Multiresonant Composite Optical Nanoantennas by Out-ofplane Plasmonic Engineering

Transcription

1 Supporting Information for Multiresonant Composite Optical Nanoantennas by Out-ofplane Plasmonic Engineering Junyeob Song and Wei Zhou* Department of Electrical and Computer Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States *

2 Finite-difference Time-domain (FDTD) simulation conditions For numerical optical simulations, we used the 3D finite-difference time-domain (FDTD) method with a commercial software (Lumerical Inc, Canada). A uniform mesh size of 3 nm was used in x, y, and z directions. Optical constants of Ag were selected from the literature. 1 We used Bloch boundary condition in the x and y directions with a periodicity of 400 nm and perfectly matched layer (PML) boundary condition in the z direction. The index of the background in air was 1 and the substrate of glass was 1.5. Incident light is a linear-polarized plane wave propagating perpendicular to the surface. Table S1 summarizes the parameters for the FDTD simulations. Material for the metal Ag Diameter of the nanoantenna 100 nm Background index 1 Insulator index 1.5 Substrate index 1.5 Mesh step size 3 nm Simulation time 300 fs Source wavelength 300~1600 nm Boundary condition (x, y) Bloch Boundary condition (z) PML Table S1. Simulation parameters used to calculate optical properties

3 Far-field optical properties of multiresonant composite nanoantennas with different incident angles. Figure S1. Dependence of multiresonant optical response on the incident angle and the polarization of the excitation light. FDTD-simulated scattering and absorption spectra for a MIMIMIM composite nanoantenna with 3 dielectric layers under (A-B) p-polarized and (C-D) s-polarized plane wave excitations at different incidence angles (0, 10, 20, 30, and 40 ).

4 Mode volume calculation We used FDTD simulations to calculate the electromagnetic mode energy density W and the mode volume V m for a composite nanoantenna. Briefly, we illuminate the plasmonic nanoantenna with a linearly polarized plane wave at the normal incidence angle. The energy density of the simulation system is given by: 2, 3 W(r, ω) = 1 2 ( [ωε(r,ω)] ε ω 0 E(r, ω) 2 + μ 0 H(r, ω) 2 ), where ε(r, ω) is the permittivity at position r. To correctly account for the negative permittivity and dispersive properties of silver, we use the term [ωε(r,ω)] for the electrical energy ω density in the metal. Since ε(r, ω) of metal is a complex number, W(r, ω) is also complex in the metal. We calculated the effective mode volume V m by integrating the energy density over the whole simulation volume including the plasmonic nanostructure, and normalizing it to the maximum value of W(r, ω) at each ω, which always occurs at the metal-dielectric interface with a real value by taking the optical constant of the dielectric medium: V m (ω) = W(r,ω)d3 r max [W(r,ω)] (S1). (S2) Since W(r, ω) is complex, V m (ω) also include real part Re(V m ) associated with the energy density, and the imaginary part Im(V m ) associated with the energy dissipation. Commonly, we just account for the real part Re(V m ) and the imaginary part Im(V m ) is neglected. 2 By normalizing with the cube of free space wavelength 3, we can calculate the unit less normalized mode volume V m / 3. Fabrication method of multiresonant composite nanoantennas. For fabrication of composite nanoantenna arrays on glass, we used a polydimethylsiloxane (PDMS) photomask replicated from a silicon master patterned with array of nanopillars. 4 The mask was in contact with a positive-tone photoresist (Microposit S1805) on a silicon substrate during UV exposure process (SUSS MA6). Photoresist pillar posts were developed (Mircroposit 351) and a thin Cr layer was deposited using e-beam evaporation (PVD250, Kurt J. Lesker) followed by sonication with acetone to create Cr hole arrays (periodicity = 400 nm). Using reactive ion etching (RIE-1C from Samco) with O 2 and CF 4 mixtures, Si was etched through Cr hole arrays. A 150 nm-thick gold metal film was deposited on the hole-array using e-beam evaporation. This gold nanoholearray was lifted-off by using Cr etchant (CHROMIUM ETCHANT 1020 from Transene) and transferred onto a glass substrate. A series of deposition was performed to stack alternating Ag-SiO 2 layers and to create multilayered composite nanodisks in Au nanoholes. Finally, we can expose composite nanoantenna arrays on the substrate by peeling off gold nanohole arrays using a scotch tape.

5 References 1. Johnson, P. B.; Christy, R. W. Phys Rev B 1972, 6, (12), Chikkaraddy, R.; de Nijs, B.; Benz, F.; Barrow, S. J.; Scherman, O. A.; Rosta, E.; Demetriadou, A.; Fox, P.; Hess, O.; Baumberg, J. J. Nature 2016, 535, (7610), Sauvan, C.; Hugonin, J. P.; Maksymov, I. S.; Lalanne, P. Phys Rev Lett 2013, 110, (23). 4. Henzie, J.; Lee, M. H.; Odom, T. W. Nat Nanotechnol 2007, 2, (9),