Scattering Amorphous materials

Gjpnnes, J. Disorder and defect scattering, thermal diffuse scattering, amorphous materials. In Electron Diffraction Techniques, Cowley, J.M., Ed. Oxford University Press New York, 1993 Vol. 2, 223-259. 

Percent Crystallinity. For samples that consist of a mixture of crystalline and amorphous material, it is possible to determine the percent of crystallinity by measuring the integrated intensity of sharp Bragg reflections and the integrated intensity of the very broad regions due to the amorphous scattering. 

In some cases (amorphous materials as polymers or glasses), the scattering of phonons with tunnelling states is also relevant. This process leads to an approximate [40-42,94,95] dependence as T1 2 of k (see Table 3.4) and to a plateau in the 2K < T < 20K range (see Fig. 3.18). 

Las but not least, sample preparation is also an important issue. If we want to examine nanocrystalline powder samples. The grain size must be just a few nanometers, the layer, formed by these nanocrystals must be as thin as possible (to minimize dynamic difiraction), continuous and self-supporting. In many cases not all these requirements are fulfilled simultaneously. The nanocrystalline material to be studied is frequently present on a thin supporting carbon layer. In such cases peak decomposition can not yield an acceptable fit unless the presence of the amorphous material (in the form of a few diffuse rings) is taken explicitly into account in the model to be fitted. The size of the background is also affected by scattering in such a carbon support. 

Amorphous materials can be oriented by stretching. In some instances, this orientation is also accompanied by crystallization [3]. Isoprene rubber exhibits such behavior. The positions of the maxima in the amorphous scattering pattern provide a measure of the average intermolecular spacing. Bragg s law may be used to calculate the size of the interplanar spacing [3],... 

The rule of the conservation of momentum k does not apply strictly in the case of ill-defined crystallites, solids without translational symmetry (amorphous materials or small scattering volumes), and colored materials, in which both the incoming and scattered light waves are strongly attenuated (i.e., in the case of resonance with electronic transitions). 

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