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