slides

Atomic resolution electron microscopy:
Challenges on data treatment and modelling at the nanoscale
Daniel G. Stroppa
[email protected]
Quantitative Electron Microscopy, INL, Braga, Portugal
02/12/2014
Checklist
1 – Electron Microscopy introduction
2 – Experimental setup automation
3 – Intensity maps and 3D reconstruction
4 – Atomistic models simulation and refinement
5 – Some other possibilities
(S)TEM Introduction
Imaging
Diffraction
Spectroscopy
Electron-matter interaction (after Williams and Carter)
(S)TEM Introduction
TEM and STEM basic instrumentation
(S)TEM Introduction
Bright Field TEM
High resolution TEM
C: Mass-thickness
C: Diffraction
Interference pattern!
Si (Claudio, T.) and ZrO2 (Dalmaschio, C.)
(S)TEM Introduction
Annular Scattering
Scattering
cross sections
HAADF
ABF
>80 mrad
Z contrast (~Z2)
~ 13 – 23 mrad
contrast for low Z
GaAs – AlGaAs (Claro, M.) and YH2 (Ishikawa, R.)
(S)TEM Introduction
Electron Energy
X-rays Energy
Loss Spectroscopy Dispersive Spectroscopy
EELS – Energy loss chart and instrumentation scheme
(S)TEM Introduction
Aberrations
Spherical
aberration
Chromatic
aberration
Corrector
Based on EM
multipoles
And many others!
Limits on electron microscopy – Part 1
Envelope functions
Spatial coherence
Temporal coherence
(S)TEM Introduction
Materials limitations
State of the art
Spatial resolution (TEM)
50 pm (@300kV)
Spatial resolution (STEM)
63 pm (@300kV)
Energy resolution
10 meV (@100kV)
Sample instability
Actual energy loss
170 meV
Dose and signal limits (SNR and SBR)
Chemical element imaging
H-U
Chemical element spectroscopy
H-U
Signal delocalization
Sample preparation
Single atoms imaging and spectroscopy!
Practical aspects
Atomic resolution 3D reconstruction!
Experiments Automation
What limits (S)TEM nowadays?
Data extraction
Modelling and simulation
Limits on electron microscopy – Part 2
Experimental setup automation
Trivia
1) Total analyzed volume by TEM until today ~
Facts
1931 – First TEM prototype
a) 10 mm3
1939 – First commercial TEM
b) 1 cm3
1970 – HRTEM imaging
c) 100 cm3
d) 10 m3
e) 1 km3
~
5.103 instruments worldwide
Experimental setup automation
3mm
Trivia
1) Total analyzed volume by TEM until today ~
a) 10 mm3
b) 1 cm3
c) 100 cm3
d) 10 m3
e) 1 km3
Experimental setup automation
Automated image collection
???
Experimental image analysis
104 images, projection of single (few) objects
Single particle analysis
Intensity maps and 3D reconstruction
Inorganic systems
Typically poly-disperse
Important questions at nanoscale
Size: d, A, V
Terminations / Capping
Distortions / Defects
Few approaches available
Restricted / “Handcraft”
ZrO2 (Dalmaschio, C.)
Intensity maps and 3D reconstruction
IHAADF  Z~2 (t)
Images – SW 1
(DM)
Peak finder – SW 2
(CMr)
STEM - HAADF imaging
CeO2
Intensity maps and 3D reconstruction
“Quantization”
Atomic columns thickness
Intensities classification (GMM)
GMM – SW 3 (Igor)
Approximate 3D model
d, A, V
Symmetry operations
Model construction – SW 4 (CMr)
Intensity maps and 3D reconstruction
Image simulation
Results display
SW 5 (Megacell) and SW 6 (Dr. Probe)
SW 7 (Chimera)
Intensity maps and 3D reconstruction
Mini summary
Atomic resolution images
Counting atoms
3D reconstruction
Approximate d, A, V
2 nanoparticles (200 nm3)
1 month
(7 + x) SW
Atomistic models simulation and refinement
HRTEM imaging
FT indexing
Crystallography analysis
Modelling
Image simulation
Matching
Approximate 3D model
d, A, V
Sb-doped SnO2 (Silva, R.)
Atomistic models simulation and refinement
Projected potential
!!
WF phase x thickness
!!
Crystal model
Multislice image simulation (up to EPWF)
Atomistic models simulation and refinement
Multislice image simulation (from EPWF)
!!
MgO (Jia, C.) – Nature Materials, Sept 14
Some other possibilities
Single atoms detection
Re-doped MoS2 (Yadgarov, L.)
Some other possibilities
Single atoms identification
HAADF monitoring
EELS - SI
~1000 spectra
Reference region
Re-doped MoS2 (Yadgarov, L.)
Some other possibilities
Species quantification
Ce3+ (%cat)
Gd (%cat)
VO (%sites)
Exp.
-
30.0 ± 8.2
37.7 ± 4.1
Theo.
25.2
30.0
13.8
Gd-doped CeO2 (Dalmaschio, C.)
Some other possibilities
Species quantification
Ce3+ (%cat)
Gd (%cat)
VO (%sites)
Exp.
-
30.0 ± 8.2
37.7 ± 4.1
Theo.
25.2
30.0
13.8
Gd-doped CeO2 (Dalmaschio, C.)
Conclusion
Atomic Resolution Electron Microscopy
Materials characterization “to the atom”
A lot of useful information there
(not just “pretty” images)
Science and Technology impact
Very limited analysis range:
Sampling
“Handcraft” analyses
Conclusion
HL: I would like to do HRTEM on every material I grow! (~10 a week)
DGS: @#$%&#$!!! (2014)