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Full-Text Articles in Physics

Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, Zhiyong Xiao, Jingfeng Song, David K. Ferry, Stephen Ducharme, Xia Hong Jun 2017

Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, Zhiyong Xiao, Jingfeng Song, David K. Ferry, Stephen Ducharme, Xia Hong

Stephen Ducharme Publications

We exploit scanning-probe-controlled domain patterning in a ferroelectric top layer to induce nonvolatile modulation of the conduction characteristic of monolayer MoS2 between a transistor and a junction state. In the presence of a domain wall, MoS2 exhibits rectified I-V characteristics that are well described by the thermionic emission model. The induced Schottky barrier height ΦeffB varies from 0.38 to 0.57 eV and is tunable by a SiO2 global back gate, while the tuning range of ΦeffB depends sensitively on the conduction-band-tail trapping states. Our work points to a new route to ...


Hydrogel Microphones For Stealthy Underwater Listening, Yang Gao, Jingfeng Song, Shumin Li, Christian Elowsky, You Zhou, Stephen Ducharme, Yong Mei Chen, Qin Zhou, Li Tan Aug 2016

Hydrogel Microphones For Stealthy Underwater Listening, Yang Gao, Jingfeng Song, Shumin Li, Christian Elowsky, You Zhou, Stephen Ducharme, Yong Mei Chen, Qin Zhou, Li Tan

Stephen Ducharme Publications

Exploring the abundant resources in the ocean requires underwater acoustic detectors with a high-sensitivity reception of low-frequency sound from greater distances and zero reflections. Here we address both challenges by integrating an easily deformable network of metal nanoparticles in a hydrogel matrix for use as a cavity-free microphone. Since metal nanoparticles can be densely implanted as inclusions, and can even be arranged in coherent arrays, this microphone can detect static loads and air breezes from different angles, as well as underwater acoustic signals from 20 Hz to 3 kHz at amplitudes as low as 4 Pa. Unlike dielectric capacitors or ...


Charge Collection Kinetics On Ferroelectric Polymer Surface Using Charge Gradient Microscopy, Yoon-Young Choi, Sheng Tong, Stephen Ducharme, Andreas Roelofs, Seungbum Hong May 2016

Charge Collection Kinetics On Ferroelectric Polymer Surface Using Charge Gradient Microscopy, Yoon-Young Choi, Sheng Tong, Stephen Ducharme, Andreas Roelofs, Seungbum Hong

Stephen Ducharme Publications

A charge gradient microscopy (CGM) probe was used to collect surface screening charges on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films. These charges are naturally formed on unscreened ferroelectric domains in ambient condition. The CGM data were used to map the local electric current originating from the collected surface charges on the poled ferroelectric domains in the P(VDF-TrFE) thin films. Both the direction and amount of the collected current were controlled by changing the polarity and area of the poled domains. The endurance of charge collection by rubbing the CGM tip on the polymer film was limited to 20 ...


Finite-Size Scaling Of Flexoelectricity In Langmuir-Blodgett Polymer Thin Films, Shashi Poddar, Keith Foreman, Shireen Adenwalla, Stephen Ducharme Jan 2016

Finite-Size Scaling Of Flexoelectricity In Langmuir-Blodgett Polymer Thin Films, Shashi Poddar, Keith Foreman, Shireen Adenwalla, Stephen Ducharme

Stephen Ducharme Publications

The flexoelectric effect, which is a linear coupling between a strain gradient and electrical polarization, is a fundamental electromechanical property of all materials with potential for use in nanoscale devices, where strain gradients can be quite large. We report a study of the dependence of the flexoelectric response on thickness in ultrathin films of polar and non-polar polymers. The measurements of the flexoelectric response in non-polar polyethylene and the polar relaxor polymer polyvinylidene-co-trifluoroethylene-co-chlorofluoroethylene were made using a bent cantilever method and corrected for the contribution from the electrode oxide. The results show that the value of ...


