Transcript Nanophotonics Lecture 2

Nanophotonics II
• Plasmonics
• Biophotonics
• Exotics
What is a surface plasmon
polariton?
Transverse EM wave coupled
to a plasmon (wave of charges
on a metal/dielectric interface)
= SPP
(surface plasmon polariton)
Note: the wave has to have the
component of E transverse to the
surface (be TM-polarized).
Polariton – any coupled oscillation of photons and dipoles in a medium
Barnes et al. Nature 2003
Surface plasmons
Plasmons can be confined to
nanoscale and propagate along
nanostrips, through nanoholes, etc.
See derivation of plasmon dispersion on white board
Surface Plasmon Resonance (SPR) in different materials
Calculated dispersion of surface plasmon-polaritons propagating at a
Ag/air, Ag/glass, and Ag/Si interface, respectively.
Plasmon resonance frequency strongly depends on geometry
Plasmon absorption by metallic nanoparticles in
stained glass windows, glass cups, ceramic pots
The shape of the nanoparticle extinction and scattering spectra, and in
particular the peak wavelength λmax, depends on nanoparticle
composition, size, shape, orientation and local dielectric environment.
Effect of size and shape on LS PR extinction spectrum for silver nanoprisms and
nanodiscs formed by nanosphere lithography. The high-frequency signal on the
spectra is an interference pattern from the reflection at the front and back surfaces
of the mica.
Anker et al., Nature Mat. 2008
Nanoshells: control of SPR wavelength over a broad range
Halas, OPN 2002
H. Atwater, Scientific American 2007
Note: we cannot excite SPP by simply illuminating the surface!
ki
i
kSPP
Excitation condition
ki sin i  kSPP
Impossible to satisfy!
ki is always less than kSPP
Calculated dispersion of surface plasmon-polaritons propagating at a
Ag/air, Ag/glass, and Ag/Si interface, respectively.
Maier & Atwater, JAP 2005
Excitation of SPP:
Kretschmann configuration
Note: these SPP are not
particularly small-size
Nevertheless, this technique is simple and can be used when we
don’t care about having short SPP wavelength
Chem-Bio Sensing in the Kretschmann configuration
Example of SPR spectrum
Note: the angle is in the TIR range!
Integrated biosensor (Cambridge Consultants Ltd)
SPR systems can detect kinetic information, such as the rate
of complex formation and disintegration of biological species.
Example of kinetic measurement enabled by spatial imaging SPR. A moving
front of betamercaptoethanol binding to gold (a). The top image is taken a
few seconds after the bottom one (b).
Cambridge Consultants Ltd.
Exciting SPP (or any mode of your choice) by scattering
light off grating
i
d
ki
kSPP
This is effectively a (quasi-)momentum
conservation
Grating changes longitudinal wave vector of a photon by
K g  m
2
; m  1,2,...
d
Coupling to SPP is achieved when
ki sin  i  K g  k SPP
Grating can be also used to extract SPPs:
Bozhevolnyi 2007
Photon momentum conservation in
photonic crystals
d
Kg 
2m
, m  1,2,...
d
kin
When Kg = 2kin: incoming wave
is reflected
+
Kg
=
kout
Localized (near-field) excitation of SPPs by a metallic tip of
a near-field microscope illuminated by laser light
Atwater et al. 2007
Detection of SPPs by a tip of nearfield microscope
Sondergaard & Bozhevolnyi 2007
Detection of SPPs with photon scanning
tunneling microscope (PSTM)
Imaging SPP with PSTM
Zia et al, Mat. Today 2006
Propagation of a SP along a 40-nm thick, 2.5m wide gold stripe, imaged by PSTM …
… and through the right-angle bend
Weeber et al. 2007
Elements of integrated photonic chips based on SPP
Plasmon waveguides made from chains of nanoparticles
Hohenau et al. 2007
SPP in periodic structures:
Merging plasmonics with photonic crystals
Experimental observation of SPP photonic bandgap
Barnes, Nat 2003
Transmission through 2D SPP photonic crystal waveguides
Gold scatterers on the gold surface
Sondergaard & Bozhevolnyi 2007
More of the same
Sondergaard & Bozhevolnyi 2007
Transmission through arrays of
subwavelength holes
Wavelength of transmitted light
depends on the hole diameter and
array period
Barnes, Nat 2003
THE DREAM: Plasmonic chips
Plasmonic switches (“plasmonsters”)
Slot waveguide
H. Atwater, Sci. Am. 2007
Invent your own technique for
excitation, detection,
