Chemical bonding effects on the diffraction intensities in amorphous silicon and carbon

Building blocks for electron density in free molecules and in condensed matter phases

“…Energy band theory has been applied to this lattice to calculate the periodic crystal density, p (r). Although such band structure calculations are in good agreement with X-ray scattering data, an equally good account of these Bragg reflection intensities is given by a localized bond picture, worked out specifically for silicon by Stenhouse et al [21]. The reason this particular investigation was carried out was, in fact, to examine the scattering of both X-rays and electrons from amorphous silicon, in which the long-range order of the crystal is lost, though local tetrahedral bonding and the associated short-range order remain.…”

“…But the band calculation relies on Bloch's theorem and Brillouin zones, consequences of the perfect periodicity. The localized bond picture remains useful when only short-range order obtains, and as shown by Stenhouse et al [21], it can give also a quantitative account of both X-ray and electron scattering from amorphous silicon.…”

“…We shall begin by briefly summarizing the work of Stenhouse et al [21] on amorphous silicon, in relation to the diffraction measurements using both X-rays and electrons [22,23]. Then, we shall return to the alkalis and, in particular, to consider Li metal crystal in the bodycentered cubic phase, and then, another disordered system, following the treatment of amorphous Si; namely, liquid metal potassium near its freezing point.…”

“…Calculations for the density in an individual Si-Si bond were first carried out by the classical chemical approach using sp3 hybrid orbitals [21]. The localized bond density resulting from this approach is shown in Figure 6(a), being obtained by the linear combination of these atomic hybrid orbitals.…”

Supercooled molecular liquids and the glassy phases of chemically bonded N, P, As, Si and Ge

“…Even with directional d-bonding in a transition metal like Ni, it has not, to date, proved possible to make a monatomic metallic glass. Returning briefly to Si and Ge, we have already stressed that: (a) in these liquids, both materials are quadrivalent metals; (b) in the amorphous phase they are well described structurally by a continuous random network model [19]; and (c) until very recently, the glassy phases were obtained from silane and germane. Point (c) has been developed in recent studies by Deb et al [20] and by Hedler et al [21].…”