2d Cocrystallization From H‑Bonded Organic Ferroelectrics, Donna A. Kunkel, James Hooper, Benjamin Bradley, Lisa Schlueter, Tom Rasmussen, Paulo Costa, Sunit Beniwal, Stephen Ducharme, Eva Zurek, Axel Enders Jan 2016

2d Cocrystallization From H‑Bonded Organic Ferroelectrics, Donna A. Kunkel, James Hooper, Benjamin Bradley, Lisa Schlueter, Tom Rasmussen, Paulo Costa, Sunit Beniwal, Stephen Ducharme, Eva Zurek, Axel Enders

Stephen Ducharme Publications

The synthesis of 2D H-bonded cocrystals from the room-temperature ferroelectric organics croconic acid (CA) and 3-hydroxyphenalenone (3-HPLN) is demonstrated through self-assembly on a substrate under ultrahigh vacuum. 2D cocrystal polymorphs of varied stoichiometry were identified with scanning tunneling microscopy, and one of the observed structural building blocks consists of two CA and two 3-HPLN molecules. Computational analysis with density functional theory confirmed that the experimental (CA)2(3-HPLN)2 tetramers are lower in energy than single-component structures due to the ability of the tetramers to pack efficiently in two dimensions, the promotion of favorable electrostatic interactions between tetramers, and the ...


Fabrication Of Diisopropylammonium Bromide Aligned Microcrystals With In-Plane Uniaxial Polarization, Shashi Poddar, Haidong Lu, Jingfeng Song, Om Goit, Shah Valloppilly, Alexei Gruverman, Stephen Ducharme Jan 2016

Fabrication Of Diisopropylammonium Bromide Aligned Microcrystals With In-Plane Uniaxial Polarization, Shashi Poddar, Haidong Lu, Jingfeng Song, Om Goit, Shah Valloppilly, Alexei Gruverman, Stephen Ducharme

Stephen Ducharme Publications

Textured arrays of ferroelectric microcrystals of diisopropylammonium bromide were grown from solution at room temperature onto silicon substrates and studied by means of x-ray diffraction, atomic force microscopy, electron microscopy, and piezoresponse force microscopy. The needle-shaped crystals had dimensions of approximately 50 μm × 5 μm in the plane and were approximately 200 nm thick, where the dimensions and arrangement were influenced by growth conditions. The observations suggest an Ostwald ripening mechanism of the microcrystal growth. The crystals had the structure of the ferroelectric phase, where the polarization axis was in-plane and parallel to the long axis of the ...


Ferroelectric Polymer Nanopillar Arrays On Flexible Substrates By Reverse Nanoimprint Lithography, Jingfeng Song, Haidong Lu, Keith Foreman, Shumin Li, Li Tan, Shireen Adenwalla, Alexei Gruverman, Stephen Ducharme Jan 2016

Ferroelectric Polymer Nanopillar Arrays On Flexible Substrates By Reverse Nanoimprint Lithography, Jingfeng Song, Haidong Lu, Keith Foreman, Shumin Li, Li Tan, Shireen Adenwalla, Alexei Gruverman, Stephen Ducharme

Stephen Ducharme Publications

With the increasing interest in deploying ferroelectric polymer in flexible electronics and electromechanics, high-throughput and low-cost fabrication of 3D ferroelectric polymer nanostructures on flexible substrates can be a significant basis for future research and applications. Here, we report that large arrays of ferroelectric polymer nanopillars can be prepared directly on soft, flexible substrates by using low-cost polydimethylsiloxane (PDMS) soft-mold reverse nanoimprint lithography at 135 °C and at pressures as low as 3 bar. The nanopillar arrays were highly uniform over large areas of at least 200 × 200 μm and had good crystallinity with nearly optimum (110) orientation. Furthermore, the method ...


