Optical grazing angle

L. F. De La Torre-Quintana, S. P. Hemandez-Rivera, Characterization of thermal inkjet technology TNT deposits by fiber optic-grazing angle probe FTIR spectroscopy. Sensors, and Command, Control, Communications, and Intelhgence (C3I) Technologies for Homeland Security and Homeland Defense IV Edward M. Carapezza Ed., Proc. SPIE, 5778, 543-552 (2005). 

Though a powerfiil technique, Neutron Reflectivity has a number of drawbacks. Two are experimental the necessity to go to a neutron source and, because of the extreme grazing angles, a requirement that the sample be optically flat over at least a 5-cm diameter. Two drawbacks are concerned with data interpretation the reflec-tivity-versus-angle data does not directly give a a depth profile this must be obtained by calculation for an assumed model where layer thickness and interface width are parameters (cf., XRF and VASE determination of film thicknesses. Chapters 6 and 7). The second problem is that roughness at an interface produces the same effect on specular reflection as true interdiffiision. 

Figure 2. Optical schematic of the chamber for grazing angle measurements. Heaters and one thermocouple are located directly behind the sample (A). Gas inlet and outlet are near the IR transmitting windows (B). The mirrors (C) can be rotated and tilted to maximize signal and eliminate stray light. The entire cell (D) can be translated to change the angle of incidence.

M.L. Hamilton, B.B. Perston, PW. Harland, B.E. Williamson, M.A. Thomson and P.J. Melling, Grazing-angle fiber-optic IRRAS for in situ cleaning validation, Org. Process Res. Dev., 9, 337-343 (2005). 

The application of FT-IR to a wide variety of interfacial phenomena is possible using either attenuated total reflectance (ATR) or grazing angle reflection -absorption. The details of these optical techniques are discussed in a subsequent chapter, in the context of characterization of Langmuir - Blodgett films and self-assembled mono and multilayers. However, ATR has been applied in a number of other areas which will be mentioned here. 

Reflection-absorption (RA) or grazing-angle spectroscopy, is a very useful technique that gives information about the direction of transition dipoles in a sample. Figure 3 present an optical setup for a grazing-angle experiment (22). 

Optical cell grazing angle optical cell, - long path length optical cell... 

In this work the first method for detection and quantification of a chemical agent s simulants on metallic surfaces using sample smearing on surface as transfer method was evaluated as a proof of concept experiment. Spectroscopic characterization of thin layer deposits was achieved using the powerful technique of Grazing Angle Probe-Fiber Optic Coupled-FTTR developed for surface analysis . This methodology relies on... 

Reflection-Absorption Infrared Spectroscopy (RAIS) operating at the grazing-angle which is one of the most powerful resonance absorption phenomenon and is the most sensitive optical absorption technique available for measuring low concentrations of chemical componnds adhered to surfaces and even allows for the non-destractive mono layer chemical analysis on the surface. Figure 6 shows the FOC-GAP-FTIR spectra 5 and 10 ug/cm 2-CEES deposited as a trace residue on stainless steel surface. It is clear from the spectra shown that low limits of detection (LOD) achievable could be as low as nanograms/cm (milligrams/m ). 

Layers on Metals. The bands in IRRAS are positive, independent of the angle of incidence, as in the absorption spectrum. The band shape is sensitive to the dielectric properties of the metal substrate and the angle of incidence The band shape becomes asymmetrical with decreasing optical conductivity of the metal and at grazing angles. 

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