Chapter 12 Experimental Determination of Structure

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.