Photoemission spectroscopy chemical analysis

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

One other very important attribute of photoemitted electrons is the dependence of their kinetic energy on chemical environment of the atom from which they originate. This feature of the photoemission process is called the chemical shift of and is the basis for chemical information about the sample. In fact, this feature of the xps experiment, first observed by Siegbahn in 1958 for a copper oxide ovedayer on a copper surface, led to his original nomenclature for this technique of electron spectroscopy for chemical analysis or esca. 

X-Ray Photoelearon Spectroscopy X-Ray Photoemission Spectroscopy Electron Spectroscopy for Chemical Analysis X-Ray Photoelectron Diffraction Photoelectron Diffraction Kinetic Energy... 

From the perspective of this symposium, analysis of the atomic dynamics and electronic structure of surfaces constitutes an even more exotic topic than surface atomic geometry. In both cases attention has been focused on a small number of model systems, e.g., single crystal transition metal and semiconductor surfaces, using rather specialized experimental facilities. General reviews have appeared for both atomic surface dynamics (21) and spectroscopic measurements of the electronic structure of single-crystal surfaces (, 22). An important emerging trend in the latter area is the use of synchrotron radiation for studying surface electronic structure via photoemission spectroscopy ( 23) Moreover, the use of the very intense synchrotron radiation sources also will enable major improvements in the application of core-level photoemission for surface chemical analysis (13). 

Four UHV spectroscopies used for the compositional and chemical analysis of surfaces are discussed. These are X-ray Photoemission, Auger Spectroscopy, Secondary Ion Mass Spectroscopy, and Ion Scattering (both low and high energy). Descriptions of the basic processes and information contents are given, followed by a comparative discussion of the surface sensitivities, advantages and disadvantages of each spectroscopy. 

In the mid-50 s it was observed that the energy of a photoelectron, ejected from the core of an atom by an X-ray photon, is a rather sensitive probe of the chemical environment of the atom. From this observation has evolved a major research technique named electron spectroscopy for chemical analysis (ESCA) by the Uppsala group 1,2) which pioneered the subject and called X-ray photoemission spectroscopy (XPS) by many others. The field has developed rapidly a third generation of spectrometers is in use at many laboratories and the understanding of the spectra observed is improving apace. A view of the current status of X-ray photoelectron spectroscopy in application to metals and alloys is presented in this article. We have not been encyclopedic in describing what has been done we have instead attempted to cover the classes of results obtained and the kinds of problems encountered in interpretation of these results. 

The elemental composition of the surface can be obtained with ESCA (Electron Spectroscopy for Chemical Analysis or X-ray Photoemission), Auger (24) or X-ray fluorescence. In addition, the information on the chemical bonds can be recovered from the energy shifts in ESCA studies. 

Photoemission spectroscopy applied to chemistry and electronic properties studies is a fairly recent development. The x-ray photoemission spectroscopy (XPS) technique was developed, primarily to be a chemical analysis tool (1). In particular it was observed that the absolute binding energies of the atomic-like electron core levels are dependent on the chemical state of the atom under study. This observation led to the widespread use of XPS for basic and applied chemistry studies. Many studies were also undertaken to better understand the physics of the various excitation processes involved. Consequently, XPS has become a powerful tool for studying electronic structure of the outer electron states in solids. 

In summary, photoemission spectroscopy provides a useful means for measuring the binding energy of core and valence electrons. Thereby the chemical composition of a sample surface can be determined (Electron Spectroscopy for Chemical Analysis ESCA. A recent review on ESCA has been published by Seah (1980).) Furthermore, the valence band DOS can be probed and the valence state of surface atoms can be examined. Atoms in different... 

Since its introduction into the modem world of chemical analysis methods 1 K. Siegbahn, et al (1), photoelectron spectroscopy has become an increasingly important method for studying semiconductor surfaces. Not only is it widely emplc ed as a surface analytic method but also it finds wide application in chemically characterizing layered structures and interfaces which are important to semiconductor device manufacture. In this tutorial paper, a brief outline of the photoemission experiment will be presented. Modern instrumentation employed in semiconductor characterization will be surveyed and examples will be discussed which demonstrate the power of photoelectron spectroscopy in characterizing semiconductors and semiconductor device structures. 

In this chapter we describe advances in the femtosecond time-resolved multiphoton photoemission spectroscopy (TR-MPP) as a method for probing electronic structure and ultrafast interfacial charge transfer dynamics of adsorbate-covered solid surfaces. The focus is on surface science-based approaches that combine ultrafast optical pump probe excitation to induce nonlinear multi-photon photoemission (MPP) from clean or adsorbate covered single crystal surfaces. The photoemitted electrons transmit spectroscopic and dynamical information, which is captured by their energy analysis in real or reciprocal space. We examine how photoelectron spectroscopy and microscopy yield information on the unoccupied molecular structure, electron transfer and relaxation processes, light induced chemical and physical transformations and the evolution of coherent single particle and collective excitations at solid surfaces. 

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