Thermoplasmonics under optically coupled regime: A Numerical Study of Dimers, Nanolenses, and Switchable Clusters

TL;DR

This work demonstrates that heat generation in plasmonic nanostructures can be precisely controlled through optical coupling by engineering gap distances, polarization, and hierarchical geometries. It develops a rigorous computational pipeline combining EM response via boundary-element methods with Laplace Matrix Inversion–based temperature mapping, plus effective-medium treatments for complex clusters. Key findings include size- and geometry-dependent heating in single nanoparticles, polarization- and gap-tunable heating in dimers, nano-heat-lensing in silver nanolenses, and large, switchable heat differences in nanoparticle clusters, all with the insight that heat can serve as a design element rather than a parasitic byproduct. The framework enables targeted, dynamic thermal management at the nanoscale with potential impact on catalysis, health, and active photonic devices, particularly when exploiting pulsed illumination to maintain sharp thermal gradients on nanosecond timescales.

Abstract

The management of thermal effects in plasmonic nanostructures is frequently viewed as a detrimental waste rather than a useful, controllable entity. We show that optical coupling of plasmonic nanoparticles enables precise spatiotemporal control over nanoscale heating. Through numerical investigation of experimentally-achievable systems from individual nanoparticles and dimers to nanolenses and switchable clusters, we demonstrate how plasmon hybridization and near-field coupling dictate the magnitude and spatial distribution of temperature. Our results highlight the critical role of polarization and gap distance in tuning the thermal output of dimers, the ability of a trimer nanolens to focus heat into a sub-diffraction volume, and the pronounced thermal difference in a switchable nanoparticle cluster. This work establishes a framework for designing advanced thermoplasmonic systems where heat is not merely a detriment, but a dynamically controllable element for applications in catalysis, health, or active photonic devices.

Figures (4)

• Figure 1: Thermoplasmonic response of an individual Au nanoparticle: diameter dependence. (a) Maximum absorption wavelength ($\lambda_{abs}$) as a function of nanoparticle diameter. The shaded regions indicate the dominant plasmonic modes: dipole (red), quadrupole (green), and octupole (black). (b) Temperature increase ($\delta$T) of the nanoparticle at $\lambda_{abs}$ as a function of its diameter (excitation irradiance: $10^9$ W/m$^2$). (c, d) Extinction, absorption, and scattering cross-section spectra for nanoparticles with diameters of 50 nm (c) and 140 nm (d). Insets show the corresponding surface charge distribution and electric field maps in the plane of vibration (defined by the wave vector and E-field polarization) at $\lambda_{abs}$. (e, f) Heat power density (q) maps in the plane of vibration for the 50 nm (e) and 140 nm (f) nanoparticles. (g, h) Steady-state temperature profiles for the 50 nm (g) and 140 nm (h) nanoparticles.
• Figure 2: Thermoplasmonic response of Au nanoparticle dimers: gap distance and polarization dependence. (a) Maximum absorption wavelength as a function of interparticle gap for three E-field polarizations: transverse to the dimer axis (pol. 1), longitudinal along the dimer axis (pol. 2), and at 90$^0$ orientation to the axis (pol. 3). The inset shows an illustrative TEM micrograph of dimers enabled by the DNA origami technique (reproduced from Ref. Xin2019; Copyright 2019 American Chemical Society). (b) Temperature increase of each nanoparticle ($\delta$T$_1$, solid marks, and $\delta$T$_2$, hollow marks) at $\lambda_{abs}$ as a function of the gap for each polarization (as indicated in (a)). $\delta T^*=Q(1+a/d)/4\pi\kappa_ma$ (dashed line) is an approximation of collective temperature of each nanoparticle with radius $a$ and gap $d$ delivering equal heat power $Q$ (calculated for a single nanoparticle, see Ref. Baffou_2017). Excitation irradiance: $10^9$ W/m$^2$. (c, d) Steady-state temperature profiles for dimers with gaps of 10 nm (c) and 200 nm (d).
• Figure 3: Thermoplasmonic response of Ag nanoparticle nanolens: size ratio and polarization dependence. (a) Experimental TEM micrograph of trimer nanolenses (reproduced with permission from Ref. Lloyd2017; Copyright 2017 American Chemical Society). (b) Scheme of the self-similar nanolens, where D$_1$, D$_2$, and D$_3$ are the nanoparticle diameters, g$_{12}$ and g$_{23}$ are the gap between D$_1$-D$_2$ and D$_2$-D$_3$, respectively, and $\kappa$ is the self-similar factor. All the results are for fixed D$_3 = 8$ nm and g$_{23} = 1$ nm. (c, d) Extinction, absorption, and scattering cross-section spectra of a nanolens with $\kappa=2.5$ under transverse (c) and longitudinal (d) excitations. Insets: Surface charge distributions at the three principal absorption resonances $\lambda_{abs,i}$ ($i=1,2,3$, as indicated by the vertical dashed lines). (e, f) Evolution of the resonance absorption wavelengths with the self-similar factor $\kappa$ for transverse (e) and longitudinal (f) polarizations. (g, h) Temperature increase of individual nanoparticles ($\delta$T$_1$, $\delta$T$_2$, and $\delta$T$_3$) at $\lambda_{abs,i}$ as a function of $\kappa$, for both transverse (g) and longitudinal (h) polarizations. Excitation irradiance: $10^9$ W/m$^2$. (i, j) Steady-state temperature profiles for nanolens with $\kappa=2.5$ at $\lambda_{abs,i}$ under transverse (i) and longitudinal (j) polarizations.
• Figure 4: Thermoplasmonic response of gold nanoparticle clusters confined within a silica shell: aggregated and dispersed states. (a, b) Extinction, absorption, and scattering cross-section spectra for aggregated (a) and dispersed (b) nanoparticle arrangements. Each cluster consists of seven Au nanoparticles on average within a silica shell. The spectra result from averaging over 15 distinct random nanoparticle positions for each state. Insets show experimental TEM micrographs of Au nanoparticle clusters in the two states (adapted from Ref. Snch2018; reproduced with permission). (c, d) Increase of temperature of individual nanoparticles for representative aggregated (c) and dispersed (d) configurations, excited at $\lambda_{agg}=632$ nm. Excitation irradiance: $10^9$ W/m$^2$. (e, f) Steady-state temperature profiles (xz-plane at y = 0 nm) for the aggregated (e) and dispersed (f) states at $\lambda_{agg}=632$ nm. Dashed black line indicates the shell inner surface