martin fränzl*, stefan moras, dietrich r. t. zahn

© J. A. Woollam Co., Inc.

Characterization • Spectroscopic ellipsometry, reflectance and transmittance

measurements:

• Analysis with the WVASE® software

• Modeling of porous silicon by effective medium theories [3]

• Imaging by scanning electron microscopy

Motivation • 1D photonic crystals + metal nanoparticle arrays:

• Tuning the photonic bandgap to the plasmonic resonance:

Interaction of Porous Silicon 1D Photonic Crystals and Plasmonic Nanostructures for Surface-Enhanced Raman-Spectroscopy

Martin Fränzl*, Stefan Moras, Dietrich R. T. Zahn

Summary • Fabrication of metal nanoparticle arrays on top of 1D photonic crystals:

Electrochemical etching of porous silicon Nanosphere lithography of silver nanoparticle arrays

• Interaction if the plasmonic resonance coincides with the photonic bandgap of the photonic crystal

• The already very strong Raman enhancement of the silver nanoparticle arrays [4] is further enlarged by a factor of 1000

References [1] Sailor, M. J., Porous Silicon in Practice, Wiley (2012)

[2] Weekes, S. M. et al., Macroscopic Arrays of Nanostructures form Self-Assembled Nanosphere Templates, Langmuir 23, (2007) 1057

[3] Petrik, P. et al., Optical Models for the Ellipsometric Characterization of Porous Silicon Structures, Phys. Stat. Sol. 2, (2005) 3319

[4] Ludemann, M. et al., Surface-Enhanced Raman Effect in Ultra-Thin Films Employing Periodic Silver Nanostructures, J. Nanopart. Res. 13, (2011) 5855

+

Sample Preparation

• Porous silicon: Electrochemical etching of p-type silicon in hydrofluoric acid: [1]

Results

500 nm

+ →

Power Supply

Platinum Electrode HF (50 %) : Ethanol = HF (15 %)

Aluminum Electrode

Viton

(100) Silicon (0.01 Ωcm)

Teflon

• Periodic etching current leads to a periodic change in the porosity:

• Nanosphere lithography: Self-assembly of polystyrene spheres as mask for evaporation [2]

Substrate Glass

• Silver evaporation + removal of the spheres:

Polystyrene

Water

→

100 nm 250 nm

→ VASE® (J.A. Woollam Co., Inc.)

100 nm

←

15 min at 250 C°

250 nm

500 nm

D = 450 nm

L ≈ 100 nm

Ag

500 nm

𝜗 = 15°

d1 ≈ 130 nm

d2 ≈ 75 nm

1 µm

H ≈ 50 nm

500 nm 1 µm

d1 = 4 n1

λPBG d2 =

4 n2

λPBG

n1 ≈ 1.3 n2 ≈ 2.2

*martin.fraenzl@physik.tu-chemnitz.de

www.tu-chemnitz.de/~fraem www.tu-chemnitz.de/physik/hlph

Glass

Silver

Porous Silicon 1D Photonic Crystals

Plasmonic Nanostructures

Plasmonic Nanostructures on Top of Porous Silicon 1D Photonic Crystal

Surface-Enhanced Raman Spectroscopy

→

EPBG = 2.0 eV