Surface and Material Characterization Techniques

In the analysis of adhesion bonding, possessing knowledge of the composition and structure of the adherend surface is important. Characterization of bonding surfaces aids both in design and failure analysis of a bond, should the adhesion bond fail. 

Surface analysis is the use of microscopic chemical and physical probes that give information about the surface region of a sample. (The term sample refers to any piece of material, structure, device, or substance that is under study). The probed region may be the extreme top layer of atoms (the only true surface, for purists), or it may extend up to several microns (millionths of a meter) beneath the sample surface, depending on the technique used. Analysis provides information pertaining to chemical composition, level of trace impurities, and physical structure or appearance of the sampled region. Such information is important to researchers and manufacturers who must understand the materials in order to verify a theory or to create a better product.  

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This chapter has been adapted from Surface and Material Characterization Techniques in Surface Treatment of Materials for Adhesion Bonding, S. Ebnesajjad C.F. Ebnesajjad 2006 Elsevier Inc. 

The properties of the original constituents of a composite are often well known or easily measured however, the properties of the interface are not. Some of the difficulties with obtaining interfaciai properties arise because interfaciai reactions often produce phases which do not exist in bulk. Because of the difficulty of obtaining interfaciai properties, they are frequently inferred from correlations between bulk properties and information about the interfaces determined using surface and interfaciai characterization techniques. The information usually sought is whether or not there has been mass transport across the interface and what reactions have occurred between the constituents. The surface and interfaciai microcharacterization techniques which are most commonly used for obtaining the above information are described in the lead volume of this series. Encyclopedia of Materials Characterization. 

The theories and hypotheses proposed are traditionally based on results from an array of surface and stractural characterization techniques that are linked to catalyst performance evaluation (discussed in Sect. 3). It is also very likely that the real identity and behavior of the active site structure(s) in non-PGM catalysts is material-dependent and relates to the particular synthesis procedures and conditions selected. It is therefore important to gain a fundamental understanding into each particular system of M-N-C catalysts. Along with overlying trends, estabhshed in the field of non-PGM catalysis, this progress is essential toward achieving an established PEFC performance metrics. 

Rutherford back-scattering spectroscopy (RBS) is one of the most frequently used techniques for quantitative analysis of composition, thickness, and depth profiles of thin solid films or solid samples near the surface region. It has been in use since the nineteen-sixties and has since evolved into a major materials-characterization technique. The number and range of applications are enormous. Because of its quantitative feature, RBS often serves as a standard for other techniques. 

Structural and Surface Characterization of Carbon Products. Carbon products of the process were analyzed by a number of material characterization techniques, including x-ray diffraction, scanning electron microscopy. Auger electron spectroscopy, x-ray photoelectron spectroscopy, and others. X-ray diffraction studies revealed an ordered graphite-like (or turbostratic) structure of carbon products (Figure 4). 

Plasma emission spectrometers have shown a rapid growth. This holds also for NMR spectrometer sales because of new applications in biomedical research and more sophisticated experimental methods using increased computing power. Similarly, Raman spectroscopy, traditionally used in academic research, is gaining acceptance in industrial R D and quality control applications. Materials research and surface analysis in a variety of industries keeps the sales of electron microscopic, electron spectroscopic, ion spectroscopic, and X-ray instruments growing. Details of the various techniques on surface and interface characterization which are also important in R D of chemical sensors themselves, can be found in Chapter 3, Section 3.4.2. 

Adhesion is an interfacial phenomenon that occurs at the interfaces of adherends and adhesives. This is the fact underlying the macroscopic process of joining parts using adhesives. An understanding of the forces that develop at the interfaces is helpful in the selection of the right adhesive, proper surface treatment of adherends, and effective and economical processes to form bonds. This chapter is devoted to the discussion of the thermodynamic principles and the work of adhesion that quantitatively characterize the surfaces of materials. Laboratory techniques for surface characterization have been described which allow an understanding of the chemical and physical properties of material surfaces. 

Solids can be measured in transmission or reflection (reflectance) modes. Both specular reflection and diffuse reflection are used. Diffuse reflection accessories include the Praying Mantis from Harrick Scientific Products, Inc., and a variety of integrating spheres available from most major instrument companies. Specular reflection is used for highly reflective materials diffuse reflectance for powders and rough surfaced solids. Materials characterization relies heavily on techniques like these. 

X-ray photoelectron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA), and Auger electron spectroscopy (AES) are widely used materials characterization techniques belonging to the general class of methods referred to as surface analysis. Each of these techniques provides, to varying degrees, semi-quantitative elemental, chemical-state and electronic-structure information from the top 10 nm of a material. Another widely used surface analytical method covered in this book is secondary ion mass spectrometry. Chap. 4. 

The analysis of the pore structure of materials continues to attract attention of researchers interested in fuel storage, heterogeneous catalysis, removal of trace impurities and separation processes. Gas adsorption is a fast and convenient characterization technique. These measurements depend on the internal physical and chemical structure of the material and on the nature of the adsorbate molecule. Thus the results of these measurements, mainly at low pressures, are sources of valuable information about adsorbate-adsorbent interaction, and structural and energetical properties of the surface materials [1]. 

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