zaluzec 1 instrumentation.ppt

8/9/2019 Zaluzec 1 Instrumentation.ppt

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Introduction toIntroduction to

Transmission/Scanning TransmissionTransmission/Scanning TransmissionElectron Microscopy and MicroanalysisElectron Microscopy and Microanalysis

Nestor J. ZaluzecNestor J. Zaluzec

zaluzec@[email protected]@[email protected]

http:http://tpm//tpm..amcamc..anlanl..govgov

Electron Microscopy CenterMaterials Science Division, Argonne National Laboratory


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Electron Microscopy CenterMaterials Science, Division, Argonne National Laboratory

AcknowledgementsAcknowledgements

Travel Support AMMSTravel Support AMMSR&D Support U.S.R&D Support U.S. DoEDoE & ANL& ANL

People contributing toPeople contributing tothisthispresentationpresentationinclude:include:

ANL EMC Group, Mansfield, Eades, Calderon, Jiao,Newbury, Okeefe, numerous text books, and

apologies to all those from whom I cant remembercollecting images/figures over the years.


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A Few References:

Principles and Techniques of Electron Microscopy: Biological Applications

M.A. Hayat CRC Press 1989

Electron Microscopy of Thin CrystalsHirsch, Howie, Nicholson, Pashley, Whelan Kreiger Press 1977

Electron Diffraction Techniques Vols 1 & 2, IUCr Monographs

Cowley ed., Oxford Press 1992

Defect Analysis in Electron MicroscopyLoretto & Smallman , Halsted Press 1975

Transmission Electron MicroscopyReimer Springer-Verlag 1989

Transmission Electron Microscopy A textbook for Materials ScienceWilliams & Carter Plenum Press 1996

Introduction to Analytical Electron MicroscopyHren, Goldstein, Joy Plenum Press 1979


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18971897 JJ Thompson - Discovery of the ElectronJJ Thompson - Discovery of the Electron19261926 H. Bush Magnetic/Electric Fields as LensesH. Bush Magnetic/Electric Fields as Lenses19291929 E.E. RuskaRuska PhD Thesis Magnetic lensesPhD Thesis Magnetic lenses19311931 Knoll andKnoll and RuskaRuska 1st EM built1st EM built19321932 DavissonDavisson andand CalbrickCalbrick - Electrostatic Lenses- Electrostatic Lenses

19341934 Driest & Muller - EMDriest & Muller - EM surpasessurpases LMLM19391939 vonvon BorriesBorries && RuskaRuska - 1st- 1st CommericalCommerical EMEM

~ 10 nm resolution~ 10 nm resolution19451945 ~ 1.0 nm resolution (Multiple Organizations)~ 1.0 nm resolution (Multiple Organizations)19651965 ~ 0.2 nm resolution (Multiple Organizations)~ 0.2 nm resolution (Multiple Organizations)19681968 A. Crewe - U.of Chicago - Scanning Transmission Electron MicroscopeA. Crewe - U.of Chicago - Scanning Transmission Electron Microscope

~ 0.3 nm resolution probe - practical Field Emission Gun~ 0.3 nm resolution probe - practical Field Emission Gun19861986 Ruska etalRuska etal - Nobel Prize- Nobel Prize19991999< 0.1 nm resolution achieved (OM< 0.1 nm resolution achieved (OM ))2009 0.05 nm (TEAM)2009 0.05 nm (TEAM)

A Historical Time Line inA Historical Time Line in

Electron Optical InstrumentationElectron Optical Instrumentation

19381938

19991999


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Introductory Remarks

Instrumentation

Electron SourcesElectron OpticsElectron Detectors

Electron Beam Interations ->Operating Modes

Electron ScatteringDiffractionImagingOther Modes

STEMHREM? Others ?

X-ray Energy Dispersive SpectroscopyElectron Loss Spectroscopy

Tutorial OutlineTutorial Outline


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Transmission Electron MicroscopyTransmission Electron Microscopy


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Experimental methodologies which employs (electron-optical )Experimental methodologies which employs (electron-optical )instrumentation to spatially characterize matter on scales which rangeinstrumentation to spatially characterize matter on scales which rangefrom tenths of a millimeter to tenths of a nanometer. The principlefrom tenths of a millimeter to tenths of a nanometer. The principlemodalities employed are:modalities employed are:

ImagingImagingScanning Electron MicroscopyScanning Electron Microscopy


Scanning Transmission Electron MicroscopyScanning Transmission Electron Microscopy

FocussedFocussed Ion BeamIon Beam

DiffractionDiffractionElectron BackscatteredElectron Backscattered DifrractionDifrraction

