Nanoplasmonics and Metamaterials with
Low Loss and GainGuohua Zhu
Center for Materials Research, Norfolk State University, Norfolk, VA
Collaborators:M. A. Noginov, V. I. Gavrilenko, N. Noginova, M. Bahoura, M. Mayy,
A. M. Belgrave, H. Li, J. Adegoke and B. A. RitzoNorfolk State University
V. M. Shalaev, E. E. Narimanov and V. P. DrachevPurdue University
U. Wiesner, S. Stout, E. Herz and T. SuteewongCornell University
V.A. PodolskiyUniversity of Massachusetts at Lowell
A. Urbas and Jarrett VellaAFRL
$$$:NSF PREM grant DMR-0611430, NSF NCN grant EEC-0228390, AFOSR grant FA9550-09-1-0456, and the UTC/AFRL grant #10-S567-0015-02-C4.
Outline
� Introduction
� Enhancement of localized surface plasmon (SP) by gain� SPASER (Nanolaser)
� Enhancement of propagating surface plasmon polariton(SPP) by gain
� Stimulated emission of SPPs
� Enhancement of SPP without Gain� Metal-free optical materials with negative electric permittivity
� Transparent conductive oxides
� High concentrated laser dyes
� Summary
Introductions
EinducedEinduced
SPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
EzSPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
EzSPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
Ez
Localized surface
plasmons (SP)
Dielectric
Metal• Electrons movement at metallic surface
• Oscillations of the
movement upon an EM field interactions
Surface plasmons
polaritons (SPP)
Introductions
Areas and applications of nanoplasmonics:
• Surface Enhanced Raman Scattering
• Near- field microscopy and spectroscopy
• Negative Index Materials - Optical cloaking
• Medical applications, and many others …
Most of existing and potential applications of nanoplasmonics are suffered from the LOSS caused by metal absorption
Enhancement of localized SPs by gains
Enhancement of Localized surfac plasmon (LSP) in the presence of optical gain.
Theoretical predictions:
Localized SP in metallic sphere: Field enhancement in
metallic sphere (R<<λ) with complex dielectric constant ε1 surrounded by dielectric medium with complex dielectric constant ε2:
))(2)(
)()((
21
12
0 ωωωωεεεεωωωωεεεε
ωωωωεεεεωωωωεεεε
++++
−−−−∝∝∝∝
E
Einduced
Lawandy, APL, 2004.
Re=0; Im=0
EinducedEinduced
)]("2)("[)]('2)('[)(2)( 212121 ωωωωεεεεωωωωεεεεωωωωεεεεωωωωεεεεωωωωεεεεωωωωεεεε ++++++++++++====++++ i
LSP enhancement in the presence of optical gain
532 nm laser
pumpR6G&Ag
filterpinhole
mirrormirror
R6G laser
fiber
The mixture of Ag
aggregate and rhodamine
6G dye was pumped at 532
nm and probed at 560 nm.
The scattering of the 560
nm light was studied as a
function pumping.
The enhanced scattering was
used as the evidence of the
plasmon enhancement.
LSP enhancement in the presence of optical gain
0
1
2
3
4
5
6
7
0.001 0.01 0.1 1 10
Pumping (mJ)
Scattering (re
l. u
nits)
Six-fold enhancement of scattering was observed at the increase of
the pumping.
Scattering enhancement ⇒⇒⇒⇒plasmon enhancement
[Noginov, Zhu et.al., ArXiv, 2005; Appl. Phys B, 2006; Opt. Lett. 2006]
Demonstration of Spaser (nanolaser)
Surface Plasmon Amplification by Stimulated Emission of Radiation
Gold Gold w/ Si shell Gold/Si/dye
14 nm 44 nm
58 nm
69 nm
TEM and SEM images of Au/silica particles before the
fluorescent dye was added to the surface
Nanoparticle synthesis –by Cornell
Absorption, Emission and Excitation
SP absorption overlaps with emission and
excitation (absorption) of the Oregon Green 488
dye.
