FEM And Near-field Simulations: A Vital Mechanistic Toolfor Studying Silver-based Plasmonic Systems
Ramesh Asapu1, Sammy Verbruggen1,2, Nathalie Claes3, Sara Bals3, Siegfried Denys1 and Silvia Leanerts1
1Department of Bioscience Engineering, DuEL, University of Antwerp, Belgium2Centre for Surface Chemistry and Catalysis, COK, KU Leuven, Belgium3Department of Physics, EMAT, University of Antwerp, Belgium
Silver Plasmonic Systems: What and Where?
Surface Plasmon Resonance:
Collective oscillation of conduction electrons at the dielectric-metal interface of a nanoparticle stimulated by incident light of matching wavelength.
Highest near field enhancement by silver among the plasmonic noble metals like Au, Ag, Pt, Cu etc.
Size tuneable plasmonic properties – FEM vital tool for analysis
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*Darya Radziuk et al. Phys. Chem. Chem. Phys., 2015, 17, 21072
Applications:
Biophotonics
Sensing, Imaging and Therapeutics
SERS
Identification of chemical species
Plasmon enhanced semiconductor photocatalysis – TiO2 systems.
Time domain simulation of Ag NP (~20 nm) in air, λinc = 355 nm
Modeling of plasmonic nanoparticles in COMSOL
COMSOL Wave Optics physics in wavelength domain study.
Solution to Maxwell’s electromagnetic wave equation:
𝛻 ×1
µr𝛻 × E − K0
2(Ɛr−j σ
ωƐ0)E = 0
where E – scattered electric field
K0 - wavenumber in free space
µr - relative permeability of medium
Ɛr – permittivity of medium
PML layers to truncate the domain and avoid internal reflections
Linear polarized plane wave
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Where Qh is total power dissipation density
relPoavx,y,z are the time average power flow of relative fields
Z0_const is the scaling factor
Mie solution to Maxwells’s equations: Implementation in COMSOL
• Mie Solution to Maxwell’s wave equation to calculate the extinction efficiency. (for particles d<< λ)
Absorption cross section Cabs =𝑊𝑎𝑏𝑠
𝐼𝑖1*
Scattering cross section Csca = 𝑊𝑠𝑐𝑎
𝐼𝑖2*
Wabs, Wsca are energy rates absorped and scattered by particle and Ii is energy flux of the incident wave.
Cext= Cabs + Cabs
Qext = 𝐶𝑒𝑥𝑡
𝑔𝑒𝑜𝑚𝑒𝑡𝑟𝑖𝑐 𝑐𝑟𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒3*
*Bohren and Huffman, Absorption and scattering of light by small particles, 1983 Wiley
DOI: 10.1002/9783527618156
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Ag NP
𝐶𝑎𝑏𝑠 = 𝑒𝑤𝑓𝑑. 𝑄ℎ𝐸20
2 ∗ 𝑍0_𝑐𝑜𝑛𝑠𝑡
𝐶𝑠𝑐𝑎 = (𝑛𝑥∗ 𝑒𝑤𝑓𝑑. 𝑟𝑒𝑙𝑃𝑜𝑎𝑣𝑥 +𝑛𝑦 ∗ 𝑒𝑤𝑓𝑑. 𝑟𝑒𝑙𝑃𝑜𝑎𝑣𝑦 + 𝑛𝑧 ∗ 𝑒𝑤𝑓𝑑. 𝑟𝑒𝑙𝑃𝑜𝑎𝑣𝑧)
𝐸202 ∗ 𝑍0_𝑐𝑜𝑛𝑠𝑡
(volume integral over the nanoparticle)
E0
(Surface integral over the nanoparticle)
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Modeling of Ag nanoparticle
Ag silver nanoparticles exhibit high near field enhancement
Prone to oxidation forming a diffuse Ag2O layer effecting the near field enhancement significantly.
Not suitable for applications over long period of time or oxidative conditions.
λInc = 355 nm
E
k5 nm
Ag2O shell 2 nm
λInc = 355 nm
E
k5 nm
a) b)
E-Field enhancement contour of Ag nanoparticle
λInc = 355 nm
E
k5 nm
Ag2O shell 2 nm
λInc = 355 nm
E
k5 nm
a) b)
E-Field enhancement contour of Ag@Ag2O nanoparticle
Silver colloidal nanoparticles stability test in air
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Ultrastable Ag nanoparticles:
Encapsulation of Ag NPs with ultrathin protective polymer shell using LbL method.
