Substrate/surface characterization Spectroscopy

Fourier-transformed infrared spectroscopy (FT1R), either in the transmission mode(70), the grazing incidence reflection (GI) mode(7,5) or the attenuated total reflection (ATR) mode(7,2), has been the most widely used experimental tool for the characterization and structure determination of SA monolayers. GI-IR is especially useful in determining the molecular orientation in the film structures because it senses only the vibrational component perpendicular to the substrate surface(7,5). Polarized ATR-IR can also be used to study molecular orientation(7,77). McKeigue and Gula-ri(72) have used ATR-IR to quantitatively study the adsorption of the surfactant Aerosol-OT. 

The attenuation and velocity of acoustic energy in polymers are very different from those in other materials due to their unique viscoelastic properties. The use of ultrasonic techniques, such as acoustic spectroscopy, for the characterization of polymers has been demonstrated [47,48]. For AW devices, the propagation of an acoustic wave in a substrate causes an oscillating displacement of particles on the substrate surface. For a medium in intimate contact with the substrate, the horizontal component of this motion produces a shearing force. In such cases, there can be sufficient interaction between the acoustic wave and the adjacent medium to perturb the properties of the wave. For polymeric materials, attenuation and velocity of the acoustic wave will be affected by changes in the viscoelastic behavior of the polymer. 

A major difference between SFG and other surface vibrational spectroscopy techniques is the presence of a non-resonant background, because, in part, of the metal substrate. This background is usually treated as independent of the frequency and characterized as a constant ( nr). although this treatment is not always possible. In electrochemical systems, /nr is not usually independent of the applied potential. This is because of potential-dependent changes in the electronic state... 

From a methodological point of view, of particularly interest have been improvements in the chemical sensitivity of STM and AFM characterization. This is especially desirable for electrochemists, as electrochemical environments prevent the combined characterization by other surface techniques, as are frequently used for composition determinations in vacuum. Tunneling spectroscopy measurements to obtain 7 y and d//dV y relationships may provide a certain degree of information regarding the electronic structure of the substrate surface and adsorbed molecules [77], and the use of ionic liquids of large electrochemical windows is favorable in this respect. One major enhancement would be to complement SPM with other spatial, time- and energy-resolved surface in-situ techniques. For example, a combination of scanning electrochemical microscopy and atomic force microscopy... 

Thin films with thickness values below 20 nm may be obtained on the polymer substrate by a traditional lift-off process, without the use of adhesion layers that limit optical performance. The maximum internal transmission measured at 4.2 nm deposition thicknesses and at 530 nm wavelengths was 75%. Surface characterization methods, such as X-ray photoelectron spectroscopy, provide a better analysis of... 

Some surface characterization techniques, such as Raman and infrared reflectance spectroscopies (see Appendix 3), have been used extensively in corrosion experiments in some laboratories, but the techniques are not considered sufficiently universal to be discussed here. Moreover, instrument operation and data interpretation are, at the moment, sufficiently complex and specialized that production of a series of protocols to suit most corrosion situations would be difficult. Other techniques such as XRD have been used frequently for routine characterization of thick corrosion layers (often after mechanical separation from the substrate). However, XRD has not been used on films much thinner than 2-3 pm, and, where it is used, a major problem has been the inability to determine the precise location of the various phases whose XRD patterns were reflected from the surface. Grazing-incidence XRD may provide some of this depth resolution in the future. Another technique on the horizon is SPM, which is described within the major corrosion application below. 

When investigating adsorption phenomena a key requirement is to study the cleanliness of a given substrate before the adsorption process and to determine the chemical compositions of the products formed in the subsequent adsorption. For this purpose techniques which are sensitive to the presence of different elements on a substrate surface are required. Although virtually all of the methods discussed here can be used in one way or another to follow an adsorption process, a technique which provides direct information on the chemical composition of a surface is very often a necessary prerequisite for fully characterizing the behavior of a particular adsorption system. In the following we will discuss first secondary ion mass spectroscopy, or SEVtS, and then two variants of photoelectron spectroscopy. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). 

Monolayers of alkanetliiols adsorbed on gold, prepared by immersing tire substrate into solution, have been characterized by a large number of different surface analytical teclmiques. The lateral order in such layers has been investigated using electron [1431, helium [144, 1451 and x-ray [146, 1471 diffraction, as well as witli scanning probe microscopies [122, 1481. Infonnation about tire orientation of tire alkyl chains has been obtained by ellipsometry [149], infrared (IR) spectroscopy [150, 151] and NEXAFS [152]. 

Infrared spectroscopy, including Fourier-transform infrared (FTIR) spectroscopy, is one of the oldest techniques used for surface analysis. ATR has been used for many years to probe the surface composition of polymers that have been surface-modified by an etching process or by deposition of a film. RAIR has been widely used to characterize thin films on the surfaces of specular reflecting substrates. FTIR has numerous characteristics that make it an appropriate technique for... 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

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