Selected Area Electron DiffractionSelected Area Electron Diffraction

Convergent Beam Electron DiffractionConvergent Beam Electron DiffractionReflection High Energy Electron DiffractionReflection High Energy Electron Diffraction

SpectroscopySpectroscopyX-ray Energy DispersiveX-ray Energy Dispersive

Electron Energy LossElectron Energy Loss

Auger ElectronAuger Electron

Microscopy & MicroanalysisMicroscopy & Microanalysis


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SEMSEMScanning Electron MicroscopyScanning Electron Microscopy

TEM - STEM - HREMTEM - STEM - HREMTransmission - Scanning Transmission -Transmission - Scanning Transmission -

High Resolution Electron MicroscopyHigh Resolution Electron Microscopy

AEMAEMAnalytical ElectronAnalytical Electron

MicroscopyMicroscopy

Morphology, Crystallography, Elemental , Chemical , Electronic StructureMorphology, Crystallography, Elemental , Chemical , Electronic Structure

Role ofRole of TraditonalTraditonal Electron MicroscopyElectron Microscopy


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Elastic ScatteringElastic Scattering SpectroscopiesSpectroscopies

Electron Microscopy (EM),Electron Microscopy (EM),

Scanning Electron Microscopy (SEM),Scanning Electron Microscopy (SEM),

SEM-based Electron Channeling Patterns (ECP),SEM-based Electron Channeling Patterns (ECP),

Transmission Electron Microscopy (TEM),Transmission Electron Microscopy (TEM),

Transmission Electron Diffraction (TED),Transmission Electron Diffraction (TED),

Convergent Beam Electron Diffraction (CBED)Convergent Beam Electron Diffraction (CBED)

Selected Area Electron Diffraction (SAED)Selected Area Electron Diffraction (SAED)

Scanning Transmission Electron Microscopy (STEM),Scanning Transmission Electron Microscopy (STEM),

Reflection High Energy Electron Diffraction (RHEED)Reflection High Energy Electron Diffraction (RHEED)

Low Energy Electron DiffractionLow Energy Electron Diffraction(LEED)(LEED)

X-ray Diffraction (XRD),X-ray Diffraction (XRD),

Scanning Transmission X-ray Microscopy (STXM)Scanning Transmission X-ray Microscopy (STXM)

Neutron Diffraction (ND).Neutron Diffraction (ND).


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Secondary Electron Imaging (SEI)Secondary Electron Imaging (SEI)

Backscattered Electron Imaging (BEI/BSI)Backscattered Electron Imaging (BEI/BSI)

Auger Electron Spectroscopy (AES),Auger Electron Spectroscopy (AES),

Electron Energy Loss Spectroscopy (EELS),Electron Energy Loss Spectroscopy (EELS),

EXtendedEXtendedEnergy Loss Fine Structure (EXELFS),Energy Loss Fine Structure (EXELFS),

Energy Loss Near Edge Fine Structure (ELNES),Energy Loss Near Edge Fine Structure (ELNES),

X-ray Emission Spectroscopy (XES),X-ray Emission Spectroscopy (XES),

X-ray Energy Dispersive Spectroscopy (XEDS),X-ray Energy Dispersive Spectroscopy (XEDS),

Wavelength DispersiveWavelength DispersiveSpectroscopy (WDS),Spectroscopy (WDS),

CathodoluminescenceCathodoluminescence(CL(CL))

X-ray Photoelectron Spectroscopy (XPS),X-ray Photoelectron Spectroscopy (XPS),X-ray Photoelectron Microscopy (XPM),X-ray Photoelectron Microscopy (XPM),

Ultraviolet Photoelectron Spectroscopy (UPS),Ultraviolet Photoelectron Spectroscopy (UPS),

X-ray Absorption Spectroscopy (XAS),X-ray Absorption Spectroscopy (XAS),

EXtendedEXtendedX-ray Absorption Fine Structure (EXAFS),X-ray Absorption Fine Structure (EXAFS),

X-ray Absorption Near Edge Fine Structure (XANES)X-ray Absorption Near Edge Fine Structure (XANES)

X-Ray Fluorescence (XRF).X-Ray Fluorescence (XRF).

InelasticInelasticScatteringScattering SpectroscopiesSpectroscopies

ee--!!ee--

ee--!!""

""!!ee--

""!!""

TypeType


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Source Brightness

(particles/cm2/sR/eV)

Elastic Mean

Free Path

(nm)

Absorption

Pathlength

(nm)

Attainable

Probe Size

(nm)

Neutrons 1014 107 108 106

X-rays 1026 103 105 ~ 30

Electrons 1029 101 102 < 0.1

Comparison Source CharacteristicsComparison Source Characteristics


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Reflection / Scanning MicroscopyDeals Mainly with Near Surface Region

Transmission MicroscopyDeals Mainly with Internal Structure

Specimen

Modern EM's can depending upon the specimen operate in both modes


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What are the limits of Resolution?What are the limits of Resolution?

