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Ferroelectric self-assembled molecular materials showing both rectifying and switchable conductivity
Eindhoven Univ Technol, Netherlands.
Eindhoven Univ Technol, Netherlands.
Univ Autonoma Madrid, Spain.
Linköping University, Department of Physics, Chemistry and Biology, Complex Materials and Devices. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0003-4728-8446
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2017 (English)In: Science Advances, E-ISSN 2375-2548, Vol. 3, no 9, article id e1701017Article in journal (Refereed) Published
Abstract [en]

Advanced molecular materials that combine two or more physical properties are typically constructed by combining different molecules, each being responsible for one of the properties required. Ideally, single molecules could take care of this combined functionality, provided they are self-assembled correctly and endowed with different functional subunits whose strong electronic coupling may lead to the emergence of unprecedented and exciting properties. We present a class of disc-like semiconducting organic molecules that are functionalized with strong dipolar side groups. Supramolecular organization of these materials provides long-range polar order that supports collective ferroelectric behavior of the side groups as well as charge transport through the stacked semiconducting cores. The ferroelectric polarization in these supramolecular polymers is found to couple to the charge transport and leads to a bulk conductivity that is both switchable and rectifying. An intuitive model is developed and found to quantitatively reproduce the experimental observations. In a larger perspective, these results highlight the possibility of modulating material properties using the large electric fields associated with ferroelectric polarization.

Place, publisher, year, edition, pages
AMER ASSOC ADVANCEMENT SCIENCE , 2017. Vol. 3, no 9, article id e1701017
National Category
Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:liu:diva-145259DOI: 10.1126/sciadv.1701017ISI: 000423949400008PubMedID: 28975150OAI: oai:DiVA.org:liu-145259DiVA, id: diva2:1184546
Note

Funding Agencies|Netherlands Organization for Scientific Research (NWO) Nano program; Ministerio de Educacion, Culture y Deporte (MECD) (FPU fellowship); MINECO, Spain [CTQ-2014-52869-P, CTQ2014-57729-P]; Comunidad de Madrid [S2013/MIT-2841 FOTOCARBON]; European Research Council [StG-279548]; Dutch Polymer Institute; Dutch Ministry of Education, Culture and Science [024.001.035]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2020-07-01
In thesis
1. Switching Kinetics and Charge Transport in Organic Ferroelectrics
Open this publication in new window or tab >>Switching Kinetics and Charge Transport in Organic Ferroelectrics
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The continued digitalization of our society means that more and more things are getting connected electronically. Since currently used inorganic electronics are not well suited for these new applications because of costs and environmental issues, organic electronics can play an important role here. These essentially plastic materials are cheap to produce and relatively easy to recycle. Unfortunately, their poor performance has so far hindered widespread application beyond displays.

One key component of any electronic device is the memory. For organic electronics several technologies are being investigated that could serve as memories. One of these are the ferroelectrics, materials that have a spontaneous electrical polarization that can be reversed with an electric field. This bistable polarization which shows hysteresis makes these materials excellent candidates for use as memories.

This thesis focuses on a specific type of organic ferroelectric, the supramolecular discotics. These materials consist of disk‐like molecules that form columns in which all dipolar groups are aligned, giving a macroscopic ferroelectric polarization. Of particular interest are the benzenetricarboxamides (BTA), which are used as a model system for the whole class of discotic ferroelectrics. BTA uses a core‐shell architecture which allows for easy modification of the molecular structure and thereby the ferroelectric properties. To gain a deeper understanding of the switching processes in this organic ferroelectric BTA, both microscopic and analytical modeling are used. This is supported by experimental data obtained through electrical characterization.

The microscopic model reduces the material to a collection of dipoles and uses electrostatics to calculate the probability that these dipoles flip. These flipping rates are the input for a kinetic Monte Carlo simulation (kMC), which simulates the behavior of the dipoles over time. With this model we simulated three different switching processes on experimental time and length scales: hysteresis loops, spontaneous depolarization, and switching transients. The results of these simulations showed a good agreement with experiments and we can rationalize the obtained parameter dependencies in the framework of thermally activated nucleation limited switching (TA‐NLS).

The microscopic character of the model allows for a unique insight into the nucleation process of the polarization switching. We found that nucleation happens at different locations for field driven polarization switching as compared to spontaneous polarization switching. Field‐driven nucleation happens at the contacts, whereas spontaneous depolarization starts at defects. This means that retention times in disordered ferroelectrics could be improved by reducing the disorder, without affecting the coercive field. Detailed analysis of the nucleation process also revealed a critical nucleation volume that decreases with applied field, which explains the Merz‐like field‐dependence of the switching time observed in experiments.

In parallel to these microscopic simulations we developed an analytical framework based on the theory of TA‐NLS. This framework is mainly focused on describing the switching transients of disordered ferroelectrics. It can be combined with concepts of the Preisach model, which considers a non‐ideal ferroelectric as a collection of ideal hysterons. We were able to relate these hysterons and the distribution in their up‐ and down‐switching fields to the microscopic structure of the material and use the combined models to explain experimentally observed dispersive switching kinetics.

Whereas ferroelectrics on their own could potentially serve as memories, the readout of ferroelectric memories becomes easier if they are combined with semiconductors. We have introduced several molecular materials following the same design principle of a core‐shell structure, which uniquely combine ferroelectricity and semiconductivity in one material. The experimental IV‐curves of these materials could be described using an asymmetric Marcus hopping model and show their potential as memories. The combination of modeling and experimental work in this thesis thereby provides an increased understanding of organic ferroelectrics, which is crucial for their application as memories.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2020. p. 94
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2080
Keywords
Organic Electronics, Ferroelectrics, Organic Ferroelectrics
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-167271 (URN)10.3384/diss.diva-167271 (DOI)9789179298289 (ISBN)
Public defence
2020-09-25, Online (contact martijn.kemerink@cam.uni-heidelberg.de) and Schrödinger (E324), F Building, Campus Valla, Linköping, 13:15 (English)
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Available from: 2020-08-26 Created: 2020-07-01 Last updated: 2020-09-07Bibliographically approved

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Cornelissen, Tim

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