Abstract
It is possible to prepare homogeneous samples without columnar structure, this kind of structure being due to growth with incomplete coalescence. This homogeneous material produces a typical glass-like fracture and exhibits no resolvable structure. Using high-resolution electron microscopy (HREM), scanning electron microscopy (SEM), and small-angle neutron scattering on these homogeneous samples (a-Si, a-Si:H, a-Si:D), the chapter shows that hydrogen seems to be concentrated along linear defects that it decorates. These defects may be disclination cores, a geometrical locus of the more disturbed bonds in the material, possibly a linear torsion defect. This kind of conformation favors an electronic structure characteristic of a medium-range order. HREM are capable of providing unambiguous structural information in crystalline solids at the atomic level. It is possible to prepare a-Si:H, where structural defects because of incomplete coalescence (columnar structure) are absent. In this kind of homogeneous amorphous material hydrogen clusters along a filamentary network, the distance between these linear defects is about 30 Å.
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