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Chatdanai Lumdee and Pieter G. Kik
CREOL, the College of Optics and Photonics, UCF, Orlando, FL, USA
Effect of nanoscale surface roughness on surface-tuned nanoparticle plasmon resonances
1NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 2
Outline
Introduction: substrate-coupled metal nanoparticles Attractiveness Resent studies
All inorganic substrate-coupled gold nanoparticles Resonance control using Al2O3 coatings Stability under laser irradiation
Effect of surface roughness on gold nanoparticle resonances Observations ExperimentModel and simulation
Summary
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 3
Introduction
Substrate-coupled nanoparticles: attractiveness- High field enhancement in the gap
--+ ++++
- --k
Einc
At 633 nm
60 nm diameter Au NP on Al2O3 coated Au film
CST Microwave Studio®
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 4
Introduction
Substrate-coupled nanoparticles: attractiveness- High field enhancement in the gap- Easy to control coupling strength
d
d
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 5
Introduction
60 nm diameter Au NPs on 3.4 nm Al2O3 coated gold film
Substrate-coupled nanoparticles: attractiveness- High field enhancement in the gap- Easy to control coupling strength- Robust, reproducible, simple, and inexpensive
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 6
substrate-coupled nanoparticles- Effective polarizability of a point dipole near a metal surface
P. R. Antoniewicz, J. Chem. Phys. 1972, 56 (p.1711)
- A sphere couple to a metal substrateT. Takemori, et al. J. Phys. Soc. Jpn. 1987, 56 (p.1587)
- Absorption by a small sphere above a substrateR. Ruppin, Phys. Rev. B 1992, 45 (p.5663)
(Not very) Recent studies
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 7
Recent studies
substrate-coupled metal nanoparticles (examples)
- Distance-dependent plasmon resonant coupling between a gold nanoparticle and gold filmJ. J. Mock, et al. Nano Lett. 2008, 8 (p.2245)
- Substrates matter: Influence of an adjacent dielectric on an individual plasmonic panoparticleM. W. Knight, et al. Nano Lett. 2009, 9 (p.2188)
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 8
Recent studies
substrate-coupled metal nanoparticles (examples)- SensorsPlasmonic smart dust for probing local chemical reactionsA. Tittl, et al. Nano Lett. 2013, 13 (p.1816)
Tailoring surface plasmons of high-density gold nanostar assemblies on metal films for surface enhanced Raman spectroscopyJ. Lee, et al. Nanoscale 2014, 6 (p.616)
- Plasmonic rulerPlasmon ruler with angstrom length resolutionM. W. Knight, et al. ACS Nano 2012, 6 (p.9237)
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 9
Recent studies
substrate-coupled nanoparticles (examples)- Plasmonic absorberControlled-reflectance surfaces with film-coupled colloidal nanoantennasA. Moreau, et al. Nature 2012, 492 (p.86)
Near-infrared broadband absorber with film-coupled multilayer nanorodsX. Chen, et al. Optics Letters 2013, 38 (p.2247)
- Nonlinear opticsPlasmon gap mode-assisted third-harmonic generation from metal film-coupled nanowiresK. Li, et al. Applied Physics Letters, 104, 2014 (p.261105)
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 10
Recent studies
substrate-coupled nanoparticles (examples)- Photoluminescence enhancementGap-plasmon enhanced gold nanoparticle photoluminescneceC. Lumdee, et al. (submitted)
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 11
Recent studies
substrate-coupled nanoparticles (examples)- Photoluminescence enhancementGap-plasmon enhanced gold nanoparticle photoluminescneceC. Lumdee, et al. (submitted)
Glass substrate
Gold film
Au NPAl2O3
PL
500 550 600 650 700 750 800
0.25
0.50
0.75
1.00
Sca
tte
rin
g (
a.u
.)
