Material defects identification

The application of Raman spectroscopy to the study of semiconductors is an area of interest with a long history from the perspective of both QC and failure analysis. The general applicability of Raman spectroscopy to semiconductors is covered in depth in Chapter 12 and has been the subject of a number of articles and reviews [154-157]. During the last 10 years, the opportunity to move beyond the research Raman microscopes for materials research to Raman analyzers for QC analysis has been explored. Some of the major areas of interest from a quality control/failure analysis standpoint are contamination, defect identification, materials characterization, and strain mapping at interfaces (between components and between silicon and attached circuitry). 

A number of diamagnetic defects are also beheved to exist in vitreous siUca. Because there is no direct way to study these species, their identification is either done indirecdy, such as by uv absorption, or by employing esr after the material has been made paramagnetic using ionizing or laser irradiation. 

Fabrication tolerances are covered in this subsection. The tolerances permitted for shells for external pressure are much closer than those for internal pressure because the stability of the structure is dependent on the symmetry. Other paragraphs cover repair of defects during fabrication, material identification, heat treatment, and impact testing. 

The ability of STM to image at the atomic scale is particularly exemplified by the two other chapters in the book. Thornton and Pang discuss the identification of point defects at Ti02 surfaces, a material that has played an important role in model catalyst studies to date. Point defects have been suggested to be responsible for much of the activity at oxide surfaces and the ability to identify these features and track their reactions with such species as oxygen and water represents a major advance in our ability to explore surface reactions. Meanwhile, Baddeley and Richardson concentrate on the effects of chirality at surfaces, and on the important field of surface chirality and its effects on adsorption, in a chapter that touches on one of the fundamental questions in the whole of science - the origins of life itself ... 

In principle LVM spectroscopy is not the only way to evidence the presence of hydrogen in bulk materials not intentionally doped with hydrogen. Shinar et al. (1986) attributed optically detected electron nuclear double resonance (ODENDOR) lines to hydrogen associated with a PGa antisite-related defect in GaP. However the identification of these ODENDOR lines is not unambiguous as it has been recently proposed that these lines could be P-related (Watkins, 1989). 

Microspectroscopy applies the identification power of infrared spectroscopy to the microscopic realm. Contaminants on printed circuit boards, blemishes in coatings, and other production defects can be isolated in situ and analyzed (see Electronics, coatings). Analysis of flaws that develop during use illuminates the method of failure. Microscopic samples, such as particulates filtered from air, can be analyzed individually. The forensic applications are many paint chips, single fibers, explosive residues, and inks on currency can all be identified nondestmctively (see Forensic chemistry). The structures of layered materials, such as laminated polymer films, are studied via microspectroscopy by cross-sectioning the materials and examining the individual layers edge on (47). 

Techniques of transmission electron microscopy have proved valuable in many areas of solid state science. Use of electron diffraction permits identification of crystal types, determination of unit cell sizes and characterization of crystal defects in the phases. Measurement of Energy Dispersive X-ray (EDS) line intensity allows calculation of the elemental composition of the phases. It is difficult to overestimate the value of such applications to metallic alloys, ceramic materials and electron-device alloys (T-4V Applications to coal and other fuels are far fewer, but the studies also show promise, both in characterization of mineral phases and in determination of organic constituents (5-9. This paper reports measurements on a particular feature of coal, the spatial variation of the organic sulfur concentration. 

This method is particularly useful for analysis of the qualitative composition of trace amounts of various substances secured as material evidence in court cases, analysis of the homogeneity of a sample, identification of inclusions and contaminations on a surface, and detection of defects in a structure. Its main drawback is the fact that the physical nature of the microsample can affect the photometric accuracy of measurement and cause distortion of the obtained spectra. 

One of the problems where the use of the cluster approach is more appealing is in the study of surface defects. Only recently it has been recognized by the surface science community that these centers are often the most interesting ones from the point of view of the physical and chemical properties of a material. Several chemical reactions taking place at an oxide surface are directly or indirectly connected to the presence of point and extended defects. Unfortunately, defect centers are elusive species because of their low concentration even in the bulk material, and their identification by spectroscopic methods can be rather difficult. This is even more dramatic when one is interested in surface defects because the distinction from bulk defects may be extremely subtle. For all these reasons the theoretical modeling of defect centers at the surface of oxides is attracting an increasing interest. 

In magnetic fields, bound excitons have unique Zeeman spectral characteristics, from which it Is possible to identify the types of centers to which the free excitons are bound. Bound exciton spectroscopy Is a very powerful analytical tool for the study and Identification of Impurities and defects in semiconductor materials. Magneto-Optical Spectroscopy Techniques... 

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