Nonlinear Bleaching, Absorption and Scattering of 532-nm-Irradiated
Plasmonic Nanoparticles
V. Liberman, M. Sworin, R. P. Kingsborough, G. P. Geurtsen and M. Rothschild
Lincoln Laboratory, Massachusetts Institute of Technology
244 Wood Street, Lexington, MA 02420
SUPPLEMENTAL INFORMATION
Nanoparticles synthesis and characterization
1. Commercial nanoparticles
Commercial Au nanospheres with nominal diameters of 30, 50 and 80 nm were procured
from nanoComposix. The coefficient of variation (CV) of the size distribution was <15%, as
confirmed by the vendor with transmission electron micrographs (TEMs) for each batch of
nanoparticles delivered. Nanoparticles in aqueous suspensions were tested with two different
chemical terminations, polyvinylpyrrolidone (PVP) and citrate, and no difference in behavior
was found that could be attributed to the different termination chemistries. Additionally, larger
Au nanospheres of diameters 100 nm and 150 nm were obtained from BBInternational with
citrate termination. The CV of these two sizes was < 8%. Ag nanospheres with PVP termination
with diameters 60, 80 and 100 nm were obtained from nanoComposix. The CV for these sphere
sizes was < 15%.
Particle concentration was provided by the vendor with every batch and was correlated
by us with the optical density (OD) of the suspension. The concentration of the tested material,
as shown in Table I, was obtained by scaling the concentration by the actual OD tested,
assuming the linearity of OD with concentration from Beer’s law.
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2. Custom synthesized nanoparticles
In addition to the commercially procured nanospheres, Ag nanodisks with PVP
termination were custom synthesized using solvothermal synthesis method.1 For this synthesis, a
1x10-3 M solution of AgNO3 in dimethylformamide (DMF) was prepared. PVP was added to the
solution in the ratio of 5:1 by weight, PVP:Ag. The solution was transferred to a Teflon vessel,
which was placed inside the stainless steel container and heated at 160C for 72 hours. After the
solution cooled, it was centrifuged down to remove the supernatant and re-dispersed in water. A
final filtration step of nanoparticle suspension was performed with 100-nm track-etched
membrane filters (Whatman, Ltd.)
The absolute nanodisk concentration in the suspension was determined independently
with Atomic Absorption (AA). In this method, the Ag content was assayed using a Thermo
Electron iCE3400 graphite furnace atomic absorption spectrometer. Samples were digested with
2N nitric acid. Absorbance was measured at 328.1 nm using a silver hollow cathode lamp and
Zeeman-effect background correction. For each measurement, 20 µL of sample was injected
into an extended lifetime cuvette. The furnace program consisted of a drying step (100°C, 30 s),
an ash step (450°C, 20 s), atomization (1100°C, 3 s), and a clean (2500°C, 3 s). An argon purge
was used throughout, except during the atomization step, when the absorbance was measured.
Samples were measured in triplicate.
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Table I. Nominal size and concentration of all the nanoparticle suspensions tested.
Particle
Concentration (#/cc)
30 nm Au sphere
2×1011
50 nm Au sphere
3×1010
80 nm Au sphere
6×109
100 nm Au sphere
5 ×109
150 nm Au sphere
2×109
60 nm Ag sphere
8 ×1010
80 nm Ag sphere
1×1010
100 nm Ag sphere
4×109
45 nm Ag disk
2×1010
Spatial distribution of susceptibility enhancement factors
The spatial distribution of fre and fim in plasmonic nanoparticles is obtained from
Equations (7) and (8) in the main body of the paper and has been calculated utilizing full-field
analysis with a finite difference time-domain method.. Figure 1 depicts the calculated
distribution in two nanospheres and Ag nanodisks. In this Figure, the beam propagates along the
y-axis, and the electric field is linearly polarized along the x-axis for nanospheres. For nanodisks,
both in- and out-of-plane polarizations are considered. Note that all the plots have reflection
symmetry along the x-axis and some asymmetry along the y-axis, which is the direction of the
propagation vector. The differences between the Au and Ag nanospheres can be attributed to the
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proximity of the surface plasmon resonance in Au as opposed to Ag. Previous theoretical
calculations of (3) enhancement in plasmonic nanostructures reveal that in the vicinity of
plasmonic resonance, both imaginary and real parts of the enhancement show strong peaks.2 The
real part of susceptibility enhancement has a negative peak near resonance.3 On the other hand,
the imaginary part can be either positive or negative, depending on the excitation geometry. The
resonance wavelength of the imaginary part is shifted from that of the real part. Indeed, in our
simulations, for the case of strongly enhanced electric fields, such as Au nanoparticles and Ag
nanodisks for in-plane excitation, fr is negative, whereas fim is strongly positive for Ag nanodisks,
but switches sign inside Au nanospheres.
REFERENCES
1
2
3
Y. Yang, S. Matsubara, L. Xiong, T. Hayakawa, and M. Nogami, “Solvothermal synthesis of
multiple shapes of silver nanoparticles and their SERS properties,” J. Phys. Chem. C 111, 9095
(2007).
J. Zhu, X. Huang, J.-J. Li, and J.-W. Shao, “Theoretical calculation of enhancement factor of
third-order nonlinear susceptibility in gold nanowire and nanotube ” J. Optoelectron. Adv. M. 11,
56 (2009).
N. Pincon, B. Palpant, D. Prot, E. Charron, and S. Debrus, “Third-order nonlinear optical
response of Au:SiO2 thin films: Influence of gold nanoparticle concentration and morphologic
parameters,” Eur. Phys. J. D 19, 395 (2002).
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A
B
C
D
E
F
H
G
Figure 1. Spatial maps of fim and fre at 532 nm (see main text, Equations (7)-(8) for definitions). For all
cases, fim,re have been set to 0 outside the nanoparticle volume. For all cases, light is incident from the
bottom of the page along the y-axis. Polarization is in the plane of the page for nanospheres and as
indicated below for Ag nanodisks. A, B: Au nanospheres, 60 nm diameter. C,D: Ag spheres, 60 nm
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diameter. E, F: Ag nanodisks, polarization perpendicular to the plane of the disk. G,H: Ag nanodisks,
polarization along the plane of the disk.
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