Electronic and chemical structure of
metal-semiconductor interfaces
We have begun an application of ab initio quantum
molecular dynamics to study
the growth of boron films on silicon substrates, and vice versa,with
particular attention to the dependence upon growth conditions
of chemical bonding at the interface, interface sharpness, and
interlayer stress. These are critical factors in the ultimate
performance of B/Si multilayer optics now being developed
for extreme ultraviolet imaging.
At present we are concerned specifically with the interaction
of B clusters with the surface of amorphous Si.
The
electrons are treated within the framework of density-functional theory,
with a pseudopotential approximation for the valence-core interaction and a
plane-wave orbital basis. A bulk amorphous Si sample has been prepared by
heating and annealing a 64-atom system with periodic boundary
conditions; an amorphous Si surface is then made by doubling the size of the
supercell in one direction, and annealing. A study of the "reconstruction"
of this surface is in progress.
The structure of B clusters has
been investigated by the same approach, and comparison made with all-electron
calculations and mass-spectrometric measurements.
In agreement with H.~Kato et al. (1991 J. Comp. Chem. 12, 1097)
we find that the the B12
icosahedral structure is metastable; it can withstand heating up to
temperatures of about 8000 K.
This project is carried out in collaboration with a group at the
Institut fuer Festkoerperforschung, Forschungsanlage Juelich (Germany),
and involves the development of a parallel quantum molecular dynamics
code.