Abbe (Diffraction) Limit:

Defines the minimum resolvable distance between theimage of two point objects using a perfect lens.

In any magnifying system a point object (i.e. zero dimension)cannot be imaged as a point but is imaged as a distribution ofintensity having a finite width.

"= wavelength of the imaging radiation#= index of refraction of the lens!= illumination semi-angleNA = numerical aperture = #sin(!)

"=0.6#

$sin(%)

Resolution of an imaging system


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ResolutionResolution vsvs. Magnification. Magnification

Magnification in these images is constant ! Do not confuse the two concepts.

"=0.6#

$sin(%)


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eV=m

0v 2

2

p =mv = 2m0eV

"() =h

p=

h

2m0eV #

12.27

V(volts)

"=h

p=

h

2m0eV 1+eV

2m0c2

#

$%

&

'(

) 12.27

V(1+ 0.978x10*6V)


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LightLight vsvsElectronsElectrons

Light Microscope Electron Microscope

~

0.5 m

=

h

2moeV

o

= 0.068 30 kV)

=

1.5 glass)

=

1.0 Vacuum)

$~ 70

o

$< 1

o

%&0 21

m = 2100

%&4 1

"=0.6#

$sin(%)


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From Ants to AtomsFrom Ants to Atoms

Microscopy is needed nearly everywhereMicroscopy is needed nearly everywhere

Human Eye OpticalMicroscopy

X-ray

Microscopy

Electron

Microscopy


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Depth of FieldDepth of Field

The distance parallel to the optical axis of the microscope that a feature onThe distance parallel to the optical axis of the microscope that a feature onthe specimen can be displaced without loss of resolutionthe specimen can be displaced without loss of resolution


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Depth of FieldDepth of Field

Varies with MagnificationVaries with Magnification

!

$

D


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The distance parallel to the optical axis of the microscope that aThe distance parallel to the optical axis of the microscope that a

feature on the specimen can be displaced without loss offeature on the specimen can be displaced without loss of

resolutionresolution

Depth of Focus/FieldDepth of Focus/Field


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Depth of FocusDepth of Focus


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Depth of Focus (Specimen Plane)Depth of Focus (Specimen Plane)

Pre Specimen Semi-AnglesPre Specimen Semi-Angles

!

$

D

D=$

!

In an EM# is controlled by both Apertures & the Lens Magnification


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Depth of Field (Image Plane)Depth of Field (Image Plane)

Post Specimen Semi-AnglesPost Specimen Semi-Angles

Dim = = M2

im

%$ob

!

$im Dim

$ob

!

%

Lens

5 m50kX10 mR2 nm

5 km500kX10 mR0.2 nm

DimM ! $ob


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Illumination SourceIllumination Source

Illumination LensIllumination Lens

SpecimenSpecimen

Magnifying LensMagnifying Lens

Detector/ViewerDetector/Viewer

Basic Components of All MicroscopesBasic Components of All Microscopes

That Use LensesThat Use Lenses


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Transmission Electron MicroscopeTransmission Electron Microscope


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Transmission Electron Microscope

Basic Components of anBasic Components of anElectron MicroscopeElectron Microscope


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SpecimenSpecimen






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Sources for Electron MicroscopySources for Electron Microscopy

ThermionicThermionic,, Thermally Assisted,Thermally Assisted,

andandField EmissionField Emission

Conductionelectrons mustovercome the workfunction &if theyare to be emittedfrom the cathodeinto the vacuum.


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jc =ATC2exp("#/ kTC)

Thermionic sources

Richardson law gives the current density :

k is Boltzmanns constant, TCis the cathode temperature and Aand &are a constants depending on material. Note that jc'T.

W has TCof 2500-3000 K (melting point 3650 K)LaB6has a TCof 1400-2000 K

Heating usually produced by running acurrent through the material!


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Field emission and Schottky sources

The width b of the potential barrier at the metal-vacuum boundarydecreases with increasing electric field E.

For |E|>107V/cm the width b < 10 nm and electrons can penetratethe potential barrier by the wave mechanical tunneling effect.