Wavelength (nm)
Measured
Single particle scattering spectrum
10 µm
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 12
Recent studies
substrate-coupled nanoparticles (examples)- Photoluminescence enhancementGap-plasmon enhanced gold nanoparticle photoluminescneceC. Lumdee, et al. (submitted)
500 600 700 800500 600 7000
500
1000
1500
exc
= 633 nm
Wavelength (nm)
Au NP on Au film
Au film only(b)
Wavelength (nm)
Pho
tolu
min
esce
nce (
a.u
.)
Au NP on Au film
Au film only
exc
=532 nm
(a)
Very fun!Want to know more? Meet after the talk> 4 orders of magnitude enhancement
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 13
Outline
Substrate-coupled metal nanoparticles Attractiveness (simple, robust, reproducible) Resent studies
All-inorganic substrate-coupled gold nanoparticles Resonance control using Al2O3 coatings Stability under laser irradiation
Effect of surface roughness on gold nanoparticle resonances Observations ExperimentModel and simulation
Summary
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 14
Outline
Substrate-coupled metal nanoparticles Attractiveness (simple, robust, reproducible) Resent studies – applications need resonance control
All-inorganic substrate-coupled gold nanoparticles Resonance control using Al2O3 coatings Stability under laser irradiation
Effect of surface roughness on gold nanoparticle resonances Observations ExperimentModel and simulation
Summary
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 15
Why?Previous attempts Organic molecule spacer layer Organic background Possibly not very stable
Our structureGold nanoparticles on aluminum and gold film Stable Al2O3 coating on the surface
All-inorganic substrate-coupled gold nanoparticles
Silicon substrate
Aluminum film
Au NP
Al2O3
Glass substrate
Gold film
Au NP
Al2O3
C. Ciraci, et al. Science 2012, 337, p. 1072
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 16
Gold nanoparticles on aluminum film Anodizing aluminum to control Al2O3 thickness NP-to-NP resonance tuning range from 580 – 550 nm
All-inorganic substrate-coupled gold nanoparticles
Before Anodization
3 V
6 V 9 V
Microscopy images
C. Lumdee, et al. ACS Nano 2012, 6(7), p. 6301−6307
Scattering spectra (from one NP)
C. Lumdee, et al. J. Phys. Chem. C 2013, 117(37), p. 19127−19133
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 17
Gold nanoparticles on aluminum film Improve tuning range limited by 3.6 nm native Al2O3
Tuning range from 690 – 610 nm for 0 – 3.4 nm Al2O3
All-inorganic substrate-coupled gold nanoparticles
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 18
Gold nanoparticles on Al2O3 coated substrates Wide tuning range of 140 nm (690-550 nm = far red to green)
500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
Norm
aliz
ed S
cattering (
a.u
.)
Wavelength (nm)
native Al2O
3
0 5 10 15
550
600
650
700
Peak p
ositio
n (
nm
)
Al2O
3 thicknesss (nm)
AuNPs on Al2O
3/Au
AuNPs on Al2O
3/Al
All-inorganic substrate-coupled gold nanoparticles
C. Lumdee, et al. ACS Nano 2012, 6(7), p. 6301−6307
C. Lumdee, et al. J. Phys. Chem. C 2013, 117(37), p. 19127−19133
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 19
Gold nanoparticles on Al2O3 coated substrates stability
100 W/mm2 !
polarization
All-inorganic substrate-coupled gold nanoparticles
C. Lumdee, et al. J. Phys. Chem. C 2013, 117(37), p. 19127−19133
Stable structure good for applications e.g. sensing and photoluminescence
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 20
Outline
Substrate-coupled metal nanoparticles Attractiveness (simple, robust, reproducible) Resent studies – applications need resonance control
All inorganic substrate-coupled gold nanoparticles Resonance control using Al2O3 coatings Stability under laser irradiation
Effect of surface roughness on gold nanoparticle resonances Observations ExperimentModel and simulation
Summary
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 21
Effect of surface roughness on gold nanoparticle resonances
Why?Previous works Resonance tuning of Au NPs
on all inorganic substrates Spectral variations
Q1: What causes this?A1: Particles, size and shape.Q2: What about surface of substrate?
