Examples of Examples of nanoscale nanoscale characterization of

Examples of nanoscale
characterization of highhigh-tech
materials with TEM
by Konstantinos P. Giannakopoulos
Outline
 Defects (Dislocations etc)
 Diffraction (SAED, CBED)
 Analytical TEM (EDS, EELS)
 ZnO nanostructures
 Materials for magnetic recording media
1
Outline
 Defects (Dislocations etc)
 Diffraction (SAED, CBED)
 Analytical TEM (EDS, EELS)
 ZnO nanostructures
 Materials for magnetic recording media
Find the crystal Orientation: Kikuchi maps
Kikuchi lines
 Diffraction of inelastically scattered electrons
 In thick crystals
Kikuchi map (Diamond)
Diffraction Pattern on thick Al
2
Defects
Defect Imaging- Dislocations
The origin of diffraction contrast at an edge
dislocation (cross-sectional view):
 Local lattice strain means that at along a certain line the
planes are bent into the Bragg condition
 Locallyy the crystal
y
diffracts strongly
gy
 In bright field the image shows a dark line
Defects - Dislocations
Relaxation of strained layers:
Formation of a misfit dislocation network
3
Defects - Dislocations
BaTiO3(20nm)/SrTiO3 interface (plan views)
Imaging Conditions:
g =[110], bright field
g=[200], dark field
Defects - Dislocations
InGaAs/GaAs interfaces
Dislocations on the interface of a “relaxed” layer
Planar views of a misfit dislocation
network (mixed/60°)
• Mixture
Mi t
off edge
d and
d 60° dislocations
di l
ti
• Vicinal Interface
• The angle between of the 60° dislocations
depends on wafer offcut angle
The beginning of strain relaxation
4
Defects - Dislocations
Where does surface morphology come from?
InGaAs surface - Nomarski optical micrograph
Notice the angle of the striations
They are caused by 60° and not by edge dislocations
Outline
 Defects (Dislocations etc)
 Diffraction (SAED, CBED)
 Analytical TEM (EDS, EELS)
 ZnO nanostructures
 Materials for magnetic recording media
5
Diffraction
Mixture of 2 crystallographic phases
Crystallographic Information from very small areas, in
contrast to X-ray and Neutron scattering
Diffraction - CBED
CBED - Convergent Beam Electron Diffraction
 Focusing of the beam right on the region of interest
(crystallite, ~10 nm)
 Information on crystal symmetry
 Calculation of the lattice constants (stress, chemical
composition) with an accuracy of 0,2%
0 2% with the use of
simulation
6
Diffraction - CBED
Cu-Al Alloy (for an Interconnect)
With increasing Al concentration
orientation: [114]
HOLZ lines
Measurement
Simulation
Outline
 Defects (Dislocations etc)
 Diffraction (SAED, CBED)
 Analytical TEM (EDS, EELS)
 ZnO nanostructures
 Materials for magnetic recording media
7
Analysis in TEM ?
Structural/defect analysis
Phase determination

Measurement of the Diffraction spot distances

Measurement of the d –spacing seen in HR (Inverse Fourier Transform)
Chemical analysis

