Photon spectroscopies, surface

In this context it is instructive to mention the work function 4>. Here, eFermi level of a solid into vacuum far away from the surface [107], The work function can be measured for example by ultraviolet photon spectroscopy (for a discussion see Ref. [108]). 

A second consideration is the ambient environment required for analysis. All techniques using particles require moderate or high vacuum conditions, i.e. pressures of 10-5 torr or lower. However, techniques using only photons work in any fluid environment, including liquids, with the provision, of course, that the wavelengths of interest are not appreciably absorbed or emitted by the environment. Thus in situ studies of such phenomena as catalysis and corrosion in typical ambient environments are possible with photon spectroscopy. Further, in many cases the surface film to be studied will be quite air stable and analysis outside of a vacuum chamber can result in a great savings in time and effort. 

Electrons Auger Electron Spectroscopy, Extended X-Ray Absorption Fine Structure, Low-Energy Electron Diffraction, Scanning Electron Microscopy, Surface Extended X-Ray Absorption Fine Structure, Ultraviolet Photoelectron Spectroscopy, X-Ray Absorption Near Edge Fine Structure, and X-Ray Photon Spectroscopy. 

It is important to consider the connection between the two types of studies. One often refers to the "pressure gap" that separates vacuum studies of chemisorption and catalysis from commercial catalytic reactions, which generally run above —often well above — atmospheric pressure. There is simply no way to properly simulate high pressure conditions in a surface analysis system. Reactions can be run in an attached reaction chamber, which is then pumped out and the sample transferred, under vacuum, into an analysis system equipped for electron, ion and photon spectroscopies. However, except for some optical and x-ray methods that can be performed in situ, the surface analytical tools are not measuring the system under reaction conditions. This gap is well recognized, and both the low- and high-pressure communities keep it in mind when comparing their results. 

Figorc 7.22a Electron spectroscopies for surface analysis. Auger electron spectroscopy. X-ray photon spectroscopy, and ultraviolet photon spectroscopy. 

It has been found that the most powerful technique for probing the chemical nature of the electrochemical interface in a Li-ion battery context is X-ray Photon Spectroscopy (XPS) surface XRD or Raman spectroscopy are considerably less versatile in this respect. Although a number of XPS studies have been performed on different Mn-oxides, there is a noticeable lack of XPS surface investigations for the LiMnp system. For this reason, we shall focus particularly on results from XPS studies in this discussion. Examples of typical XPS spectral bands are given in Figure 1. 

The past decade has seen the emergence of analytical imaging, which is imaging using the signals from various analytical instruments, such as FTIR and Raman microscopy, x-ray microscopy, and imaging by surface analysis using secondary ion mass spectrometry (SIMS) and x-ray photon spectroscopy (XPS). 

In this chapter we review some of the most important developments in recent years in connection with the use of optical teclmiques for the characterization of surfaces. We start with an overview of the different approaches available to tire use of IR spectroscopy. Next, we briefly introduce some new optical characterization methods that rely on the use of lasers, including nonlinear spectroscopies. The following section addresses the use of x-rays for diffraction studies aimed at structural detenninations. Lastly, passing reference is made to other optical teclmiques such as ellipsometry and NMR, and to spectroscopies that only partly depend on photons. 

There have been a few other experimental set-ups developed for the IR characterization of surfaces. Photoacoustic (PAS), or, more generally, photothemial IR spectroscopy relies on temperature fluctuations caused by irradiating the sample with a modulated monocliromatic beam the acoustic pressure wave created in the gas layer adjacent to the solid by the adsorption of light is measured as a fiinction of photon wavelength... 

Perhaps the best known and most used optical spectroscopy which relies on the use of lasers is Raman spectroscopy. Because Raman spectroscopy is based on the inelastic scattering of photons, the signals are usually weak, and are often masked by fluorescence and/or Rayleigh scattering processes. The interest in usmg Raman for the vibrational characterization of surfaces arises from the fact that the teclmique can be used in situ under non-vacuum enviromnents, and also because it follows selection rules that complement those of IR spectroscopy. 

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