Surface corrosion, ESCA

Upper Surface. All ESCA spectra for the upper surface of the brown leaves show that they are covered by a layer dominated by the hydrocarbon parts of the cuticle material, which is incapable of preventing significant amounts of air-induced oxidation. Although reduced in comparison to the other leaf surfaces, the limited amount of oxygen found by grazing incidence is predominantly on the outermost surface. The waxy esterified parts of the cuticle appear to be dissipated and thus, as previously mentioned, all surfaces exposed to air, even the most non-reactive, are subject to at least some O2- and H20-induced oxidation. Thus, what we call natural passivation is indicative of extensive oxidation, which prevents further corrosive oxidation [33, 202]. Hence, in the case of the brown leaf we observe the botanical equivalent of metal corrosion. 

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is a useful measure to know chemical environment of elements in material surface. The strength of XPS is its ability to identify different chemical states. This function is useful in physics, chemistry and material science, such as oxidation/corrosion products, adsorbed species or thin-film growth processes. Analysis of insulators is possible, and XPS is also capable of semiquan-titative analysis. 

In this review results from two surface science methods are presented. Electron Spectroscopy for Chemical Analysis (ESCA or XPS) is a widely used method for the study of organic and polymeric surfaces, metal corrosion and passivation studies and metallization of polymers (la). However, one major accent of our work has been the development of complementary ion beam methods for polymer surface analysis. Of the techniques deriving from ion beam interactions, Secondary Ion Mass Spectrometry (SIMS), used as a surface analytical method, has many advantages over electron spectroscopies. Such benefits include superior elemental sensitivity with a ppm to ppb detection limit, the ability to detect molecular secondary ions which are directly related to the molecular structure, surface compositional sensitivity due in part to the matrix sensitivity of secondary emission, and mass spectrometric isotopic sensitivity. The major difficulties which limit routine analysis with SIMS include sample damage due to sputtering, a poor understanding of the relationship between matrix dependent secondary emission and molecular surface composition, and difficulty in obtaining reproducible, accurate quantitative molecular information. Thus, we have worked to overcome the limitations for quantitation, and the present work will report the results of these studies. 

The importance of surface and chemical analysis techniques in electronics corrosion testing cannot be overstated. These powerful tools contribute to solving problems and elucidating corrosion mechanisms in simple and complex systems. Chemical analysis techniques include infrared (IR), ultraviolet (UV), and RAMAN spectroscopy X-ray diffraction atomic adsorption emission and mass spectroscopy gas and liquid chromatography and optical and transmission electron microscopy. Surface analytical techniques include electron spectroscopy for chemical analysis (ESCA), Auger, secondary ion mass spectroscopy (SIMS), and ion scattering spectroscopy (ISS). These important techniques used in conjunction with corrosion tests are described in another section of this manual. 

S. (Steven) J. Harris received a Ph.D. frotn. Southampton University. United Kingdom, in 19SH. He joined the Materials Sciences Department at Sowerby Rc.search Centre (B, c) in October 1988, and has been in charge of the Surface Analysis facilities at British Aerospace since 1989. His major interests are adhesion, corrosion, diffusion bonding and sealants. He is a member of ISO TC201 "Surface Chemical Analysis" and is currently the secretary of the UK ESCA Users Group. 

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