Chapter 13 - STEM

7/31/2019 Chapter 13 - STEM

http://slidepdf.com/reader/full/chapter-13-stem 1/13

MSE-603 Aut umn 2011 STEM Mar co Cantoni

14. STEM

Scanning Tr ansmission Elect r on Micr oscopy

a) STEM, principle, basics,TEM / STEM wit h t he same inst r ument

Tr ansmission Elect r on Micr oscopya Textbook f or Mater ials ScienceDavid B. Will iams and Barr y Cart er

I SBN 0-306-45247-2

b) Analyt ical Elect r on Micr oscopy (AEM)Pr act ical Analyt ical Elect r on Microscopy in Mat erials Science

David B. Will iamsI SBN 0-9612934-0-3

c) High angle annular dark- f ield, HAADFZ- cont rast

Handbook of Micr oscopy, Met hods I IS. Amelinckx , D. van Dyck, J . van Landuyt, G. van Tendeloo

I SBN 3-527-27920-2

13 - 1


CTEM/ SEM pr inciples

Conventional TransmissionElectron Microscope

ScanningElectron Microscope

Slide Projector TV

What you

see is whatthe

detectorsees !!!

13 - 2




TEM-SEMint eract ion of elect r ons wit h t he sample

Specimen

I n c i d e n t

b e a m

Auger electrons

Backscattered electrons

BSE

secondary electrons

SE Characteristic

X-rays

visible light

“absorbed” electrons electron-hole pairs

elastically scattered

electrons

direct beam inelastically

scattered electrons

Bremsstrahlung

X-rays

1-100nm

13 - 3


Det ect or sin S(T)EM

• Secondary Electrons

• Backscattered Electrons

• X-rays

• EELS

• Bright field

• Dark field

• (Absorbed current)

13 - 4




Advant ages and disadvant ages of Scanning BeamMicr oscopy

TEM <-> STEM (SEM)

Advant ages

• Parallel det ect ion ofdif f er ent signals

• Easy posit ioning of t hebeam (EDX, EELS)

• Small int er act ionvolume, High ener gy(EDX)

Disadvant ages

• Longer acquisi t ion t imes(line by line)

• I mage dist or t ions(def lect ion coils)

• Mor e complicat edalignment procedur e

• Mor e expensive…

13 - 5


STEM <-> (C)TEM

13 - 6




a) Pr inciple

13 - 7


Recipr ocit y

A B

S o u r c e

D e t e c t o r

S p e c i m e n

Lens

A B

CTEM

Cowley (1969): for the same lenses, apertures and system dimension

the image contrast must be the same for CTEM and STEM

2STEM = 2CTEM

2STEM = 2 CTEM

STEM

Lens

22

22

Cowley, 1989

13 - 8




I lluminat ion / opt icsTEM / STEM wit h t he same inst r ument

13 - 9


Source

Illumination

Scanning

“descanning” /

Detection

13 - 10




Beam cur r ent versus pr obe size

100keV electron beam: beam current:1nA, probe size: 1nm

150MW/mm2 !!!

Field emission guns

• provide high emission current

• from a small source (~1nm)

• require small demagnification

->small probe size

13 - 11


Dif f r act ion pat t er n = st at ionar y pat t er nBF/ DF det ect or s

13 - 12



MSE-603 Aut umn 2011 STEM Mar co Cantoni 13 - 13


Au par t icles on a C f ilmSTEM BF:

Detection of transmitted

electrons:

contrast similar to

CTEM BF image

(objective aperture

selects only transmitted

electrons)

STEM ADF:

Detection of diffracted

electrons on the annular

DF detector:

(integration of multiple

CTEM DF images)

Diffraction pattern

13 - 14




Br ight f ield/ Annular Dar k f ield det ect orinf luence of camera lengt h and convergence angle

The selected camera-length (magnification of the diffraction pattern)

determines what the detectors “sees”

Big camera length small camera length

ADF

BF

13 - 15


Br ight f ield TEM <->STEM

13 - 16




Br ight f ield TEM STEM

CTEMCTEM

Effect of increasing detection angle (decreasing camera length)

on STEM BF image contrast: Loss of dynamical diffraction contrast

STEM

STEM

STEM

13 - 17


ADF STEM

• The ADF image provides a signal which depends strongly on the

bragg scattering (Al2O3).

• Single atoms scatter electrons incoherently to higher angles

~ “z-contrast”

Single atoms (or

small groups of

atoms) of Pt on

crystalline Al2O3

13 - 18




b) Analyt ical Elect r on Microscopy(EDS)

• Thin samples -> cor r ect ion f act or s weak (A and F can beneglect ed), quant if icat ion “easy”

• Ver y weak beam br oadening -> high spat ial resolut ion ~ beamdiamet er (~nm)

• STEM: beam cont r ol and posit ioning

13 - 19


I nt eract ion volumeSEM (30KeV), bulk

versusTEM (300KeV), t hin f ilm

PZTceramics

bulk

20nmthick PZT

Small interactionvolume -> high spatialresolution for EDXAnalysis!

TEM

13 - 20




STEM point analysisPbMg1/ 3Nb2/ 3O3 (bulk)

Processing option : Oxygen by stoichiometry (Normalised)

Spectrum Mg Si Nb Pb O Total

Spectrum 1 30.02 13.32 56.66 100.00

Spectrum 2 19.15 7.96 4.11 11.72 57.06 100.00

Spectrum 3 6.01 12.49 22.13 59.37 100.00

Spectrum 4 5.65 12.39 22.67 59.29 100.00Spectrum 5 5.63 12.48 22.52 59.36 100.00

Spectrum 6 5.98 13.66 20.11 60.25 100.00

Spectrum 7 5.55 12.45 22.66 59.34 100.00

Spectrum 8 5.49 12.96 21.84 59.72 100.00Spectrum 9 5.63 12.19 23.04 59.14 100.00

Max. 30.02 13.32 13.66 23.04 60.25Min. 5.49 7.96 4.11 11.72 56.66

All results in Atomic Percent

13 - 21


Pb(Zr,Ti)O3 Thick f ilms f or MEMS

SEM image of a wet et ched(in HF/ HCl solut ion) side-wall

of 2 µm PZT f ilm. All t he 8int erf aces cor r esponding t ot he int ermediat ecrystalli zat ion st eps becamevisible indicat ing acomposit ional gradient(pr ef erent ial et ching) across

t he PZT layer s.

13 - 22




CTEM dar k f ield image

13 - 23


STEM dar k f ield

STEM dar k f ieldimages.The r amps in t he gr aylevel indicat e changes

of densit y orchemical composit ion(~at omic number ).

13 - 24




EDX Line-scan

13 - 25


EDX point analysis

Quant it ati ve EDX Analysis of t he point s indicat ed in t he imagePr ocessing opti ons : Oxygen by st oichiomet r y (normalised)r esult s a Percent

Spect rumZr Ti Pb O Tot al Zr / Ti

1 8.43 12.60 18.45 60.52 100.0 40/ 60

2 9.92 9.98 20.15 59.95 100.0 49/ 51

3 12.07 7.61 20.49 59.84 100.0 61/ 39

13 - 26

Documents

Chapter 13 - STEM