Surface contamination, investigation

By using a laser with less power and the beam spread over a larger area, it is possible to sample a surface. In this approach, after each laser shot, the laser is directed onto a new area of surface, a technique known as surface profiling (Figure 2.4c). At the low power used, only the top few nanometers of surface are removed, and the method is suited to investigate surface contamination. The normal surface yields characteristic ions but, where there are impurities on the surface, additional ions appear. 

During the past twenty or so years numerous sophisticated surface analytical techniques have been successfully employed to investigate and understand the nature of bonding surfaces and their interaction with the environment. Some of these, e.g., HR-SEM and XPS have been mentioned above, with details of these and many more techniques covered in Chapter 6. In this section emphasis will be placed on those somewhat less sophisticated techniques that are employed in or in close conjunction with bond shops. What they lack in sophistication they often make up for in the ability to quickly and cheaply evaluate whether problems such as surface contamination or out-of-spec surface treatment procedures are... 

The aspect of sample preparation and characterization is usually hidden in the smallprint of articles and many details are often not mentioned at all. It is, however, a very crucial point, especially with surface and interface investigations since there might be many unknown parameters with respect to surface contaminations, surface conformations, built-in stresses, lateral sample inhomogeneities, roughness, interfacial contact etc. This is in particular important when surfaces and interfaces are investigated on a molecular scale where those effects may be quite pronounced. Thus special care has to be taken to prepare well defined and artifact free specimens, which is of course not always simple to check. Many of these points are areas of... 

In many instances the problem of surface contamination has been principally studied 3-5, 7-10,16,17, 19, 22). However, early in the DDT studies on citrus fruits, it became evident that appreciable amounts of this insecticide penetrated into certain components of the peel. Following this disclosure, suitable techniques were investigated and an evaluation of the penetration of DDT and later of parathion into various kinds of fruit was undertaken. 

A number of experimental techniques have been developed to investigate the interaction of low-energy electrons with atomic and molecular solids. To avoid surface contamination and... 

Therefore, the interpretation of such structures should be performed carefully and preferably in combination with other experimental or theoretical techniques. Nevertheless, the large database of STM results, which in combination with other experimental and theoretical surface science investigations have solved many problems correctly, often rely on the Tersoff Hamann interpretation (62-65). In this sense, the Tersoff-Hamann theory has proved itself very successful, but when applying it to STM characterizations of more complicated samples, one has to be aware of the limitations of the model. The sample wave functions may be distorted by the close proximity of the tip to the surface, and the forces between the tip and sample may lead to geometric relaxations of the atoms in the surface layer beneath the tip (66). Moreover, the tip is in this model represented by a simple x-wave, so that the chemical composition of the tip is neglected. In reality the nature of the tip may, however, differ significantly from this situation because of adsorbates or other contaminants present on the tip apex (53). 

Most of the sputtering data are for pure materials. In fact, most investigators have attempted to avoid surface contamination in order to make measurements truly representative of the substrate material. In a Tokamak reactor the wall will be sputter cleaned and hence these data are relevant. The actual conditions in today s operating Tokamaks are more complex. For example, carbon and other materials layers have been shown to build up on the surface of walls, and hence it is desirable to have sputtering data on samples with impurity layers195. ... 

Similar logical tests can be applied to increases in surface contamination levels, which may be due to increases in source intensity, or decreases in the efficiency of barrier controls or cleaning and sanitizing procedures. Flow charts illustrating the logical evaluation of data, and investigation of out-of-limit results are useful as starting points in the development of corrective action plans. ... 

Whereas contamination corresponds to the addition of matter which is very different from the surface under investigation, other defects can be generated by... 

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