Surface phenomena internal reflection

Attenuated total reflection (ATR), also called internal reflection, is based on the phenomenon of total internal reflection. In ATR the infrared beam is directed into an infrared-transmitting crystal so that it strikes the crystal surface at less than the critical angle and undergoes total internal reflection. 

Raman Spectroscopy. As mentioned earlier, the Raman effect is an emission phenomenon, which means that front-surface sampling is possible. An irregularly shaped solid may be used in the spectrometer without processing it to make it flat, as required for internal reflection, or without processing it to a film or powder for transmission IR. Another sampling convenience is that Raman is more easily applicable to water solutions than IR. 

Polymethylmethacrylate exhibits a phenomenon known as total internal reflection. That term means that a light beam transmitted through a solid tube made of PMMA reflects off the inner surface of the tube. This property allows a light beam to be transmitted around corners and bends and out the end of a tube made of PMMA. 

The evanescent wave depends on the angle of incidence and the incident wavelength. This phenomenon has been widely exploited to construct different types of optical sensors for biomedical applications. Because of the short penetration depth and the exponential decay of the intensity, the evanescent wave is absorbed mainly by absorbing compounds very close to the surface. In the case of particularly weak absorbing analytes, sensitivity can be enhanced by combining the evanescent wave principle with multiple internal reflections along the sides of an unclad portion of a fiber optic tip. 

Over recent years, internal reflectance infrared studies have tended to concentrate on the study of relatively thick films of conducting polymers or layers, (see, for example, the work of Pham and coworkers [49, 50], or Kvarn-strom, Nauer, Neugebauer and coworkers [51-54]) in which sensitivity was not a particular problem, or on the semiconductor-electrolyte interface, (see the work of Chazalviel and coworkers [35, 40, 41]), in which the SPP excitation approach is not appropriate. However, interest has focused again on this phenomenon with the surface-enhanced infrared absorption spectroscopy (SEIRAS) studies of Osawa and coworkers [19, 26, 27, 46, 55, 56], who have combined the application of the Kretschmann configuration with step-scan FTIR spectroscopy to study fast, reversible electrochemical processes on timescales down to microseconds [26, 46, 57-60]. 

Attenuated total reflection (ATR) spectroscopy is one of the most widely used techniques for surface infrared analysis. Although the phenomenon of total internal reflection of light was described by Newton in the early 17th century, it was not until much later that Harrick and, independently, Fahrenfort were to exploit this phenomenon to obtain absorption spectra and develop the ATR technique. When applied to the study of in situ kinetics of adsorption and reaction of species at liquid/ solid interfaces, ATR spectroscopy can yield valuable surface-chemical data. Such studies have been carried out in a variety of research and technological areas, including biomembranes, biofilms, thin film structure and reactivity, and electrochemistry. ... 

The phenomenon of internal reflection was first reported in IR spectroscopy in 1959. It was observed that if certain conditions are met, IR radiation entering a prism made of a high refractive index IR transmitting material (ATR crystal) will be totally internally reflected (Figure 4.3). This internal reflectance creates an evanescent wave which extends beyond the surface of the crystal into the sample held in intimate contact with the crystal. In regions of the IR spectrum where the sample absorbs energy, the evanescent wave will be attenuated. 

Attenuated total reflection (ATR) Attenuation of the reflected wave intensity in total internal reflection due to energy losses in the medium which covers the face where reflection occurs. This phenomenon is used to monitor the excitation of surface polaritons in Otto and Kretschmann configurations. 

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