X-rays

EELS
combined with Energy Filtered TEM (EFTEM) for Compositional
Mapping
Electron--Specimen Interactions
Electron
8
Analytical TEM - EDS
EDS Spectrum of a catalyst support
Inelastic Scattering of Electrons
Origin:
Incident electrons that interact with the specimen and loose energy; they are then transmitted
through the rest of the specimen.
 Exploited
p
in TEM ((mainly)
y)
Electron Energy Loss Spectroscopy (EELS) spectrum
Origin:
The spectrum of loss of energy of the transmitted electrons
 Characteristic of the elements and their bonding state in the sample
 Exploited to extract compositional and bonding (i.e. oxidation state) information and to
acquire elemental maps
9
Electron--Specimen Interactions
Electron
Analytical TEM - EELS
EELS:
a way to exploit the
inelastically scattered
electrons
350
300
Ge L
Er M
counts x103
250
Si K
200
150
100
50
0
1200
1400
1600
1800
2000
eV
10
Analytical TEM - EELS
V.B.
eEo
ΔE
Electron Energy Loss
Spectroscopy
520
L
K
O K-edge
Intensity (arbitr. units)
C.B.
540
560
580
Energy loss ΔΕ (eV)
eEo-ΔΕ
Outline
 Defects (Dislocations etc)
 Diffraction (SAED, CBED)
 Analytical TEM (EDS, EELS)
 ZnO nanostructures
 Materials for magnetic recording media
11
ZnO Nanostructures
Why ZnO?
Main Disadvantage:
p-type doping…
•
•
Wide band gap (3,36 eV @ RT)
CdO-ZnO-MgO: large band gap range (2.2 to 7.9
eV)) with a smaller variation off the lattice parameter
than in nitrides
• Ferromagnetic semiconductor (+Mn)
• Piezoelectric
• Large exciton binding energy (60 meV)
• Very large shear modulus of 45.5 GPa
• Existing ZnO substrates (still expensive)
• Resistant to radiation
• Non-toxic (used in sun-blocking creams)
• Cheap: 1600 euros/ton (GaN 540 euros for 5 g)
ZnO Nanostructures
Applications:
UV optoelectronics:
Short wavelength LED (+Mg,
(+Mg for UV)
Displays
Optical Storage
Transparent electronics
Solar blind UV detectors
Light Bulbs (85% less consumption)
Hi h T electronics
High-T
l t i
Surface acoustic wave devices (>5GHz) for
cellular phones
Gas sensors
Spintronics (quantum computers ?)
12
ZnO Nanostructures
Nanodots
Process flow:
Electron beam evaporation of pure Zn metal on SiO2
Annealing in O2 atmosphere for 1h at 570K -700K
700K
Zn dot growth conditions:
Substrate temperature: 190 to 300 K
Vacuum 4x10-8 Torr
Evaporation rate: 0.05 to 0.6 nm/s
Equivalent thickness: 0.5 to 5 nm
Plan view image of ZnO nanodots
Insets:
a) Electron Diffraction with ZnO rings
b) HRTEM of one dot
ZnO Nanostructures
Cross-section TEM image of ZnO nanodots
Inset: HRTEM of one dot
Photoluminescence spectra, at 10 K
Excitation source: He-Cd laser (325 nm)
13
ZnO Nanostructures
 Dot diameters: 3 - 50 nm
 C axis vertical to the substrate
 Only near band edge photoluminescence (3.36eV)
