Transcript k sp - University of Colorado Boulder

Magnificent Optical Properties of Noble Metal
Spheres, Rods and Holes
Peter Andersen and Kathy Rowlen
Department of Chemistry and Biochemistry
University of Colorado, Boulder
Funded by the National Science Foundation
Enhanced Optical Processes from Nanometric Noble Metal Particles
1970’s  surface enhanced Raman scattering
1980’s  106 enhancement of Raman scattering
1980’s  second harmonic generation
1997  1014 enhancement of Raman scattering
2000 106 enhancement of fluorescence in nanorods
2001 surface plasmon optics
Surface Plasmons: coherent oscillations of electron
density at metal/dielectric interface
Enhanced Optical Transmission
Ebbesen et al. “Extraordinary Optical Transmission
Through Sub-Wavelength Hole Arrays”
Nature, 1998, 391, 667-669
• 200 nm Ag film v.d. onto quartz
• focused ion beam lithography
• 150 nm holes
• 600 nm to micron spacing
Saloman et al. Phys. Rev. Lett. 2001, 86(6), 1110
Ghaemi et al. Phys. Rev. B 1998, 58(11), 6779
Measured Near-Field Distribution
Closest to simulated c (previous), hole d = 500 nm
Thio et al., J. Opt. Soc. Am. B., 1999, 16(10), 1743
• 200 nm thick Ag
• 150 nm holes
• 900 nm spacing
• Transmission efficiency =
fraction of light transmitted/
fraction of surface area holes
= 2.
• More than twice the light
that impinges on the holes is
transmitted through the film!
Ebbesen et al. Nature 1998, 391,667
• Hole spacing determines peak position
•Peak position independent of hole d
• Independent of metal (Ag, Cr, Au)
• Must be metal (Ge doesn’t work)
Ebbesen et al. Nature 1998, 391,667
T scales with d2, independent of 
versus (d/ )4 for Bethe sub- aperture
Calculated Enhancement Factor
5e+7
=500 nm
4e+7
3e+7
2e+7
1e+7
0
0
100
200
300
Aperture Diameter (nm)
400
Enhancement / Transport Mechanism?
Not cavity resonance since peak position (in spectrum)
does not significantly depend on hole dimensions
Not waveguiding because film thickness too small (200 nm)
Surface plasmon tunneling?
Surface plasmon scattering?
•
For a surface that can support a surface plasmon,
the wave vector, ksp is:
2
k sp 
1/ 2
  m s 

 m  s 
i 
• The difference between the in-plane wave vector of light,
ki, and the surface plasmon wave vector, ksp, can be
compensated for by diffraction on periodic surface structure:
max (i, j )  ao
 m s
m  s
i j
2
2
min (i, j )  ao
s
i2  j 2
Ag
Ag/Ni
Ni
Grupp et al., Appl. Phys. Lett. 2000, 77(11), 1569
Transmission relatively independent of wall metal
Grupp et al., Appl. Phys. Lett. 2000, 77(11), 1569
Further evidence for surface plasmon involvement
Sonnichsen et al., Appl. Phys. Lett. 2000, 76(2), 140
Sonnichsen et al., Appl. Phys. Lett. 2000, 76(2), 140
Left: Calculated near-field
transmission intensity
[(c) = 300 d, 900 nm a, 800 nm ]
Calculated intensity
enhancement near
hole edge ~ 500x
15 nm above
100 nm above
Saloman et al. Phys. Rev. Lett. 2001, 86(6), 1110
Thio et al., Physica B, 2000, 279, 90
Grupp et al. Adv. Matr. 1999, 11(10), 860
Surface Plasmon Activated Devices
Thio et al., Physica B, 2000, 279, 90
Transmission through single hole
with array of dimples
Single hole in smooth surface
Grupp et al. Adv. Matr. 1999, 11(10), 860
For coherent 670 nm light
T is 60x greater than typical
NSOM tapered fiber with
200 nm aperture
Thio, Lezec, Ebbesen Physica B, 2000, 279, 90
Applications, Applications, Applications!
Reflection mode?
SERS at edges?
Field in channel?
Surface Plasmon Optics:
• use SP’s for manipulation of optical fields
• SP lenses, mirrors and flashlights
(e.g., Smolynaninov et al. Phys. Rev. B. 1997, 56(3) 1601-1611.)
Lithographic Design for Optical Enhancement
hn
Field Enhanced
Electron-Beam Nanolithography (Peter Andersen)
Si substrate
Spin coat substrate with PMMA resist
Expose to electron beam
Develop in MIBK/IPA
Metalize by vapor deposition
Reflection Grating Behavior
Reflected Intensity (arb. units)
4000
3500
3000
2500
2000
1500
1000
500
0
100
200
300
400
500
600
Wavelength (nm)
700
800
900
First Attempt: Top-View AFM
AFM Micrograph of Second Attempt!
Grating Constant (ao)
target ao
450 nm
measured ao 450 nm
Photolithography (Michele Jacobson)
Lens
Pinhole
Nd:YAG Laser
 =  / 2sin 
Au Mirror
To be continued…..