0
0.2
0.4
0.6
0.8
1
1.2
300 400 500 600 700
Wavelength (nm)
Emission, Absorption (rel. units)
12 3
Absorption (1), excitation (2), spontaneous emission (3).
0
100
200
300
400
500
600
700
490 510 530 550 570 590 610 630 650
Wavelength (nm)
225mW
90mW
45mW
20mW
12.5mW0
5
10
15
20
25
490 510 530 550 570 590 610 630 650
Wavelength (nm)
225mW
90mW
45mW
20mW
12.5mW
0
100
200
300
400
500
600
700
0 100 200 300
(Pumping (mW
(Em
issio
n (re
l. u
nits
Pumping: λλλλ=488 nm, tpulse ≈≈≈≈ 5 ns
At dilution, the signal decreased, but its shape and the ratio between the spontaneous and the stimulated
emission did not ⇒⇒⇒⇒Emission occurs in single nanoparticles!
0
0.2
0.4
0.6
0.8
1
490 510 530 550 570 590 610 630 650
Wavelength (nm)
Em
issio
n (
rel. u
nits) more than 100
times diluted
Demonstration of Spaser (nanolaser)
Dye absorption is low, emission and SP resonance are strong
0
0.2
0.4
0.6
0.8
1
1.2
300 400 500 600 700
Wavelength (nm)
12
3
4
Position of the Spaser line
Absorption (1),
Exciatation (2),
Spontaneous emission (3).
Spaser line (4)
[Noginov, Zhu, et. al., Nature 2009]
Surface Plasmon Polaritons (SPPs)
Surface Plasmon Polariton (SPP) is an
electromagnetic wave propagating at
the interface between metal and
dielectric.
At critical angle θθθθ0, when kphotsinθθθθ =
kSPP , light wave excites SPP ⇒⇒⇒⇒ there is a “dip” in the reflection curve.
ω
c⋅ n ⋅ sin θ 0 =
ω
c⋅
ε1 ⋅ε 2
ε1 + ε 2
kphot kSPP
0
0.2
0.4
0.6
0.8
1
1.2
61 63 65 67 69
Angle (dergee)
Refle
ction
red diamonds - experiment
blue line - theory
metal (Ag)glass prism
dielectric
SPPεεεε2
εεεε1
εεεε0=n2
θ0
SPP
0
0.2
0.4
0.6
0.8
1
60 62 64 66 68 70 72
Angle (θ)
PMMA&R6G: εεεε2’ = 1.52, εεεε2”= -0.006gain=422 cm-1
Glass: εεεε0’=1.7842
Silver: εεεε1’ = -15, εεεε1”=0.85
PMMA&R6G: εεεε2’ = 1.52
Thickness of the
silver film ≈≈≈≈39 nm
0
0.0005
0.001
0.0015
0.002
0.0025
0.0E+00 2.0E-07 4.0E-07 6.0E-07 8.0E-07 1.0E-06
Time (s)
Re
fle
ctivity s
ign
al (r
el. u
nits) reflectivity kinetics under
pumping(luminescence is subtracted)
Thin film
d=39nm
Relative enhancement of the reflectivity signal as high as 280% !
SPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
Ez
pumping
Enhancement of SPPs by gains
[Noginov, Zhu, et. al., Optics Express 2008]
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.00E+00 2.00E-07 4.00E-07 6.00E-07 8.00E-07 1.00E-06
Time (s)
Re
fle
ctivity s
ign
al (r
el. u
nits)
Thickness of the silver film is ~ 90 nm
0.000001
0.0001
0.01
1
100
10000
1000000
-0.014 -0.010 -0.006 -0.002
ε " 2
R
1 23 4
5
Trace #1 - 50nm; trace #2 - 60nm;
trace #3 - 70nm; trace #4 - 80nm;
trace #5 - 100nm.
