Supplementary material of “Controllable plasmonic antennas with ultra narrow
bandwidth based on silver nano-flags”
Xiao-Yang Zhang,1,4 Tong Zhang,1,4, a) A. Hu,2 Yuan-Jun Song,1 and W. W. Duley3
1
School of Electronic Science and Engineering, Southeast University, and Key Laboratory of
Micro-Inertial Instrument and Advanced Navigation Technology, Ministry of Education, Nanjing,
210096, People’s Republic of China
2
Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University
Avenue West, Waterloo, ON, N2L 3G1, Canada
3
Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo,
ON, N2L 3G1, Canada
4
Suzhou Key Laboratory of Metal Nano-Optoelectronic Technology, Suzhou Research Institute of
Southeast University, Suzhou, 215123, People’s Republic of China
Corresponding author:
a) E-mail: tzhang@seu.edu.cn
1
Three-dimensional finite element method was used to simulate the optical properties of the silver
nanostructures accurately. For short silver nano-flags, short nanowire (L = 300 nm) and the nanoplates,
the numerical model is illustrated in Figure S1. The nanostructures were placed in the center of a
rectangle with side widths of several micrometers. As the size of the short nano-flags is only 300 nm,
they can be used as nano-antennas to trap and enhance the intensity of light with certain wavelengths
significantly in nanoscale. To investigate the polarization-dependent spectral signature of the short
nano-flag under the excitation of polarized incident light with controllable incident angle, the top
boundary condition was set to be the input light source with rectangular wave (transverse magnetic
(TM) 01 mode). To realize a certain incident polarization direction in the simulation, we kept the
original polarization angle of the incident light unchanged and rotated the nanostructure according to
the center of the input boundary along z axis. Scattering boundary condition1 was used at the other
outer boundaries. We found that the light excitation processes can be efficiently simulated when TM 01
mode was used as the source boundary. The validity of our numerical model are confirmed as the
simulation results shown in Fig 1 (b) and (c) are well matched with the experimental and theoretical
results reported by other researchers.2-5
2
Figure S1. Illustration of the simulation cell and boundary conditions of the short nano-flag seen from
the views of x-y plane (a) and y-z plane (b), respectively. The light source boundary was labeled in red
color. The dashed lines illustrate the positions of light the source boundary and the integrated nanoplate,
respectively.
For long silver nano-flags and long nanowires (L = 2 µm), the numerical model is illustrated in
Figure S2. The nanostructures were placed in a rectangle with side width of ~ 2µm and a length of ~
5µm. To simulate the end excitation strategy of the long nano-flag and long nanowires as shown in the
inset of Figure 2 (b), we set a light boundary as illustrated in Figure S2 (a) and (b). A square with a side
width of 300 nm labeled in red show the position of the input light source with rectangular wave
(transverse magnetic 01 mode). The end excitation strategy was used because such long nano-flags can
3
be used as resonators or switches controlled from the far-end.2 From Figure S2 (b) one can see the
distance between the plane of the light source boundary and the nano-flag is 300 nm in z direction.
Scattering boundary condition was used at the other area of the outer boundary of the rectangle.
Non-uniform meshes are adopted to reduce the memory requirement and ensure high accuracy. Finer
meshes with a maximum element size of ~1 nm – 2 nm, and an element growth rate of ~1.05 – 1.1
were used in the sub-domains such as the end of the nanowire and the tip of the nanoplate shown in
Figures S2 (c) and (d). Meshes with a maximum element size of 8 nm – 15 nm, and an element growth
rate of ~1.1 – 1.15 were used in the other domains of the nanostructures, such as the junction of the
nanowire and the nanoplate shown in Figure S2 (e).
4
Figure S2. Illustration of the simulation cell and boundary conditions of the long nano-flag seen from
the views of x-y plane (a) and y-z plane (b), respectively. The light source boundary was labeled in red
color. The dashed lines illustrate the positions of light the source boundary and the integrated nanoplate,
respectively. (c) - (e) show the details of the mesh grids of the nano-flag at the end of the nanowire, the
tip of the nanoplate, and the junction of the nanowire and the nanoplate from the view of x-y plane,
respectively.
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