Probing nanoparticle substrate interactions with synchrotron infrared nanospectroscopy: Coupling gold nanorod Fabry-Pérot resonances with SiO2 and h−BN phonons

Abstract

Spectroscopic interrogation of materials in the midinfrared with nanometer spatial resolution is inherently difficult due to the long wavelengths involved, reduced detector efficiencies, and limited availability of spectrally bright, coherent light sources. Technological advances are driving techniques that overcome these challenges, enabling material characterization in this relatively unexplored spectral regime. Synchrotron infrared nanospectroscopy (SINS) is an imaging technique that provides local sample information of nanoscale target specimens in an experimental energy window between 330 and 5000 cm −1 . Using SINS, we analyzed a series of individual gold nanorods patterned on a SiO 2 substrate and on a flake of hexagonal boron nitride. The SINS spectra reveal interactions between the nanorod photonic Fabry-Pérot resonances and the surface phonon polaritons of each substrate, which are characterized as avoided crossings. A coupled oscillator model of the hybrid system provides a deeper understanding of the coupling and provides a theoretical framework for future exploration.

Near-field enhancement of optical second harmonic generation in hybrid gold–lithium niobate nanostructures

“…Splitting is readily observed in strongly-coupled NLO polariton systems 46 , such that weak interactions between the Au NPs and microsphere are expected. The theory is in good agreement with this observation, as the weak coupling condition 47 , 48 is satisfied for all r 0 . The equations of motion of the LiNbO 3 Mie modes can, thus, be solved perturbatively to capture the effects of these exchanges on the power radiated from the microsphere.…”

Localizing Low-Grade Heat Using Hybrid Photonic-Phononic Materials

“…Figure a displays an SEM image of the gold nanowire structures which support thermally active FP modes that can be tuned throughout the IR by changing the nanowire length. − The nanowires were prepared on a silicon nitride (SiN) membrane that was subjected to Ohmic heating (Figure b) while the STEM electron beam was used for spectroscopic characterization (Figure c). A detailed description of the nanowire fabrication and STEM characterization can be found in the Supporting Information (SI).…”

“…The optical response of a material is fully captured by its induced Green’s function and its closely related local density of states (LDOS), − where the LDOS measures the availability of electromagnetic modes at a particular point in space per unit frequency . The spatial and spectral characteristics of each mode can be dramatically altered when coupled to their local environment, such as a neighboring nanostructure, ,, an optical cavity, , or an underlying substrate. ,, The thermally dressed Stokes Γ EEL (ω) and anti-Stokes Γ EEG (ω) scattering signals are related to the spontaneous Stokes scattering Γ EEL 0 (ω) at T = 0 K by normalΓ normalE normalE normalL ( ω ) = [ n false( ω false) + 1 ] normalΓ normalE normalE normalL 0 ( ω ) normalΓ normalE normalE normalG ( ω ) = n ( ω ) normalΓ normalE normalE normalL 0 ( ω ) via the Bose–Einstein statistical factor n (ω)=[exp(ℏω/ kT ) – 1] −1 . , The ratio of the EEG and EEL signals at a common temperature yields the Boltzmann distribution, Γ EEG /Γ EEL = exp(− ℏ ω/ kT ), illustrating that the gain and loss processes obey the principle of detailed balance when the STEM electron probes the system in a state of static thermal equilibrium. This statistical relation between the thermally assisted EEG and EEL observables has been recently employed for performing high-resolution thermometry measurements, , allowing for a mapping of nanoscale temperature distributions.…”

“…49 The spatial and spectral characteristics of each mode can be dramatically altered when coupled to their local environment, 50 such as a neighboring nanostructure, 32,51,52 an optical cavity, 53,54 or an underlying substrate. 17,38,55 The thermally dressed Stokes Γ EEL (ω) and anti-Stokes Γ EEG (ω) scattering signals are related to the spontaneous Stokes scattering Γ EEL 0 (ω) at T = 0 K by…”