8 Modulations of Electronic States in Plasmonic Strong Coupling …
139
Fig. 8.4 a A SEM image of the typical Au nanochain structure. b Extinction spectra of Au
nanochains with a different chain length; 601, 636, 672, 707, 742, 778, 813, 848, 884, 919, 954,
990, 1025, 1061 nm from the bottom. c Absorption spectrum of the PVAc film deposited on a
silicon substrate in the mid-infrared wavelength region. d Extinction spectra of PVAc-coated Au
nanochains with a different chain length; 601, 636, 672, 707, 742, 778, 813, 848, 884, 919, 954,
990, 1025, 1061 nm from the bottom
Figure 8.4c indicates absorption spectrum of PVAc film deposited on a silicon
substrate in the mid-infrared wavelength region. A distinct C=O stretching vibrational mode can be seen at 1740 cm
−1 while CH 3 and C–O–C asymmetry stretching
vibrational mode near the Si–O–Si asymmetry stretching vibrational mode was
also observed at 1370 cm
−1 and 1240 cm
−1 , respectively. Importantly, extinction
spectra of PVAc-coated Au nanochains as shown in Fig. 8.4d is modulated around
the wavenumbers of 1740 and 1240 cm
−1 . Here, we focus on the spectrum dip at
1740 cm
−1 because the spectral dip cannot be seen in Fig. 8.4b. It is noteworthy that
there appear to be two peaks across 1740 cm
−1 or there appears to be a spectral dip at
1740 cm
−1 . When guidelines are added to the two peaks in Fig. 8.4d, it can be seen
that the two guidelines show an anti-crossing behavior. Figure 8.5 shows a dispersion curve which was made by plotting the two peak energies of the spectrum in
Fig. 8.4d to the bare LSPR peak wavenumber (Fig. 8.4b). An anti-crossing behavior
which is a characteristic of strong coupling can be seen. By fitting the plot using a
harmonic oscillator model, the vacuum Rabi splitting energy ( R ) can be estimated
to be 12 meV, which is slightly smaller than that obtained by using a Fabry–Pérot
microcavity mode in the former study [9]. Almost similar results measured by using
microcavities as an optical mode were obtained even by using the LSPR modes.
139
Fig. 8.4 a A SEM image of the typical Au nanochain structure. b Extinction spectra of Au
nanochains with a different chain length; 601, 636, 672, 707, 742, 778, 813, 848, 884, 919, 954,
990, 1025, 1061 nm from the bottom. c Absorption spectrum of the PVAc film deposited on a
silicon substrate in the mid-infrared wavelength region. d Extinction spectra of PVAc-coated Au
nanochains with a different chain length; 601, 636, 672, 707, 742, 778, 813, 848, 884, 919, 954,
990, 1025, 1061 nm from the bottom
Figure 8.4c indicates absorption spectrum of PVAc film deposited on a silicon
substrate in the mid-infrared wavelength region. A distinct C=O stretching vibrational mode can be seen at 1740 cm
−1 while CH 3 and C–O–C asymmetry stretching
vibrational mode near the Si–O–Si asymmetry stretching vibrational mode was
also observed at 1370 cm
−1 and 1240 cm
−1 , respectively. Importantly, extinction
spectra of PVAc-coated Au nanochains as shown in Fig. 8.4d is modulated around
the wavenumbers of 1740 and 1240 cm
−1 . Here, we focus on the spectrum dip at
1740 cm
−1 because the spectral dip cannot be seen in Fig. 8.4b. It is noteworthy that
there appear to be two peaks across 1740 cm
−1 or there appears to be a spectral dip at
1740 cm
−1 . When guidelines are added to the two peaks in Fig. 8.4d, it can be seen
that the two guidelines show an anti-crossing behavior. Figure 8.5 shows a dispersion curve which was made by plotting the two peak energies of the spectrum in
Fig. 8.4d to the bare LSPR peak wavenumber (Fig. 8.4b). An anti-crossing behavior
which is a characteristic of strong coupling can be seen. By fitting the plot using a
harmonic oscillator model, the vacuum Rabi splitting energy ( R ) can be estimated
to be 12 meV, which is slightly smaller than that obtained by using a Fabry–Pérot
microcavity mode in the former study [9]. Almost similar results measured by using
microcavities as an optical mode were obtained even by using the LSPR modes.