Infrared spectroscopy Interface properties

The interface properties can usually be independently measured by a number of spectroscopic and surface analysis techniques such as secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS), specular neutron reflection (SNR), forward recoil spectroscopy (FRES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), infrared (IR) and several other methods. Theoretical and computer simulation methods can also be used to evaluate H t). Thus, we assume for each interface that we have the ability to measure H t) at different times and that the function is well defined in terms of microscopic properties. 

Most earlier papers dealt with the mercury electrode because of its unique and convenient features, such as surface cleanness, smoothness, isotropic surface properties, and wide range of ideal polarizability. These properties are gener y uncharacteristic of solid metal electrodes, so the results of the sohd met electrolyte interface studies are not as explicit as they are for mercury and are often more controversial. This has been shown by Bockris and Jeng, who studied adsorption of 19 different organic compounds on polycrystaUine platinum electrodes in 0.0 IM HCl solution using a radiotracer method, eUipsometry, and Fourier Transform Infrared Spectroscopy. The authors have determined and discussed adsorption isotherms and the kinetics of adsorption of the studied compounds. Their results were later critically reviewed by Wieckowski. ... 

Lambert reviews the role of alkali additives on metal films and nanoparticles in electrochemical and chemical behavior modihcations. Metal-support interactions is the subject of the chapter by Arico and coauthors for applications in low temperature fuel cell electrocatalysts, and Haruta and Tsubota look at the structure and size effect of supported noble metal catalysts in low temperature CO oxidation. Promotion of catalytic activity and the importance of spillover are discussed by Vayenas and coworkers in a very interesting chapter, followed by Verykios s examination of support effects and catalytic performance of nanoparticles. In situ infrared spectroscopy studies of platinum group metals at the electrode-electrolyte interface are reviewed by Sun. Watanabe discusses the design of electrocatalysts for fuel cells, and Coq and Figueras address the question of particle size and support effects on catalytic properties of metallic and bimetallic catalysts. 

Vibrational spectroscopy provides an excellent tool for examining interfacial properties. Experiments have been carried out using both the infrared and Raman techniques [12-14]. Discussion is limited here to Fourier transform infrared spectroscopy (FTIR) in the reflection mode. It is important to understand how the infrared radiation interacts with dipolar adsorbates at the interface. Consider an electromagnetic wave travelling in the (x, z)-plane, which strikes the interface located in the (x, y)-plane at an angle 0 with respect to the interface (see fig. 10.7). The electrical field vector associated with the wave can be resolved into two components, one oscillating in the (x, z)-plane (the parallel or p-component)... 

Hirschmugl CJ (2002) Frontiers in infrared spectroscopy at surfaces and interfaces. Surf Sci 500 577-604 Hochella MF Jr (1988) Auger electron and photoelectron spectroscopies. Rev Mineral 18 573-637 Hochella MF Jr (1995) Mineral surfaces Their characterization and their chemical, physical, and reactive properties. In Vaughan DJ, Pattrick RAD (eds) Mineral Surfaces, Mineral Soc Ser 5, Chapman Hall, London, p 17-60... 

Although Raman spectroscopy does not employ absorption of infrared radiation as its fundamental principle of operation, it is combined with other infrared spectroscopies into a joint section. Results obtained with various Raman spectroscopies as described below cover vibrational properties of molecules at interfaces complementing infrared spectroscopy in many cases. A general overview of applications of laser Raman spectroscopy (LRS) as applied to electrochemical interfaces has been provided [342]. Spatially offset Raman spectroscopy (SORS) enables spatially resolved Raman spectroscopic investigations of multilayered systems based on the collection of scattered light from spatial regions of the samples offset from the point of illumination [343]. So far this technique has only been applied in various fields outside electrochemistry [344]. Fourth-order coherent Raman spectroscopy has been developed and applied to solid/liquid interfaces [345] applications in electrochemical systems have not been reported so far. 

The surface properties of amorphous silicas are largely influenced by the nature of the surface silanol (SiOH) groups [1-3]. Lewis acid—base sites are absent unless the silica has been activated at very high temperatures, Brpnsted acidity at the gas—solid interface is low or nonexistent, and the sUoxane bridges are relatively unreactive toward most molecules. This chapter discusses some methods that employ chemical modiflcation and H-D exchange to probe the nature of the surface hydroxyl groups on silica. Infrared spectroscopy is the main technique used, and one objective has been to compare the silanol groups on a fumed silica with those on a precipitated silica. 

