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Fabrication of Ion-Shaped Anisotropic Nanoparticles and their Orientational Imaging by Second-Harmonic Generation Microscopy

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ABSTRACT

Ion beam shaping is a novel and powerful tool to engineer nanocomposites with effective three-dimensional (3D) architectures. In particular, this technique offers the possibility to precisely control the size, shape and 3D orientation of metallic nanoparticles at the nanometer scale while keeping the particle volume constant. Here, we use swift heavy ions of xenon for irradiation in order to successfully fabricate nanocomposites consisting of anisotropic gold nanoparticle that are oriented in 3D and embedded in silica matrix. Furthermore, we investigate individual nanorods using a nonlinear optical microscope based on second-harmonic generation (SHG). A tightly focused linearly or radially-polarized laser beam is used to excite nanorods with different orientations. We demonstrate high sensitivity of the SHG response for these polarizations to the orientation of the nanorods. The SHG measurements are in excellent agreement with the results of numerical modeling based on the boundary element method.

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Characterization of vertically oriented (0°) gold NR and NW particles.(a) HAADF cross-sectional image of an isolated Au nanorod (length 100 nm, diameter 14,5 nm, and aspect ratio ) and (b) corresponding high-resolution plasmon field intensity map across the particles obtained by electron energy loss spectroscopy (EELS). Resonant modes are observed at 1.15, 1.65, and 1.91 eV, which correspond to the dipolar as well as the first and second higher-order longitudinal modes. (c) HAADF cross-sectional image of an isolated gold NW (length 224 nm, diameter 8 nm, and aspect ratio 28) and (d) corresponding EELS plasmon map. Resonant modes are observed at 0.73 ± 0.05 eV, 1.17 ± 0.05 eV, 1.45 ± 0.05 eV and 1.64 ± 0.05 eV.
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f2: Characterization of vertically oriented (0°) gold NR and NW particles.(a) HAADF cross-sectional image of an isolated Au nanorod (length 100 nm, diameter 14,5 nm, and aspect ratio ) and (b) corresponding high-resolution plasmon field intensity map across the particles obtained by electron energy loss spectroscopy (EELS). Resonant modes are observed at 1.15, 1.65, and 1.91 eV, which correspond to the dipolar as well as the first and second higher-order longitudinal modes. (c) HAADF cross-sectional image of an isolated gold NW (length 224 nm, diameter 8 nm, and aspect ratio 28) and (d) corresponding EELS plasmon map. Resonant modes are observed at 0.73 ± 0.05 eV, 1.17 ± 0.05 eV, 1.45 ± 0.05 eV and 1.64 ± 0.05 eV.

Mentions: We investigated both NRs and NWs obtained by ion irradiation. Figure 2a and c show HAADF cross-sectional images of single NRs and NWs oriented perpendicular to the sample surface. The experimental plasmon maps obtained by EELS analysis are shown in Fig. 2b and d. As both nanostructures exhibit a high aspect ratio, i.e., ~7 for the NR and ~28 for NW, both dipolar and higher-order longitudinal modes (along the particle long axis) are expected. In fact, these modes arise from Fabry-Pérot-type resonances of cylindrical surface plasmons that propagate along the particle surface and are reflected at both ends of the nanoparticle55. On the other hand, the intensity of the transverse mode is relatively weak due to the small cross section of the nanostructures (<14 nm). For the NRs, three longitudinal LSPR peaks are observed at 1.15 ± 0.05 eV (dipolar mode), 1.65 ± 0.05 eV (first higher-order of longitudinal mode) and 1.91 ± 0.05 eV (second higher-order mode). For the NWs, four LSPR peaks are observed at 0.73 ± 0.05 eV, 1.17 ± 0.05 eV, 1.45 ± 0.05 eV and 1.64 ± 0.05 eV. For both nanostructures the transverse mode is located at 2.30 ± 0.05 eV (not shown in the figure). Note specifically that the dipolar mode of the NRs and the first higher-order mode of the NWs occur at about the same energy. Moreover, this energy matches the fundamental wavelength (1.16 eV) used in our SHG microscopy, which should be beneficial for the SHG response. As the energy of the dipolar mode of the NRs is the closest one to our laser source, its intensity is higher than that of the first higher-order longitudinal mode of the NWs, we choose to analyze only NRs by SHG microscopy.


