Surfaces, studies attenuated total internal reflection

The absorption is very intense, so direct measurement of absorption spectra requires very thin films. When the sample surface is smooth enough, the absorption can be calculated by Kramers-Kronig inversion of the reflectance, which can be done rather accurately for a well-isolated transition [113]. A strongly scattering sample must be studied by attenuated total internal reflectance. 

In this study SPR measurements were performed in air with p-polarized He-Ne laser (wavelength, 632.8 nm) as a light souree. An attenuated total internal reflection setup using the Kretschmann geometry was adopted for the excitation of the surface plasmon. Winspall 2, which is data analysis software (developed at the Max-PIanck-Institute for Polymer Research), was applied to simulate the reflectivity curves. 

The surfaces of infrared-transparent materials that are available in the form of shaped and polished crystals, such as silicon or germanium, can be studied with good sensitivity by using attenuated total internal reflection (ATR) in conjunction with multiple reflection procedures. 

Nucleic acid biosensors based on optical modes of detection represent another common approach for generating analytical signals based on nucleic acid hybridization. The methods discussed herein are based on methods that are suitable for the study of materials on surfaces. There are a number of different optical methods that have been described, with the most common being attenuated total reflectance (ATR), total internal reflection fluorescence (TIRF) and surface plasmon resonance (SPR) [15]. All of these methods work... 

The use of evanescent waves is very valuable to the study of interfacial properties. Techniques such as total internal reflection fluorescence (TIRF) and attenuated transmitted reflectance (ATR) use the energy of evanescent waves to probe thin regions in the vicinity of an interface to determine surface concentrations of interfacial species. 

In ATR-FTIR excitation occurs only in the immediate vicinity of the surface ol the reflection element, in an evanescent wave resulting from total internal reflection. The intensity of the evanescent field decays exponentially in the direction normal to the interface with a penetration depth given by (1.7.10.121, which for IR radiation is of the order of a few hundreds of nm. Absorption leads to an attenuation of the totally reflected beam. The ATR spectrum is similar to the IR transmission spectrum. Only for films with a thickness comparable to, or larger than, the penetration depth of the evanescent field, do the band intensities depend on the film thickness. Information on the orientation of defined structural units can be obtained by measuring the dichroic ratio defined as R = A IA, where A and A are the band absorbances for radiation polarized parallel and perpendicular with respect to the plane of incidence, respectively. From this ratio the second-order parameter of the orientation distribution (eq. [3.7.13]) can be derived ). ATR-FTIR has been extensively used to study the conformation and ordering in LB monolayers, bilayers and multilayers of fatty acids and lipids. Examples of various studies can be found... 

Specific spectroscopic techniques are used for the analysis of polymer surface (or more correctly of a thin layer at the surface of the polymer). They are applied for the study of surface coatings, surface oxidation, surface morphology, etc. These techniques are typically done by irradiating the polymer surface with photons, electrons or ions that penetrate only a thin layer of the polymer surface. This irradiation is followed by the absorption of a part of the incident radiation or by the emission of specific radiation, which is subsequently analyzed providing information about the polymer surface. One of the most common techniques used for the study of polymer surfaces is attenuated total reflectance in IR (ATR), also known as internal reflection spectroscopy. Other techniques include scanning electron microscopy, photoacoustic spectroscopy, electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy, secondary ion mass spectroscopy (SIMS), etc. 

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. ... 

A large number of different biochemical systems have been studied by optical measurement on continuous surfaces, using ellipsometry, attenuated total refiection, interference techniques and total internal reflection fluorescence (reference 6 lists 45 different experiments). It is therefore likely that evanescent wave spectroscopy will become a widely applied technique in the future. 

Internal reflection spectroscopy (2), also known as attenuated total reflectance (ATR), is a versatile, nondestructive technique for obtaining the IR spectrum of the surface of a material or the spectrum of materials either too thick or too strongly absorbing to be analyzed by standard transmission spectroscopy. The technique goes back to Newton who, in studies of the total reflection light at the interface between two media of different retractive indices, discovered that an evanescent wave in the less dense medium extends beyond the reflecting interface. Infrared spectra can conveniently be obtained by measuring the interaction of the evanescent wave with the external less dense medium. 

The use of infrared spectroscopy in the Earth and environmental sciences has been widespread for decades however, until development of the attenuated total reflectance (ATR) technique, the primary use was ex situ material characterization (Chen and Gardella, 1998 Tejedor-Tejedor et al., 1998 Degenhardt and McQuillan, 1999 Peak et al., 1999 Wijnja and Schulthess, 1999 Aral and Sparks, 2001 Kirwan et al., 2003). For the study of environmental systems, the strength of the ATR-Fourier transform infrared (FTIR) technique lies in its intrinsic surface sensitivity. Spectra are collected only from absorptions of an evanescent wave with a maximum penetration depth of several micrometers from the internal reflection element into the solution phase (Harrick, 1967). This short optical path length allows one to overcome any absorption due to an aqueous phase associated with the sample while maintaining a high sensitivity to species at the mineral-water interface (McQuillan, 2001). Therefore, ATR—FTIR represents a technique capable of performing in situ spectroscopic studies in real time. 

A number of sample cells are used to study surfaces by infrared. Figure 16 shows schematic diagrams of three types of reflectance cell. An internal reflection technique commonly used is attenuated total reflectance or ATR, with a typical ATR cell shown in Figure 16a. Samples such as polymer films, oils, or gels are coated onto a crystal of high refractive index... 

Sampling systems based on the multiple internal reflection (MIR) technique, also called attenuated total reflectance (ATR) spectroscopy [916], are very useful for the study of polymer surface degradation [476,1437]. 

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