1. Doctoral
Thesis
Summary
Thesis
title:
Chemical
Reactions
on
the
Silicon
(001)
Surface
for
Quantum
Computer
Fabrication
and
Molecular
Electronics
Summary:
The
development
of
novel
technologies
such
as
silicon-­‐based
quantum
computing
and
molecular-­‐scale
electronics
is
increasingly
reliant
on
a
detailed
understanding
of
the
behaviour
of
atoms
and
molecules
on
the
silicon
surface.
In
this
Thesis
the
chemical
reaction
pathways
of
phosphorus
atoms,
aminoxyl
radicals,
and
pyridine
molecules
on
the
silicon
(001)
surface
are
investigated
using
density
functional
theory
(DFT)
and
a
variety
of
transition
state
search
methods.
Of
particular
importance
is
the
growing
string
method
(GSM)
for
finding
transition
states
[Peters
et
al.,
J.
Chem.
Phys.
120,
7877
(2004)]
which
is
developed
into
a
new
software
program
(SydGSM)
for
use
in
this
Thesis.
Reaction
pathways
are
identified
for
the
diffusion
of
phosphorus
adatoms
on
the
surface,
incorporation
of
phosphorus
atoms
into
the
surface
and
diffusion
of
incorporated
phosphorus
atoms
within
the
surface.
These
calculations
show
that
the
diffusion
of
phosphorus
atoms
within
the
surface
is
likely
to
occur
at
the
temperatures
required
to
thermally
desorb
the
hydrogen
resist
from
the
surface.
Two
competing
pathways,
the
homodimer
pathway
and
the
addimer
pathway
are
considered
for
the
high-­‐temperature
desorption
of
P2
molecules
from
the
surface,
with
the
latter
pathway
found
to
be
the
most
probable
under
the
prevailing
experimental
conditions.
The
reactions
of
aminoxyl
radicals
are
investigated
using
the
smallest
aminoxyl
radical,
H2NO,
with
selected
tests
involving
the
larger
dimethyl
aminoxyl
and
TEMPO
(2,2,6,6-­‐tetramethyl-­‐1-­‐
piperidinyloxy).
It
is
found
that
aminoxyl
radicals
are
likely
to
dissociate
via
the
N−O
bond
at
room
temperature
on
the
clean
(001)
surface,
but
are
stable
on
the
hydrogen
terminated
surface.
Thermal
investigation
in
this
Thesis
considers
pyridine
on
the
silicon
(001)
surface.
Reaction
pathways
between
three
experimentally
observed
adsorption
configurations
are
found.
The
results
expose
a
fundamental
problem
in
the
DFT
description
of
this
particular
adsorbate
system.