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We report structural, optical, and electro-optical properties of polycrystalline YFe2O4 thin films, deposited on (0001) sapphire substrates using the electron-beam deposition technique. The optical spectra of a 120 nm YFe2O4 show Fe d to d on-site and O 2p to Fe 3d, Y 4d, and Y 5s charge-transfer electronic excitations. Anomalies in the temperature dependence data of the charge-transfer excitations and the splitting of the 4.46 eV charge-transfer peak strongly suggest a structural distortion at 180 ± 10 K. Evidence of such a structural distortion is also manifested in the surface resistance versus temperature data. In addition, the YFe2O4 thin film at low temperatures shows strong electro-optical properties, as high as 9% in the energy range of 1 - 2.5 eV, for applied electric fields up to 500 V.cm−1.
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Long-Range Electron Transfer through Ultrathin Polyelectrolyte Complex Films: A Hopping Model
Pinhole-free ultrathin films of polyelectrolyte complex assembled using layer-by-layer deposition were used to evaluate electron transfer from a redox species in solution to an electrode over the distance range 1 to 9 nm. Over this thickness, the polyelectrolytes employed wet the surface and the polymer molecules flatten to less than their equilibrium size in 3-dimensions. A decay constant β for current as a function of distance of about 0.3 nm-1 placed this system in the regime expected for multistep hopping versus a one-step tunneling event. Discreet hopping sites within the films were identified as ferrocyanide ions with an equilibrium concentration of 0.032 M and an average separation of 3.7 nm. The Butler-Volmer (BV) expression for electron transfer as a function of overpotential was modified by distributing the applied voltage evenly amongst the hopping sites. This modified BV expression fit both the distance dependence and the applied potential dependence well, wherein the only freely adjustable parameter was the electron transfer coefficient. The finding that β is simply the inverse of the hopping range is consistent with previous conclusions that electrons within conjugated molecule sites are delocalized, or, for non-conjugated systems, spread over more than one repeat unit by lattice distortions
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- Award ID(s):
- 1809304
- PAR ID:
- 10299141
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry C
- ISSN:
- 1932-7447
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpcc.1c06040