waveguiding of plasmons!
Biophotonics
Evanescent field sensors with substrate sensitized to a specific
molecule
Adsorbed molecules change the excitation angle of EM mode
Monitoring of three-step oligonucleotide hybridization reaction
Near-field microscopy for imaging nanoobjects and single molecules
PSTM
Tip collects the evanescent light
created by laser illuminating the
sample from the back
SNOM
Tip illuminates the sample;
Scattered light is collected
Note: your tool (PSTM, NSOM etc.) can strongly perturb
your sample and distort its properties.
When you do experiment, make sure you understand
what you measure.
Always have a reference case to compare with and a
control case for which you know what results you should
obtain.
Nano-Biosensors based on
localized plasmons
• Luminescence of sensitized metal
nanoparticles
• Surface enhanced Raman scattering and
CARS
Light incident on the nanoparticles induces the conduction
electrons in them to oscillate collectively with a resonant frequency
that depends on the nanoparticles’ size, shape and composition. As
a result of these LSPR modes, the nanoparticles absorb and
scatter light so intensely that single nanoparticles are easily
observed by eye using dark-field (optical scattering) microscopy.
This phenomenon enables noble-metal nanoparticles to serve as
extremely intense labels for immunoassays, biochemical sensors
and surface-enhanced spectroscopies.
The shape of the nanoparticle extinction and scattering spectra, and in
particular the peak wavelength λmax, depends on nanoparticle
composition, size, shape, orientation and local dielectric environment.
Effect of size and shape on LS PR extinction spectrum for silver nanoprisms and
nanodiscs formed by nanosphere lithography. The high-frequency signal on the
spectra is an interference pattern from the reflection at the front and back surfaces
of the mica.
Anker et al., Nature Mat. 2008
What to observe?? (a) shift of the SPR spectrum
When molecules bind to a nanoparticle, the SPR peak wavelength is shifted:
Anker et al., Nature Mat. 2008
Anker et al., Nature Mat. 2008
What to observe?? (b) increase in temperature caused by
optically heating the nanoparticle and its environment
You can track these particles by
scattering the probe beam off a
thermally induced change in the
refractive index!
Anker et al., Nature Mat. 2008
How to identify molecules?
Couple SPR shift measurement with SERS!
Tuning the LSPR to maximize the SERS
signal. a, SERS spectrum of benzenethiol
on AgFONs with varying nanosphere
diameters and corresponding resonances:
at 532 nm, sphere diameter D = 390 nm
(green), at 677 nm, D = 510 nm (orange),
and at 753 nm, D = 600 nm (red). T he
reflection spectrum is shown in the insets,
with minimal reflection corresponding to
maximum LSPR induced absorbance and
scattering.
Anker et al., Nature Mat. 2008
Anti-Stokes
laser
Stokes
laser
Stokes
laser
SERS: Surface enhanced Raman spectroscopy
Molecular
vibrations
Raman scattering
Coherent anti-Stokes
Raman Scattering
(CARS)
Measured quantity: Raman shift laser- Stokes
Usually signal is very weak, but it gets greatly
enhanced near SPR!
Raman spectrum of liquid 2-mercaptoethanol (above )and SERS spectrum
of 2-mercaptoethanol monolayer formed on roughened silver (below).
Biochip for multiplexed SPR detection
Anker et al., Nature Mat. 2008
Anker et al., 2008
The first in vivo SERS implantable glucose sensor. a, Experimental setup used
for in vivo SERS measurements in rats. b, Fabrication and functionalization of
SERS -active surfaces: formation of a nanosphere mask, silver deposition
resulting in formation of the silver film over nanospheres (AgFON) surface,
incubation in decanethiol, and incubation in mercaptohexanol. c, Atomic-force
micrograph of a typical AgFON surface. d, Reflection spectrum of AgFON
optimized for in vivo experiments.
Left-handed materials
1>0
2>0
L. Mandelshtamm, 1944
Recent review: Physics of Negative
Refraction (Eds. C.M. Krowne, Y Zhang)
(Springer, 2007).
1>0
2<0
 

k  H   0E ,
 

k  E   0H
k 
2

c
2
2

See derivation of light propagation in LHM on white board
“Superlens” and its challenges
Zhang & Liu, Nat. Mat. 2008
Zhang & Liu, Nat. Mat. 2008