Eiichi Sudo

Attenuated Total Reflection Surface-Enhanced Infrared Absorption Microspectroscopy for Identification of Small Thin Layers on Material Surfaces

Attenuated total reflection surface-enhanced infrared absorption microspectroscopy (micro-ATR-SEIRA) was developed for the identification of sub-mm size and nm-thick layers on material surfaces by using gold island films deposited on the surface of micro-ATR crystals. A thin layer of triphenyl phosphate (TPP) on a poly(tetrafluoroethylene) (PTFE) membrane filter was used to evaluate the enhancement of the absorption bands. Three types of crystals: diamond, silicon, and germanium, were evaluated. Diamond gave the greatest enhancement with a 12 nm thick gold island film. The enhancement factor was 200 times compared to bare diamond crystal, whereas it was 10 times for germanium crystal. This variation of enhancement factor according to crystal types was presumed to be due to the morphology of the gold films on the crystals. We also obtained an enhanced ATR map over an area of approximately 2 × 6 mm for a thin layer (approximately 1 nm thick) of di-2-ethylhexylphthalate on PTFE using gold-coated hexagonal silicon micro-ATR crystals. This micro-ATR-SEIRA technique has major potential for analyzing small and thin substances on material surfaces.

Attenuated Total Reflection Surface-Enhanced Infrared Absorption (ATR SEIRA) Spectroscopy for the Analysis of Fatty Acids on Silver Nanoparticles:

The application of attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR SEIRA) to the analysis of fatty acids on silver nanoparticles was investigated. Attenuated total reflection measurements using four types of internal reflection elements (IREs)—zinc selenide, diamond, silicon, and germanium—were performed for silver nanoparticles modified with fatty acids, and germanium IRE was shown to be suitable for the analysis of silver nanoparticles, even when the sample had a high refractive index. Fatty acids coating the silver nanoparticles could be directly identified by SEIRA enhancement, because both symmetric carboxylate stretching vibration and methylene wagging vibration were strongly detected. Furthermore, the peak positions for methylene wagging vibration differed depending on the carbon number of the fatty acid, so that information from the ATR SEIRA spectra makes it possible to identify substances coating silver nanoparticles. Therefore, ATR SEIRA would appear to have significant potential as a technique for the identification of substances coated on metal nanoparticle surfaces.