Strong-Field-Enhanced Spectroscopy in Silicon. Nanoparticle Electric and Magnetic Dipole. Resonance near a Metal Surface

Transcription

1 Supplementary Information Strong-Field-Enhanced Spectroscopy in Silicon Nanoparticle Electric and Magnetic Dipole Resonance near a Metal Surface Zengli Huang, Jianfeng Wang, *, Zhenghui Liu, Gengzhao Xu, Yingmin Fan, Haijian Zhong, Bing Cao,, Chinhua Wang,, and Ke Xu *, Suzhou Institute of Nano-tech and Nano-bionics, CAS, Suzhou , People s Republic of China College of Physics, Optoelectronics and Energy and Collaborative Innovation Center of Suzhou Nano Science and Technology, and Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou , People s Republic of China *jfwang2006@sinano.ac.cn *kxu2006@sinano.ac.cn

2 Methods Numerical calculations. The optical response of the hybrid nanoparticle-metal was modeled by solving 3D Maxwell equations with finite-difference time-domain simulations (FDTD). The permittivity of Ag was described by the Drude model:ε m = ε b E p 2 [E(E iγ)] 1, ε b = 5, E p = 9.5 ev, γ = 0.04 ev. Refractive index for Si (ε c ) and SiO2 (ε d ) are taken from Palik. The extinction, absorption, scattering cross-section spectra and field distributions have been calculated using FDTD calculations. A commercial software package was used to perform the FDTD calculations. A simulation box size of um with perfectly matched layer conditions on every boundary was used. The light source was a broadband ( nm) plane wave, with normal incidence to the substrate. The mesh grid was set to the automatic non-uniform meshes, with a 4 nm refinement mesh around the particle volume and a 0.5 nm refinement mesh over the Ag surface. A total-field scattered-field method was used to directly calculate the scattered and absorption power by means of frequency-domain transmission monitors positioned in the scattered and absorption field region. The extinction power is the sum of the scattered and absorption power. The two-dimensional frequency-domain field monitor cross-cutting the particle in its center and the gap was used to calculate the electric field intensity distribution.

3 Figure S1. Electric field vectors distributions of ED and MD resonance modes for a Si sphere in air. For these graphics, the radius of the Si sphere is 65 nm. The size of each map is 250 nm 250 nm. White dashed lines indicate particle positions. The MD response originates from the circular displacement current excited inside the particle by incident light.

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5 Figure S2. The electric field vectors distributions of Fst mode and the two separated resonance modes (indicated by the blue and red arrows in Figure 2a) of a Si sphere on Ag substrate with the SiO2 gap size g of 5-65 nm. As we see, the Fst resonance mode shows a hybrid ED mode characteristics. The large electric vectors around the Si/Ag interface would form a current loop around the strongly localized magnetic field in the gap (as shown in Figure 1f). With the gap size g increasing, the strong Fst mode gradually evolves into two separated resonance modes properties. One mode is blueshifted (indicated by the blue circles in the inset), which gradually becomes a suppressed ED mode. The other is the redshifted (indicated by red circles in the inset), which gradually becomes an enhanced MD mode.

6 Figure S3. The dependence of the peak wavelength (a) and scattering intensity (b) of the Fst resonance mode on the Si particle size obtained for a Si nanoparticle on four different metal substrates. For these graphics, the Si nanoparticle size is r=95 nm and the gap size is g=1 nm.

7 Figure S4. Calculated reflection spectra of these four different metal substrates for the wavelength range under study.

8 Figure S5. The dispersion curve of imaginary part of refractive index of the four different metal materials.