Experimental result is just as the model predicted !
SPPs with optical gain
[Noginov, Zhu, et. al., Optics Express 2008]
SPP spectra recorded at
different
decoupling angles
Emission of SPPs
SPPs can be excited via emission of R6G
molecules in the R6G-PMMA film
SPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
Ez
pumping
Stimulated emission of SPPs
0
0.2
0.4
0.6
0.8
1
1.2
550 570 590 610 630 650
Wavelength, nm
Em
issio
n
below threshold
above threshold
Emission spectra considerably narrowed in comparison to those at low pumping.
00.511.52
0 0.2 0.4 0.6 0.8 1 1.2Pumping (mJ)Emission (rel. units)
The dependence of the emission intensity shows strongly nonlinear with the distinct threshold.
[Noginov, Zhu, et. al., PRL 2009]
Enhancement of SPs w/o optical gain
Density of states
Energy
EF1
4s
3d
∆E
δE
EF2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
7000 12000 17000 22000 27000 32000
Energy (cm-1)
ε"
594.1 nm
12
34
5
6
7
Trace #1, according to the Drude model
Trace #2, from the first principles for bulk silver;
Traces #3-6, for the surface of silver slabs consisting of
7, 10, 13, and 16 monolayers. .
Modifying surface states of bound electrons Changing Fermi level of a metallic layer
0
0.2
0.4
0.6
0.8
1
1.2
61 63 65 67 69
Angle, θ
R
W1
W2
~ 30% elongation of the
SPP propagation length when the dye conc. is
about 30 g/l !
Elongation of propagation length of SPs –
modify the interface
PMMA film with high concentration of R6G dye was deposited on the silver film.
SPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
EzSPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
EzSPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
Ez
[Zhu, et. al., APL 2009]
[Bobb, Zhu, et. al., APL 2009]
Elongation of propagation length of SPs –
mechanical alloy
0500100015002000
300 800 1300 1800 2300Wavelength, nmPenetration depth lp(nm)
Ag Au lp = λ/20
50
100
150
200
250
300
350
0.4 0.8 1.2 1.6 2
Wavelength, um
Intensity Enhancement
Ag
Au
Plasmonics based on silver and gold
loss their compactness above 539 nm
and 660 nm respectively.
Maximal SPP field
enhancements of silver and
gold centered ONLY around
900nm, very lower at mid-
infrared.
A search for plasmonic materials with higher compactness and efficient
in the infrared, is of high importance.
ld,m =1
Im kd,mz( )
= Imλ
2π
εd +εm
εd,m2
Metal-free plasmonic materials ~ IR range
Metal-free plasmonic materials
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1200 1400 1600 1800 2000
Wavelength (nm)
Reflectance (rel. units)
0
0.2
0.4
0.6
0.8
1
1
1
2 3
2 3
Heavily doped degenerate wide-band-gap
semiconductors in near-infrared spectral
range with strong confinement of SPPs
and low loss.
-10-8-6-4-2024
800 1300 1800Wavelength, nm
ε,'ε "
ITO
ZITO
AZO
ITZO
Metal-free plasmonic materials-
Semiconductors
0
20
40
60
80
100
0.1 0.2 0.3 0.4 0.5
l d /λ
Qsp
p
1
2
3
4
5
SPP Q-factor on lp/λ for silver (1), gold (2), ITO (3), ZITO (4) and AZO (5).
