Auger electron spectroscopy experiments

At 77 K H2O is chemisorbed without dissociation [586, 587]. The chemisorption energy of H2O is 54.6-66 kJ/mole [586, 587]. Sputtering of the surface does not destroy the passivating effect of the adsorbed H2O [588], while the electron beam during a Auger electron spectroscopy experiment leads to oxidation and destruction of the passivation [588]. 

For example, consider the dissociative adsorption of methane on a Ni(lOO) surface. If the experiment is performed above 350 K, methane dissociates into carbon atoms and hydrogen that desorbs instantaneously. Consequently, one determines the uptake by measuring (e.g. with Auger electron spectroscopy) how much carbon is deposited after exposure of the surface to a certain amount of methane. A plot of the resulting carbon coverage against the methane exposure represents the uptake curve. 

We have undertaken a series of experiments Involving thin film models of such powdered transition metal catalysts (13,14). In this paper we present a brief review of the results we have obtained to date Involving platinum and rhodium deposited on thin films of tltanla, the latter prepared by oxidation of a tltanliua single crystal. These systems are prepared and characterized under well-controlled conditions. We have used thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and static secondary Ion mass spectrometry (SSIMS). Our results Illustrate the power of SSIMS In understanding the processes that take place during thermal treatment of these thin films. Thermal desorption spectroscopy Is used to characterize the adsorption and desorption of small molecules, In particular, carbon monoxide. AES confirms the SSIMS results and was used to verify the surface cleanliness of the films as they were prepared. 

Accompanying the photoemission process, electron reorganisation can result in the ejection of a photon (X-ray fluorescence) or internal electronic reorganisation leading to the ejection of a second electron. The latter is referred to as the Auger process and is the basis of Auger electron spectroscopy (AES). It was Harris at General Electric s laboratories at Schenectady, USA, who first realised that a conventional LEED experiment could be modified easily to... 

The characterization of evaporated alloy films can be carried out at widely different levels of sophistication. At the very least, it is necessary to determine the bulk composition, probably after the film has been used for an adsorption or catalytic experiment. Then various techniques can be applied, e.g., X-ray diffraction, electron diffraction, and electron microscopy, to investigate the homogeneity or morphology of the film. The measurement of surface area by chemisorption presents special problems compared with the pure metals. Finally, there is the question of the surface composition (as distinct from the bulk or overall composition), and a brief account is given of techniques such as Auger electron spectroscopy which might be applied to alloy films. 

Figure 13. Reaction of surface O with CO for several fixed CO pressures over Pt measured by Auger electron spectroscopy. Key Fixed CO pressures (Pa) are 1 < X 10-7 (1), 6.27 X 10 7 (2). 1.67 X 10 s (3), 2.8 X 10 s (4), and 4.8 X 10 s (5) The light and dark symbols denote separate experiments (26).

These experiments also show the value of NEXAFS as a technique for following the kinetics of surface processes. We have shown that experiments can be tailored so a specific reaction can be studied, even if gas evolution is not involved. This represents an advantage over thermal desorption experiments, where several steps may be required in order to desorb the products to be detected. Another advantage of NEXAFS is that rates are measured isothermally, so the kinetic parameters can be determined with accuracy. Finally, NEXAFS is not a destructive technique, so we need not to worry about modifying the surface compounds while probing the system, as would be the case with other techniques such as Auger electron spectroscopy. 

The tools used for the experiments described below have been described in several books and review articles (1-3). Surface structure is determined by low energy electron diffraction (LEED), surface composition by Auger electron spectroscopy (AES), and reaction kinetics and mechanism by temperature programmed reaction spectroscopy (TPRS). Standard ultra-high vacuum technology is used to maintain the surface in a well-defined state. As this article is a consolidation of previously published work, details of the experiments are not discussed here. 

Auger electron spectroscopy (29) is a type of electron spectroscopy that is used for determining solid surface elemental and electronic composition. An experiment is conducted by bombarding a solid surface with an electron beam of energy ranging from 1 keV to 10 keV. Alternatively, an x-ray source can be used. The Auger electrons, emitted from an atom by means of a radiationless transition, are... 

Although not capable of the micrometer-sized lateral resolutions available with the aforementioned techniques, the surface spectroscopy, electron spectroscopy for chemical analysis (ESCA), also deserves mention. The ESCA experiment involves the use of X-rays rather than electrons to eject core electrons (photoelectrons), and it has comparable surface specificity and sensitivity to that of Auger electron spectroscopy (AES) (25, 26, 29). The principal advantage of ESCA relative to AES is that small... 

The experiments were performed in stainless steel UHV chambers which were equipped with the instrumentation necessary to perform Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), UV Photoelectron Spectroscopy (UPS), Low Energy Electron Diffraction (LEED), work function measurements (A( )), High Resolution Electron Energy Loss Spectroscopy (HREELS), and Temperature Programmed Desorption (TPD). The Au(lll) crystal was heated resist vely and cooled by direct contact of the crystal mounting block with a liquid nitrogen reservoir. The temperature of the Au(lll) crystal was monitored directly by means of a... 

Several other microanalytical methods in common use potentially have application on soil and sediments section samples. Laser-ablation inductively coupled plasma mass spectrometery (LA-ICP-MS) has been used on soil thin-sections from a controlled field experiment (21) but required special resins in the preparation. There is presently (May 2006) no reported use of this method on archaeological soil samples. Likewise, for extremely fine-resolution studies (i.e. <10 pm) with low minimum detection limits and despite difficult calibration, secondary ion microscopy (SIMS) has a potential role in examining archaeological soil thin sections. At even higher lateral resolutions ( 100 nm) Auger electron spectroscopy (AES) could also be considered for surface (<5 nm deep) analyses. At present however, the use of these methods in soil systems is limited. SIMS has been focused on biochemical applications (22), whereas AES... 

The HREELS, Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS) experiments were carried out in a UHV chamber described previously.6 Briefly, the chamber was equipped with a HREELS spectrometer for vibrational analysis, a single-pass cylindrical mirror analyzer for AES measurements and a quadrupole mass spectrometer for TDS measurements. The HREELS spectra were collected in the specular direction with an incident energy of 3.5 eV and with a spectroscopic resolution of 50-80 cm-1. The TDS data were obtained by simultaneously monitoring up to 16 masses, with a typical heating rate of about 1.5 K s-1. 

Details of the experiment have been described [77, 92, 106]. The authors examined Ir(110) microfacetted by Ir(lll) and a polycrystalline Pt foil by using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and thermal desorption (TD). 

Auger Electron Spectroscopy (AES) experiments were carried out on catalyst C. AES examination would indicate the position of the potassium contaminant on the surface of the catalyst. 

The experiments were performed in two different ultra high vacuum (UHV) chambers using two different Pt(lll) single crystals. The X-ray photoelectron spectra were obtained in a chamber with a base pressure of lxlO" Torr. The system has been described in detail elsewhere. In brief, the UHV chamber is equipped with low energy electron diffraction (LEED), an X-ray photoelectron spectrometer (XPS), a quadrupole mass spectrometer (QMS) for temperature programmed desorption (TPD), and a Fourier transform infrared spectrometer (FTIR) for reflection absorption infrared spectroscopy (RAIRS). All RAIRS and TPD experiments were performed in a second chamber with a base pressure of 2 X 10 ° Torr. The system has been described in detail elsewhere. In brief, the UHV chamber is equipped for LEED, Auger electron spectroscopy (AES) and TPD experiments with a QMS. The chamber is coupled to a commercial FTIR spectrometer, a Bruker IFS 66v/S. To achieve maximum sensitivity, an... 

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