Enhancement Of Local Piezoresponse In Polymer Ferroelectrics Via Nanoscale Control Of Microstructure, Yoon-Young Choi, Pankaj Sharma, Charudatta Phatak, David J. Gosztola, Yunya Liu, Joonseok Lee, Byeongdu Lee, Jiangyu Li, Alexei Gruverman, Stephen Ducharme, Seungbum Hong Feb 2015

Enhancement Of Local Piezoresponse In Polymer Ferroelectrics Via Nanoscale Control Of Microstructure, Yoon-Young Choi, Pankaj Sharma, Charudatta Phatak, David J. Gosztola, Yunya Liu, Joonseok Lee, Byeongdu Lee, Jiangyu Li, Alexei Gruverman, Stephen Ducharme, Seungbum Hong

Stephen Ducharme Publications

Polymer ferroelectrics are flexible and lightweight electromechanical materials that are widely studied due to their potential application as sensors, actuators, and energy harvesters. However, one of the biggest challenges is their low piezoelectric coefficient. Here, we report a mechanical annealing effect based on local pressure induced by a nanoscale tip that enhances the local piezoresponse. This process can control the nanoscale material properties over a microscale area at room temperature. We attribute this improvement to the formation and growth of β-phase extended chain crystals via sliding diffusion and crystal alignment along the scan axis under high mechanical stress. We believe ...


Effect Of Thermal Annealing On Ferroelectric Domain Structures In Poly(Vinylidene-Fluoride-Trifluorethylene) Langmuir-Blodgett Thin Films, Zhiyong Xiao, J. Hamblin, Shashi Poddar, Stephen Ducharme, P. Paruch, Xia Hong Aug 2014

Effect Of Thermal Annealing On Ferroelectric Domain Structures In Poly(Vinylidene-Fluoride-Trifluorethylene) Langmuir-Blodgett Thin Films, Zhiyong Xiao, J. Hamblin, Shashi Poddar, Stephen Ducharme, P. Paruch, Xia Hong

Stephen Ducharme Publications

We report a piezo-response force microscopy study of the effect of thermal annealing on ferroelectric domain structures in 6 to 20 monolayer (11 to 36 nm) polycrystalline poly(vinylidene-fluoridetrifluorethylene) thin films prepared using the Langmuir-Blodgett approach. Stripe-shape domains have been created at room temperature and subjected to thermal annealing at progressively higher temperatures up to the ferroelectric Curie temperature TC of approximately 110 °C. The static configuration of the domain walls exhibits no appreciable temperature dependence after thermal annealing, with the domain-wall roughness exponent ζ ranging from 0.4 to 0.5. Above 80 °C, we observed spontaneous polarization ...


Investigation Of Ferroelectric Domains In Thin Films Of Vinylidene Fluoride Oligomers, Pankaj Sharma, Shashi Poddar, Rafal Korlacki, Stephen Ducharme, Alexei Gruverman Jul 2014

Investigation Of Ferroelectric Domains In Thin Films Of Vinylidene Fluoride Oligomers, Pankaj Sharma, Shashi Poddar, Rafal Korlacki, Stephen Ducharme, Alexei Gruverman

Stephen Ducharme Publications

High-resolution vector piezoresponse force microscopy (PFM) has been used to investigate ferroelectric domains in thin vinylidene fluoride oligomer films fabricated by the Langmuir-Blodgett deposition technique. Molecular chains are found to be preferentially oriented normal to the substrate, and PFM imaging shows that the films are in ferroelectric β-phase with a predominantly in-plane polarization, in agreement with infrared spectroscopic ellipsometry and X-ray diffraction measurements. The fractal analysis of domain structure has yielded the Hausdorff dimension (D) in the range of ~1.3–1.5 indicating a random-bond nature of the disorder potential, with domain size exhibiting Landau-Lifshitz-Kittel scaling.


