Spectroscopy techniques photoelectron

R. Kotz reviews the application of the most powerful surface physics technique, photoelectron spectroscopy, for the elucidation of the composition of electrodes. He exemplifies the potential of this technique for materials which play a key role in electrochemical oxidation processes or are used in some other electrochemical process. 

Over the past 10 years a multitude of new techniques has been developed to permit characterization of catalyst surfaces on the atomic scale. Low-energy electron diffraction (LEED) can determine the atomic surface structure of the topmost layer of the clean catalyst or of the adsorbed intermediate (7). Auger electron spectroscopy (2) (AES) and other electron spectroscopy techniques (X-ray photoelectron, ultraviolet photoelectron, electron loss spectroscopies, etc.) can be used to determine the chemical composition of the surface with the sensitivity of 1% of a monolayer (approximately 1013 atoms/cm2). In addition to qualitative and quantitative chemical analysis of the surface layer, electron spectroscopy can also be utilized to determine the valency of surface atoms and the nature of the surface chemical bond. These are static techniques, but by using a suitable apparatus, which will be described later, one can monitor the atomic structure and composition during catalytic reactions at low pressures (< 10-4 Torr). As a result, we can determine reaction rates and product distributions in catalytic surface reactions as a function of surface structure and surface chemical composition. These relations permit the exploration of the mechanistic details of catalysis on the molecular level to optimize catalyst preparation and to build new catalyst systems by employing the knowledge gained. 

The quantum structure and properties of empty fullerenes C are extensively studied with the help of the powerful photoelectron (photoabsorption) spectroscopy technique [2,11]. As for the spectroscopy of gas phase doped... 

The adsorption of N-substituted tetrazoles on surfaces was studied by means of the X-ray photoelectron spectroscopy technique <2000MI130, 2004MI1371>. 

Recently, new instrumental techniques have become available for determining surface structures on an atomic scale. These include X-ray fine structure (EXAFS), electron spectroscopies, ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), ion spectroscopies, secondary-ion... 

The term action spectroscopy refers to those techniques that do not directly measure the absorption, but rather the consequence of photoabsorption. That is, there is some measurable change associated with the absorption process. There are several well known examples, such as photoionization spectroscopy [42], multiphoton ionization spectroscopy [48], photoacoustic spectroscopy [49], photoelectron spectroscopy [50, 51], vibrational predissociation spectroscopy [52] and optothermal spectroscopy [53, M]- These techniques have all been applied to vibrational spectroscopy, but only the last one will be discussed here. 

The tunability of X-rays greatly facilitates techniques such as X-ray absorption fine structures (XAFS), an element sensitive tool for local structure and bonding investigation, and photoelectron spectroscopy (PES) and related phenomena such as Auger and X-ray fluorescence and emission spectroscopy. The photoelectron technique is surface sensitive and with the added advantage of tunability, it can be used widely in surface analysis. 

In our opinion the paper by Moses et al. [36] on the scintillation mechanisms in CeF.3 is a fine example of how scintillators should be studied from a fundamental point of view. A combination of techniques was u.sed, viz. (time-resolved) luminescence spectroscopy, ultraviolet photoelectron spectroscopy, transmission spectroscopy, and the excitation region was extended up to tens of eV by using synchrotron radiation. Further, powders as well as crystals with composition Lai-xCexFy were investigated,... 

Chemical reactions at the gas-surface interface can be followed by monitoring gas-phase products with, for example, a mass spectrometer, or by directly analyzing the surface with a spectroscopic technique such as Auger electron spectroscopy (AES), photoelectron spectroscopy (PES), or electron energy loss spectroscopy (EELS), all of which involve energy analysis of electrons, or by secondary ionization mass spectrometry (SIMS), which examines the masses of ions ejected by ion bombardment. Another widely used surface probe is low-energy electron diffraction (LEED), which can provide structural information via electron diffraction patterns. At the gas-liquid interface, optical reflection elHpsometry and optical spectroscopies are employed, such as Eourier transform infrared (ET IK) and laser Raman spectroscopies. 

The energy position of the 4f level depends on the chemical environment of the particular lanthanide atom from which the 4f electron is ionized (chemical shift). Since the environment for a surface atom is different than for a bulk atom, one expects a shifted 4f level binding energy for a surface atom relative to a bulk atom. This will here be referred to as a surface shift of the 4f level. Due to its surface sensitivity the photoelectron spectroscopy technique is well suited for studies of these shifts. 

Among the number of surface sensitive techniques, photoelectron spectroscopy is one of the most used either by chemists, physicists and material scientists. XPS infact provides information from the sample surface and relative to the presence. 

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