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Brookhaven Science AssociatesU.S. Department of Energy
JEOL TEM/STEM course2010F FasTEM
University of Michigan
27 – 29 June 2006
Robert KlieCenter for Functional NanomaterialsBrookhaven National Laboratory
Brookhaven Science AssociatesU.S. Department of Energy
Day 2: TEM/STEM Imaging and Diffraction: Lecture before lunch, demo before lunch a. Koehler 1) Skewed thoughts on Parallelism – measuring and understanding beam
convergence 2) High Contrast Aperture Measurement of Convergence Positional accuracy of diffraction and shadow image. Camera length variation with focused patterns L U N C H STEM: Lecture after lunch, Hands-on lab after lunch
• STEM conditions/camera lengths• Gun Conditions: finding the optimum values• Ultra high resolution
- A2 – change value- Objective lens angle – underfocus to overexcite
Condenser 3 lens Sample: Si/SiO2/SrTiO3
Syllabus:Syllabus:
Brookhaven Science AssociatesU.S. Department of Energy
Syllabus (contd)Syllabus (contd) Day 3: FasTEM/STEM: EDS
• 1. Aperture selection• 2. Analytical measurements
– A. Hole Counts– B. P/B– C. Film Count– D. NiK and NiL ratio: detector test and specimen stage position
EELS• 1. Effect of gun• 2. Collection angle• 3. STEM Diffraction/TEM Diffraction• 4. PL Crossover
Sample: Si/SiO2/SrTiO3 Sample: NiOx on Carbon on Mo grid
Brookhaven Science AssociatesU.S. Department of Energy
Parallel illumination:Parallel illumination:
Parallel illumination is needed for:
SAD: to minimize the spot diameterDiffraction contrast: Since illumination angle differs by (β(r)2+Φ(r)2)1/2, shifting illumination would mean changing incident illumination angle.CBD: α changes resolution in CBD pattern
HRTEM: α affects the quality of HRTEM images
Brookhaven Science AssociatesU.S. Department of Energy
Obtaining parallel illuminationObtaining parallel illumination
The effect of changing C3:
Condenser 3 lens changes the convergence angle off the illumination, but this is only 1/3 of the story.
Brookhaven Science AssociatesU.S. Department of Energy
Convergence angles in a TEM: Convergence angles in a TEM: Convergence angles α and β Convergence angles Φ
All three angles have to minimized for truly parallel illumination!
Brookhaven Science AssociatesU.S. Department of Energy
Convergence angle αConvergence angle α
β
α
Brookhaven Science AssociatesU.S. Department of Energy
Convergence angle αConvergence angle α
α is the semi-angle subtended by the electron source.
α gives rise to the finite size of diffraction spots for β=0.
by de-magnifying the electron source and CA, α can be reduced.
α is proportional to 1/illuminated area.
Measuring K:1) Parallel Illumination, measure half-angle of focused diffraction spots. K is product of divergence and radius of divergence. 2) Focused Illumination, measure half-angle of diffraction spots and FHWM of focused spot.
K
Brookhaven Science AssociatesU.S. Department of Energy
Reducing electron source size:Reducing electron source size:
Demagnification of electron source:
Changing the spot size will reduce the effective source size by demagnifying the source image.
Brookhaven Science AssociatesU.S. Department of Energy
Convergence angle βConvergence angle β
Underfocus,β < 0
Overfocus,β > 0
Overfocus,β > 0
Overfocus,β = 0
CL must be focused on OL FFP!
Brookhaven Science AssociatesU.S. Department of Energy
Convergence angle βConvergence angle β
β
β
G is typically 200-300 mm, CA of 200-300 μm to get β~ 1mrad
Gc/o is 1/100 of G, so 2-3 μm required for similar β in conventional OL
c/o
Brookhaven Science AssociatesU.S. Department of Energy
Convergence angle ΦConvergence angle Φ
Φ for β=0In a magn. field electrons spiral around field lines with:
For small angles:
Brookhaven Science AssociatesU.S. Department of Energy
Parallel Illumination modeParallel Illumination mode
α
αα
β
Brookhaven Science AssociatesU.S. Department of Energy
Obtaining parallel illuminationObtaining parallel illumination
Bragg line rotation method:Focused probe: β = 0
Brookhaven Science AssociatesU.S. Department of Energy
Obtaining parallel illuminationObtaining parallel illumination
Wobble OL, and change CL3
If illumination is not parallel, probe will change size when wobbling OL!
