Surface Enhanced Infrared Absorption (SEIRA) Spectroscopy 07/15/08 Benjamin Dach

The Theory Molecules adsorbed on metal island films or particles exhibit 101 – 103 times more intense infrared absorption than without the metal. The electromagnetic (EM) interactions of the incident photon field with the metal and molecules predominantly cause the enhancement. Surface Enhanced Raman Scattering (SERS) is a very similar phenomenon to SEIRA, yet it’s enhancement is on the order of <106. The metal islands are polarized by the incident photon field through the excitation of collective electron resonance, or localized plasmon modes, and the dipole p induced in an island generates a local EM field stronger than the incident photon field around the island Topics Appl. Phys. 2001, 81, 163–187

Attenuated Total Reflection (ATR) Spectroscopy This reflection forms the evanescent wave which extends into the sample. The observed band intensities depend on the polarization and angle of incidence of the infrared radiation. Coupling ATR with SEIRA can give signal enhancement at least on the order of 104.

First Finding of SEIRA in 1980 The IR absorption from molecular monolayers of 4-nitro-benzoic acid, benzoic acid, and 4-pyridine-COOH is enhanced by a factor of 20 by thin metal overlayers or underlayers with the use of ATR. The total enhancement, including contributions from the ATR geometry, is almost 104. Phys. Rev. Lett. 1980, 45(3), 201-204 of 4-nitro-benzoic acid. on metal overlayer thickness.

On Low Reflective Surfaces - BaF2, Ge, microscope slide glass, and poly(acrylonitrile-butadiene-styrene) resin. The sensitivity of the reflection IR spectroscopy at these surfaces is remarkably improved by evaporating very thin layer films on the sample surfaces. Anal. Chem. 1993, 65, 556-562

The Importance of Metal Morphology Enhanced IR absorption of C60 on thin evaporated Pd island films onto surface-oxidized (Si_Ox) Si(100) and hydrogen-terminated (Si_Hterm) Si(111) substrates Isr. J. Chem. 2006, 46, 257-263

H2@C60? Can surfaced enhanced IR techniques be used to detect the H2 inside the C60? Off center translational motion creates a dipole on the H2@C60 complex detectable by mid-infrared spectroscopy. Will the surface enhancement give a more powerful signal?

Post-annealing temperature dependence of infrared absorption enhancement of polymer on evaporated silver films Thin Solid Films 2007, 515, 3073-3078

Conclusions SEIRA is a relatively recent innovation in detecting vibrational modes on surfaces. Ultrathin films adsorbed onto metal island films can be detected most readily. Metal layer morphology, thin film thickness, temperature effects, and angle of incident beam are important factors in maximizing the enhanced signal Future Research: Bilayers and monolayers at a liquid–liquid interface Adsorption monolayers and Langmuir (water-insoluble) monolayers at an air–water interface Adsorption films and self-assembled monolayers (SAMs) at a liquid–solid interface Langmuir–Blodgett films, cast (deposit) films, and spin-coat films at an air–solid interface.