In situ surface analytical methods

Theoretical and experimental studies of the initial stages of building of a metal crystal lattice introduced a major advancement in the interpretation of the deposition processes and resulted in a series of new models [1, 16]. Experimental studies include applications of in situ surface analytical methods [17-21], including scanning tunneling microscopy (STM) and atomic force microscopy (AFM). 

Conventional electrochemical methods provide a vast amount of kinetic and mechanistic information about heterogeneous redox processes. However, it is desirable to supplement this with the molecular structural information that can now be provided by several in-situ surface analytical techniques [1, 2]. Of the techniques available, infrared spectroscopy is well suited for this task since the spectral data can yield valuable information on the identity as well as the reactivity of the interfacial species. This is especially true when examining multistep reactions involving adsorbed intermediate. 

Surface analytical methods — X-ray absorption spectroscopy, XAS — Figure. Electrochemical cell for in situ XAS measurements in reflection, set up with a gracing incident X-ray beam, beam shaping slit, ionization chambers for the intensity measurement of incoming (ii) and reflected beam (I2) and beam stop for the direct nonreflected beam [vii]... 

Surface analyses have been one of the key technologies for corrosion control and surface finishing. It is very important that the most appropriate apparatus for the purpose of the analyses should be selected from various analytical techniques. In this chapter, surface analytical methods for corrosion control and surface finishing, mainly ex situ techniques, are described. 

In contrast to investigations of adsorption from the gas phase, the number of methods applicable to adsorption from the liquid phase is very small. On the one hand this is caused by the fact that not all methods using either electrons or ions can be applied in situ. In addition the adsorbents are normally powders with no plane surfaces. As a consequence the results of quantitative adsorption measurements are usually calculated from the difference between the liquid concentrations before and after the adsorption process. In principle, any analytical method may be used provided it has sufficient sensitivity pH measurements with a glass electrode and atomic adsorption spectroscopy (AAS) are standard, but complexometry and ion-selective electrodes can also be used. Radiochemical methods are useful in the case of small final concentrations. If electrochemical methods are used, one has to consider that activities, not concentrations, are obtained. In the case of partially soluble adsorbents, such as transition aluminas, their concentration should also be determined, as well as those of all other constituents of the solution, e.g., CO3. ... 

Nowadays it is becoming common practice to bring multiple analytical techniques to bear on the characterization of catalysts. Very often bulk and surface analysis methods are combined to yield detailed complementary information. A typical scheme of catalyst parameters to be determined and of appropriate analytical methods has been presented by Delmon [ I). who reviewed the potential of surface analysis in the characterization of hydrodesulfurization (HDS) catalysts. This scheme, redrawn, is shown in Fig. 1. Unfortunately, due to certain inherent problems, the whole range of well-e.stablished surface spectro.scopic methods cannot be applied in every case. Another disadvantage is that the application of surface-specific spectroscopies requires the transfer of catalyst samples into vacuum, thus restricting the possibilities for genuine in situ surface analysis of working catalyst.s. 

The growth may be examined by the evaluation of electrochemical currents and charges taking into account the corrosion current density as described above. Other methods are based on the application of in situ ellipsometry or electrochemical quartz crystal micro-balance or of surface analytical methods working in UHV like XPS, AES, ISS, and RBS, sometimes in combination with sputter depth profiling. Examples are given in the following section. 

Samples may either be those in which the surface of interest has been exposed to the environment before analysis, or the surface to be examined is created in the UHV chamber of the instrument. The latter method is generally preferable, and also argon-ion bombardment is commonly used to clean sample surfaces in situ in the spectrometer. In metallurgical studies, the fracture sample is particularly important the sample is machined to fit the sample holder, and a notch is cut at the desired point for fracture. The fracture stage is isolated from the analytical chamber and is pumped down to UHV. Liquid nitrogen cooling is often provided, as this encourages... 

Coupling an electrochemical cell to an analytical device requires that hindering technical problems be overcome. In the last years there has been a considerable improvement in the combined use of electrochemical and analytical methods. So, for instance, it is now possible to analyze on-line electrode products during the simultaneous application of different potential or current programs. A great variety of techniques are based on the use of UH V for which the emersion of the electrode from the electrolytic solution is necessary. Other methods allow the in situ analysis of the electrode surface i.e the electrode reaction may take place almost undisturbed during surface examination. In the present contribution we shall confine ourselves to the application of some of those methods which have been shown to be very valuable for the study of organic electrode reactions. 

When cells are suspended in a biological fluid or culture medium, both serum proteins and cells interact with the surface substrate. Serum protein adsorption behavior on SAMs has been examined with various analytical methods, including SPR [58-61], ellipsometry [13, 62, 63], and quartz QCM [64—66]. These methods allow in situ, highly sensitive detection of protein adsorption without any fluorescence or radioisotope labeling. SPR and QCM are compatible with SAMs that comprise alkanethiols. In our laboratory, we employed SPR to monitor protein adsorption on SAMs. 

To put things into perspective, we. can broadly classify these analytical methods into bulk, dry surface, and in situ interfacial techniques. This chapter focuses on the last category, illustrating two in situ techniques used to study anion binding at the goethite (a-FeOOH)-water interface titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. In fact, CIR-FTIR could prove to be extremely powerful, since it allows direct spectroscopic observation of ions adsorbed at the mineral-water interface. 

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