 Compatible with Si technology
ZnO Nanostructures
Nanorods
Chemical process by: H. Yu et. al.: J. Am. Chem. Soc. 127, 2378 (2005)
•
•
•
•
•
Formamide solution in water
Zn Source: Zn foil
Substrates: Si (111), glass, Zn foil and ZnO on Si (111), glass
Deposition time: 1 to 24 hours
Solution Temperature: 40-80 ºC
Top view SEM image of ZnO nanorods
14
ZnO Nanostructures
Bright field TEM image of a
ZnO nanorod grown on
ZnO thin film/glass
substrate
Inset: selected area electron
diffraction pattern
(High resolution TEM image
of the same ZnO nanorod
ZnO Nanostructures
 Nanorod size and morphology can be tuned
with deposition conditions and substrate choice
• Fabrication of self-assembled ZnO
nanostructures
15
ZnO Nanostructures
ZnCoO Nanorods
Magnetic Semiconductors
Spintronics
Questions:
• Are ZnCoO nanorods really created?
• Is Co substituting Zn in ZnO lattice?
PLD , University of Leipzig:
CoO
ZnO
ZnO Nanostructures
Bright Field
Images
50
50 nm
nm
EELS mapping of Co and O in ZnCoO nanorods (EFTEM)
ZnCoO creates a shell around
the ZnO nanorod
Co map
O map
16
ZnO Nanostructures
Co Valence State in ZnCoO nanorods
L3
L3 and L2 Co EELS peaks correspond to
the electronic transition:
Intensity (a.u.)
CoZnO
2p3/2 and 2p1/2 to 3d
L2
760
780
800
820
L3/L2
Co oxidation state
Electron energy loss (eV)
Comparison of L3/L2 with reference materials:
Cobalt acetate Co(CH3COO)2
Co2O3
(Co+2)
(Co+3)
Intensity (a.u.)
ZnO Nanostructures
L3
ZnCoO
Co acetate
Co2O3
Co(CH3COO)2: L3/L2 = 4.4
L3/L2 =3.3
Co2O3:
ZnCoO:
L3/L2 = 4.1
L2
780
800
820
Electron energy loss (eV)
Therefore Co in the nanorods has a valence state near to +2
Co replaces Zn in the lattice…
17
ZnO Nanostructures
Co metal
ZnCoO
L2 and L3 peaks of metallic Co have tails
because of free electron contribution
800
850
eV
There is no free electron contribution in the ZnCoO EELS spectra
Therefore Co in ZnCoO is NOT in a metallic state
Outline
 Defects (Dislocations etc)
 Diffraction (SAED, CBED)
 Analytical TEM (EDS, EELS)
 ZnO nanostructures
 Materials for magnetic recording media
18
Materials for magnetic recording media
MRAM
Materials for magnetic recording media
Pt
Co
Co, Pt
CoPt
a = 3.766 Å c = 3.766 Å
Ku ~ 0.5 MJ/m3
a = 3.803
3 803 Å c = 3.701
3 701 Å
Ku ~ 5 MJ/m3
M
M
H
H
19
Materials for magnetic recording media
E-beam co-evaporation of CoPt nanoparticles
Substrate
Temp. Sub.
Thi k
Thickness
ox. Si (100)
RT - 750°C
0 9 – 15 nm
0.9
Thickness Å
Ts
9
RT
17
300
Analysis
Structure: TEM (EELS, EDX),
XRD
Magnetic: MOKE, SQUID
17
450
35
450
35
750
85
600
85
750
As-deposited
?!
CoPt
Pt
~ 85 Å
750ºC
o
(111)
fct - CoPt
Intensity (Arb. Units)
(111)fcc - CoPt 3
CoPt
Co
05
0,5
M/Mmax
o
1,0
o50
nm
Ann. 120
20 min 750
150
750
//

