Quantitative Surface Analysis by XPS (X-Ray Photoelectron Spectroscopy): Application to Hydrotreating Catalysts — XPS is an ideal technique to provide the chemical composition of the extreme surface of solid materials, vastly applied to the study of catalysts. In this article, we will show that a quantitative approach, based upon fundamental expression of the XPS signal, has enabled us to obtain a consistent set of response factors for the elements of the periodic table. In- depth spadework has been necessary to know precisely the transmission function of the spectrometer used at IFP. The set of response factors obtained enables to perform, on a routine basis, a quantitative analysis with approximately 20% relative accuracy, which is quite acceptable for an analysis of such a nature. While using this quantitative approach, we have developed an analytical method specific to hydrotrea - ting catalysts that allows obtaining the sulphiding degree of molybdenum quite reliably and reproduci - bly. The usage of this method is illustrated by two examples for which XPS spectroscopy has provided with information sufficiently accurate and quantitative to help understand the reactivity differences bet - ween certain MoS 2 /Al 2 O 3 or NiMoS/Al 2 O 3 -type hydrotreating catalysts.

The objective of this work is to determine the origin of a decohesion problem that occurs during the fabrication process of certain integrated circuits. This decohesion takes place at the Ti/dielectric interface with the dielectric being either SiO 2 or borophosphosilicate glass (BPSG). The frequency of the decohesion increased when the dielectric is BPSG. In order to understand the reason for the difference in decohesion rates for the two dielectrics, a comparative study was performed before and after annealing. X-ray Diffraction was used to determine the microstructure of the different layers and Transmission Electron Microscopy coupled to Electron Energy Loss Spectroscopy and X-ray Energy Dispersive Spectroscopy was mainly used to characterize the interfaces and nanophases that had formed during annealing. A fundamental difference observed was the Ti/dielectric interface reactivity: in the case of BPSG, an amorphous layer rich in P is formed before the Ti 5 Si 3 silicide. Two hypothesis are put forward in order to explain adhesion failures: a decrease in the rate of Ti 5 Si 3 formation kinetics and/or a decrease of the glass transition temperature induced by P enrichment.

Petroleum industry is interested in polyethylene as a promising material for designing containers and pipes destined to contain or convey oil products because of their chemical insensitivity to oil by-products, their high resistance to corrosion, and their low cost of production. Nevertheless polyethylenes suffer from a severe drawback: they lack impermeability to gasoline components. X-ray photoelectron spectroscopy has been used to control the efficiency of a polymer fluorination procedure, designed to produce a layer impermeable to the organic compounds contained in gasoline. Analysis of the different environments of carbon showed the presence after treatment of -CHF- groups attached to -CF{sub 2}- groups, and the amounts of these groups have been quantified. The presence of CF{sub 3} end groups has also been detected, suggesting breakage of the polymer chains during fluorination. Ion beam erosion during XPS analysis provides information on the thickness of the fluorinated layer. The lack of improvement in the polymer performance in permeation tests is probably due to the low thickness of the layer and the presence short chain fragments. (A.C.)

photoelectron spectroscopy has been used to control the efficiency of a polymer fluorination procedure, designed to produce a layer impermeable to the organic compounds contained in gasoline. Analysis of the different environments of carbon showed the presence after treatment of -CHF-groups attached to -CF2-groups, and the amounts of these groups have been quantified. The presence of CF3 end groups has also been detected, suggesting breakage of the polymer chains during fluorination. ton beam erosion during XPS analysis provides information on the thickness of the fluorinated layer. The lack of improvement in the polymer performance in permeation tests is probably due to the low thickness of the layer and the presence of short chain fragments.

