Chemical bonding and properties of Condensed Phases of Carbon and Silicon

sp3 hybrids plus a linear combination of atomic orbitals description of the Si -Si “bond density” are shown to explain quantitatively both the measured X-ray and the electron scattering intensities from amorphous Si, when combined with a random network model of structure. Appealing to results from computer simulation, amorphous Si is then compared and contrasted with liquid Si. Amorphous carbon is also considered, first from the point of view of the admixture of sp3 and sp’ hybrids and then again in relation to the liquid phase of C. Some surface properties of crystalline Si are then treated using chemical bonding models. Porous Si is also considered, the relation to bonding and surface properties, with the additional factor of quantum confinement being discussed. Finally, some results are presented for small-angle X-ray scattering based on a vacancy model of porous Si