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Properties
associated with Covalent Solids
· The directional-
and strong-bonding yields materials that are rigid and hard, with high melting
points. The low melting points of polymers come from the secondary bonds
linking the polymer chains.
· The electrons are shared between
the atoms giving rise to materials that are electronic insulators or semiconductors.
· The bound electrons give strong absorption
of light above intrinsic absorption edge (ultra-violet
or visible
wavelengths).
· When
pure, the crystalline solids are transparent at infrared wavelengths.
· They may be elemental or compound solids.
· Binding energy (eV per molecule): Si -> 3.7; InSb ->
3.5;
Diamond -> 7.5; SiC -> 12.4
·
Crystal
structures: Diamond, Si, -> Diamond Cubic; SiC -> Hexagonal
(Wurtzite);
InSb -> Cubic (Zinc Blende), with nearest neighbor distance:
Si -> 0.235
nm; InSb -> 0.28 nm; Diamond -> 0.154
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