Direct observation of narrow mid-infrared plasmon linewidths of single metal oxide nanocrystals

Abstract

Infrared-responsive doped metal oxide nanocrystals are an emerging class of plasmonic materials whose localized surface plasmon resonances (LSPR) can be resonant with molecular vibrations. This presents a distinctive opportunity to manipulate light–matter interactions to redirect chemical or spectroscopic outcomes through the strong local electric fields they generate. Here we report a technique for measuring single nanocrystal absorption spectra of doped metal oxide nanocrystals, revealing significant spectral inhomogeneity in their mid-infrared LSPRs. Our analysis suggests dopant incorporation is heterogeneous beyond expectation based on a statistical distribution of dopants. The broad ensemble linewidths typically observed in these materials result primarily from sample heterogeneity and not from strong electronic damping associated with lossy plasmonic materials. In fact, single nanocrystal spectra reveal linewidths as narrow as 600 cm−1 in aluminium-doped zinc oxide, a value less than half the ensemble linewidth and markedly less than homogeneous linewidths of gold nanospheres.

Probing Polaritons in 2D Materials with Synchrotron Infrared Nanospectroscopy

“…The extinction spectrum of individual particles was, then, clearly identified (Figure c,d). These nanoparticles are, so far, one of the smallest objects from which SINS spectra were obtained . Spectra taken from the same nanoparticle were reproducible and presented a blueshift relative to the far field, which is an expected feature from tip‐sample interaction.…”

“…Figure a,b respectively shows AZO and ITO nanoparticles with lateral sizes of a few tens of nanometers . They clearly show size and shape heterogeneities, which may in principle affect their plasmonic properties.…”

“…e) SINS (solid) and far‐field (dashed) spectra of AZO and ITO nanoparticles. Adapted under the terms of the Creative Commons CC BY 4.0 license . Copyright 2016, Springer Nature.…”

“…To probe individual AZO and ITO nanoparticles, Johns et al used SINS. Synthesized nanoparticles were spin coated on a gold substrate and the substrate proximity with the conductive AFM tip (<25 nm apex) created a near‐field hot spot for the incident synchrotron radiation, which lead to the increased overlap between radiation and nanoparticle.…”

Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals

“…To extend the versatility of doping and tunability of the plasmonic band, Murray and co-workers reported cationanion co-doping in the form of F-In co-doped CdO (FICO) nanocrystals. [56] Theb road LSPR of the ensemble mainly arises from the heterogeneity of dopant incorporation in different nanocrystals present in the ensemble. Particularly,s uch ac ation-anion co-doping strategy is useful for achieving LSPR at lower wavelengths.…”