21 February 2008 Infrared spectroscopic imaging with high spatial resolution and high sensitivity
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Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) is a very sensitive imaging technique for the characterization of molecular films. In order to achieve a spatial resolution close to the diffraction limit a very small pinhole which acts as a point-source has to be used. However, such a small pinhole, the typical diameter would be app. 100 μm, may reduces dramatically the intensity of the infrared beam. Using a common FTIR spectrometer the spatial resolution is mainly limited by the brilliance of the globar infrared source. Therefore, an improvement in lateral resolution requires a more brilliant light source. The free electron laser (FEL) is such a high brilliant infrared source. The combination of the FEL with the PM-IRRAS imaging system is a new approach to capture spectroscopic images with an excellent spatial resolution close to the diffraction limit. PM-IRRAS images of a self assembly monolayer of phosphonic acid molecules onto a microstructures gold / aluminum oxide surface where characterized. The spectroscopic image exhibits a spatial resolution of app. 5 μm. An evaluation of characteristic absorbance bands of the phosphate group reveals that phosphonic acid molecules bound with a high degree of orientation but differently at the gold and aluminum oxide surfaces. However, the spectroscopic image reveals also several domains of disordering across the surface. Such domains have a dimension of only few micrometers and can be identified in a high resolved PM-IRRAS image.
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Valdas Sablinskas, Valdas Sablinskas, Gerald Steiner, Gerald Steiner, Justinas Ceponkus, Justinas Ceponkus, Reiner Salzer, Reiner Salzer, } "Infrared spectroscopic imaging with high spatial resolution and high sensitivity", Proc. SPIE 6869, Plasmonics in Biology and Medicine V, 68690X (21 February 2008); doi: 10.1117/12.768977; https://doi.org/10.1117/12.768977

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