Optical methods, surface analysis

To relate the wettability changes more firmly to the photooxidation processes and products, a detailed study was carried out with polystyrene. This polymer was selected because the formation of oxidation products in the hydrocarbon surface gave rise to large changes in wettability and because these products would be readily accessible to optical methods of analysis. The ultraviolet absorption spectrum of polystyrene shows a sharp cut-off, and the extinction coefficients for the radiation absorbed are sufficiently high that almost all of the photochemical reaction should be confined to the surface layers. 

Analysis of Surface Molecular Composition. Information about the molecular composition of the surface or interface may also be of interest. A variety of methods for elucidating the nature of the molecules that exist on a surface or within an interface exist. Techniques based on vibrational spectroscopy of molecules are the most common and include the electron-based method of high resolution electron energy loss spectroscopy (hreels), and the optical methods of ftir and Raman spectroscopy. These tools are tremendously powerful methods of analysis because not only does a molecule possess vibrational modes which are signatures of that molecule, but the energies of molecular vibrations are extremely sensitive to the chemical environment in which a molecule is found. Thus, these methods direcdy provide information about the chemistry of the surface or interface through the vibrations of molecules contained on the surface or within the interface. 

Complete characterization of poisoned catalysts, of course, requires much more than chemical analysis. For example, the interaction of poisons with catalyst constituents and with each other has been studied by X-ray diffraction and by electron microscopy, the morphology of the poison deposits by optical methods, the distribution within the catalyst pellets and washcoats by the microprobe, and the distribution of poison on the surface of the active metals by Auger spectroscopy. 

Optical microscopy is often the first step in surface analysis, since it is fast and easy to perform. It can be an aid in selecting the area of interest on a sample for further analysis with more complex methods. The application of classical optical microscopy to surface science is, however, limited because the maximum lateral resolution is in the order of the optical wavelength ( 500 nm). For opaque solids, the light penetrates into the material, giving optical microscopy a poor surface sensitivity. In addition, the depth of field is limited which calls for flat, polished surfaces or allows only plane sections of the sample to be viewed. 

Recent developments in surface-characterization methods have been made possible to a great extent by technological advances in areas such as lasers, ultra-high vacuum, charged-particle optics, and computer science. The surface-analysis techniques are commonly used to probe the interface between two phases after one phase is removed, but there is now a growing demand for additional methods for in situ interface characterization. 

To combine optical SFG spectroscopy with the more traditional surface analysis methods (e.g., LEED, AES, TPD, XPS), the basic requirement is to simply add IR-transparent windows (e.g., CaF2 or BaF2) to a UHV chamber. However, if SFG spectroscopy is to be carried out at high pressure or during catalytic reactions, instruments combining a EIHV surface analysis system with an SFG-compatible... 

Establishing the surface area is the next concern. Electrode surfaces are seldom flat. Instead, they tend to display a set of different crystal faces. Sliver Iodide electrodes, prepared by amalgamation of silver with mercury, followed by vapour deposition of iodine, look smooth and shiny to the naked eye but reveeil crystallites under the electron microscope. Surface Irregularities not only complicate the assessment of the real area, they may also Interfere in the analysis of impedance spectra In terms of equivalent circuits. After drying, the surface may be studied by the usual optical methods (sec. 1.2) with the famlllrir caveat that drying may change these properties. Anyway, for a number of oxides and silver iodide It Is now established that electrodes can be made which have... 

It is important to consider the connection between the two types of studies. One often refers to the "pressure gap" that separates vacuum studies of chemisorption and catalysis from commercial catalytic reactions, which generally run above —often well above — atmospheric pressure. There is simply no way to properly simulate high pressure conditions in a surface analysis system. Reactions can be run in an attached reaction chamber, which is then pumped out and the sample transferred, under vacuum, into an analysis system equipped for electron, ion and photon spectroscopies. However, except for some optical and x-ray methods that can be performed in situ, the surface analytical tools are not measuring the system under reaction conditions. This gap is well recognized, and both the low- and high-pressure communities keep it in mind when comparing their results. 

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... 

Ellipsometry and Other Optical Methods for Surface and Thin Film Analysis" Abeles, F. Ed. J. de Physique-Colloque. 

Ebuchi N, Kawamura H, Toba Y (1987) Fine structure of laboratory wind-wave surface studied using an optical method. Bound Layer Meteorol 29 133-151 Hughes BA (1978) The effect of internal waves on surface wind waves. 2. Theoretical analysis. J Geophys Res 83 455-465 Hughes BA, Grant HL (1978) The effect of internal waves on surface wind waves. 

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. 

Among the ex situ methods that can be employed in surface analysis, low-energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) can give the crystal structure and the nature of the surface ad-layers after the electrochemical and adsorption experiments as explained in this chapter [31,32]. Among the in situ non-electrochemical techniques, the radiotracer method [33] gives information about the adsorbed quantities however, infrared spectroscopy in FTIR mode [34] allows the identity of the bonding of the adsorbed molecules, and finally ellipsometry [35] makes possible the study of extremely thin films. Recently, some optical methods such as reflectance, x-ray diffraction, and second harmonic generation (SHG) [36] have been added to this list. 

A. Campion, Paper presented at Ellipsometry and other Optical Methods for Surface and Thin Film Analysis, Paris, France, June 1983. 

This chapter discussed the application of the electro-optical reflection method in the in situ observation of the adsorption and desorption of bioactive substances at an electrode surface acting as a simple model of charged sites at a biosurface. This method should find extensive application in various bioelectrochemical fields as a potent means of surface analysis. Electrode surfaces, though much simpler than biosurfaces, still provide data reflecting actual occurrences at biosurfaces in some respects. Electro-optical studies on the behavior of bioactive substances at electrode surfaces should provide some indication of how such substances behave at biosurfaces. 

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