Magnificent Optical Properties of Noble Metal Spheres, Rods and Holes

Peter Andersen and Kathy RowlenDepartment of Chemistry and Biochemistry

University of Colorado, Boulder

Funded by the National Science Foundation

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 Processes from Nanometric Noble Metal Particles

Enhanced Optical Transmission

Ebbesen et al. “Extraordinary Optical TransmissionThrough Sub-Wavelength Hole Arrays”

Nature, 1998, 391, 667-669

Saloman et al. Phys. Rev. Lett. 2001, 86(6), 1110

• 200 nm Ag film v.d. onto quartz• focused ion beam lithography• 150 nm holes• 600 nm to micron spacing

Ghaemi et al. Phys. Rev. B 1998, 58(11), 6779

Thio et al., J. Opt. Soc. Am. B., 1999, 16(10), 1743

Measured Near-Field Distribution

Closest to simulated c (previous), hole d = 500 nm

Ebbesen et al. Nature 1998, 391,667

• 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 lightthat 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)

T scales with d2, independent of

versus (d/ )4 for Bethe sub- aperture

=500 nm

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?

Enhancement / Transport Mechanism?

•For a surface that can support a surface plasmon, the wave vector, ksp is:

 

 •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: 

2/1

2

sm

smi

spk

max 2 2( , )

m s

m soi j ai j

min 2 2( , ) s

oi j ai j

Grupp et al., Appl. Phys. Lett. 2000, 77(11), 1569

Ag

Ag/Ni

Ni

Grupp et al., Appl. Phys. Lett. 2000, 77(11), 1569

Transmission relatively independent of wall metal

Sonnichsen et al., Appl. Phys. Lett. 2000, 76(2), 140

Further evidence for surface plasmon involvement

Sonnichsen et al., Appl. Phys. Lett. 2000, 76(2), 140

Saloman et al. Phys. Rev. Lett. 2001, 86(6), 1110

Left: Calculated near-fieldtransmission intensity[(c) = 300 d, 900 nm a, 800 nm ]

Calculated intensityenhancement nearhole edge ~ 500x

15 nm above 100 nm above

Thio et al., Physica B, 2000, 279, 90

Grupp et al. Adv. Matr. 1999, 11(10), 860

Thio et al., Physica B, 2000, 279, 90

Surface Plasmon Activated Devices

Grupp et al. Adv. Matr. 1999, 11(10), 860

Transmission through single holewith array of dimples

Single hole in smooth surface

Thio, Lezec, Ebbesen Physica B, 2000, 279, 90

For coherent 670 nm lightT is 60x greater than typicalNSOM tapered fiber with200 nm aperture

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.)

Optical Enhancement via Surface Plasmon Coupling

h Field enhanced detection region

Light harvesting indentations

Surface plasmon mirrorTransmission channel

Surface plasmon lense

Si substrate Spin coat substrate with PMMA resist

Expose to electron beam

Develop in MIBK/IPA

Metalize by vapor deposition

Electron-Beam Nanolithography (Peter Andersen)

Reflection Grating Behavior

First Attempt: Top-View AFM

AFM Micrograph of Second Attempt!

target ao 450 nm measured ao 450 nm

Grating Constant (ao)

Lens Pinhole Au MirrorNd:YAG Laser

= / 2sin

Photolithography (Michele Jacobson)

To be continued…..