Specimen preparation method selection

The need to be able to thin complex microelectronic devices, and to select and thin specific regions within them has resulted in ever-more sophisticated specimen preparation methods involving precision ion polishing. This requirement culminated in the development of the focused ion beam (FIB) technique, which is able to slice out electron-transparent foils from any multilayer, multiphase material with extreme precision. Overwijk et al. (1993) have described such a technique for producing cross-section TEM specimens from (e.g.) integrated circuits. 

The increased use of optical and electron microscopy applied to polymer research has been the result of widespread acceptance of the techniques and extended property requirements of the polymer materials. It is known that the structures present in a polymer reflect the process variables, and further that they greatly influence the physical and mechanical properties. Thus, the properties of polymer materials are influenced by their chemical composition, process history and the resulting morphology. Morphological study involves two aspects prior to the study itself selection of instrumental techniques and development of specimen preparation methods. Structural observations must be correlated with the properties of the material in order to develop an understanding of the material. 

Once the objective of the experiment is known and the specimens selected for study, the next major step is the selection of the microscopy techniques and the specimen preparation methods required to image the polymer structures of interest (Table 7.2). If lamellar crystals must be... 

Once the objective of the experiment is known and the specimens selected for study, the next major step is the selection of the microscopy techniques and the specimen preparation methods required to image the polymer structures of interest (Table 6.2). If lamellar crystals must be evaluated, for instance, there is no point in considering most optical techniques as they will only provide an overview of these structures. Comparisons are made in this section regarding the various techniques, in both the text and tables, as an aid in this selection process. Observations of... 

A major consideration in the selection of preparation methods for microscopy study is the nature of the potential artifacts formed, although time, cost and the capital equipment required are also important factors. In a busy laboratory time considerations are very important, especially if time consuming methods also have potential artifacts. The accessory equipment available must also be considered, although for this discussion it will be assumed that the laboratory has the equipment required for most general preparations. A complete discussion of specimen preparation methods can be found in Chapter 4. Typical preparations for microscopy will be outlined here with emphasis on the nature of potential artifacts. 

The most important issues in the solution of structural problems are image interpretation and development of structure-property relations. Imaging techniques and preparative methods must be chosen that provide images of the needed structures by the most efficient experiments. Several major principles have been emphasized for imaging of structures. First, the problem solving protocol (Table 6.1) should be considered prior to developing an experimental plan. As part of this protocol the important properties of the material to be studied should be determined and the overall objective of the study developed. The size of the polymer structures required should be determined (Tables 6.2 and 6.3) as an aid to the selection of the appropriate microscopy techniques. Specimen preparation methods should be selected after considering the nature of the specimen itself, the types of structures to be determined and the potential artifacts. If a specimen can be examined directly, that is preferred over a less direct specimen preparation method, especially... 

Eiquid- or solid-phase extraction methods have been adopted for the isolation of catecholamines and their metabolites from urine samples. The liquid extraction system is ordinarily based on the formation of a complex, in alkaline medium, between diphenylborate and the diol group in the catecholamines. However, the liquid extraction methods reported in the literature are relatively tedious and often involved multiple extraction steps.For the more widely used solid-phase extraction methods, catecholamines may be selectively isolated from the urine sample by adsorption with activated alumina," " phenylboronic acid or cation-exchange resins. All the specimen preparative procedures are specific for the free catecholamines, i.e. the extracted catecholamines do not include the conjugated fraction. 

Both the transmission electron microscope and the scanning probe microscope (particularly the atomic force microscope) are the highest-resolution-imaging devices available for biochemical research. While knowledge of the instruments is important, the selection of appropriate methods of specimen preparation and the correct execution of those methods are critical for accurate ultrastructural data. In fact, use of more than one method can be quite desirable, especially if alternative methods of data corroboration are not available. 

The intensity of a spectral line can be strongly influenced by two major sources of error, namely, selective absorption of the primary beam and absorption and enhancement of the fluorescent radiation. These effects may be further complicated by physical phenomena that are already present, or are introduced as a result of specimen preparation procedures. The dependence of x-ray spectral intensity upon the physical state of the specimen is well known. Effects such as surface roughness, particle shape, particle size, and size distribution can all lead to nonproportional relationships between spectral intensity and elemental composition. This chapter discusses the problems associated with specimen preparation. The basic techniques are covered briefly and special attention is devoted to several methods in common use today. 

Samples of aluminum foil were prepared by each of the above techniques and, as expected, they produced essentially the same thinned specimen with the exception that the grain boundaries were less obvious in the sectioned sample (probably owing to the lack of any preferential thinning). The ion beam-thinned sample was more irregular since the initial surface was not perfectly flat. Since the sample is readily thinned by electropolishing, this would be the normal method selected. 

The experimental method for this program is to measure the uniaxial tensile strength of product ceramics as the dependent variable with selected processing variables serving as the Independent ones, A slicing machine for specimen preparation was obtained, The first six of a series of alumina plates were cut Into tensile test specimens,... 

Standard photoactivity measurements were performed on all specimens prepared by spray pyrolysis subjected to secondaiy calcination at 823K, and a selection of impregnated and coprecipitated specimens. Results presented in Table 2. show a marked decrease in the photocatalytic activity of specimens prepared by the spray pyrolysis method with increasing iron content, Fig.3. 

For composite materials, the exposure to critical environment is also an important issue therefore while selecting an appropriate test method for evaluating composite mechanical properties the extreme conditions experienced during service for a particular application must be taken into account. Environmental exposure can be accidental during the specimen preparation and instrumentation, or planned to investigate the moistnre effect, chemical attack, or cycling... 

Table 4.4 includes functional groups and polymers and their respective etchants. Chemical etching, such as with solvents and acids, and ion and plasma etching are conducted in order to reveal selectively structures in polymers that may not be observed directly. In all these methods, interpretation of the structures formed can be more difficult than specimen preparation. Accordingly, the etching methods are best used to complement other methods, such as microtomy, fractography and staining. Controls are essential to any experiment of this type, but, with care, the structures of semicrystalline polymers and polymer blends may be observed. 

The steps involved in the problem solving protocol are outlined in Table 7.1. They are rather simple and do not take much time to consider and such a protocol can save time in the long run. The protocol involves steps typical of scientific inquiry collect all the currently known facts, determine the nature of the problem, state the objective of the study, obtain the correct specimen, be sure to have experimental controls, look at the sample with the naked eye and then with a stereo microscope. These provide an aid to selection of the specific microscopy techniques and preparation methods needed to begin to address the objectives. The result should be that clearly defined analyses are conducted. 

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