Journal: Nature Communications

Article Title: Light-induced symmetry breaking for enhancing second-harmonic generation from an ultrathin plasmonic nanocavity

doi: 10.1038/s41467-021-24408-x

Figure Lengend Snippet: a Schematic of a gold particle-on-film nanocavity construct. b Illustration of the SHG enhancement mechanism in plasmonic nanostructures: breaking structural symmetry allows SH coupling to a bright mode of the nanostructure and acts as a switch for SH emission. c Schematic of a CTAB-coated gold nanoparticle (AuNP) coupled to a gold thin film on a silica substrate, equivalent to an extremely asymmetric virtual nanoparticle dimer (VND) in analogy to a symmetric real nanoparticle dimer (RND) made of two identical gold nanospheres as indicated in the inserts in ( e ). An AuNP diameter is ~100 nm and a CTAB shell thickness is ~1 nm. d Calculated near-field intensity distribution in the nano-construct in ( c ) at a plasmonic resonance wavelength of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$850\,{\rm{nm}}$$\end{document} 850 nm for the electric field perpendicular to the film. e Dark-field scattering spectra of a gold VND (red) and an RND (gray) both with the same geometric parameters as in ( c ). Insets schematically illustrate the coupled dipole modes in the VND and RND structures corresponding to their respective resonance peaks.

Article Snippet: Gold colloidal nanoparticles with a nominal diameter \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$100\pm 8\;{\rm{nm}}$$\end{document} 100 ± 8 nm (Nanoseedz Inc., Hong Kong) are rinsed and diluted in deionized water to reach a relatively low concentration, after which a droplet of the as-prepared nanoparticles is directly cast onto the previously prepared Au-silica substrate and left dry in air.

Techniques: Construct

Journal: Nature Communications

Article Title: Light-induced symmetry breaking for enhancing second-harmonic generation from an ultrathin plasmonic nanocavity

doi: 10.1038/s41467-021-24408-x

Figure Lengend Snippet: a – c Schematics of the SH origin in the nanodimers with varying degrees of structural asymmetry defined by the particle size ratio, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\delta ={r}_{2}/{r}_{1}$$\end{document} δ = r 2 / r 1 . Red thick arrows indicate the dipolar response to the driving field oriented along the nanogap, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${E}_{\perp }$$\end{document} E ⊥ , with the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\omega$$\end{document} ω -hot-spot forming between the nanoparticles for boosting the nonlinear source. Purple arrows represent the induced \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2\omega$$\end{document} 2 ω dipoles responsible for the far-field SH radiation. d – f Simulated near-field polarization distributions, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${P}_{z,\omega }$$\end{document} P z , ω , at the fundamental wavelength of 850 nm for the structures in ( a )–( c ) with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${r}_{1}=100$$\end{document} r 1 = 100 nm and a gap \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$g=1$$\end{document} g = 1 nm. Scale bar in ( d ) is 2 nm. g – i Calculated near-field polarization distributions, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${P}_{z,2\omega }^{0}$$\end{document} P z , 2 ω 0 , at the SH wavelength induced by the respective fundamental fields (Eq. )), which are significant only at the interface of the centrosymmetric metal. j – l SH polarization distributions resulting from the non-resonant plasmonic coupling of the surface nonlinear sources in ( g )–( i ) to the nanodimers. Note that spatial nonlocality and quantum tunneling are not considered in the electrodynamic calculations since they only begin to emerge in narrower metal nanogaps ( \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$<{\;}1\;{\rm{nm}}$$\end{document} < 1 nm ) , .

Article Snippet: Gold colloidal nanoparticles with a nominal diameter \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$100\pm 8\;{\rm{nm}}$$\end{document} 100 ± 8 nm (Nanoseedz Inc., Hong Kong) are rinsed and diluted in deionized water to reach a relatively low concentration, after which a droplet of the as-prepared nanoparticles is directly cast onto the previously prepared Au-silica substrate and left dry in air.

Techniques:

Journal: Nature Communications

Article Title: Light-induced symmetry breaking for enhancing second-harmonic generation from an ultrathin plasmonic nanocavity

doi: 10.1038/s41467-021-24408-x

Figure Lengend Snippet: a Dark-field image of two separate areas containing gold nanospheres dispersed on silica and gold films, respectively. On a silica substrate, the bright yellow spots correspond to the RND structures (with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\delta$$\end{document} δ typically ranging from 1.0 to 1.26 as confirmed by the AFM imaging), while the green spots correspond to gold nanosphere monomers. On a gold substrate, 5 VNDs appear as green spots. Inset shows the SEM micrograph of a single VND. The scale bar is 50 nm. b Calculated intensity distributions for the three field components of a highly focused laser beam at the focal plane of a 100× objective (numerical aperture 0.95). The incident beam is polarized along the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$x$$\end{document} x direction and has a wavelength of 850 nm, corresponding to the SHG experimental conditions. c , d SHG confocal images of RNDs (left) and VNDs (right) under off- (( c ), 980 nm) and on-resonance (( d ), 850 nm) fs-laser excitation. The time duration of the laser beam dwelling at each pixel is 18 μs. The double-headed red arrows indicate the polarization direction of the fundamental light. Insets in ( c ) show the images for the RNDs and VNDs scanned with higher resolution and longer pixel dwelling time (72 μs). The color bars indicate the SH intensity in photon counts per μs. Only several RNDs are visible in the SHG images with the axes oriented along with the fundamental light polarization (see Supplementary Note ). Scale bar in ( a ), ( c ) is 5 μm.

Article Snippet: Gold colloidal nanoparticles with a nominal diameter \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$100\pm 8\;{\rm{nm}}$$\end{document} 100 ± 8 nm (Nanoseedz Inc., Hong Kong) are rinsed and diluted in deionized water to reach a relatively low concentration, after which a droplet of the as-prepared nanoparticles is directly cast onto the previously prepared Au-silica substrate and left dry in air.

Techniques: Imaging

Journal: Nature Communications

Article Title: Light-induced symmetry breaking for enhancing second-harmonic generation from an ultrathin plasmonic nanocavity

doi: 10.1038/s41467-021-24408-x

Figure Lengend Snippet: a , b Emission spectra of the VND ( a ) and the RND ( b ) labeled by solid squares in Fig. . The solid lines are fittings to the SHG (blue) and TPL (green and red) spectra, respectively. The two TPL peaks in ( b ) are related to two resonances observed in the scattering spectrum (Fig. ). c Calculated SHG radiation pattern of a single VND (blue) and a comparison to the SHG radiation pattern of a horizontal electric dipole above a silica substrate, emulating an RND (red). d Measured (blue dots) and simulated (blue line) polar plots of the polarization of the SHG light from an individual VND. The red curve represents the calculated SHG polarization orientation for an RND emulated with an electric dipole. The measured pattern is slightly stretched along \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$x$$\end{document} x -axis due to the polarization response of the experimental setup. e , f Comparison between the SHG confocal images of the VND scanned using linearly ( e ) and circularly ( f ) polarized fundamental light. Insets show the calculated driving longitudinal field | E z | 4 in the focal plane. Scale bar in ( e ), ( f ) is 1 μm.

Article Snippet: Gold colloidal nanoparticles with a nominal diameter \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$100\pm 8\;{\rm{nm}}$$\end{document} 100 ± 8 nm (Nanoseedz Inc., Hong Kong) are rinsed and diluted in deionized water to reach a relatively low concentration, after which a droplet of the as-prepared nanoparticles is directly cast onto the previously prepared Au-silica substrate and left dry in air.

Techniques: Labeling, Comparison