As dimensions of a microelectronic device shrink funher, the surface and interface propenies of its components become increasingly determinant of its properties. A low energy electron beam, with a very shon penetration depth in the material, is thus an ideal probe to examine its characteristics. Electron-induced vibrational flngerprints should provide a unique tool for investigation of the polymer substrates, like in infrared spectroscopy ... 

In this framework, in the specially designed mortars consisting of binders of either lime and metakaolin or natural hydraulic lime and fine aggregates of carbonate nature, nano-titania of anatase (90 per cent) and rutile (10 per cent) form has been added (4.5-6% w/w of binder). The aim was to study the effect of nano-titania in the hydration and carbonation of the above binders and to compare the physico-chemical properties of the nano-titania mortars with those mortars without nano-titania, used as reference. Thermal analysis (DTA-TG), infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed to investigate the evolution of carbonation, hydration and hydraulic compound formation during a six-month curing period. Furthermore, the stone-mortar interfaces, the adhesion resistance to external mechanical stress, relative to the physicochemical characteristics of the stone-mortar system and the role of the nano-titania as additive, were reported and are discussed in this chapter. 

The difficulty in studying the above properties thus far had been the unavailability of suitable techniques for reliable in situ investigation of solid-liquid interfaces [10]. Techniques such as infrared spectroscopy and ellipsometry involve ex situ procedures such as freezing, drying in vacuo, etc., and/or have necessitated the use of ideal surfaces. Clearly, these methods have limited applicability for studying surfactant adsorption onto particulate solids in aqueous media. 

The present analysis by C-D stretching infrared spectroscopy has clarified several conformational properties of the alkyl chain in the Ci2E3-water system. The conformational change at the phase transition from L2 to L is not significant and only a small increase in the trans fraction is observed for the C-C bonds close to the alkyl/oxyethylene interface. This implies that the conformational states of the alkyl chain in the L2 and L phases in the vicinity of their boundary are substantially not different. In the L phase, when the composition or the temperature approaches the region of the phase separation or transition, the trans fractions for the C-C bonds closer to the alkyl/oxyethylene interface and those closer to the chain terminal decrease. These observations indicate that the conformational transformation from trans to gauche at these chain positions makes the lamellar structure less stable and leads eventually to the structural destruction. 

One interesting aspect of the application of IR spectroscopy relates to thin (micrometer) and ultrathin (<50 nm) polymer films, polymer surfaces, and polymer-substrate interfaces [23]. So-called external reflection methods can be used to determine the important properties of thin films (comprising monolayers and multilayers) such as thickness, anisotropy, molecular orientation, and composition. The most frequently applied methods include IR ellipsometry (IRE) [63-67] and IR reflection absorption spectroscopy (IRRAS), which may also be referred to as reflection absorption infrared spectroscopy (RAIRS) [1,23]. 

Surface forces measurement is a unique tool for surface characterization. It can directly monitor the distance (D) dependence of surface properties, which is difficult to obtain by other techniques. One of the simplest examples is the case of the electric double-layer force. The repulsion observed between charged surfaces describes the counterion distribution in the vicinity of surfaces and is known as the electric double-layer force (repulsion). In a similar manner, we should be able to study various, more complex surface phenomena and obtain new insight into them. Indeed, based on observation by surface forces measurement and Fourier transform infrared (FTIR) spectroscopy, we have found the formation of a novel molecular architecture, an alcohol macrocluster, at the solid-liquid interface. 

Vibrational sum-frequency spectroscopy (VSFS) is a second-order non-linear optical technique that can directly measure the vibrational spectrum of molecules at an interface. Under the dipole approximation, this second-order non-linear optical technique is uniquely suited to the study of surfaces because it is forbidden in media possessing inversion symmetry. At the interface between two centrosymmetric media there is no inversion centre and sum-frequency generation is allowed. Thus the asynunetric nature of the interface allows a selectivity for interfacial properties at a molecular level that is not inherent in other, linear, surface vibrational spectroscopies such as infrared or Raman spectroscopy. VSFS is related to the more common but optically simpler second harmonic generation process in which both beams are of the same fixed frequency and is also surface-specific. 

The development of infrared reflection-absorption spectroscopy to study gas-phase/solid interface started as a necessary step to avoid the practical limitations imposed by the use of oxide-supported metals [20]. This improvement opened the possibility of studying adsorbed species on well-defined metal surfaces, from which a considerable knowledge of the vibrational properties at the gas-phase/metal interface has been gained [21]. This information from ultrahigh vacuum (UHV) systems provides the basis for the application of the infrared technique to studying the (more complex) electrochemical interface. 

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