brookhaven science associates u.s. department of energy jeol tem/stem course 2010f fastem university...

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


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:


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


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


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.


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!


Convergence angle αConvergence angle α

β

α


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


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.


Convergence angle βConvergence angle β

Underfocus,β < 0

Overfocus,β > 0

Overfocus,β > 0

Overfocus,β = 0

CL must be focused on OL FFP!


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


Convergence angle ΦConvergence angle Φ

Φ for β=0In a magn. field electrons spiral around field lines with:

For small angles:


Parallel Illumination modeParallel Illumination mode

α

αα

β



Bragg line rotation method:Focused probe: β = 0



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:


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.



NBD mode:CM on

CBD mode:CM off

Different illumination modes:


Measuring convergence anglesMeasuring convergence anglesFor 200 keV instrument with Bz=3 T: Φ/r=1.7 mrad/μm


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



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:



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 Å²


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.


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:


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


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.


Keeping the Diffraction Focus constant:Keeping the Diffraction Focus constant:

brookhaven science associates u.s. department of energy jeol tem/stem course 2010f fastem university...

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