1. Nanophotonics II
Plasmonics
Biophotonics
Exotics

2. Plasmonics!

3. 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

4. Surface plasmons Barnes et al. Nature 2003
Plasmons can be confined to nanoscale and propagate along nanostrips, through nanoholes, etc.
See derivation of plasmon dispersion on white board

5. 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.

6. Plasmon resonance frequency strongly depends on geometry

7. Plasmon absorption by metallic nanoparticles in stained glass windows, glass cups, ceramic pots

8. 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

9. Nanoshells: control of SPR wavelength over a broad range
Halas, OPN 2002

10. H. Atwater, Scientific American 2007

11. Note: we cannot excite SPP by simply illuminating the surface!ki
kSPP
Excitation condition
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

12. Excitation of SPP:
Kretschmann configuration
Note: these SPP are not particularly small-size

13. 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!

14. Integrated biosensor (Cambridge Consultants Ltd)

15. 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.

16. Exciting SPP (or any mode of your choice) by scattering light off grating
This is effectively a (quasi-)momentum conservation d ki
kSPP
Grating changes longitudinal wave vector of a photon by
Coupling to SPP is achieved when

17. Grating can be also used to extract SPPs:
Bozhevolnyi 2007

18. Photon momentum conservation in photonic crystalsd
kin
When Kg = 2kin: incoming wave is reflected + Kg =
kout

19. Localized (near-field) excitation of SPPs by a metallic tip of a near-field microscope illuminated by laser light
Atwater et al. 2007

20. Detection of SPPs by a tip of near-field microscope
Sondergaard & Bozhevolnyi 2007

21. Detection of SPPs with photon scanning tunneling microscope (PSTM)
Imaging SPP with PSTM
Zia et al, Mat. Today 2006

22. Propagation of a SP along a 40-nm thick, 2
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

23. Elements of integrated photonic chips based on SPP

24. Plasmon waveguides made from chains of nanoparticles
Hohenau et al. 2007

25. SPP in periodic structures: Merging plasmonics with photonic crystals

26. Experimental observation of SPP photonic bandgap
Barnes, Nat 2003

27. Transmission through 2D SPP photonic crystal waveguides
Gold scatterers on the gold surface
Sondergaard & Bozhevolnyi 2007

28. More of the same
Sondergaard & Bozhevolnyi 2007

29. Transmission through arrays of subwavelength holes
Wavelength of transmitted light depends on the hole diameter and array period
Barnes, Nat 2003

30. THE DREAM: Plasmonic chips
Plasmonic switches (“plasmonsters”)
Slot waveguide
H. Atwater, Sci. Am. 2007

31. Invent your own technique for excitation, detection, waveguiding of plasmons!

32. Biophotonics

33. Evanescent field sensors with substrate sensitized to a specific molecule

34. Adsorbed molecules change the excitation angle of EM mode

35. Monitoring of three-step oligonucleotide hybridization reaction

36. Near-field microscopy for imaging nanoobjects and single molecules
SNOM
PSTM
Tip collects the evanescent light created by laser illuminating the sample from the back
Tip illuminates the sample;
Scattered light is collected

37. Note: your tool (PSTM, NSOM etc
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.

38. Nano-Biosensors based on localized plasmons
Luminescence of sensitized metal nanoparticles
Surface enhanced Raman scattering and CARS

39. 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.

40. 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

41. 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

42. Anker et al., Nature Mat. 2008

43. 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

44. 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

45. SERS: Surface enhanced Raman spectroscopy
Stokes
laser
Stokes
Anti-Stokes
laser
laser
Molecular
vibrations
Coherent anti-Stokes Raman Scattering
(CARS)
Raman scattering
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).

46. Biochip for multiplexed SPR detection
Anker et al., Nature Mat. 2008

47. 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.

48. Left-handed materials
1>0
1>0
2>0
2<0
L. Mandelshtamm, 1944
Recent review: Physics of Negative Refraction (Eds. C.M. Krowne, Y Zhang) (Springer, 2007).
See derivation of light propagation in LHM on white board

49. “Superlens” and its challenges
Zhang & Liu, Nat. Mat. 2008

50. Zhang & Liu, Nat. Mat. 2008