Grazing internal reflection

Very thin films (monolayer or multilayer) can be studied by IR spectroscopy, provided that the IR beam crosses a reasonably large fraction of the monolayer this can be done by (i) grazing-angle techniques (whereby the IR beam angles of incidence and reflection are of the order of 1° to 3°) or (ii) multiple internal reflections of the IRbeam inside the monolayer (infrared reflectance and absorbance spectroscopy (IRRAS). Fig. 11.19 shows the chemical structure of an analyte (Fullerene-fcz s-[ethylthio-tetrakis(3,4-dibutyT2-thiophene-5-ethenyl)-5-bromo-3,4-dibutyl-2-thiophene] malonate),... 

Unique information about the unit cell in quasi-crystaUine monolayers can be obtained from X-ray °, neutron , heUum or low energy electron diffraction (LEED) data. In the grazing incidence X-ray diffraction (GIXD) experiment the beam is directed at the coated surface at a low angle and experiences total internal reflection from the metal support underneath the monolayer. The analysis of reflectivity and diffraction pattern of this reflected beam provides information about the molecular structure of the crystalline films, the thickness and refractive index of the layers and the roughness of the surface s . These experiments, however, require sophisticated and expensive equipment and are not therefore used routinely for monolayer characterization. 

IR transmission of the Si-bonded wafers at a grazing angle of is a highly sensitive technique and does not require multiple internal reflections (which would necessitate a beveled Si substrate). The resulting spectra are the best for... 

Although the optimum conditions for a number of simple systems are known (e.g., for ultrathin films on metals reflection-absorption (IRRAS) at grazing angles of incidence is commonly used, and for ultrathin films on transparent substrates, multiple internal reflection (MIR) is most suitable in many cases), the spectral contrast can be further enhanced by employing additional special technical approaches. 

Masuko, M., Toda, Y. and Suzuki, A., Grazing-angle reflection FT-IR spectroscopy of adsorbed molecular films on the rubbed steel surface. Proc. Intern. Trib. Conf, Nagasaki, Oct. 2000, pp. 493-497. publ. JST, Tokyo. 

The interior side walls are coated with an IR-reflective gold film, and the beam remains confined within the pipe by grazing-incidence total internal refiection. 

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