[Noginov, Gu, Zhu, et. al, OSA 2010, accepted by APL, 2011]
-20
-10
0
10
20
30
40
300 400 500 600 700 800
Wavelength, nm
ε',
ε"
Theoretical predictions
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
300 400 500 600 700 800
Wavelength, nm
ε',
ε"
-1
0
1
2
3
4
5
6
7
300 400 500 600 700 800
Wavelength, nm
ε',
ε"
Kramers-Kronig Relations
)(")('))(
Im())(
Re()(
''
1))'(
Re(1
))(
Im(
''
))'(
Im(1
1))(
Re(
00
0
0
0
0
ωεωεε
ωε
ε
ωεωε
ωωω
ε
ωε
πε
ωε
ωωω
ε
ωε
πε
ωε
ii
dP
dP
+=+=
−
−
−=
−+=
∫
∫
∞
∞−
∞
∞−
Increase of peak absorption leads to negative permittivity
εεεε’<0
εεεε’< 0and
εεεε”~ 0
Experimental samples: Films of several laser dyes
Films preparation:
Dissolved in a solvent
Deposited onto a glass substrate
Dried to a solid state.
Thickness of the film
Film thickness45nm -180 nm
(Dektak-6M profilometer)
Rhodamine-6G film
Rhodamine-6G
(C28H31N2O3Cl) Zn-TPP
HITC (C29H33N2I)
Reflection and transmission spectra
00.050.10.150.20.250.30.350.40.450.5
300 500 700 900 1100 1300Wavelength, nmR
00.10.20.30.40.50.60.70.80.91
300 500 700 900 1100 1300Wavelength, nmT
Reflection is as high as 47% ( λ = 874nm )
HITC film: thickness ~ 63nm
)",'()(;)",'()( 21 εεεεεεεελλλλεεεεεεεελλλλ FTFR ======== ),()(";),()(' 21 RTfRTf ======== λλλλεεεελλλλεεεε
Permittivity (HITC) extracted from R(λλλλ) and T (λλλλ)
ε’max = 10.2 at λ = 864nm
ε’min = -0.2 at λ = 606nm
M. Mayy, Zhu, …, Noginov, JAP, 2009
-10123456789
300 500 700 900 1100 1300wavelength, nm
ε"
ε’’max = 7.98 at λ = 844nm
-202468
1012
300 500 700 900 1100 1300Wavelength, nm
ε '
Permittivity (HITC) extracted from R(λλλλ) and T (λλλλ)
-10123456789
300 500 700 900 1100 1300wavelength, nm
ε"
ε’max = 10.2 at λ = 864nm
ε’min = -0.2 at λ = 606nm
ε’’max = 7.98 at λ = 844nm
-202468
1012
300 500 700 900 1100 1300Wavelength, nm
ε '
)(")('))(
Im())(
Re()(
''
1))'(
Re(1
))(
Im(
''
))'(
Im(1
1))(
Re(
00
0
0
0
0
ωωωωεεεεωωωωεεεεεεεε
ωωωωεεεε
εεεε
ωωωωεεεεωωωωεεεε
ωωωωωωωωωωωω
εεεε
ωωωωεεεε
ππππεεεε
ωωωωεεεε
ωωωωωωωωωωωω
εεεε
ωωωωεεεε
ππππεεεε
ωωωωεεεε
ii
dP
dP
++++====++++====
−−−−
−−−−
−−−−====
−−−−++++====
∫∫∫∫
∫∫∫∫
∞∞∞∞
∞∞∞∞−−−−
∞∞∞∞
∞∞∞∞−−−−
-10123456789
300 500 700 900 1100 1300wavelength, nm
ε"
Permittivity (HITC) extracted from R(λλλλ) and T (λλλλ)
-202468
1012
300 500 700 900 1100 1300Wavelength, nm
ε '
ε’max = 10.2 at λ = 864nm
ε’min = -0.2 at λ = 606nm
ε’’max = 7.98 at λ = 844nm
)(")('))(
Im())(
Re()(
''
1))'(
Re(1
))(
Im(
''
))'(
Im(1
1))(
Re(
00
0
0
0
0
ωωωωεεεεωωωωεεεεεεεε
ωωωωεεεε
εεεε
ωωωωεεεεωωωωεεεε
ωωωωωωωωωωωω
εεεε
ωωωωεεεε
ππππεεεε
ωωωωεεεε
ωωωωωωωωωωωω
εεεε
ωωωωεεεε
ππππεεεε
ωωωωεεεε
ii
dP
dP
++++====++++====
