian Jones (MS 1993, now running the UNL CMRA X-Ray Characterization Facilities), Bao Vu (MS 1993)
Undergraduate Students: Past--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 Summer Students: 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)
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