1. Plasmonics of Normal and Inverted Core-Shell Nanostructures
Sudip Kumar Pal1, Sujit Kumar Ghosh1
1. Department of Chemistry, Assam University, Silchar , India
Introduction: Our work focuses on the synthesis of normal and inverted gold-silver core-shell nanostructures following the method of Pal group. The normal and inverted core-shell nanostructures so formed have been characterized by transmission electron microscopic and UV-visible spectroscopic techniques. We have simulated the electric field generated using finite difference time domain (FDTD) and discrete dipole approximation (DDA) method and validated the experimental results with theoretical calculations.
Figure 4. Absorption spectra of different thickness of Aucore-Agshell
A two dimensional layered motif has been considered to model the plane wave interaction with the hybrid layered spheroid morphology. The electromagnetic coupling is shown through the surface plot as given in Figure 5. b c d a
a = 10 µL, 10 mM HAuCl4 solution
b = 20 µL, 10 mM HAuCl4 solution
c = 30 µL , 10 mM HAuCl4 solution
d = 40 µL, 10 mM HAuCl4 solution
a = 10 µL , 10 mM AgNO3 solution
b = 20 µL, 10 mM AgNO3 solution
c = 30 µL, 10 mM AgNO3 solution
d = 40 µL, 10 mM AgNO3 solution
Figure 5. FEM of Aucore-Agshell
FEM Simulation of Normal and Inverted Core Shell of Different Thickness: Finite difference time domain (FDTD) calculations of the nanostructures signify their respective monopolar and multipolar nature. Figure 6 shows the results obtained for a plane wave interacting with a fixed size core with different shell thickness.
Figure 1. Synthesis of normal and inverted core-shell nanostructures
Computational Methods: Electromagnetic field generated on the surface due to the light-matter interaction has been modeled with the RF module, setting corresponding incident wavelength as recorded from the absorption spectra.
Figure 6. FDTD simulation of core-shell of different shell thickness
Results: As the amount of silver nitrate solution added increases, the peak of silver become more prominent with increasing thickness for Aucore-Agshell, but reverse phenomenon is observed for Agcore-Aushell nanostructures.
DDA Simulation of Normal and Inverted Core- Shell of Different Thickness: The extinction profile shows that as the thickness increases, the peak shifted to the higher wavelength for both normal and inverted core-shell nanostructures.
Figure 3. Absorption spectra of different shell thickness of Aucore-Agshell
Figure 4. Absorption spectra of different shell thickness of Agcore-Aushell
Figure 7. DDA simulation of different shell thickness of Aucore-Agshell
Figure 8. DDA simulation of different shell thickness of Agcore-Aushell
Conclusions: We have successfully introduced FEM and DDA simulations to account for different thickness of normal and inverted core-shell structures.
Transmission Electron Micrographs of Normal & Inverted Core-Shell Nanostructures: Core-shell structure shows a more dense interior core of gold surrounded by a thinner shell and inverted core-shell structure shows a less dense interior core of silver surrounded by a thicker shell.
References:
Ghosh, S.K.; Pal, T. Chem. Rev. 2007, 107, 4797.