Atomic structures Auger electron spectroscopy

Auger electron spectroscopy. X-ray photoelectron spectroscopy, low-energy electron diffraction, and in situ STM have been employed to investigate two-step alternate electrodeposition of Cd and Te atomic layers, forming finally, CdTe monolayers (electrochemical ALE on Au(lll)) [451]. STM images suggest that previously proposed hexagonal structures for CdTe may not be correct. 

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. 

Acronyms abound in photoelectron and related spectroscopies but we shall use only XPS, UPS and, in Sections 8.2 and 8.3, AES (Auger electron spectroscopy), XRF (X-ray fluorescence) and EXAFS (extended X-ray absorption fine structure). In addition, ESCA is worth mentioning, briefly. It stands for electron spectroscopy for chemical analysis in which electron spectroscopy refers to the various branches of spectroscopy which involve the ejection of an electron from an atom or molecule. However, because ESCA was an acronym introduced by workers in the field of XPS it is most often used to refer to XPS rather than to electron spectroscopy in general. 

The chemical, physical and technical properties of catalysts and many other porous technical materials are to a very great degree determined by both their texture and their structure, but the analytical composition of the surface also plays a role. Modern surface analysis techniques, like auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) have revealed that in many cases the atomic composition of the surface of a solid material deviates strongly from the composition of the bulk material. 

The (1 X 1) structure, representative of the clean Pt-Rh(lOO) surface, changes into the c(2 x 2) surface structure after exposure to a reaction mixture of 1 X 10 mbar NO and 5 x 10 mbar H2. Analysis of the c(2 X 2) surface by means of TDS, auger electron spectroscopy (AES), and HREELS indicated that atomic nitrogen was the main species present. For comparison, similar experiments were carried out on the Rh(lOO), Pd(lOO), and Pt(lOO) surfaces (78-80). Figure 16 illustrates some of the results. 

In Auger electron spectroscopy (AES) [31], the intensity of electrons scattered from a surface is measured as a function of their kinetic energy. Characteristic peaks in the energy distribution identify the elements present within the near surface region. AES is most often used in conjunction with LEED to characterise the composition and atomic structure of a surface or film. Knowing both the periodicity and relative composition of an overlayer is indispensable to deducing its atomic structure. 

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 surface and the bulk PSC crystal quality was studied by reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD). Surface chemical compositions were determined with Auger electron spectroscopy (AES) and secondary-ion mass spectrometry (SIMS). Atomic force microscopy (AFM), transmission and scanning electron microscopy (TEM and SEM) were used to monitor PSC morphology and structure. 

Porous anodic alumina is a very promising material for nanoelectronics. The injection of different types of impurities inside an alumina matrix can substantially improve its electrophysical properties. It is very important to study the local environment (chemical bonds, electronic structure, etc.) of injected atoms for understanding physical principles of the electronic elements formation. A number of techniques can be used to determine a chemical state of atoms in near surface layers. The most informative and precise technique is X-ray photoelectron spectroscopy. At the same time, Auger electron spectroscopy (AES) is also used for a chemical analysis [1] and can be even applicable for an analysis of dielectrics. The chemical state analysis of Ti and Cu atoms implanted into anodic aliunina films was carried out in this work by means of AES. 

The present paper reviews the physical and chemical evidence for the above rules obtained over the last several years from ultrahigh vacuum surface science studies of molybdenum single crystals chemically modified by 0, C, S, and B. Additionally, the results of recent studies of methylcyclopropane hydrogenolysis will be presented which illustrate the influence of surface acid/base sites on catalytic hydrocarbon conversions. The surface coverage of each modifier was determined by quantitative Auger electron spectroscopy or x-ray photoelectron spectroscopy (XPS). The atomic structure of oxygen, carbon, and sulfur adlayers below one monolayer (ML)... 

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