4 layers Ag/(PAH/PAA)2
shell 1.4 nm
8 layers Ag/(PAH/PAA)4
Shell 2.4 nm
Bare Ag nanoparticle dia~18nm
Effect of polymer shell on the field enhancement of core-shell nanoparticles.
polymer shell thickness (nm)
0 2 4 6 8 10
Ma
xim
um
en
ha
nce
me
nt fa
cto
r |E
/E0|2
0
100
200
300
400
500
TEM Characterization
Centrifuge to remove excess
polymer
Ag NP
Polyelectrolyte
Ag NPOne cycle
each of
polycationand polyanion= One Bilayer
20 min stirring under dark
Centrifuge Final washing step
Redispersed in Milli-Q water
Validation of models:
Parametric sweep of incident wavelength to generate extincion plots (Mie solution implementation in COMSOL in water and npolymershell = 1.48
Experimental absorption spectra compared with COMSOL model and Mie analytical solution using Bohren and Huffman’s BHCOAT (implemented in MATLAB) for coated nanoparticles. Data from J&C – Jhonson and Christy
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4.34.8
5.4
400.9
386.9 386.7
405.2
391.7 392.1
365
370
375
380
385
390
395
400
405
410
415
0
2
4
6
8
10
12
14
Experimental Mie Analytical J&C Comsol J&C
Surface P
lasmo
n R
eson
ance λ
SPR
max
Red
sh
ift
in S
urf
ace
Pla
smo
n R
eso
on
ance
(n
m)
SPR Red shift SPR-Layer 0 SPR-Layer 4
8 layers Ag/(PAH/PAA)4 2.4 nm shell
4 layers Ag/(PAH/PAA)2 1.4 nm shell
Bare Ag anoparticle 18 nm
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Ultrastable Ag plasmonic nanoarrays for multi-domain applications:
Ag nanoparticle arrays generate hot spots SERS : EF4 ~ 108-1011
Engineering of Nano arrays based on the feedback from E-field simulations. Mesh convergence study for core-shell nanoparticle dimers
Mesh Density Number of Elements Computation time [s] Max point of (Norm. E-field)2
Normal 10374 9 3.13E+05
Fine 16588 11 4.64E+05
Finer 42048 24 4.21E+05
Extra fine 135833 85 3.50E+05
Extremely fine 647861 609 3.45E+05
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Ag plasmon enhanced TiO2 gas phase photocatalysis
Application of silver nanoparticles for long-term stable plasmonenhanced gas phase photocatalysis.
Acetaldehyde as a model pollutant in gas phase photocatalysis
FEM numerical simulations to corroborate experimental evidence to identify the major mechanism responsible for plasmonic enhancement.
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18.6
25.2
21.0
17.0
19.821.3
18.216.8
22.0
0
5
10
15
20
25
30
P25 P25_Ag P25_Ag_L4
% A
ceta
ldeh
yde
deg
rad
atio
n
Long term stability study of Ag-TiO2 photocatalytic system using 4 layered Ag core-shell nanoparticles
t=0 t=4 weeks t=16 weeks
*Ramesh Asapu et al. Applied Catalysis B: Environmental, 200 (2017), 31-38
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Ag plasmon enhanced TiO2 photocatalysis
Ag@polymer core@shell nanoparticles to study near-field / charge transfer
Insulating polymer spacer layer rules out charge transfer
So how distant the near field enhancement is helpful!
FEM simulations provide an estimation feedback for experimental synthesis
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TiO2
Substrate
EF d
istr
ibu
tio
n m
aps:
log
(E2/E
02)
TiO2
TiO2
TiO2
TiO2
TiO2
TiO2Ag NP
Ag core-shell NP
1.4 nm
Ag core-shell NP
4 nm
Influence of spacer layer between Ag plasmon and TiO2 nanoparticles on the enhancement
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Conclusion:
FEM simulations can provide crucial insights: from synthesis, design and application perspective
Study the effect of medium and design of nanoparticle plasmonic system for wide domain of applications
Vital mechanistic tool : plasmon enhanced photocatalysis and hotspot applications
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Thanks for your attention