Transcript Document

JEOL TEM/STEM course
2010F FasTEM
Robert Klie
Center for Functional Nanomaterials
Brookhaven National Laboratory
University of Michigan
27 – 29 June 2006
Brookhaven Science Associates
U.S. Department of Energy
Syllabus:
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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
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STEM conditions/camera lengths
Gun Conditions: finding the optimum values
Ultra high resolution
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A2 – change value
Objective lens angle – underfocus to overexcite
Condenser 3 lens
Sample: Si/SiO2/SrTiO3
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Syllabus (contd)
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Day 3: FasTEM/STEM:
EDS
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1. Aperture selection
2. Analytical measurements
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EELS
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A. Hole Counts
B. P/B
C. Film Count
D. NiK and NiL ratio: detector test and specimen stage position
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
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Parallel illumination:
Parallel illumination is needed for:
SAD: to minimize the spot diameter
Diffraction 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
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Obtaining 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.
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Convergence angles in a TEM:
Convergence angles α and β
Convergence angles Φ
All three angles have to minimized for truly parallel illumination!
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Convergence angle α
β
α
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Convergence 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.
K
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.
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Reducing electron source size:
Demagnification of electron source:
Changing the spot size will reduce the effective source size
by demagnifying the source image.
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Convergence angle β
Underfocus,
β<0
Overfocus,
β>0
Overfocus,
β>0
CL must be focused on OL FFP!
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Overfocus,
β=0
Convergence angle 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
β
β
c/o
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Convergence angle Φ
In a magn. field electrons spiral around
field lines with:
For small angles:
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Φ for β=0
Parallel Illumination mode
β
α
α
α
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Obtaining parallel illumination
Bragg line rotation method:
Focused probe:
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β=0
Obtaining parallel illumination
Wobble OL, and change CL3
Convergent Probe:
Convergent Probe:
If illumination is not
parallel, probe will
change size when
wobbling OL!
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If illumination is parallel,
probe-size will remain
some when wobbling OL!
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.
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Obtaining parallel illumination
Different illumination modes:
NBD mode:
CM on
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CBD mode:
CM off
Measuring convergence angles
For 200 keV instrument with Bz=3 T:
Φ/r=1.7 mrad/μm
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Measuring convergence angles
M 2 (s)  kF 2 (s)  CTF 2 (s)  E 2 (s)  N 2 (s)
F = Structure factor
E = envelope functions
N = noise function
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E 2 s   Gsc (s)  Gtc (s)
Gsc (s)  exp( 2 2 (Cs 2 s 3  fs) 2 )
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 E  4
Gtc (s)  exp((
Cc2 2 
 s ))
16ln 2
 E 
2
2
GSC= spatial coherence
GTC= temporal coherence
Measuring convergence angles
Fitting of the CTF:
Determine Noise:
0.5
12
8
0.4
Raw intensities
10
0.3
Fit
0.2
6
0.1
SNR
Intensity
8
6
0
0.25
0.3
0.35
0.4
0.25
0.3
0.35
0.4
4
4
2
2
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
0.05
0.1
0.15
0.2
Spatial Frequency (1/A)
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Measuring convergence angles
1
Envelope
0.8
0.6
0.4
Gtc: 2eV, 1 ppm
Gsc: 0.1 mrad
0.2
Gsc * Gtc
Gaussian: B=9 Ų
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0
0.1
0.2
0.3
Spatial frequency (1/Å)
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0.4
0.5
Measuring convergence angles
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Parallel Illumination for EELS:
Image modes for EELS:
Convergence angle:
To EELS
PL focus has to be fixed to maintain focus of EELS spectrometer.
Convergence angle is determined by SEA and imaging mode.
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Collection conditions:
INCIDENT BEAM
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q
Q
b
q
k1
k0
Parallel component as fraction
of total spectral weight
C-AXIS
1.0
0.8
0.6
 =0
0.2
0
f
 =90
0.4
0
10
20
30
q c/ q E
40
50
APERTURE
Can enhance or reduce orientation effects with C3 and projector lenses
Browning, Yuan & Brown, Phil Mag A 67, 261 (1993)
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Introduction
Bulk [001]
Bulk [100]
B
Mg
B K-edge
Intensity (arb. units)
Intensity (arb. units)
B K-edge
180
185
190
195
200
205
Energy loss (eV)
210
215
220
180
185
190
195
200
205
210
215
Energy loss (eV)
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
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220
Position 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.
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Keeping the Diffraction Focus constant:
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