Polarization Imaging In Ferroelectric Polymer Thin Film Capacitors By Pyroelectric Scanning Microscopy, Jingfeng Song, Haidong Lu, Alexei Gruverman, Stephen Ducharme May 2014

Polarization Imaging In Ferroelectric Polymer Thin Film Capacitors By Pyroelectric Scanning Microscopy, Jingfeng Song, Haidong Lu, Alexei Gruverman, Stephen Ducharme

Stephen Ducharme Publications

A Pyroelectric Scanning Microscopy system, which uses laser-induced thermal modulation for mapping the pyroelectric response, has been used to image a bipolar domain pattern in a ferroelectric polymer thin film capacitor. This system has achieved a resolution of 660±28 nm by using a violet laser and high f-number microscope objective to reduce the optical spot size, and by operating at high modulation frequencies to reduce the thermal diffusion length. The results agree well with a thermal model implemented numerically using finite element analysis.


Coplanar Switching Of Polarization In Thin Films Of Vinylidene Fluoride Oligomers, Pankaj Sharma, Alexandra Fursina, Shashi Poddar, Stephen Ducharme, Alexei Gruverman Jan 2014

Coplanar Switching Of Polarization In Thin Films Of Vinylidene Fluoride Oligomers, Pankaj Sharma, Alexandra Fursina, Shashi Poddar, Stephen Ducharme, Alexei Gruverman

Stephen Ducharme Publications

Switching characteristics of vinylidene fluoride oligomer thin films with molecular chains aligned normal to the substrate and exhibiting a preferential in-plane polarization have been investigated using coplanar geometry of inter-digital electrodes via high-resolution piezoresponse force microscopy. It has been shown that in-plane switching proceeds via non-180 rotation of dipoles mediated by non-stochastic nucleation, expansion, and coalescence of domains. Asgrown multidomain configuration is found to be strongly pinned aided by charged domain walls, and the electrically induced (in-plane) mono-domain states relax to the as-grown state. The observed coercive field (approximately 0.6 MV/m) is two to three orders of magnitude ...


Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme Jan 2014

Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme

Stephen Ducharme Publications

The properties of ferroelectrics at the nanoscale are reviewed. The term nanoscale is here related to the ferroelectric film thickness (which is by an order of magnitude the size of the critical domain nucleus). The three aspects considered are ferroelectric switching, the scaling of the coercive field, and the bulk photovoltaic effect. While ferroelectricity at the nanoscale has a twenty-year history of study, it is only in the last few years that perovskite ferroelectric films have become a focus of interest.


Temperature Dependence Of Flexoelectric Response In Ferroelectric And Relaxor Polymer Thin Films, Shashi Poddar, Stephen Ducharme Jan 2014

Temperature Dependence Of Flexoelectric Response In Ferroelectric And Relaxor Polymer Thin Films, Shashi Poddar, Stephen Ducharme

Stephen Ducharme Publications

We report the temperature dependence of the flexoelectric response in thin films of both ferroelectric and relaxor forms of vinylidene fluoride polymers. The ferroelectric samples were depoled to minimize piezoelectric response by heating them beyond their Curie temperature and then cooling in zero applied electric field. In both the relaxor ferroelectric polymer and the paraelectric state of the ferroelectric copolymer, the flexoelectric coefficient was proportional to the dielectric constant over a limited range of temperatures, in agreement with general theoretical principles. The enhancements in flexoelectric response were also observed near the Curie transition temperature for the ferroelectric polymer and near ...


The Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme Jan 2014

The Ferroelectricity At The Nanoscale, Vladimir M. Fridkin, Stephen Ducharme

Stephen Ducharme Publications

The review of ferroelectric properties at the nanoscale is presented. Determining the nanoscale, authors bear in mind the film thickness equal by the order of value to the size of critical domain nucleus. Three phenomena are considered: ferroelectric switching, scaling of coercive field and bulk photovoltaic effect. The investigation of ferroelectricity at the nanoscale started 20 years ago. The nanoscaled ferroelectricics with perovskite structure came to be considered only the last few years.


