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 62 nd Annual Spectroscopy Symposium Ohio State University June 21, 2007

Presentation Overview Surface Plasmons Extraordinary Transmission Surface Plasmon Spectroscopy (SPEIRA) Effect of Coatings TiO 2 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. Optically thick metal Incoming Light “Transmitted” Light Surface Plasmon propagation Radio Wave Connecting Wire Non-transmitting Barrier Oscillating currents in metal surface Radio Wave 3  m Thick

Extraordinary Infrared Transmission 1 using Nickel Mesh 6.5  m 12.7  m 6.5  m 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 (2003) % of light that hits metal gets transmitted! (1,0) + Peak from Symmetric Front-Back Plasmon Coupling (1,0) - Peak from Asymmetric Front-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

TiO 2 NanoCoatings Compare to Raether’s Fig  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

Resonance Shifts due to Nanocoatings at  incidence Front-Back Coupling through the Holes ~ coating

`m`m `s`s `d`d CD Ni/NiO Ni  ` m,s Calculated fit for  (1,0) + ~ -  (cm -1 ) ~ 6.2cm -1 shift of the 105 nm TiO 2 coating simulated Pockrand’s Theoretical Model for Coating Shift I. Pockrand, Surf. Sci., 72, 577, (1978). C & D values calculated from dielectric permittivities of Ni, TiO 2, and Air

Interaction of SP with a Vibration Rodriguez et al., JCP, 126, (2007)

Interaction of SP with a Vibration

Stark Effects with FTIR Spectrometer Stark shift of up to 3 cm -1 observed when CH 2 rocking vibration near Plasmon Resonance Hexadecane CH 2 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 CHE