Scattering processes grain boundaries

The D band, the disorder induced mode, normally appears between 1250 and 1450 cm. This band is activated in the first-order scattering process of sp2 carbons by the presence of in-plane substitutional hetero-atoms, vacancies, grain boundaries or other defects and by finite-size effects [134], The G band is the second-order overtone of the D band. 

Scattering is the main cause of resistivity. The electron wave can be scattered in a variety of ways, of which three are of most importance. The first is the interaction of the electron wave with lattice vibrations, called phonons. This is called thermal scattering. As the temperature increases so do the lattice vibrations, and the resistivity rises. At low temperatures the resistivity drops gradually to a finite value, maintained at absolute zero (Figure 13.5), except for the superconductors, described later in this chapter. This is an intrinsic property of a metal and cannot be altered. Structural imperfections present in the solid also contribute to resistivity. These are mainly defects such as dislocations and grain boundaries, or else impurities. As with lattice vibrations, they scatter the electron waves and so increase resistivity. Defects and impurities are extrinsic features that can be removed by careful processing. 

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