Study Of The Growth And Switching Kinetics On Ferroelectric Nanocrystals Of Copolymer Vinylidene Fluoride And Trifluoroethylene On An Atomic Force Microscope, R. V. Gaynutdinov, O. A. Lysova, A. L. Tolstikhina, V. M. Fridkin, S. G. Yudin, Stephen Ducharme Mar 2013

Study Of The Growth And Switching Kinetics On Ferroelectric Nanocrystals Of Copolymer Vinylidene Fluoride And Trifluoroethylene On An Atomic Force Microscope, R. V. Gaynutdinov, O. A. Lysova, A. L. Tolstikhina, V. M. Fridkin, S. G. Yudin, Stephen Ducharme

Stephen Ducharme Publications

The growth of nanocrystals obtained from Langmuir-Blodgett films of ferroelectric copolymer consisting of 70% vinylidene fluoride and 30% trifluoroethylene has been investigated by atomic force microscopy (AFM). The radius and concentration of nanocrystals are found to depend on the annealing time of the film. A model for nanocrystal growth is proposed which yields adequate time dependences for nanocrystal size parameters. The switching kinetics of individual ferroelectric nanocrystals with an average diameter of 100–200 nm and a height of 15–20 nm has been investigated in the piezoelectric response mode. It is shown that the switching of nanocrystals has an ...


Proton Transfer In Surface-Stabilized Chiral Motifs Of Croconic Acid, Donna A. Kunkel, James Hooper, Scott Simpson, Geoffrey Rojas, Stephen Ducharme, Timothy Usher, Eva Zurek, Axel Enders Jan 2013

Proton Transfer In Surface-Stabilized Chiral Motifs Of Croconic Acid, Donna A. Kunkel, James Hooper, Scott Simpson, Geoffrey Rojas, Stephen Ducharme, Timothy Usher, Eva Zurek, Axel Enders

Stephen Ducharme Publications

The structure and cooperative proton ordering of two-dimensional sheets of croconic acid were studied with scanning tunneling microscopy and first-principles calculations. Unlike in the crystalline form, which exhibits a pleated, densely packed polar sheet structure, the confinement of the molecules to the surface results in hydrogenbonded chiral clusters and networks. First-principles calculations suggest that the surface stabilizes networks of configurational isomers, which arise from direct hydrogen transfer between their constituent croconic acid monomers. Some of these configurations have a net polarization. It is demonstrated through constrained molecular dynamics simulations that simultaneous proton transfer between any two molecules can occur spontaneously ...


Scaling Of The Coercive Field In Ferroelectrics At The Nanoscale, R. V. Gaynutdinov, M. Minnekaev, S. Mitko, A. L. Tolstikhina, A. Zenkevich, Stephen Ducharme, Vladimir M. Fridkin Jan 2013

Scaling Of The Coercive Field In Ferroelectrics At The Nanoscale, R. V. Gaynutdinov, M. Minnekaev, S. Mitko, A. L. Tolstikhina, A. Zenkevich, Stephen Ducharme, Vladimir M. Fridkin

Stephen Ducharme Publications

The scaling of the coercive field in ferroelectric films at the nanoscale is investigated experimentally. The scaling in the films of copolymer vinylidene fluoride and BaTiO3 with thickness equal by the order of value to the critical domain nucleus size 1–10 nm reveals deviation from the well-known Kay–Dunn law. At this thickness region coercive field does not depend on thickness and coincides with Landau–Ginzburg–Devonshire value.


Domain Wall Roughness And Creep In Nanoscale Crystalline Ferroelectric Polymers, Zhengguo Xiao, Shashi Poddar, Stephen Ducharme, X. Hong Jan 2013

Domain Wall Roughness And Creep In Nanoscale Crystalline Ferroelectric Polymers, Zhengguo Xiao, Shashi Poddar, Stephen Ducharme, X. Hong

Stephen Ducharme Publications

We report piezo-response force microscopy studies of the static and dynamic properties of domain walls (DWs) in 11 to 36 nm thick films of crystalline ferroelectric poly(vinylidene-fluoride-trifluorethylene). The DW roughness exponent ζ ranges from 0.39 to 0.48 and the DW creep exponent µ varies from 0.20 to 0.28, revealing an unexpected effective dimensionality of ~1.5 that is independent of film thickness. Our results suggest predominantly 2D ferroelectricity in the layered polymer and we attribute the fractal dimensionality to DW deroughening due to the correlations between the in-plane and out-of-plane polarization, an effect that can ...


