Supporting information:

Transcription

1 Supporting information: Wavevector-Selective Nonlinear Plasmonic Metasurfaces Kuang-Yu Yang, 1,# Ruggero Verre, 2, # Jérémy Butet, 1,#, * Chen Yan, 1 Tomasz J. Antosiewicz, 2,3 Mikael Käll, 2 and Olivier J. F. Martin. 1 1 Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology Lausanne (EPFL), 1015 Lausanne, Switzerland. 2 Department of Physics, Chalmers University of Technology, Göteborg, Sweden. 3 Centre of New Technologies, University of Warsaw, Banacha 2c, Warsaw, Poland. # These authors contribute equally to this work *Corresponding authors: ruggero.verre@chalmers.se; jeremy.butet@epfl.ch 1

2 Sample fabrication The samples were produced using the colloidal hole mask lithography technique. The samples substrates (cover glass, 0.4mm thickness, Marienfeld, Gmbh) were first cleaned in Acetone and IPA in ultrasonic bath. PMMA A4 950k (Microlithography Chemicals Corp., Germany) was then spun on the sample at 3000 rpm and annealed in an oven at 180 C for 10 minutes for a measured resist thickness of 240 nm. A quick oxygen plasma (50 W for 5 s) rendered the surface hydrophilic and a PDDA-water solution (0.2%) was dispersed on the samples for 30 s and rinsed in deionized water for 10s. Polystyrene beads (Microparticles gmbh, Germany- 100 nm in diameter, 0.05% diluted in deionized water) were subsequently dispersed on the substrate by dropcasting. 1 A 10 nm Au mask was deposited on the sample and the beads removed by tape stripping. The PMMA underneath the Au holed mask was then etched by O 2 plasma, at 50 W at 250 mmtorr for 7 minutes in order to produce a large undercut. Ti (1 nm) and Au with variable thicknesses as indicated in the main text were deposited at glancing angles from 0 to 30. The glancing angle deposition allows the formation of tilted nanopillars and shrinking of the mask induces the tapering of the structure. All samples were annealed at 150 C for 10 minutes prior to characterization and imaged using a SUPRA scanning electron microscope (Zeiss, Germany). Sample characterization in air The samples were characterized in extinction, using a fiber coupled halogen lamp (HL-2000, Ocean Optics) as an illumination source and the light was collected by a fiber coupled spectrometer (BRC711E, B&W Tek). All measurements were normalized using the transmission through a bare glass slide as reference. 2

3 Supporting figures - Linear characterization. Figure S1: Linear optical characterization of the samples studied in Fig. 2 (diameter of the basis = 100 nm and height h = 170 nm). (a) Extinction under normal incidence illumination using a TM polarized light. (b) Extinction as a function of the incidence angle in the (O, x, z) plane. Figure S2: Calculated linear extinction spectra for periodic arrays of tilted gold nanopillars mimicking to those studied in Fig. 2 (base diameter d = 100 nm and height h = 170 nm). The tilt angle ξ varies from 0 and 30. Two modes, associated with longitudinal (λ 750 nm) and transverse (λ 550 nm) oscillations, are observed. 3

4 Figure S3: Tilt angle of the net dipole moment with respect to the substrate normal versus wavelength for normal illumination and different nanopillar tilt angles ξ. Supporting figures - Nonlinear characterization Figure S4: Second harmonic intensity versus pump power demonstrating the second order nonlinearity of the recorded signal. 4

5 Figure S5: Second harmonic intensity versus emission angle for the nanopillar array with h = 130 nm and tilt angle ξ = 30 for an excitation angle of θ = 5. The divergence of the specular second harmonic beam is estimated to 3. Figure S6: Second harmonic emission patterns for single nanopillars embedded in a homogenous medium with a refractive index n = 1.4. The fundamental wavelength is 780 nm. 5

6 Figure S7: Asymmetry parameter ζ, defined as I SHG (-θ) / I SHG (+θ), for tilted gold nanopillars with base diameter d = 100 nm and height h = 170 nm as a function of (a) illumination angle (from experimental data shown in Fig. 3) and (b) as a function of excitation wavelength (from numerical data shown in Fig. 4). In a), the incident wavelength is fixed at 780 nm while in b), the illumination angle giving the highest asymmetry parameter was selected. (c) Asymmetry parameter ζ for tilted gold nanopillars with base diameter d = 100 nm and tilt angle ξ = 30 versus illumination angle (from experimental data shown in Fig. 5) 6

7 Figure S8: Optical properties versus nanopillar height. SEM images (top row), scattering spectra (centre row), and angular dependences of the specular second harmonic intensity (bottom row) for an incident wave in the (O, x, z) plane with a TM polarization (red circles) and a TE polarization (blue crosses). The nanopillar height is (a) 50 nm, (b) 90 nm and (c) 130 nm. The tilt angle is 30 in all cases. For the measurement of the SHG, the wavelength of the incident laser beam is 780 nm. The scale bar in the SEM image corresponds to 500 nm. 7

8 Figure S9: Nonlinear Fourier imaging of a silver mirror References 1. Fredriksson, H.; Alaverdyan, Y.; Dmitriev, A.; Langhammer, C.; Sutherland, D. S.; Zäch, M.; Kasemo, B. Hole Mask Colloidal Lithography. Adv. Mater. 2007, 19,