Reflection based techniques

With the exception of SIMS, the above techniques along with various other related spectrometric and spectroscopic techniques are summarized in Appendix A. 10. For completeness sake, various microscopies of interest are covered in Appendix A. 11., whereas various diffraction and reflection-based techniques are summarized in Appendix A.12. 

A number of surface diffraction techniques can be employed in the structural study of electrochemical interfaces, depending on the details of the system under study. For bulk materials or thick films (such that the X-ray beam only samples that layer) conventional diffraction experiments can be performed and, in fact, a number of in situ X-ray diffraction studies of this type have been reported.126 129 In the case of thin films or monolayers, two different techniques can be employed and these are the reflection-diffraction technique introduced by Marra and Eisenberger,3 ), 32 and the technique based on surface truncation rods.131 In the first case, the incident X-ray beam impinges on the sample at an angle below... 

Because chemical and structural properties of natural and artificial gems are very similar in this case, the possibilities of Raman and LIBS methods are rather limited. It was found that another laser-based techniques could be very effective for rapid spectroscopic discrimination between natural and synthetic emeralds, rubies, and alexandrite (Armstrong et al. 2000a,b). The first one is DRIFTS (Diffuse Reflectance Fourier Transformed Infra-Red Spectroscopy)... 

First, surface-sensitive techniques that can operate under technologically relevant conditions, i.e., at least in the 1 —lOOOmbar pressure range, are required. In this respect, photon-based techniques such as sum frequency generation (SFG) and polarization-modulation IR reflection absorption spectroscopy (PM-IRAS) provide surface vibrational spectra of adsorbates from UHV up to atmospheric pressure. Although electron spectroscopies are typically limited to pressures <10 mbar, recent developments in XPS allow the determination of... 

Reflectance-based optical characterization techniques offer the advantages of high energy resolution and sensitivity to both macrostructural and microstructural effects while nondestructively providing real-time information with the sample in any transparent ambient. Experimental and analytical methods are discussed, and examples are given to illustrate representative applications to problems of current interest in semiconductor technology. 

This paper is intended to give a brief overview of reflectance-based optical characterization techniques and their applications to determining sample properties. The next section deals with general principles, and includes comments about Instrumentation and analytic methods. The rest of the paper consists of representative examples. Other applications can be found in several recent reviews and symposium proceedings (1-5). Length limitations preclude extensive discussions references should be consulted for further details. 

The above examples are representative of the present capabilities of reflectance-based optical characterization techniques. Other applications can be found in the general references given in the introductory paragraphs. Ir reflectance has not been discussed, not from lack of examples (31. 32), but because the major fraction of reflectance characterization has been done in the v-uv. Additional progress and new applications can be expressed in all areas. 

The synthetic effort towards combinatorial libraries of several hundred thousand compounds is considerable.Therefore, computer-based techniques were introduced to reflect and analyze compound libraries to enhance the composition, while constraining their size. 

Due to the intrinsic characteristics of flow analysis mentioned above, more and more attention is being given to this family of techniques. This is reflected in the numerous articles, books, reviews, and conference proceedings that have been published on flow analysis (see e.g.. Appendices 1.1 and 1.2). Internet databases, web pages of prominent researchers, tutorials, as well as standard, recommended, and/or official methods have recently been highlighted [22]. The ultimate objectives of this book are therefore to provide a sound scientific foundation for those interested in flow-based techniques and to familiarise a wide community of potential end-users, e.g., researchers, students and technical staff, with the... 

This chapter is not intended as a comprehensive review of in-situ studies of the near-electrode region by infrared spectroscopy, but rather the intention is to highlight the versatility of IR-based techniques (and particularly those involving external reflectance) and the wide range of application of such techniques to modern electrochemistry. 

Of the many X-ray based techniques available, a very powerful approach for probing interfacial structures is based on the measurement of X-ray reflectivity. The X-ray reflectivity is simply defined as the ratio of the reflected and incident X-ray fluxes. In the simple case of the mirror-like reflection of X-rays from a surface or interface, i.e., specular reflectivity, the structure is measured along the surface normal direction. Lateral structures are probed by non-specular reflectivity. The measurement and interpretation of X-ray reflectivity data (i.e., the angular distribution of X-rays scattered elastically from a surface or interface) (Als-Nielsen 1987 Feidenhans l 1989 Robinson 1991 Robinson and Tweet 1992) are derived from the same theoretical foundation as X-ray crystallography, a technique used widely to study the structure of bulk (three-dimensional or 3D) materials (Warren 1990 Als-Nielsen and McMorrow 2001). The immense power of the crystallographic techniques developed over the past century can therefore be applied to determine nearly all aspects of interfacial structure. An important characteristic of X-ray reflectivity data is that they are not only sensitive to, but also specifically derived from interfacial structures. 

Vibrational modes of the molecules in the film are displayed as sharp peaks on the plot of d I/dV against AV Even though both Raman and infrared active modes are also active in lETS, only modes perpendicular to the surface are observed (as is also the case in reflection spectroscopy based techniques). 

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