Photoelectron spectroscopy experimental details

In accord with the fact that XPS has become a standard surface science technique but has not been appreciated adequately in electrochemistry, it is the scope of this review chapter to bring XPS nearer to those who work on electrochemical problems and convince electrochemists to use XPS as a complementary technique. It is not the intention to treat fundamental physical and experimental aspects of photoelectron spectroscopies in detail. There are several review articles in the literature treating the basics and new developments in an extensive and competent way [9,13], In this article basic aspects are only addressed in so far as they are necessary to understand and... 

In the following a brief survey will be given of the fundamentals of the photoemission process in general. Later on (Sections 2.3 and 2.7) specific aspects of XPS data evaluation will be discussed with respect to electrochemical applications. Comprehensive reviews on photoelectron spectroscopies have been published before and have given a detailed discussion of theoretical and experimental aspects [9, 13]. 

Theory and experimental methods. Since the combined experimental-theoretical approach is stressed, both the underlying theoretical and experimental aspects receive considerable attention in chapters 2 and 3. Computational methods are presented in order to introduce the nomenclature, discuss the input into the models, and the other approximations used. Thereafter, a brief survey of possible surface science experimental techniques is provided, with a critical view towards the application of these techniques to studies of conjugated polymer surfaces and interfaces. Next, some of the relevant details of the most common, and singly most useful, measurement employed in the studies of polymer surfaces and interfaces, photoelectron spectroscopy, are pointed out, to provide the reader with a familiarity of certain concepts used in data interpretation in the Examples chapter (chapter 7). Finally, the use of the output of the computational modelling in interpreting experimental electronic and chemical structural data, the combined experimental-theoretical approach, is illustrated. 

The empirical approach adopted here integrates classical electrochemical methods with modem surface preparation and characterization techniques. As described in detail elsewhere, the actual experimental procedure involves surface analysis before and after a particular electrochemical process the latter may vary from simple inunersion of the electrode at a fixed potential to timed excursions between extreme oxidative and reductive potentials. Meticulous emphasis is placed on the synthesis of pre-selected surface alloys and the interrogation of such surfaces to monitor any electrochemistry-induced changes. The advantages in the use of electrons as surface probes such as in X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), high-resolution... 

In the study of the surface phases of the Pt-Sn system, as well as of other binary systems, a variety of experimental methods are available. Surface spectroscopies based on ion or electron interaction with the surface provide composition information with a depth resolution that can go from a few atomic layers (X-ray photoelectron spectroscopy, XPS and Auger electron spectroscopy, AES) to single atomic layer resolution. The latter can be obtained by low energy ion scattering (LEIS) a method which has been extensively used for the study ot the Pt-Sn system. Since surface spectroscopic methods are rather well known we will not review them in detail here. 

Reference [2749] reports results from [1472], and [2750] reports results from [951]. The IEP of alumina at pH 7.3 is reported in [2751] without any specific information about the source of material or about experimental conditions (probably from the literature). The IEP of titania at pH 5.6 is reported in [2752] without experimental conditions (probably from the literature). The IEP of mica at pH 3-3.5 is reported in [2753] without experimental conditions (probably from the literature). Reference [2754] reports charging curves of titania, obtained under unspecified experimental conditions, probably from previous paper. Reference [2755] reports lEPs from the literature and estimated from X-ray photoelectron spectroscopy. The PZCs reported in [2756] are probably from the literature (no experimental details are provided). lEPs from the literature ar e reported in [2757-2765,2767-2792,2794-2804,2842,2852,2894,2900,2905]. lEPs and PZCs from the literature are reported in [169,2805-2807]. The lEPs/PZCs reported in [2808] are also probably from the literature. Charging and electrokinetic curves from the literature are reported in [2809]. Electrokinetic curves from the literature are reported in [2810-2812]. PZCs from previous papers by the same authors are reported in [1165,2813-2821]. lEPs from previous papers by the same authors are reported in [111,2009,2822-2825]. Electrokinetic curves from previous papers by the same authors are reported in [2826,2827]. Reference [2828] reports PZC for an ill-defined material, and PZC from the literature. Reference [2829] reports calculated charging curves based on results from the literature. References [222, 1784,2830,2831] report surface charging data from the literature. Reference [2832] reports surface charging curves and PZCs from the literature. The PZCs in Table 1 of [947] are probably taken from the literature. References [2835,2836] probably report PZCs from the literature and [2838,2839] probably report lEPs from the literature. Reference [2840] reports PZCs from the literature that were confirmed by a nonstandard method. PZCs from the literature are also reported in [84,87,92, 114,118,188,723,780,945,968,1115,1162,1505,1533,1699,1766,1773,1975,1976,1996, 2035,2708,2766,2793,2841,2843-2845,2847-2851,2853-2893,2895-2899,2901-2904,2906-2917]. Reference [2846] reports a result of coagulation study from the literature. 

The catalysts were characterized by N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), temperature-programmed desorption of ammonia (NH3-TPD), X-ray diffraction (XRD), Raman spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). The procedures and experimental conditions have been detailed elsewhere [9]. 

The calculated frequencies do not exactly match the experimental ones the detail will depend on the particular geometry of the fragment. In addition, it is known, and confirmed by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy [60], that there are a significant amount of oxygenated species present. Since these are also likely to be at the periphery of the graphite layers, they will also influence the frequencies. These are very difficult to model since the nature of these species and their relative quantities is still uncertain. 

To illustrate to the reader the principles introduced in this section in the most direct and practical way, we present some case studies that compare the bonding properties of different ligands to the same metal center, and that compare the bonding properties of different metal functional groups to the same ligand. It is hoped that these experimental results will give the reader an appreciation of the types of detailed electronic structure information available from photoelectron spectroscopy. 

Core-electron ionization spectra contain the information not only about inner-core electrons but also about valence electrons and chemical bonds. Extensive experimental studies have measured the core-electron binding energies (CEBE) of numerous molecules [112,113] and the recent development of X-ray photoelectron spectroscopy (XPS) has enabled the detailed analysis of the satellites accompanied by the inner-shell ionization. 

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