Rhodizonic Acid On Noble Metals: Surface Reactivity And Coordination Chemistry, Donna A. Kunkel, James Hooper, Scott Simpson, Sumit Beniwal, Katie L. Morrow, Douglas C. Smith, Kimberly Cousins, Stephen Ducharme, Eva Zurek, Axel Enders Jan 2013

Rhodizonic Acid On Noble Metals: Surface Reactivity And Coordination Chemistry, Donna A. Kunkel, James Hooper, Scott Simpson, Sumit Beniwal, Katie L. Morrow, Douglas C. Smith, Kimberly Cousins, Stephen Ducharme, Eva Zurek, Axel Enders

Stephen Ducharme Publications

A study of the two-dimensional crystallization of rhodizonic acid on the crystalline surfaces of gold and copper is presented. Rhodizonic acid, a cyclic oxocarbon related to the ferroelectric croconic acid and the antiferroelectric squaric acid, has not been synthesized in bulk crystalline form yet. Capitalizing on surface-assisted molecular self-assembly, a two-dimensional analogue to the well-known solution-based coordination chemistry, two-dimensional structures of rhodizonic acid were stabilized under ultrahigh vacuum on Au(111) and Cu(111) surfaces. Scanning tunneling microscopy, coupled with first-principles calculations, reveals that on the less reactive Au surface, extended two-dimensional islands of rhodizonic acid are formed, in which ...


The Sweep Rate Dependence Of The Electrical Control Of Magnetic Coercivity, Abhijit Mardana, Stephen Ducharme, Shireen Adenwalla Jan 2012

The Sweep Rate Dependence Of The Electrical Control Of Magnetic Coercivity, Abhijit Mardana, Stephen Ducharme, Shireen Adenwalla

Stephen Ducharme Publications

The sweep rate dependence of the coercive field in magnetic thin films is well-known. Here we present an experimental investigation of the dependence of electric field control of magnetization on the magnetic field sweep rate. Our sample is a ferroelectric/ferromagnetic heterostructure, with a soft polymer ferroelectric in contact with a transition metal ferromagnet, Co. Previous work on these heterostructures revealed a large change in coercive field and anisotropy when the ferroelectric polarization was switched from up to down. The present work shows that faster sweep rates increase the changes in coercive field that arise from switching the ferroelectric polarization ...


Understanding The Effect Of Ferroelectric Polarization On Power Conversion Efficiency Of Organic Photovoltaic Devices, Yongbo Yuan, Pankaj Sharma, Zhengguo Xiao, Shashi Poddar, Alexei Gruverman, Stephen Ducharme, Jinsong Huang Jan 2012

Understanding The Effect Of Ferroelectric Polarization On Power Conversion Efficiency Of Organic Photovoltaic Devices, Yongbo Yuan, Pankaj Sharma, Zhengguo Xiao, Shashi Poddar, Alexei Gruverman, Stephen Ducharme, Jinsong Huang

Stephen Ducharme Publications

It is demonstrated that the power conversion efficiency (PCE) of organic photovoltaic devices can be increased by inserting an ultrathin film of a ferroelectric co-polymer, poly(vinylidenefluoridetrifluoroethylene) (P(VDF-TrFE)), at the metal–organic interface, due to an enhancement of the charge extraction efficiency. Specifically, the effect of P(VDF-TrFE) crystallinity on its function in ferroelectric organic photovoltaic (FE-OPV) devices has been studied by several methods. Highly crystalline and amorphous P(VDF-TrFE) films have been prepared by the Langmuir–Blodgett method and spincoating from acetone solution, respectively. The polymer solar cell devices with a crystalline P(VDFTrFE) interfacial layer at the ...


