Multiple internal reflectance MIR

The most commonly used technique for obtaining a spectrum is the attenuated total reflectance (ATR) method in the multiple internal reflectance (MIR) mode. In this method, the infrared beam is passed into a special crystal of a selenide (KRS-5). The angle of incidence is such that the beam will bounce along the crystal. A sample of the polyurethane is placed hard up against the crystal. The infrared just penetrates into the material before it continues down the crystal. A number of internal bounces are obtained along the crystal. Up to 25 reflectances are obtained from a 2 mm crystal. Figure 9.8 illustrates the infrared path in an ATR cell. 

Jackman, R.J., Queeney, K.T., Herzig-Marx, R., Schmidt, M.A., Jensen, K.F., Integration of multiple internal reflection (MIR) infrared spectroscopy with silicon-based chemical microreactors. Micro Total Analysis Systems, Proceedings 5th Y7AS Symposium, Monterey, CA, Oct. 21-25, 2001, 345-346. 

The samples of impact polystyrene and a thermoplastic polyurethane were weathered in Florida, and then examined with a scanning electron microscope and with a multiple internal reflectance (MIR) spectrophotometer with the following results. 

The macromolecular forms at the interface were characterized by determining the spreading isotherms at various temperatures and by the technique of multiple internal reflection (MIR). 

Multiple internal reflectance (MIR) and ATR are similar techniques, but MIR.prodjtces more intense spectra from multiple reflections. While a prism is normally used in ATR work, MIR uses specially shaped crystals which cause many Internal reflections, i.e. typically 25 or more (Figure 3.3b). 

Comaish (1968) has applied the technique of multiple internal reflection (MIR) to intact human skin in vivo. Using a germanium reflector plate he obtained spectra (in a Wilks Skin Analyzer ) of normal skin (Fig. 18.7) and various dermatoses (e.g., Fig. 18.8) and found gross changes from the normal in the lesions of psoriasis, eczema, and other disorders. He has also demonstrated abnormalities in the clinically normal skin of psoriatic patients. The technique measures surface changes, so that only the outer layers of stratum corneum, sweat, sebum, and extraneous materials will affect the results obtained. Lactic acid, lactate, and ammonia from sweat probably contribute substantially to the bands at 2935, 1465, 1125, and 1045 cm . After the skin was washed and dried these bands were diminished or disappeared entirely. Any contributions the stratum corneum makes to the infrared spectrum are at 2870, 1650, and 1550 cm . ... 

If the shield is thin and moderately conducting, the internal reflection phenomenon gets actuated, such that the attenuation due these multiple internal reflections (MIRs), i.e., can be expressed as [1-3,5,11,16] ... 

The Infrared Internal Reflectance Approach An interesting alternative method of minimizing the solution path-length is to employ internal reflectance or attenuated total reflectance (ATR) and this was the approach adopted by the authors of the first report on the acquisition of in situ infrared spectra Mark and Pons [39] employed the ATR approach, [or, as they termed it, frustrated multiple internal reflection (MIR)-see below], to... 

Internal reflection approaches rely upon the total reflection of the infrared beam one or more times, (multiple internal reflection, MIR), at the internal surface of an infrared transparent crystal or internal reflection element (IRE) such as Ge, Si, GaAs, or ZnSe, Medium 1 in Fig. l(a)(i and ii). If the IRE is a semiconductor such as Ge, Si, or GaAs, it can serve as the working electrode, which vras the case in the work of Mark and Pons, who employed a Ge IRE. More recently, Chazalviel and coworkers have pubhshed extensive and detailed studies on the GaAs, Ge, and Si electrolyte interfaces,... 

The MSEF formalism was used for deriving the formulas for estimating the adsorption density at the internal reflection element (IRE)-solution interface [153, 154, 166-174], Assuming that (1) species at the solid-solution interface are steplike distributed (with the maximum at the surface), (2) the refractive index of the adsorbed species is close to that of the solution, and (3) the absorption indices of the adsorbed and solvated species are close to each other, Tompkins [166] derived heuristically the following equation that describes the absorbance per reflection in the multiple internal reflection (MIR) spectrum of the species adsorbed at the IRE ... 

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. 

ATR has been found as an easy to use, non-destmctive and surface-sensitive IR sampling technique for the in situ investigation of CMP processes (Hind et al., 2001). It was initially pushed by Harrick (1967) and comprehensively treated in his early book and following editions together with Mirabella (1985). Numerous alternative and partially deceptive names are used instead of ATR spectroscopy internal reflection spectroscopy, evanescent wave spectroscopy, frustrated total internal reflection (FTIR, which should not to be confused with Fourier-transform infrared spectroscopy) and multiple internal reflection (MIR, which should not to be confused with mid-infrared )- Therefore, in the following the term ATR as defined in Section 14.4.1 and illustrated with Figure 14.8 is used exclusively. 

Internal reflection spectroscopy, also known as attenuated total reflectance (ATR) or multiple internal reflectance (MIR), is a versatile, nondestructive technique for obtaining the infrared 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. 

Figure 4.2 Schematic diagrams of some reflection spectroscopy techniques (a)-(c), internal reflection spectroscopy (a) and (b), single-reflection ATR (c), multiple internal reflection (MIR) (d) transflectance . Notes (i) collimated beam with ATR hemicylinder (ii) the component of specular reflectance (dotted line) will be superimposed on the double-pass transmission spectrum of the film in the transflectance measurement.

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]. 

Attenuated total reflection (ATR) has grown into the most widely practiced technique in infrared spectrometry. The reasons for this are fairly straightforward the technique requires little or no sample preparation, and consistent results can be obtained with relatively little care or expertise. The technique is not foolproof, but it can be very forgiving. ATR spectrometry is known by a number of alternative names, for example, multiple internal reflection (MIR), which is not to be confused with mid-infrared, frustrated multiple internal reflection (FMIR), evanescent wave spectrometry (EWS), frustrated total internal reflection (FTIR), which is not the same as Fourier transform infrared (FT-IR) spectrometry, and internal reflection spectrometry (IRS), but IRS is better known, at least in the United States, as the Internal Revenue Service. 

If the sample is placed in good contact with the surface of an optical device of high refractive index (such as a prism of KRS-5) and illuminated through the prism by IR, the beam passes into the layers in contact and is attenuated before being totally internally reflected by the system, as shown in Figure 5(b). This is called attenuated total reflectance or ATR. If the beam interacts several times, then we have multiple internal reflectance (MIR) and if the surface is horizontal, which is an advantage in setting up the sample, then it is horizontal attenuated total reflectance (HATR). 

Infrared studies of the amide I band of transferred films of jS-lacto-globulin B spread on 0.5 M KCl were obtained via the multiple internal reflection (MIR) technique by Loeb. The spectra were recorded following transfer of films maintained at different surface pressures. At a high... 

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