Imaging Infrared Plasmon Hybridization in Doped Semiconductor Nanocrystal Dimers

Abstract

Carrier-doped semiconductor nanocrystals (NCs) offer strong plasmonic responses at frequencies beyond those accessible by conventional plasmonic nanoparticles. Like their noble metal analogues, these emerging materials can harness free space radiation and confine it to the nanoscale but at resonance frequencies that are natively infrared and spectrally tunable by carrier concentration. In this work we combine monochromated STEM-EELS and theoretical modeling to investigate the capability of colloidal indium tin oxide (ITO) NC pairs to form hybridized plasmon modes, providing an additional route to influence the IR plasmon spectrum. These results demonstrate that ITO NCs may have greater coupling strength than expected, emphasizing their potential for near-field enhancement and resonant energy transfer in the IR region.

Infrared Near-Field Spectroscopy of Gold Nanotriangle Fabry-Pérot Resonances

“…Due to selection rules (see Figure a), odd numbered multipoles are not excited when the impact parameter biases the edge of the NT ( d /2). As expected, the presence of a substrate red-shifts the experimentally measured resonances relative to the simulated values, which were calculated in a background refractive index of unity. For regions inside of the NT (Figure a,b), the EEL probability of certain multipoles (at a fixed energy) exhibits strong spatial variation as a result of the electron beam probing different spatial regions of the FP mode profile.…”

Imaging Vibrational Excitations in the Electron Microscope

“…Material dielectric parameters can then be extracted from experimentally measured EEL spectrum profiles, providing unique tools to perform ellipsometry measurements at the nanoscale. Moreover, using the high energy resolution of low-loss STEM-EELS, we spectrally resolved hybridized plasmon modes in individual 10% doped indium–tin oxide (ITO) nanocrystal dimers (Figure ) and provided an experimental measure of the spatial extent of these hybridized modes . This study shows that doped semiconductors can effectively concentrate IR radiation at the nanoscale, leading to strong near electric-field enhancement factors on par with those associated with noble-metal nanoparticles in the visible spectral region.…”

“…(A) Experimental and (B) simulated EEL spectrum images showing different hybridized modes for 10% doped ITO nanocrystal dimers. Reproduced . Copyright 2021, ACS Publications.…”

Structural Control of Plasmon Resonance in Molecularly Linked Metal Oxide Nanocrystal Gel Assemblies

“…Nanoparticles with a high density of free electrons, including noble metals like gold and silver and degenerately doped colloidal metal oxides such as tin-doped indium oxide (Sn:In 2 O 3 , or ITO) nanocrystals, display strong light–matter interactions due to localized surface plasmon resonance (LSPR). In ITO nanocrystals, the resonance is widely tunable through synthetic control of the size, shape, and aliovalent doping of the inorganic core. − While deriving properties from the individual particles, nanoparticle assemblies also manifest structure-dependent collective behavior, such as LSPR coupling, motivating extensive research on the optical response of nanodimers, small clusters, and extended structures. − In periodic superlattices assembled from plasmonic nanoparticles, tuning of the optical properties has been demonstrated by varying the length of DNA links or the molecular weight of surface-grafted molecules to control nanoparticle spacing. ,− Understanding how their structures control properties has been bolstered by electromagnetic simulations of their periodic unit cells. Disordered assemblies of nanoparticles also exhibit a collective optical response, but they typically lack the precise and reproducible structural control needed to fully rationalize their spectra.…”