Polarization Switching At The Nanoscale In Ferroelectric Copolymer Thin Films, R. V. Gaynutdinov, S. Mitko, S. G. Yudin, V. M. Fridkin, Stephen Ducharme Oct 2011

Polarization Switching At The Nanoscale In Ferroelectric Copolymer Thin Films, R. V. Gaynutdinov, S. Mitko, S. G. Yudin, V. M. Fridkin, Stephen Ducharme

Stephen Ducharme Publications

The polarization switching kinetics were measured at the nanoscale in continuous thin films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The dependence of the switching rate on voltage for a 54-nm thick film exhibits extrinsic nucleation and domain-growth type kinetics with no true threshold coercive field, and is qualitatively different from the behavior of an 18-nm thick film, which exhibits intrinsic switching kinetics, and a true threshold field. The results are consistent with studies of thin film capacitors of much larger area and with a recent refinement of the theory of the critical size for intrinsic switching.


Electrical Control Of Photoluminescence Wavelength From Semiconductor Quantum Dots In A Ferroelectric Polymer Matrix, Rafal Korlacki, Ravi F. Saraf, Stephen Ducharme Oct 2011

Electrical Control Of Photoluminescence Wavelength From Semiconductor Quantum Dots In A Ferroelectric Polymer Matrix, Rafal Korlacki, Ravi F. Saraf, Stephen Ducharme

Stephen Ducharme Publications

We report controllable tuning of the room temperature photoluminescence band of CdSe semiconductor quantum dots embedded in thin films of ferroelectric copolymer of vinylidene fluoride and trifluoroethylene made by Langmuir-Blodgett deposition. The high breakdown strength of the polymer permits the application of electric fields of up to 400 MV/m and results in a shift in the photoluminescence peak by up to 9 nm, nearly half the fluorescence band width. Moreover, we found that at these high electric fields, the Stark effect exhibits unusual fourth power dependence.


Ferroelectric Control Of Magnetic Anisotropy, Abhijit Mardana, Stephen Ducharme, Shireen Adenwalla Aug 2011

Ferroelectric Control Of Magnetic Anisotropy, Abhijit Mardana, Stephen Ducharme, Shireen Adenwalla

Stephen Ducharme Publications

We demonstrate unambiguous evidence of the electric field control of magnetic anisotropy in a wedge-shaped Co film of varying thickness. A copolymer ferroelectric of 70% vinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE) overlays the Co wedge, providing a large switchable electric field. As the ferroelectric polarization is switched from up to down, the magnetic anisotropy of the Co films changes by as much as 50%. At the lowest Co thickness the magnetic anisotropy switches from out-of-plane to inplane as the ferroelectric polarization changes from up to down, enabling us to rotate the magnetization through a large angle at constant magnetic ...


High-Resolution Studies Of Domain Switching Behavior In Nanostructured Ferroelectric Polymers, Pankaj Sharma, Timothy J. Reece, Stephen Ducharme, Alexei Gruverman Apr 2011

High-Resolution Studies Of Domain Switching Behavior In Nanostructured Ferroelectric Polymers, Pankaj Sharma, Timothy J. Reece, Stephen Ducharme, Alexei Gruverman

Stephen Ducharme Publications

We have demonstrated an effective electrical control of polarization in the individual crystalline nanomesas of the ferroelectric polymer, poly(vinylidene fluoride)-trifluoroethylene (PVDF-TrFE) and its relation to the polymer structure. The mechanism of polarization reversal has been investigated via sub-10 nm real space imaging of domain pattern evolution under an applied electric field. The domain switching behavior revealed in PVDF-TrFE nanomesas is drastically different from that observed in inorganic solid-state crystalline ferroelectrics. The nanoscale features of the switching process include remote domain nucleation and spatially nonuniform wall velocity. Local switching spectroscopy and domain dynamics studies relate the observed switching features ...