Fabrication of Ion-Shaped Anisotropic Nanoparticles and their Orientational Imaging by Second-Harmonic Generation Microscopy
Characterization of vertically oriented (0°) gold NR and NW particles.(a) HAADF cross-sectional image of an isolated Au nanorod (length 100 nm, diameter 14,5 nm, and aspect ratio ) and (b) corresponding high-resolution plasmon field intensity map across the particles obtained by electron energy loss spectroscopy (EELS). Resonant modes are observed at 1.15, 1.65, and 1.91 eV, which correspond to the dipolar as well as the first and second higher-order longitudinal modes. (c) HAADF cross-sectional image of an isolated gold NW (length 224 nm, diameter 8 nm, and aspect ratio 28) and (d) corresponding EELS plasmon map. Resonant modes are observed at 0.73 ± 0.05 eV, 1.17 ± 0.05 eV, 1.45 ± 0.05 eV and 1.64 ± 0.05 eV.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121593&req=5

f2: Characterization of vertically oriented (0°) gold NR and NW particles.(a) HAADF cross-sectional image of an isolated Au nanorod (length 100 nm, diameter 14,5 nm, and aspect ratio ) and (b) corresponding high-resolution plasmon field intensity map across the particles obtained by electron energy loss spectroscopy (EELS). Resonant modes are observed at 1.15, 1.65, and 1.91 eV, which correspond to the dipolar as well as the first and second higher-order longitudinal modes. (c) HAADF cross-sectional image of an isolated gold NW (length 224 nm, diameter 8 nm, and aspect ratio 28) and (d) corresponding EELS plasmon map. Resonant modes are observed at 0.73 ± 0.05 eV, 1.17 ± 0.05 eV, 1.45 ± 0.05 eV and 1.64 ± 0.05 eV.
Mentions: We investigated both NRs and NWs obtained by ion irradiation. Figure 2a and c show HAADF cross-sectional images of single NRs and NWs oriented perpendicular to the sample surface. The experimental plasmon maps obtained by EELS analysis are shown in Fig. 2b and d. As both nanostructures exhibit a high aspect ratio, i.e., ~7 for the NR and ~28 for NW, both dipolar and higher-order longitudinal modes (along the particle long axis) are expected. In fact, these modes arise from Fabry-Pérot-type resonances of cylindrical surface plasmons that propagate along the particle surface and are reflected at both ends of the nanoparticle55. On the other hand, the intensity of the transverse mode is relatively weak due to the small cross section of the nanostructures (<14 nm). For the NRs, three longitudinal LSPR peaks are observed at 1.15 ± 0.05 eV (dipolar mode), 1.65 ± 0.05 eV (first higher-order of longitudinal mode) and 1.91 ± 0.05 eV (second higher-order mode). For the NWs, four LSPR peaks are observed at 0.73 ± 0.05 eV, 1.17 ± 0.05 eV, 1.45 ± 0.05 eV and 1.64 ± 0.05 eV. For both nanostructures the transverse mode is located at 2.30 ± 0.05 eV (not shown in the figure). Note specifically that the dipolar mode of the NRs and the first higher-order mode of the NWs occur at about the same energy. Moreover, this energy matches the fundamental wavelength (1.16 eV) used in our SHG microscopy, which should be beneficial for the SHG response. As the energy of the dipolar mode of the NRs is the closest one to our laser source, its intensity is higher than that of the first higher-order longitudinal mode of the NWs, we choose to analyze only NRs by SHG microscopy.

View Article: PubMed Central - PubMed

ABSTRACT

Ion beam shaping is a novel and powerful tool to engineer nanocomposites with effective three-dimensional (3D) architectures. In particular, this technique offers the possibility to precisely control the size, shape and 3D orientation of metallic nanoparticles at the nanometer scale while keeping the particle volume constant. Here, we use swift heavy ions of xenon for irradiation in order to successfully fabricate nanocomposites consisting of anisotropic gold nanoparticle that are oriented in 3D and embedded in silica matrix. Furthermore, we investigate individual nanorods using a nonlinear optical microscope based on second-harmonic generation (SHG). A tightly focused linearly or radially-polarized laser beam is used to excite nanorods with different orientations. We demonstrate high sensitivity of the SHG response for these polarizations to the orientation of the nanorods. The SHG measurements are in excellent agreement with the results of numerical modeling based on the boundary element method.

No MeSH data available.


Related in: MedlinePlus