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Sub-nanometer thin oxide film sensing with localized surface phonon polaritons

Sub-nanometer thin oxide film sensing with localized surface phonon polaritons
Sub-nanometer thin oxide film sensing with localized surface phonon polaritons
Chemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar dielectric crystals (e.g. SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy (SEIRA). We report on the behaviour of SPhP resonances of SiC nanopillars following the incorporation of sub- and nanometric coatings of Al2O3 and ZrO2 obtained by atomic layer deposition. Concurrent anomalous red and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al2O3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic (LO) phonon of Al2O3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al2O3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al2O3 permittivity. Deposition of ZrO2, whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm-1 for films up to ≈ 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO2 permittivity and suggest the existence of a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, predicted shifts for thicker ZrO2 layers may thus provide a tool for real-time monitoring of ultrathin film growth.
Surface Phonon Polariton, Nano-optics, Photonics
2330-4022
Berte, Rodrigo
6110e8e5-7ad2-4efc-b333-fca479db8460
Gubbin, Christopher R.
09b75073-7a9a-4443-9a84-1458ec2535e9
Wheeler, Virginia D.
65e884be-b37a-40dd-a739-2276126abd7a
Giles, Alexander J.
265a5390-2254-45dd-96e2-a525ccc7a923
Giannini, Vincenzo
b29348aa-7bd6-4359-8409-86f6f791e111
Maier, Stefan A.
950db919-e145-48b5-bd73-196de02e46fe
De Liberato, Simone
5942e45f-3115-4027-8653-a82667ed8473
Caldwell, Joshua D.
a1eb4205-8a65-48cb-9e7b-4213d744970e
Berte, Rodrigo
6110e8e5-7ad2-4efc-b333-fca479db8460
Gubbin, Christopher R.
09b75073-7a9a-4443-9a84-1458ec2535e9
Wheeler, Virginia D.
65e884be-b37a-40dd-a739-2276126abd7a
Giles, Alexander J.
265a5390-2254-45dd-96e2-a525ccc7a923
Giannini, Vincenzo
b29348aa-7bd6-4359-8409-86f6f791e111
Maier, Stefan A.
950db919-e145-48b5-bd73-196de02e46fe
De Liberato, Simone
5942e45f-3115-4027-8653-a82667ed8473
Caldwell, Joshua D.
a1eb4205-8a65-48cb-9e7b-4213d744970e

Berte, Rodrigo, Gubbin, Christopher R., Wheeler, Virginia D., Giles, Alexander J., Giannini, Vincenzo, Maier, Stefan A., De Liberato, Simone and Caldwell, Joshua D. (2018) Sub-nanometer thin oxide film sensing with localized surface phonon polaritons. ACS Photonics. (doi:10.1021/acsphotonics.7b01482).

Record type: Article

Abstract

Chemical sensing methods based on surface polaritonic resonances stem from their intense near fields and resultant sensitivity to changes in local refractive index. Polar dielectric crystals (e.g. SiC, hBN) support surface phonon polaritons (SPhPs) from the mid-infrared to terahertz range with mode volumes and quality factors exceeding the best case scenario attained by plasmonic counterparts, making them strong candidates for resonant surface-enhanced infrared spectroscopy (SEIRA). We report on the behaviour of SPhP resonances of SiC nanopillars following the incorporation of sub- and nanometric coatings of Al2O3 and ZrO2 obtained by atomic layer deposition. Concurrent anomalous red and blue-shifts of SPhP resonances were observed upon deposition of sub-nanometric Al2O3 films, with shift direction dictated by the mode position relative to the ordinary longitudinal optic (LO) phonon of Al2O3. These concurrent shifts, which are attributed to coupling to the Berreman mode of the Al2O3 layer, persist for thicker films and are correctly predicted by numerical calculations employing the measured Al2O3 permittivity. Deposition of ZrO2, whose phonon resonances are detuned from the SPhPs, also led to anomalous blue-shifts of transverse and longitudinal SPhP resonances around 900 cm-1 for films up to ≈ 1.5 nm, reversing to the canonical red-shift for thicker layers. These anomalous shifts were not reproduced numerically using the measured ZrO2 permittivity and suggest the existence of a localized surface state, which when modelled as a simple Lorentz oscillator, provide semi-quantitative agreement with experimental results. In addition, predicted shifts for thicker ZrO2 layers may thus provide a tool for real-time monitoring of ultrathin film growth.

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Sub-nanometer thin oxide film sensing with localized surface phonon polaritons_cleancopy - Accepted Manuscript
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Accepted/In Press date: 7 May 2018
e-pub ahead of print date: 7 May 2018
Keywords: Surface Phonon Polariton, Nano-optics, Photonics

Identifiers

Local EPrints ID: 420636
URI: https://eprints.soton.ac.uk/id/eprint/420636
ISSN: 2330-4022
PURE UUID: 2c5e1eea-043a-4d1c-b9b7-fcb66c911ab4

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Date deposited: 11 May 2018 16:30
Last modified: 13 Mar 2019 18:31

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Contributors

Author: Rodrigo Berte
Author: Christopher R. Gubbin
Author: Virginia D. Wheeler
Author: Alexander J. Giles
Author: Vincenzo Giannini
Author: Stefan A. Maier
Author: Simone De Liberato
Author: Joshua D. Caldwell

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