Nanoanalytical Electron Microscopy Of Cobalt Ferrite Thin Films
Author(s)
Spillane, Liam Jonathan
Type
Thesis
Abstract
Electron
energy‐loss
spectroscopy
(EELS)
is
a
powerful
method
for
providing
detailed
information
on
the
bonding,
chemical
structure
and
electronic
structure
of
materials.
In
this
work,
EELS
has
been
used
to
correlate
variations
in
magnetic
properties
of
cobalt
ferrite
films
with
film
thickness
and
post‐processing
conditions.
Magnetometry
performed
on
as‐deposited
and
oxygen
post‐annealed
films
has
shown
saturation
magnetization
(Ms)
to
be
strongly
affected
by
post
processing.
This
has
been
attributed
to
an
enhancement
in
superexchange
by
reoxidation
and
cation
ordering
processes
during
post‐anneal.
To
date
this
has
not
been
confirmed
using
nanoanalytical
techniques.
This
work
addresses
this
issue.
In
particular,
it
is
of
interest
to
determine
local
changes
in
the
degree
of
inversion
of
the
ferrite
spinel
in
order
to
link
local
chemical
changes
to
bulk
magnetic
properties.
Two
sample
preparation
techniques
were
used
to
produce
electron
transparent
sections
–
conventional
ion
beam
milling
and
focussed
ion
beam
(FIB)
milling
using
a
dual
beam
system.
The
suitability
of
each
technique
is
discussed
in
terms
of,
sample
damage,
thickness,
reproducibility
and
reliability.
Aberration
corrected
HRTEM
was
used
to
investigate
the
microstructure
of
the
thin
films.
Lattice
strain
and
defect
strain
were
quantified
at
increasing
distance
from
the
substrate/interface
in
as‐deposited
and
oxygen
post‐annealed
cobalt
ferrite
films
and
structural
defects
responsible
for
misfit
accommodation
were
characterised.
Local
variation
in
cation
valence
and
coordination
cobalt
in
an
oxygen
post‐annealed
film
was
investigated
by
monochromated
EELS
of
the
iron
and
cobalt
L2,3‐edges
in
the
electron
energy‐loss
spectrum.
A
method
to
determine
the
spinel
degree
of
inversion
(λ)
by
multiple
linear
least
squares
fitting
was
developed
using
data
acquired
from
reference
materials.
A
commercially
available
full
multiple
scattering
code
(FEFF
8.2)
was
used
to
aid
interpretation
of
reference
spectra
and
the
fitting
technique
used
to
determine
λ
was
applied
to
the
cobalt
ferrite
thin
film
in
order
to
identify
variations
in
λ.
energy‐loss
spectroscopy
(EELS)
is
a
powerful
method
for
providing
detailed
information
on
the
bonding,
chemical
structure
and
electronic
structure
of
materials.
In
this
work,
EELS
has
been
used
to
correlate
variations
in
magnetic
properties
of
cobalt
ferrite
films
with
film
thickness
and
post‐processing
conditions.
Magnetometry
performed
on
as‐deposited
and
oxygen
post‐annealed
films
has
shown
saturation
magnetization
(Ms)
to
be
strongly
affected
by
post
processing.
This
has
been
attributed
to
an
enhancement
in
superexchange
by
reoxidation
and
cation
ordering
processes
during
post‐anneal.
To
date
this
has
not
been
confirmed
using
nanoanalytical
techniques.
This
work
addresses
this
issue.
In
particular,
it
is
of
interest
to
determine
local
changes
in
the
degree
of
inversion
of
the
ferrite
spinel
in
order
to
link
local
chemical
changes
to
bulk
magnetic
properties.
Two
sample
preparation
techniques
were
used
to
produce
electron
transparent
sections
–
conventional
ion
beam
milling
and
focussed
ion
beam
(FIB)
milling
using
a
dual
beam
system.
The
suitability
of
each
technique
is
discussed
in
terms
of,
sample
damage,
thickness,
reproducibility
and
reliability.
Aberration
corrected
HRTEM
was
used
to
investigate
the
microstructure
of
the
thin
films.
Lattice
strain
and
defect
strain
were
quantified
at
increasing
distance
from
the
substrate/interface
in
as‐deposited
and
oxygen
post‐annealed
cobalt
ferrite
films
and
structural
defects
responsible
for
misfit
accommodation
were
characterised.
Local
variation
in
cation
valence
and
coordination
cobalt
in
an
oxygen
post‐annealed
film
was
investigated
by
monochromated
EELS
of
the
iron
and
cobalt
L2,3‐edges
in
the
electron
energy‐loss
spectrum.
A
method
to
determine
the
spinel
degree
of
inversion
(λ)
by
multiple
linear
least
squares
fitting
was
developed
using
data
acquired
from
reference
materials.
A
commercially
available
full
multiple
scattering
code
(FEFF
8.2)
was
used
to
aid
interpretation
of
reference
spectra
and
the
fitting
technique
used
to
determine
λ
was
applied
to
the
cobalt
ferrite
thin
film
in
order
to
identify
variations
in
λ.
Date Issued
2010
Date Awarded
2011-03
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
McComb, David
Creator
Spillane, Liam Jonathan
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)