−−−−
−−−−
−−−−====
−−−−++++====
∫∫∫∫
∫∫∫∫
∞∞∞∞
∞∞∞∞−−−−
∞∞∞∞
∞∞∞∞−−−−
Red line – K-K calculations
[M. Mayy, Zhu, et. al., JAP, 2009]
Zn-TPP Dye
0
0.2
0.4
0.6
0.8
1
300 500 700
Wavelength, nm
T
0
5E-16
1E-15
1.5E-15
2E-15
2.5E-15
3E-15
350 450 550 650 750 850
Wavelength, nm
Abs. cro
ss-s
ection, cm
2
1
Zn-TPP
R6G
HITC
ε’ZnTPP(λ=434 nm) = -1.8
0
0.1
0.2
0.3
0.4
0.5
300 500 700
Wavelength, nm
R
R(λλλλ) and T(λλλλ) of Zn-TPP
ε’ZnTPP(λ)
-3
-1
1
3
5
7
9
350 450 550 650 750
Wavelength, nm
ε'
Green – Extracted from T,R
Pink –calculation
SPP excited in ZnTPP
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
30 35 40 45 50 55 60 65
Angle
R
SPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
EzSPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
EzSPPεεεε2
εεεε1
εεεε0
θ0
SPP x
z
Ez
Zn-TPP film
λ λ λ λ = 426nm
Squares: Experiment result
Solid line : Fitting
εεεε1 = -2.6+1.9i
Air
Glass prism
λ λ λ λ = 426nm
-2-101234567
100 300 500 700 900Wavelength, nm
ε'
Dye film with gain ----- Predictions
-8-7-6-5-4-3-2-10
100 300 500 700 900Wavelength, nm
ε"
In the presence of pumping, the dye film
shows emission rather than absorption.
“Metal” with gainUnique properties Fantastic applications
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
350 550 750 950
Wavelength, nm
ε'
AF455
0
0.2
0.4
0.6
0.8
1
360 460 560 660 760 860 960
Wavelength, nm
T
0
0.05
0.1
0.15
0.2
0.25
360 460 560 660 760 860 960
Wavelength, nm
R
C138H174N6
Extracted ε’ from R,T
Dye molecules separated by
alkyl side chains
G.S. He, et al., Chem. Mater. 16, pp.185-194 (2004).
H. Kasai, et al.,.” Jpn. J. Appl. Phys., Part 2 31, L1132 (1992).
6000
8000
10000
12000
14000
16000
18000
320 330 340 350 360
Wavelength, nmE
mis
sio
n r
el. u
nit
Spectroscopy study of AF455 solution
0
0.2
0.4
0.6
0.8
1
250 350 450 550 650
Wavelength, nm
Norm
aliz
ed
Inte
nsity
Extinction
ExcitationEmission
Scattering
Pumped @ 300nm
Emission
Size distribution
Transmission/Scattering with optical pumping
ττττσσσσ
ωωωω
σσσσωωωω
1)(
*
++++⋅⋅⋅⋅
⋅⋅⋅⋅====
abs
abs
sh
Psh
P
PN
n
AF455
dye
Laser radiation
~ 426 nm
Detector #1
(Transmission)
Detector #2
(Scattering)
Normalized Scattering
Normalized Transmission
0
0.5
1
1.5
2
2.5
3
0.001 0.01 0.1 1
Pumping density (mJ/mm2)
Sig
nal (r
el.units)
op
Ground state polulation
Summary
(1) Complete compensation of the SPP loss by gain
(2) Stimulated emission of SPPs and Spaser
nanolaser
(3) Enhancement of SPPs without gain
(4) Metal-free plamonics
active plasmonics matematerials
The results pave the road to many practical
applications of nanoplasmonics and
metamaterials