Surface analytical techniques, examples

State-of-the-art TOF-SIMS instruments feature surface sensitivities well below one ppm of a mono layer, mass resolutions well above 10,000, mass accuracies in the ppm range, and lateral and depth resolutions below 100 nm and 1 nm, respectively. They can be applied to a wide variety of materials, all kinds of sample geometries, and to both conductors and insulators without requiring any sample preparation or pretreatment. TOF-SIMS combines high lateral and depth resolution with the extreme sensitivity and variety of information supplied by mass spectrometry (all elements, isotopes, molecules). This combination makes TOF-SIMS a unique technique for surface and thin film analysis, supplying information which is inaccessible by any other surface analytical technique, for example EDX, AES, or XPS. 

It is important to realize that corrosion rates may be controlled by any of several thermodynamic or kinetic properties of the alloy-scale-environment system and not just by surface or interface reactions. The three stages of high temperature oxidation of a metal, shown schematically in Fig. 1, serve as an example (7). The first or transient stage includes initial gas adsorption, two-dimensional oxide nucleation, initial three-dimensional oxide formation and finally, formation of the dominant oxide that will control the oxidation rate in Stage II. Various portions of Stage I have been widely studied using surface analytical techniques, but its duration can be very short and it is usually assumed (not always correctly) that Stage I has little impact on ultimate corrosion properties of the material. 

Corrosion processes can be very complex and, as the above examples show, surface analytical techniques can often provide unique information important for the understanding of these processes and to the solution of corrosion problems. By their basic nature, surface sensitive methods excel at examining thin layers at surfaces and interfaces that are difficult to detect and analyze by other methods but which can have a large influence in corrosion. The higher spatial resolution surface techniques are particularly useful for analysis of small area corrosion problems such as pitting and corrosion of electronic components and integrated circuits. 

The comprehensive investigation of the interactions of simple alcohols (methanol, ethanol, propan-l-ol, and butan-l-ol) with Fe203 powders (514) by a combination of surface analytical techniques and conversion measurements under high vacuum and at atmospheric pressure is an example of the attempts to establish correlations between surface structure and catalytic activity. IR and XPS data showed that methanol is chemisorbed mainly disso-ciatively, giving formate species, whereas molecular chemisorption prevails for higher alcohols, which form hydrocarbons as the major products. 

An example of the broad range of surface-analytical techniques that can be applied in order to monitor the build-up of these architectures and then further to characterize the structural and functional properties of the resulting complex lipid bilayer membranes is presented in Fig. 3 [21]. Shown in Fig. 3a is the com-... 

In the past ten years, there have been at least 200 monomers or monomer-like compounds which have been claimed to be polymerized by plasma. However, most of them have not been properly characterized. With the advent of new surface analytical techniques, e.g., ESCA (or XPS) ( ), the structures of some plasma-polymerized products have been elucidated. For example, by the ESCA technique, some polymers have been shown to be vertically homogeneous on the surface ( ). 

Structural bonds are those that are expected to undergo some form of loading for a significant part of their service life while non-structural bonds remain largely unloaded, for example, in the case of paints and lacquers. An understanding of the bond failure mechanism is critically important in explaining the performance of a particular bonding system in durability tests. Surface analytical techniques such as X-ray photoelectron spectroscopy (XPS) are widely employed in this role. ... 

Further examples of application of DRIFTS, and other surface analytical techniques, to organosilane treated fillers and interphase characterisation in organosilane modified composite, have been reviewed by Suzuki and Ishida [51]. 

A brief review of each technique will be followed by a discussion of results illustrating the application of the particular technique to adhesion. Examples are given of surface characterization of pretreated adherends, adhesive/adherend interactions, failure surface analysis, and correlation of these results to bond performance. Good summaries of the four major surface analytical techniques, namely XPS, AES, ISS, and SIMS, are given by Hercules(5) and Hofmann.( ) (See also Chapter 6 by Davis.)... 

Depth concentration measurement is an important application of surface analytical methods. Examples are depth distribution of additives in plastics, or interface analysis where polymers are in contact with metals or ceramics. All surface methods with a good depth resolution (XPS, AES, SIMS) are suitable for depth or profile measurements. Complete multilayer coating systems require analytical methods that are applicable to small sample sizes and low concentrations. Techniques for obtaining chemical composition and component distribution depth profiles for automotive coating systems, both in-plane (or slab) microtomy and cross-section microtomy, include /xETIR, /xRS, ToE-SIMS, optical microscopy, TEM, as well as solvent extraction followed by HPLC, as illustrated by Adamsons et al. [5]. Surface and interface/interphase analysis can now be done routinely on both simple monolayer coatings and complex multicomponent, multilayered... 

Just because in some techniques (e.g., STM) the quasi-two-dimensional interaction volume is exceedingly small does not mean that the specimen configuration can be similar. There is no strong relationship between the two. Since specimens have to be positioned and oriented with the naked eye, and handled in so doing with, for example, clean high-quality tweezers, it follows that they are all macroscopic. In addition, many of the surface analytical techniques, when used in routine fashion, are macroscopic in two of the three dimensions of the interaction volume SSIMS and XPS in their nonimaging forms are good examples. 

Two examples of surface modification of minerals will be discussed in order to illustrate the merits of a combined-technique approach. The breadth of the subject constrains the discussion to that dealing with strategies for gathering information and for choosing the most relevant surface analytical techniques. 

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