Convergent Probe:
If illumination is parallel, probe-size will remain some when wobbling OL!
Convergent Probe:
Brookhaven Science AssociatesU.S. Department of Energy
Diffraction Focus:Diffraction Focus:
Focusing of Kikuchi lines:
Kikuchi line are sharp if diffraction lens images OL BFP, and illumination is focused. Parallel illumination by changing CL3 to minimize diffraction spots.
Brookhaven Science AssociatesU.S. Department of Energy
Obtaining parallel illuminationObtaining parallel illumination
NBD mode:CM on
CBD mode:CM off
Different illumination modes:
Brookhaven Science AssociatesU.S. Department of Energy
Measuring convergence anglesMeasuring convergence anglesFor 200 keV instrument with Bz=3 T: Φ/r=1.7 mrad/μm
Brookhaven Science AssociatesU.S. Department of Energy
Measuring convergence anglesMeasuring convergence angles
)()()()()( 22222 sNsEsCTFskFsM
F = Structure factorE = envelope functionsN = noise function
))(exp()( 23222 fssCsG ssc
)()(2 sGsGsE tcsc
))2ln16
(exp()( 42
222
sE
ECsG ctc
GSC= spatial coherenceGTC= temporal coherence
Brookhaven Science AssociatesU.S. Department of Energy
Measuring convergence anglesMeasuring convergence angles
0
2
4
6
8
10
12
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Inte
nsity
Raw intensities
Fit
0
2
4
6
8
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Spatial Frequency (1/A)
SN
R
0
0.1
0.2
0.3
0.4
0.5
0.25 0.3 0.35 0.4
Determine Noise:Fitting of the CTF:
Brookhaven Science AssociatesU.S. Department of Energy
Measuring convergence anglesMeasuring convergence angles
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3 0.4 0.5
Spatial frequency (1/Å)
En
ve
lop
e
Gtc: 2eV, 1 ppm
Gsc: 0.1 mrad
Gsc * Gtc
Gaussian: B=9 Ų
Brookhaven Science AssociatesU.S. Department of Energy
Measuring convergence anglesMeasuring convergence angles
Brookhaven Science AssociatesU.S. Department of Energy
Parallel Illumination for EELS:Parallel Illumination for EELS:
To EELS
Image modes for EELS: Convergence angle:
PL focus has to be fixed to maintain focus of EELS spectrometer.Convergence angle is determined by SEA and imaging mode.
Brookhaven Science AssociatesU.S. Department of Energy
INCIDENT BEAM
C-AXIS
q
kk1
0
APERTURE
Can enhance or reduce orientation effects with C3 and projector lenses
0
0.2
0.4
0.6
0.8
1.0
0 10 20 30 40 50
Par
alle
l com
pone
nt a
s fr
actio
n of
tota
l spe
ctra
l wei
ght
c/E
=90
=0
Browning, Yuan & Brown, Phil Mag A 67, 261 (1993)
Collection conditions:Collection conditions:
Brookhaven Science AssociatesU.S. Department of Energy
180 185 190 195 200 205 210 215 220
Inte
nsi
ty (
arb
. un
its)
Energy loss (eV)
BMg
Bulk [001]Bulk [001]
180 185 190 195 200 205 210 215 220
Inte
nsi
ty (
arb
. un
its)
Energy loss (eV)
Bulk [100]Bulk [100]
B K-edgeB K-edgeB K-edgeB K-edge
IntroductionIntroduction
R. F. Klie, J. C. Idrobo, N. D. Browning, K.A. Regan, N.S. Rogado, and R. J. Cava, Appl. Phys. Let., 79 (12), 2001
Brookhaven Science AssociatesU.S. Department of Energy
Position of the SAD aperturePosition of the SAD aperture
SAD aperture position
The SAD aperture has to be in the image plane of the OL to obtain diffraction pattern from same area as image.
In SAM mode, use DiffFocus to adjust position of SAD.
Brookhaven Science AssociatesU.S. Department of Energy
Keeping the Diffraction Focus constant:Keeping the Diffraction Focus constant:
Brookhaven Science AssociatesU.S. Department of Energy