The thermodynamic equilibria between metallic iron, iron oxides, iron carbides and a hydrocarbon/hydrogen mixture were calculated at 600°C. On the basis of metastable Fe–C–O phase diagram, iron oxides can be converted directly into carbides in a reducing and carburizing atmosphere. Experimental results on the rate of oxide/carbide conversion are reported. Thermogravimetric measurements have been performed in an iC4H10–H2–Ar atmosphere at 600°C on preoxidized iron samples. The kinetics of the oxide layer transformation were studied by sequential exposure experiments. Scanning electron microscopy observations and x‐ray diffraction analysis have been carried out. The results lead to the conclusion that magnetite (Fe3O4) is transformed into carbide particles, acting as a catalyst for graphitic filament growth. The initial stages of the oxide/carbide transition were studied by x‐ray photoelectron spectroscopy. The results confirm that no metallic iron was formed during the transformation. Copyright © 2002 John Wiley & Sons, Ltd.

A new method of preparation of Pd supported catalysts is presented allowing to prevent the electron deficient character of highly dispersed metallic particles. Starting with a stabilised aqueous soluble Pd complex and under well-chosen activation procedure, ultradispersed Pd alumina supported particles obtained exhibit similar diene hydrogenation activity expressed by surface exposed atoms than bigger particles obtained by classical dried impregnation methods. Characterisation techniques (EXAFS, XPS, TPR, TEM) clearly evidence the non electro deficient character of these small particles. Catalytic performances (orthoxylene and butadiene hydrogenation) are discussed in relation with characterisation results.

XPS is an ideal technique to provide the chemical composition of the extreme surface of solid materials, vastly applied to the study of catalysts. In this article, we will show that a quantitative approach, based upon fundamental expression of the XPS signal, has enabled us to obtain a consistent set of response factors for the elements of the periodic table. In-depth spadework has been necessary to know precisely the transmission function of the spectrometer used at IFP. The set of response factors obtained enables to perform, on a routine basis, a quantitative analysis with approximately 20% relative accuracy, which is quite acceptable for an analysis of such a nature. While using this quantitative approach, we have developed an analytical method specific to hydrotreating catalysts that allows obtaining the sulphiding degree of molybdenum quite reliably and reproducibly. The usage of this method is illustrated by two examples for which XPS spectroscopy has provided with information sufficiently accurate and quantitative to help understand the reactivity differences between certain MoS2/Al2O3 or NiMoS/Al2O3-type hydrotreating catalysts.

SYNOPSIS In the case of cold plasma fluorination we analyzed effects of the main processing conditions (power, exposure time, nature of gas, and number of fluorinated faces) on gasoline permeability of polyethylenes. Optimization of processing conditions gave us a permeability reduction of 30% compared to untreated polyethylene. XPS analysis of fluorinated specimens before permeation experiments shows the PE to be highly fluorinated at the surface with a F/C ratio up to 2. Fluorination appeared to be homogeneous over the disk surface with a concentration depth profile showing a step decline below the extreme surface. However, significant fluorination is achieved only up to a few tens of nanometers (20 to 30). A more interesting effect is the evidence for chain breaking during the process suggests the creation of short chain segments at the surface. These segments would be highly fluorinated but easily leeched out by the diffusing molecules. Leeching seems more important with alcohol containing gasolines. These data show clearly that fluorination by cold plasmas in the conditions under studies has not a permanent effect. 0 1996 John Wiley & Sons, Inc.

A procedure for determination of the reduced thickness of the contamination layer for oxygen-inert samples was implemented. The correction algorithm is valid for the reduced thickness of a contamination layer x greater than or equal to 0.3 (x is expressed as the ratio of the layer thickness to the electron attenuation length in the contamination layer at energy 1 keV). It is shown that the linear background subtraction method traditionally used in XPS generally does not provide correct results. Application of an advanced experimental data treatment method with correction for the presence of a contamination layer to quantitative surface analysis of Al2O3, SiO2, GeO2, Fe2O3, NiO, CuO and NaF resulted in a decrease of the mean error of analysis from 27% using the elemental sensitivity factors approach to 5%.