0,0
-0,5
-1,0
-20 -15 -10 -5 0 5 10 15 20
Annealed
H (kOe)
As-deposited
30
40
2 Theta
50
60
Deposition
+
Annealing
20 minutes
1,0
M/Mmax
20
0,5
0,0
//

o50
nm
-0,5
o50
nm
-1,0
-20 -15 -10
-5 0 5 10 15 20
o5
H (kOe)
nm
20
Materials for magnetic recording media
Superparamagnetic effect
M
M
M
H
Multi Domain
Single Domain
Superparamagnetism
Hc
KKuuVV
KuV ~ kT
P ti l size
Particle
i
0
~ 9
nm
~ 3 nm
N
S
S
N
M
H
Materials for magnetic recording media
~ 8.5 nm
As-deposited
Ts = 750ºC
~ 3.5 nm
1.0
M/Mmax
M
0.5
0.0

-0.5
o50 nm
o50 nm
-1.0
-20 -15 -10 -5 0 5 10 15 20
H (kOe)
Dave ~ 15 nm
D ~ 5 nm
Annealed at 750ºC for 20 min ave
M/M
Mmax
1.0
0.5
00
0.0

-0.5
o50 nm
Dave ~ 19 nm
o50 nm
Dave ~ 5 nm
-1.0
-20
-10
0
10
H (kOe)
20
21
Materials for magnetic recording media
EFTEM-- Energy Filtered TEM
EFTEM
Study of Fe distribution in FePt nanoparticles:
Bright field image
EFTEM image: Fe mapping
Overlap of Fe position to FePt particle positions !
Acknowledgements
Prof. P. J. Goodhew
Dr A. Travlos
Dr N. Boukos
Dr L. Castaldi
22
Bibliography
Transmission Electron Microscopy, by Williams and Carter
Electron Microscopy and Analysis, by Goodhew, Humphreys
and
d Beanland
B
l d
www.amc.anl.gov
cimewww.epfl.ch
www.matter.org.uk/tem/
www.superstem.dl.ac.uk/
www.unl.edu/CMRAcfem/em.htm
www.tf.uni-kiel.de/matwis/amat/def_en/index.html
materialsfuture.eu + Forum
23
Main
Ideas:

Targeted also to those not interested in Science

Our optimistic vision for the future
Breaking down stereotypes (e.g. the crazy
scientist)
Social drive of our work
Balanced p
presentation of negative
g
sides
(pollution etc)



materialsfuture.eu
 Main tool for dissemination
 An “Experience site” on landing page, hiding an
“information site”
 Kept simple, with articles for the general public
 23 languages!
24

We work to
make our
community
visible!
Why get involved?





Help your community create
a sustainable future based on
science
Interact as an Expert with the
media and the public
Promote your work to the
public.
Develop new skills in public
outreach activities
Be part of a network of
Materials Scientists and
Science Communicators
25
How exactly can I contribute?








Become a Hub for your area and
represent the Materials
Community!
Add your research
group/work/videos
Post an article
Proof read articles
Translate
Be moderator in the Forum
Announce Events/Contests
Use our material for teaching
[email protected]
Community building
activities
26
Thank you!
contact@materialsfuture eu
[email protected]
(b)
(a)
nanoparticles
powder
Intensity (a.u.)
Intensity (a.u.)
nanoparticles
powder
1000
520
540
560
Energy Loss (eV)
580
1100
1200
1300
1400
Energy Loss (eV)
27
Intensity (a.u.)
(b)
100
101
002
30
(a)
102
40
110
50
60
2 theta (deg)
103
112
201 004
70
80
TEM - Basics
TEM Operation:








Find the Electron Beam
Find the thin area
Tilt the Sample
Obtain Bright field images (use unscattered beam)
Obtain diffraction patterns
Obtain Dark field images (use diffracted beams)
Obtain High Resolution images (use unscattered and
diffracted el.)
Obtain EDX, EELS, EFTEM etc data
Available Information:
• Crystallography: crystallite size, structure, orientation
• Defects
• Chemical Composition
28
Defects
Dark field images of screw dislocations in Si
The effect of different diffraction conditions
(i.e. of various g vector orientations)
Defects
Defect Imaging- Dislocations
 There can be angles where no planes are in Bragg
condition
 No diffraction takes place
(the transmitted beam is unaffected)
 There is no image formation by the dislocation
u: dislocation
dislocation’s
s lattice displacement vector
(u=Burger’s vector for screw dislocations)
If g·u≠0 there is dislocation contrast
If g·u=0 there is no dislocation contrast
“Invisibility criterion” for the
determination of u
diffracting planes are not bent
29
Defects
Planar Defects (Stacking Faults etc)
~ boundary between 2 wedge-shaped crystals
Defects
Crosssection
The origin of Thickness Contours
Plan view
Bright Field image from a wedge
shaped region

The intensity varies periodically with the
thickness of the crystal
30
Diffraction – Precession
Due to the electron multiple scattering:
Dynamical Conditions
We can NOT use the intensityy of the
diffracted electron beam to calculate
complex structures (as with X-rays
and Neutrons)
BUT:
Vincent & Midgley (1996): if the electron
beam is tilted and precessed along a
conical surface, having a common axis
with the TEM optical axis, the
“dynamical” behavior is reduced
Precession Electron Diffraction –
known from its equivalent in X-ray
scattering
TEM – Diffraction
[ 1 1 1 ] Cubic ( a = 11.982 A ) Ca12Al14O33 (for fuel Cells):
Dynamical Conditions
Almost kinematical Conditions (precession)
31

Download Report