This studyGold nanoparticles on a gold film Mapping local surface roughness Simulate particle’s scattering spectra Compared predicted and measured
spectral variations
C. Lumdee, et al. J. Phys. Chem. C 2013, 117(37), pp 19127−19133
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 22
How?
Dark-field microscopy and spectroscopy
scat
teri
ng
50x objective
Glass substrate
Gold film
Au NP
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 23
Results
Single gold nanoparticle scattering spectra
80 nm diameter Au NPs on Au film
What causes this?
Effect of surface roughness on gold nanoparticle resonances
Size variation cannot make this!
How we model surface roughness???
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 24
How? – Modeling surface roughness
Effect of surface roughness on gold nanoparticle resonances
Challenges1) Accessing local surface near each nanoparticle2) Randomness of surface morphology and particle locations3) Infinite number of possible scenarios infinite simulations?…
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 25
How? – Modeling surface roughness
z(x,y)
z’(x,y)z=0
Finding local height seen by a nanoparticle
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 26
NP
What to defined in simulation?Roughness period, roughness radius of curvature and height
How? – Modeling surface roughness
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 27
NP
What to defined in simulation?Roughness period, roughness radius of curvature and height
How? – Modeling surface roughness
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 28
NP
What to defined in simulation?Roughness period, roughness radius of curvature and height
How? – Modeling surface roughness
2D-FFTAngular integral
Roughness period (P) = 25 nm, Roughness radius of curvature (Rp) ~ 32 nm
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 29
NP
Roughness period (P) = 25 nm, Roughness radius of curvature (Rp) ~ 32 nm
How? – Modeling surface roughness
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 30
NP
Roughness period (P) = 25 nm, Roughness radius of curvature (Rp) ~ 32 nmRoughness height is determined by the gap size (d)
How? – Modeling surface roughness
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 31
NP
Roughness period (P) = 25 nm, Roughness radius of curvature (Rp) ~ 32 nmRoughness height is determined by the gap size (d)
How? – Modeling surface roughness
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 32
NP
How? – Numerical simulation
𝑃𝑟𝑎𝑑 ∝ 𝜇𝑧2𝜔4
C. Lumdee, et al. ACS Nano 2012, 6(7), pp 6301−6307
CST Microwave Studio® and Au dielectric function from literature
P. B. Johnson, and R. W. Christy, R. W., Phys. Rev. B 1972, 6(12), pp 4370-4379.
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 33
Results
Simulated gold nanoparticle scattering spectra
Variation due to surface roughness (gap variation)
0
1
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 34
Variation due to surface roughness (gap variation)
0
1
Effect of surface roughness on gold nanoparticle resonances
Results
Simulated gold nanoparticle scattering spectra
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 35
Variation due to surface roughness (gap variation)
0
1
Effect of surface roughness on gold nanoparticle resonances
Results
Simulated gold nanoparticle scattering spectra
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 36
Variation due to surface roughness (gap variation)
0
1
Effect of surface roughness on gold nanoparticle resonances
Results
Simulated and measured gold nanoparticle scattering spectra
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 37
SummarySurface roughness can contribute to spectral variation.
The effect is difficult to estimate due to infinite possible scenarios.
Use an AFM image to predict nanoparticle locations and model local surface.
Statistically calculate scattering spectra and spectral variation of gold nanoparticles on a thermally evaporated gold film.
The calculation seems to be in a good agreement with the measured data.
Effect of surface roughness on gold nanoparticle resonances
NanoPhotonics and Near-field Optics Group - http://kik.creol.ucf.edu/ 38
1) Introduction and current studies on substrate-coupled metal nanoparticles
2) All-inorganic substrate-couple resonances broad tuning range and stable structure
3) Significant part of spectral variation comes from surface roughness.This spectral variation can be predicted using an AFM image and numerical simulations.
Talk summary
500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d S
ca
tte
rin
g (
a.u
.)
Wavelength (nm)
native Al2O
3