Surface‐sensitive Raman microscopy with total internal reflection illumination

Abstract

A Raman microscope using a total internal reflection (TIR) annular illumination geometry through a ZnSe solid immersion lens (SIL) is described. Spectra of a thin-film sample of the transparent organic conductor poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT : PSS) on a polyethylene terephthalate (PET) substrate are presented and compared with those from a conventional confocal Raman configuration. These spectra demonstrate a significant increase in surface selectivity upon the use of TIR illumination, as the decay length of the evanescent excitation field limits the depth of sample probed in this configuration. Spectral interference from the underlying PET substrate layer is thus greatly reduced. An increase in surface selectivity is also demonstrated for spectra acquired through the SIL with uniform illumination. Raman images of a micropatterned PEDOT : PSS film acquired with TIR illumination are also reported. Enhanced lateral resolution is realized in this configuration because of the immersion effect of the SIL, and the sampling depth is limited to 150 nm by the choice of illumination geometry. This results in analysis volumes on the order of tens of femtoliters, nearly two orders of magnitude smaller than typically achieved in conventional confocal Raman microscopes. This approach yields Raman spectra and images with surface selectivity significantly greater than can be achieved in confocal Raman, and provides a valuable tool for the microanalysis of thin surface films. Published in

Recent advances in linear and nonlinear Raman spectroscopy. Part V

“…In a related paper, Jehlicka, Vitek and Edwards presented the results of Raman spectra of organic acids obtained using a portable instrument at −5°C in a mountain area at 2000 m above sea level . A Raman microscope using a total internal reflection annular illumination geometry through a ZnSe solid immersion lens was described by Michaels . Spectra of a thin‐film sample of the transparent organic conductor poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) on a polyethylene terephthalate substrate were presented and compared with those from a conventional confocal Raman configuration.…”

Surface characterization of silicate bioceramics

“…For example, a laser at 785 nm (commonly used to analyse biological samples) and an objective with NA = 0.8 provide a depth of analysis of 4.9 mm [58]. Higher surface sensitivity can be achieved with lasers at higher frequency and higher NA objectives; however, higher frequency lasers often cause fluorescence in biological samples, and may damage them.…”

Total internal reflection Raman spectroscopy

“…Greene looked at polyethylene naphthalate on polyethylene terephthalate (PET) 7 and Michaels looked at a thin poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) film on PET. 33 Michaels acquired Raman images ( figure 9) by scanning the hemispherical lens and taking spectra at each point, revealing a partially covered surface. The choice of samples is not limited to synthetic polymers: Greene and Bain looked at epicuticular leaf waxes in vivo.…”