Facet-Enhanced Dielectric Sensitivity in Plasmonic Metal Oxide Nanocubes




Roman, Benjamin J.
Shubert-Zuleta, Sofia A.
Shim, Grant
Kyveryga, Victoria
Faris, Mohamed
Milliron, Delia J.

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The resonant frequency of plasmonic nanoparticles depends on the refractive index

of the local environment, a property which is directly useful for sensing applications and

is indicative of potential utility for other applications based on near-field enhancement of

light intensity. While the morphology dependence of dielectric sensitivity has been well

studied in noble metal nanoparticles, less investigated is the sensitivity of degenerately

doped metal oxide nanocrystals, whose plasmon resonances lie in the near- to mid-

infrared. Here, we report the dielectric sensitivity of fluorine and tin co-doped indium

oxide nanocubes, its dependence on their sharp faceting that gives rise to multiple

plasmonic modes, and on their tin-dopant concentration. We find that the plasmon

mode associated with the nanocube corners is the most sensitive and that raising dopant

concentration increases dielectric sensitivity. Comparing to finite element simulations

that assume a spatially uniform free electron distribution in the nanocubes, we show that the plasmon modes associated with the edges and the faces of the nanocubes

are less sensitive than expected, and that their reduced dielectric sensitivity can be

rationalized by the presence of band bending and a resulting surface depletion layer.

Interestingly, simulations suggest that Fermi level pinning occurs predominantly on the

cube faces, reshaping the free electron volume so that the depletion layer effectively

insulates the faces and edges from the surrounding environment, while the corner mode

remains sensitive.


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