Effect of Thin Coatings on Surface Plasmon-Enhanced Infrared

Spectroscopy using Ni Mesh Microarrays

Kenneth R. Rodriguez, Shannon Teeters-Kennedy, Hong Tian, Joseph Heer, Katie

Cilwa, and James V. Coe

Presentation for the 62nd Annual Spectroscopy Symposium

Ohio State UniversityJune 21, 2007

Presentation Overview

Surface Plasmons Extraordinary Transmission Surface Plasmon Spectroscopy (SPEIRA) Effect of Coatings TiO2 Coatings – Film Thickness Hexadecane Coatings – Stark Shifts

Analogies: Raindrops and Radio Waves

Raindrop transfers momentum and energy into waves on water surface

Raindrop Photo courtesy of M. Holt

e-

Electron transfers momentum and energy into waves of conducting electron plasma on metal surface. These waves are called “surface plasmons”

Radio Waves, Plasmons, and Extraordinary Transmission

Radio waves cause oscillating surface currents in antenna, which can travel past transmission barriers

Transmitting antennas can “recreate” original radio waves from the oscillating currents.

Similarly, surface plasmons can carry light past “optically thick” metal films such as our Ni mesh.

O

pti

cally

thic

k

meta

l

Incoming Light

“Transmitted” Light

Surface Plasmon propagation

Radio Wave

Connecting Wire

Non-t

ransm

itti

ng

Barr

ier

Oscillating currents in metal surface

Radio Wave

3 m Thick

Extraordinary Infrared Transmission1 using Nickel Mesh

6.5m

12.7m

6.5m

3 m thick

26% Open area

77% Light Transmitted at Primary Resonance

1 Ebbesen et. al., Nature, 391 (1998) 667; Williams et al., J. Phys. Chem. B 107 11871-79 (2003) 11871-79

69% of light that hits metal gets transmitted!

- + - + -

(1,0)+ Peak from SymmetricFront-Back Plasmon Coupling

- + - + -

+ - + - +

(1,0)- Peak from AsymmetricFront-Back Plasmon Coupling

Advantages of Mesh-Based SPEIRA

SPEIRA (Surface Plasmon-Enhanced InfraRed Absorption) has the following advantages:

1) Enhanced Absorption Pathlengths (10 m, not 10 nm)2) Enhanced Surface Selectivity (Plasmons confined to

surface)3) Enhanced Electric Fields (3-D light energy “squeezed”

into 2-D) 4) Enhanced Access to NanoSpaces (Plasmons < 1 nm

Thick)At a very low cost! (~$300 / sheet )

“Infinite” Transmission Enhancement

TiO2 NanoCoatings

Compare to Raether’s Fig. 2.1.7

incidence

No angling

Coating Shift

Radiation Damping Shift

Rodriguez et al., JCP, In Press (2007)

•Resonance Shifts with Coating

•Transmission Attenuation (1-sided coating)

•Broader Resonances as measured by FWHM

0 10 20 30 40 50 60 70 80 90 100 110Thickness (nm)

0

5

10

15

(1,0)+

Resonance Shifts due to Nanocoatings at incidence

)(radiation~x

Front-Back Coupling through the Holes

~

coating

...n)interactio(~ x

0

60

9075

105

)coating(~x x~

`m `s `d C D

Ni/NiO -150 35 1 0.62 42

Ni -1965 35 1 0.14 20

`m ,s-67 7 1 0.76 24

22

32212

21)0,1(

~)(

724~)(

05.078.0~ dnmcm

dnmcm

Calculated fit for (1,0)+

~

-(

cm-1)

~

6.2cm-1 shift of the 105 nm TiO2 coating simulated

22

32

2 ~~~ dDdC Pockrand’s Theoretical Model for Coating Shift

I. Pockrand, Surf. Sci., 72, 577, (1978).

C & D values calculated from dielectric permittivities of Ni, TiO2, and Air

Interaction of SP with a Vibration

Rodriguez et al., JCP, 126, 151101-5 (2007)

Interaction of SP with a Vibration

Stark Effects with FTIR Spectrometer

Stark shift of up to 3 cm-1 observed when CH2 rocking vibration near Plasmon Resonance

Hexadecane CH2 Rocking Vibration

Conclusions

We can measure coating thicknesses and characterize oxidation using simple FTIR measurements on inexpensive mesh substrates.

We can generate Stark shifts of up to 3 cm-1 and get increased transmission due to interactions of surface plasmons with excited molecular vibrations in liquid films.

Mesh-based SPEIRA is a powerful and useful tool for spectroscopy on or near surfaces.

ACKNOWLEDGEMENTS

Jim Coe (PI)

Kenneth

Rodriguez

Shannon Teeters- Kennedy

Katie Cilwa

Joe Heer

Hong Tian

CHE0413077