Defect spectroscopy

Leslie, A. D., and Volmer, D. A. (2007). Dealing with the masses A tutorial on accurate masses, mass uncertainties, and mass defects. Spectroscopy 22 32, 34-39. 

Choice of moderator depends on the application of the positron beam. For implantation defect spectroscopy the priority is to maximise moderator efficiency, whereas for electrostatic systems a well-collimated parallel beam requires a planar low-(f + surface cooled to minimise thermal smearing. 

DLTS gives good results for defects in the upper half of the gap in n-type material, but in other situations the defect spectroscopy measurements are limited. DLTS is difficult in undoped a-Si H because of the need for low frequencies and its application to p-type material has been limited by the difficulty of making good Schottky contacts. There are many variations of transient capacitance and conductivity which are applied to the study of deep states (e.g. Cohen 1989, Crandall 1981, Nebel et al. 1989). 

Some defect spectroscopy measurements in n-type a-Si H have been interpreted in terms of close P D pairs (Kocka 1987) and there is also evidence of boron-phosphorus complexes in compensated a-Si H (Boyce et al. 1987). The driving force for pairing is the Coulomb interaction between oppositely charged states. Such a paired state must be treated as a distinct species in the defect reaction, which takes the form,... 

Leslie, A.D. Volmer, D.A. Dealing With the Masses a Tutorial on Accurate Masses, Mass Uncertainties, and Mass Defects. Spectroscopy 2007, 22, 3234-32,39. 

Hamers R J and Kohler U K 1989 Determination of the local electronic structure of atomic-sized defects on Si(OOI) by tunnelling spectroscopy J. Vac. Sc/. Technol. A 7 2854... 

Experimentally, local vibrational modes associated witli a defect or impurity may appear in infra-red absorjrtion or Raman spectra. The defect centre may also give rise to new photoluminescence bands and otlier experimentally observable signature. Some defect-related energy levels may be visible by deep-level transient spectroscopy (DLTS) [23]. 

Instrumental Analysis. It is difficult to distiaguish between the various acryhcs and modacryhcs. Elemental analysis may be the most effective method of identification. Specific compositional data can be gained by determining the percentages of C, N, O, H, S, Br, Cl, Na, and K. In addition the levels of many comonomers can be estabhshed usiag ir and uv spectroscopy. Also, manufacturers like to be able to identify their own products to certify, for example, that a defective fiber is not a competitor s. To facihtate this some manufacturers iatroduce a trace of an unusual element as a built-ia label. 

Another basic approach of CL analysis methods is that of the CL spectroscopy system (having no electron-beam scanning capability), which essentially consists of a high-vacuum chamber with optical ports and a port for an electron gun. Such a system is a relatively simple but powerful tool for the analysis of ion implantation-induced damage, depth distribution of defects, and interfaces in semiconductors. ... 

As mentioned earlier, CL is a powerful tool for the characterization of optical properties of wide band-gap materials, such as diamond, for which optical excitation sources are not readily available. In addition, electron-beam excitation of solids may produce much greater carrier generation rates than typical optical excitation. In such cases, CL microscopy and spectroscopy are valuable methods in identifying various impurities, defects, and their complexes, and in providing a powerful means for the analysis of their distribution, with spatial resolution on the order of 1 pm and less. ... 

For a review of how defects manifest themselves in a LEED experiment, see M. Henzler. In Electron Spectroscopy for Surface Analysis. (H. I. Ibach, ed.) Springer, Berlin, 1977. 

Raman spectroscopy is primarily a structural characterization tool. The spectrum is more sensitive to the lengths, streng ths, and arrangement of bonds in a material than it is to the chemical composition. The Raman spectmm of crystals likewise responds more to details of defects and disorder than to trace impurities and related chemical imperfections. 

In this chapter shock modification of powders (their specific area, x-ray diffraction lines, and point defects) measurements via analytical electron microscopy, magnetization and Mossbauer spectroscopy shock activation of catalysis, solution, solid-state chemical reactions, sintering, and structural transformations enhanced solid-state reactivity. 

Fig. 1. Fraction of non-hydrogenbonded ( free ) OH-groups in water, methanol and ethanol determined by IR-spectroscopy. xF is the fraction of hole defects for water71...

Using a variety of transient and CW spectroscopies spanning the time domains from ps to ms, we have identified the dominant intrachain photoexcitations in C )-doped PPV films. These are spin-correlated polaron pairs, which are formed within picoseconds following exciton diffusion and subsequent dissociation at photoinduced PPV+/Cw> defect centers. We found that the higher-energy PA band of polaron pairs is blue-shifted by about 0.4 eV compared to that of isolated polarons in PPV. 

The resulting ladder polymer LPPP 12 possesses a number average molecular weight of 25000, which corresponds to the incorporation of 65 phenylene units. No structure defects could be detected using NMR spectroscopy. LPPP 12 is... 

Differentiation between the two forms of Ag2C03 is not easy and, from the many methods used, electron spin resonance spectroscopy and thermal analysis have been most successfully applied [757]. The imperfections mentioned above occur in the low temperature decomposition product and are identified as being responsible for enhanced activity in readsorbing C02. Annealing of the residue removes these defects and reduces the reversibility of reaction. 

Another definition, taking into account polymerization conversion, has been more recently proposed.192 Perfect dendrimers present only terminal- and dendritic-type units and therefore have DB = 1, while linear polymers have DB = 0. Linear units do not contribute to branching and can be considered as structural defects present in hyperbranched polymers but not in dendrimers. For most hyperbranched polymers, nuclear magnetic resonance (NMR) spectroscopy determinations lead to DB values close to 0.5, that is, close to the theoretical value for randomly branched polymers. Slow monomer addition193 194 or polycondensations with nonequal reactivity of functional groups195 have been reported to yield polymers with higher DBs (0.6-0.66 range). 

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