  On the basis of density functional calculations and using Bader's atom in
molecule theory, this article presents quantitative microscopic analyses on the
bonding properties of amorphous silicon (a-Si) which could reflect in the
observable mechanical and electronic behaviors of this material. In addition,
the occurrence and strength of quantum confinement of charge carriers in a
composition of silicon crystal nano slabs (SiNSs) embedded in hydrogenated a-Si
(a-Si:H) semiconductor are studied. It is shown that the strongest confinement
effect happens for Si slabs limited in [100] direction. The band gap tunability
with the width of SiNSs is exhibited and a scaling law is investigated for the
size dependent behavior of energy states. It is demonstrated and argued why in
these systems the confinement of holes is stronger than electron confinement.
The computational methodology used to passivate a-Si defects by hydrogen is
also detailed.
