Total internal reflection ellipsometry

The thicknesses of free soap films and liquid films adsorbed on surfaces (Figs. 1.26d and 1.26e), which can be measured using optical techniques such as reflected intensity, total internal reflection spectroscopy, or ellipsometry as functions of salt concentration or vapor pressure, can provide information on the long-range repulsive forces stabilizing thick wetting films. We see an example of this in Chapter 11. 

Apart from optical microscopy, there are some other optical techniques which are truly surface sensitive and have found widespread use. Examples are ellipsometry (see Section 9.4.1), total internal reflection fluorescence (TIRF) [316], and surface plasmon resonance techniques [348],... 

On the other hand, optical microscopy, confocal microscopy, ellipsometry, scanning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and total internal reflection fluorescence (TIRF) are the main microscopic methods for imaging the surface structure. There are many good books and reviews on spectroscopic and chemical surface analysis methods and microscopy of surfaces description of the principles and application details of these advanced instrumental methods is beyond the scope of this book. 

As a consequence, researchers from different disciplines of the life sciences ask for efficient and sensitive techniques to characterize protein binding to and release from natural and artificial membranes. Native biological membranes are often substituted by artificial lipid bilayers bearing only a limifed number of components and rendering the experiment more simple, which permits the extraction of real quantitative information from binding experiments. Adsorption and desorption are characterized by rate constants that reflect the interaction potential between the protein and the membrane interface. Rate constants of adsorption and desorption can be quantified by means of sensitive optical techniques such as surface plasmon resonance spectroscopy (SPR), ellipsometry (ELL), reflection interference spectroscopy (RIfS), and total internal reflection fluorescence microscopy (TIRE), as well as acoustic/mechanical devices such as the quartz crystal microbalance (QCM)... 

A variety of other techniques has been used to examine the structure of proteins at surfaces, including electron microscopy (50,51), ellipsometry (52), electrophoretic mobility (53), and total internal reflection fluorescence (TIRF) (54). Several new techniques are being applied at present, including Fourier transform infrared spectroscopy (FTIR) and TIRF (see next section),... 

SHG) [610], total internal reflection fluorescence (TIRF) spectroscopy [611], UV/Vis spectroscopy, IR spectroscopy, ellipsometry [612], quartz crystal microbalance (QCM) [613], STM [614], and AFM (see Refs. [618-623] for review of in sitn spectroscopies). From those, only the vibrational methods (SHG, SERS, and IR spectroscopy) are able to provide information on both the chemical composition and the strnctnre of the species adsorbed. The IR SEC experiment is simpler and more accessible than SHG and SERS, making IR spectroscopy the dominant tool for stndying electrochemical reactions at metallic electrodes [616, 617, 624-641]. 

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. 

Ellipsometiy is another common technique in the semiconductor industry. It provides an accurate measure of the film thickness. Since many resist shrink iqx>n deprotection due to a loss of volatile components, ellipsometry has been used do monitor the extent of deprotection in the resist. However, the technique does not provide direct infotmation about chemical bonding. Fourier transform infiared (FTIR) spectroscopy provides die best detail about chemical bonding, however it is a bulk technique widi little surfiice sensitivity. Moderate surface sensitivity can be achieved by utilizing total internal reflection FTIR, however the evanescent field will still propagate 500 nm away fix>m die surface making it difficult to detect true surface chemistry changes in a resist film. 

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