Supplementary Information

Transcription

1 Supplementary Information Atomically flat single crystalline gold nanostructures for plasmonic nanocircuitry Jer Shing Huang 1,*, Victor Callegari 2, Peter Geisler 1, Christoph Brüning 1, Johannes Kern 1, Jord C. Prangsma 1, Xiaofei Wu 1, Thorsten Feichtner 1, Johannes Ziegler 1, Pia Weinmann 3, Martin Kamp 3, Alfred Forchel 3, Paolo Biagioni 4, Urs Sennhauser 2 & Bert Hecht 1, 1. Nano Optics & Biophotonics Group, Experimentelle Physik 5, Physikalisches Institut, Wilhelm Conrad Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, D Würzburg, Germany 2. EMPA, Swiss Federal Laboratories for Materials Testing and Research, Electronics/Metrology Laboratory, CH 8600 Dübendorf, Switzerland 3. Technische Physik, Physikalisches Institut, Wilhelm Conrad Röntgen Center for Complex Material Systems, Universität Würzburg, Am Hubland, D Würzburg, Germany 4. CNISM Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, Milano, Italy * jshuang@mx.nthu.edu.tw (J. S.H. current address: Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan) hecht@physik.uni wuerzburg.de 1

2 ( m) ( m) (a) Typical AFM image of the surface topography of a single-crystalline flake. (b) Distribu on of the surface height over a 1 µm 2 area. The surface roughness is smaller than 1 nm. The fluctua on of the surface height is possibly due to the surfactant and other contamina ons from the solvent. 2

3 Emission intensity (10 3 counts/s) Wavelength (nm) Supplementary Figure S2 Two photon photoluminescence (TPPL) spectra of a resonant nanoantenna as well as single and multi crystalline gold films. Due to the absence of surface roughness, unstructured single crystalline gold flake (black medium line) shows almost no TPPL signals even for 500 µw, while the unstructured multi crystalline gold film (blue thin line) exhibits much stronger TPPL signals 50,61 for the same excitation power. As the single crystalline gold film is shaped into a resonance linear dipole nanoantenna (50 nm wide, 30 nm high and 236 nm long with a 16 nm feedgap, red thick line), the TPPL signal is greatly enhanced. Note that the excitation polarization for the nanoantenna curve is along the antenna long axis and the excitation power is 50 µw (830 nm, 1 ps, N.A. = 1.4). 3

4 a Counts 50 Fe Co Cu b Cu Energy (kev) Cu Counts 35 As P Fe Co Ga Ga Cu Energy (kev) Supplementary Figure S3 EDX spectrum recorded at the FIB milled edge of a single crystalline gold flake (a) EDX spectrum recorded at the patterned edge of a single crystalline flake (b) Reference EDX spectrum from a gold coated GaAsP nanowire (see Methods). The strongest Ga ion peak, indicated with a red line in (a), is at the noise level corresponding to a concentration less than 1%. Fe, Co and Cu lines are due to electron scattering which hits the TEM column, pole piece of the objective lens and the sample holder. 4

5 Supplementary Figure S4 Schematic diagram of the simulated structures and the impulse spectra. (a) (c) Top view and cross section of a gold bowtie antenna on ITO substrate. Note that a thin (5 nm) Ti adhesion layer is added in (b) and (c), and the feedgap geometry in (c) is modified in order to simulate the effect of residual material in the gap. (d) Simulated spectra recorded at the feedgap center (red crosses) of the bowtie nanoantennas sketched in (a, thick black), (b, medium red) and (c, thin blue) with gap size of 15 (solid line) and 25 nm (dashed line). The shaded area indicates the real source spectral range, which does not hit the resonance peak but partially overlaps with the broad resonance peak. The dielectric function of gold is described by an analytical model 62 which fits the experimental data 60, while the dielectric function of the sputtered ITO layer is based on experimental data 63. 5

6 Supplementary Figure S5 Atomic force microscope (AFM) images and line cuts through singleand multi crystalline antenna arrays (a) AFM image of an area containing the multi (dashed rectangle) and single crystalline (dotted rectangle) nanoantenna arrays together with marker structures. Scale bar: 5 µm. (b) (c) Zoomed in AFM images of the multi and single crystalline nanoantenna arrays marked in (a). Scale bar: 1 µm. The lines indicate the traces along which the topography profiles in (d) are recorded. (d) Topography profiles recorded along the lines marked as L1 and L2 in (a) and the line cuts of the nanoantenna arrays recorded along the lines indicated in (b) and (c). The topography contrast of nm around nanoantennas is the sum of the respective antenna height (30 35 nm) and the ITO milling depth (20 25 nm). The baseline (height = 0 nm) of the topography is set to the level of the unpatterned ITO surface. 6

7 Supplementary Figure S6 Flake area distribution with respect to the reaction temperature. The histogram is obtained by measuring the area of 100 randomly sampled flakes from each sample suspension. While the average flake size increases with decreasing reaction temperature, the average flake thickness remains smaller than 80 nm. 7

8 Supplementary Figure S7 SEM image of an area containing chemically synthesized single- and vapor-deposited multi-crystalline gold films. (a) Overview of the area of interest including both the mul" crystalline marker structure and a single crystalline flake. Scale bar: 10 µm. The inset shows a zoomed in image of the typical surface of vapor deposited mul" crystalline gold film consis"ng of randomly orientated grains. Scale bar in the inset: 200 nm. (b) (c) Zoomed in SEM image of the dashed area in (a) before (b) and a'er (c) FIB milling. Scale bars: 5 µm. 8

9 Supplementary Figure S8 SEM image and TPPL maps of the whole antenna array obtained with various excitation polarizations. (a) Schematic diagram of the linear excitation polarization (red double arrows). Θ is defined as the angle between the excitation polarization and the long axis of the antenna. (b) SEM image of the fabricated area including arrays of single crystalline nanoantennas with nominal width of 50 nm (dashed rectangle) and 70 nm (dotted rectangle). (c) TPPL map of the same area shown in (b) with longitudinal excitation. (Θ = 0 ) (d) A series of TPPL maps for various excitation polarizations. The dependence of the TPPL signal intensity on the excitation polarization verifies that TPPL signals are mainly due to the excitation of longitudinal antenna resonance. Same intensity scale for all TPPL maps. All scale bars: 5 µm. 9

10 Supplementary Figure S9 Intensity dependence of visible TPPL signals on the average excitation power (a) Emission intensity as a function of the excitation power obtained from the areas marked with the dashed circles in the emission map (b). The emission signals from antennas with bonding (black solid squares, marked as "P1" in (b)) and antibonding (red solid dots, marked as "P2" in (b)) resonance show quadratic dependence on the excitation power while the scattering from the multicrystalline gold marker structure (blue open squares, marked as "P3" in (b)), single crystalline gold flake (yellow open triangle, marked as "P4" in (b)) and bare ITO glass area (green open circle, marked as "P5" in (b)) show weaker intensity with linear dependence on the excitation power. Scale bar: 5 µm. Supplementary References 61. Boyd, G. T., Yu, Z. H. & Shen, Y. R. Photoinduced Luminescence from the noble metals and its enhancement on roughened surface. Phys. Rev. B 33, (1986). 62. Etchegoin, P. G., le Ru, E. C. & Meyer M. An analytic model for the optical properties of gold. J. Chem. Phys. 125, (2006). 63. Laux, S. et al. Room temperature deposition of indium tin oxide thin films with plasma ion assisted evaporation. Thin Solid Films 335, 1 5 (1998). 10