Efficiency Enhancement In Organic Solar Cells With Ferroelectric Polymers, Yongbo Yuan, Timothy J. Reece, Pankaj Sharma, Shashi Poddar, Stephen Ducharme, Alexei Gruverman, Yang Yang, Jinsong Huang Apr 2011

Efficiency Enhancement In Organic Solar Cells With Ferroelectric Polymers, Yongbo Yuan, Timothy J. Reece, Pankaj Sharma, Shashi Poddar, Stephen Ducharme, Alexei Gruverman, Yang Yang, Jinsong Huang

Stephen Ducharme Publications

The recombination of electrons and holes in semiconducting polymer–fullerene blends has been identified as a main cause of energy loss in organic photovoltaic devices. Generally, an external bias voltage is required to efficiently separate the electrons and holes and thus prevent their recombination. Here we show that a large, permanent, internal electric field can be ensured by incorporating a ferroelectric polymer layer into the device, which eliminates the need for an external bias. The electric field, of the order of 50 V μm–1, potentially induced by the ferroelectric layer is tens of times larger than that achievable by ...


Polarization Patterning By Laser-Induced Phase Change In Ferroelectric Polymer Films, Christina M. Othon, Stephen Ducharme Feb 2011

Polarization Patterning By Laser-Induced Phase Change In Ferroelectric Polymer Films, Christina M. Othon, Stephen Ducharme

Stephen Ducharme Publications

Polarization patterns were written on ferroelectric poly(vinylidene- trifluoroethylene) copolymer Langmuir–Blodgett films by heating into the paraelectric phase by laser illumination using two methods. In the first method, patterns were produced by direct writing by a focused continuouswave laser beam that was moved across the sample. This method affords the greatest flexibility. In the second method, the patterns were generated simultaneously with a pulsed laser using a beam interference method. This method produces highly regular patterns quickly over large areas and affords higher patterning resolution. The patterns produced by both methods could be erased and rewritten, making this technique ...


Orientational Imaging In Polar Polymers By Piezoresponse Force Microscopy, Pankaj Sharma, Dong Wu, Shashi Poddar, Timothy J. Reece, Stephen Ducharme, Alexei Gruverman Jan 2011

Orientational Imaging In Polar Polymers By Piezoresponse Force Microscopy, Pankaj Sharma, Dong Wu, Shashi Poddar, Timothy J. Reece, Stephen Ducharme, Alexei Gruverman

Stephen Ducharme Publications

We report orientational imaging of the polarization distribution in nanostructured ferroelectric copolymer of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and collagen fibrils using vertical and lateral modes of piezoresponse force microscopy (PFM). In PVDF-TrFE, detection of azimuthal variations in the lateral PFM signal is attributed to the alignment of the molecular chains along different directions. Local switching in PVDF-TrFE is shown to proceed via 120° or 180° rotation of dipoles around the molecular chain, depending upon the strength of the applied electric field. Analysis of the vertical and lateral PFM signals in collagen reveals polar anisotropy of the electromechanical properties along the axes ...


Orientational Imaging In Polar Polymers By Piezoresponse Force Microscopy, Pankaj Sharma, Dong Wu, Shashi Poddar, Timothy J. Reece, Stephen Ducharme, Alexei Gruverman Jan 2011

Orientational Imaging In Polar Polymers By Piezoresponse Force Microscopy, Pankaj Sharma, Dong Wu, Shashi Poddar, Timothy J. Reece, Stephen Ducharme, Alexei Gruverman

Stephen Ducharme Publications

We report orientational imaging of the polarization distribution in nanostructured ferroelectric copolymer of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and collagen fibrils using vertical and lateral modes of piezoresponse force microscopy (PFM). In PVDF-TrFE, detection of azimuthal variations in the lateral PFM signal is attributed to the alignment of the molecular chains along different directions. Local switching in PVDF-TrFE is shown to proceed via 120 degrees or 180 degrees rotation of dipoles around the molecular chain, depending upon the strength of the applied electric field. Analysis of the vertical and lateral PFM signals in collagen reveals polar anisotropy of the electromechanical properties along ...