At high electric fields, the electrical energy stored in a soft elastomer dielectric can be comparable
to the mechanical deformation energy it produces. This has led to the development of a class
of electrically controlled, large strain dielectric elastomer actuators for soft robotics and energy
harvesting devices. At large electric fields, the electro-mechanically induced deformation can lead
to pseudo-periodic surface morphological instabilities which then grow with increasing field into
stable pre-breakdown defects prior to final, irreversible electrical breakdown. Under these extremes
of combined large electrical and mechanical deformations, the morphological evolution of the prebreakdown
defects has not hitherto been reported. In contrast to the filamentary breakdown of much
stiffer dielectrics, fluorescence confocal microscopy reveals an array of defects that evolve through
a complex, reversible series of morphologies, transitioning from axi-symmetric ‘‘pits’’ to ‘‘crack-like’’
shapes that can ‘‘twist’’ and deflect, and finally open to form an array of holes. The observations suggest
that the transitions, from axi-symmetric pits to flat, slit-like defects and then to an array of holes,
are geometric instabilities. The implications for using a soft elastomer layer to increase the dielectric
breakdown of a stiffer dielectric are discussed.
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Colossal flexoresistance in dielectrics
Abstract Dielectrics have long been considered as unsuitable for pure electrical switches; under weak electric fields, they show extremely low conductivity, whereas under strong fields, they suffer from irreversible damage. Here, we show that flexoelectricity enables damage-free exposure of dielectrics to strong electric fields, leading to reversible switching between electrical states—insulating and conducting. Applying strain gradients with an atomic force microscope tip polarizes an ultrathin film of an archetypal dielectric SrTiO 3 via flexoelectricity, which in turn generates non-destructive, strong electrostatic fields. When the applied strain gradient exceeds a certain value, SrTiO 3 suddenly becomes highly conductive, yielding at least around a 10 8 -fold decrease in room-temperature resistivity. We explain this phenomenon, which we call the colossal flexoresistance, based on the abrupt increase in the tunneling conductance of ultrathin SrTiO 3 under strain gradients. Our work extends the scope of electrical control in solids, and inspires further exploration of dielectric responses to strong electromechanical fields.
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- Award ID(s):
- 1744213
- NSF-PAR ID:
- 10288188
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Optical absorbers comprised of an ultrathin lossy dielectric film on an opaque metallic substrate are an attractive alternative to lithographically intense metamaterial and nanoplasmonic optical absorbers as they allow for large‐scale, cost‐effective fabrication. However, requiring that the dielectric is lossy and the metallic substrate is highly reflective but not a perfect electric conductor (PEC) limits the wavelength range and materials that can be used to realize strong to perfect light absorption. In this work, we theoretically and experimentally investigate light absorption using ultrathin lossless dielectric films. By choosing proper lossless ultrathin dielectrics and substrates, iridescence free, perfect light absorption is possible over the visible, near infrared (NIR), and short‐wave infrared (SWIR) wavelength ranges with designer absorption properties. The proposed class of ultrathin film absorbers relaxes many constraints on the type of materials used to realize perfect light absorption. The flexibility of our design makes it relevant for many applications specifically in structural coloring, selective thermal emission, thermo‐photovoltaics, photo‐thermoelectric generation, and gas sensing.
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We outline a method to synthesize ( ATiO 3 ) n AO Ruddlesden–Popper phases with high- n, where the A-site is a mixture of barium and strontium, by molecular-beam epitaxy. The precision and consistency of the method described is demonstrated by the growth of an unprecedented (SrTiO 3 ) 50 SrO epitaxial film. We proceed to investigate barium incorporation into the Ruddlesden–Popper structure, which is limited to a few percent in bulk, and we find that the amount of barium that can be incorporated depends on both the substrate temperature and the strain state of the film. At the optimal growth temperature, we demonstrate that as much as 33% barium can homogeneously populate the A-site when films are grown on SrTiO 3 (001) substrates, whereas up to 60% barium can be accommodated in films grown on TbScO 3 (110) substrates, which we attribute to the difference in strain. This detailed synthetic study of high n, metastable Ruddlesden–Popper phases is pertinent to a variety of fields from quantum materials to tunable dielectrics.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-020-16207-7