The current density of field emission can be estimated from theFowler-Nordheim formula:

j =k1 E

"exp(

k2"3 / 2

E

#

$%%

&

'((


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Comparison of Electron Sources

Type Br ightness

/Vo

A / c m

2

/sr/eV

Source

S i z e

m )

Energy

Spread

e V )

Temporal

Coherence

m )

Shot

No i se

Current

S tab i l i ty

Spat ia l

Coherence

Vacuum

Torr)

T he rm on ic H ai r pi n

Pointed

1

5

5 0

1 0

2 - 3 0 . 4

Low

Good

F a i r

Low

Moderate


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J

Probe Current Related ParametersProbe Current Related Parameters


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Why do we need a lens?Why do we need a lens?


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Why do we need a lens?Why do we need a lens?

Because all electron sources generally produce a diverging beam ofelectrons. This beam must be "focussed" onto the specimen, to increasethe intensity and thus to making the probe "smaller".


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SpecimenSpecimen






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What is a Lens?What is a Lens?

It is a device which focuses radiation.It is a device which focuses radiation.

f = focal length of the lensf = focal length of the lens


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How Does a Converging Lens Work as a Magnifier?How Does a Converging Lens Work as a Magnifier?

1

f=

1

a+

1

b

M=h

h'= "

b

a

In a TEM the function of lens are to eitherIn a TEM the function of lens are to either demagnifydemagnify the probe from the sourcethe probe from the source

point to the sample. This means that b < a resulting in a smaller electron probe.point to the sample. This means that b < a resulting in a smaller electron probe.

ItIts 2nd role as a post specimen lens iss 2nd role as a post specimen lens is magnify an image hence b > amagnify an image hence b > a

ThinLensFormulae


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Thin LensFormulae

1

f=

1

do

+1

di

M =!di

do

LensesLensesandand

MagnificationMagnification

Focus achievedusing Lorentz Force

Focus achievedusing Refraction


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Electron Lenses

Electrons are charged particles and are influenced by Electromagnetic Fields.Lenses in an TEM/STEM utilize either or combinations of Magnetic andElectrostatic Fields to direct the beams as desired.


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Types of Electron LensesTypes of Electron Lenses

Condenser Lenses ~ Type A, Objective Lenses ~ Type A B or C, Stigmators Type D


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How Does a Lens Work as a Magnifier?How Does a Lens Work as a Magnifier?

1

f=

1

a+

1

b

M=h

h'= "

b

a

In a TEM the function of lens are to eitherIn a TEM the function of lens are to either demagnifydemagnify the probethe probe

from the source point to the sample. This means that b < afrom the source point to the sample. This means that b < a

resulting in a smaller electron probe. Or to Magnify an Image b > aresulting in a smaller electron probe. Or to Magnify an Image b > a


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Magnification is achieved by

Stacking Lenses

M= M1* M2* M3

How Accurate is M ?

What are the limiting Factors?

1

f=

1

a+

1

b

M=h

h'= "

b

a


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Alignment/Deflection Coils also use Lorentz Fieldsbut they are not axially symmetric


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Tilting the Beam Translating the Beam


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Probe Astigmatism


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Image Astigmatism


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Note the locationsof the various

Apertures.

Optimum aperturesizes are neededfor variousimaging functions.

Most TEM/STEMhave 7-8 Lenses

1 Gun Lens2 Condensers1 Objective1-2 Intermediate1-2 Projectors

Most instrumentshave onlyElectromagneticRound Lenses

Gun Lens

Helps form probe

Condenser Lens

Mainly controls:Spot Sizehence total beamcurrent

Objective Lens

Mainly controlsFocus, 1st Magnification

Diffraction/Intermediate

Lens

Controls Mode

Projector Lens

Magnification

Roles of the LensesRoles of the Lenses


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ConventionalConventional

ImagingImaging

HighHigh

ResolutionResolution

ImagingImaging

DiffractionDiffraction


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Apertures.



2 Condensers1 Objective1-2 Intermediate2 Projectors


Gun Lens

Helps form probe

Condenser Lens

Mainly controls:Spot Sizehence total beamcurrent



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With Modern InstrumentsWith Modern InstrumentsSpectroscopy can be done at the Sub-Nanometer ScaleSpectroscopy can be done at the Sub-Nanometer Scale

Selection of Probe Forming Source is ImportantSelection of Probe Forming Source is Important


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Apertures.



2 Condensers1 Objective1-2 Intermediate2 Projectors


Objective Lens

Mainly controlprobe focus

Diffraction/IntermediateLens

Controls Mode

Projector Lens

Magnification



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ImagingImaging vsvs Diffraction:Diffraction:Post Specimen Lenses determine the modePost Specimen Lenses determine the mode


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When isthe Imagein Focus?


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Fresnel Fringes - Diffraction (Interference) from an Edge

I="(r,z)"*(r,z)

"(r,z) = "i(r,z)#

"2#(r)+

8$2me

h2 [E+V(r)]#(r) = 0

"1(r,z) =exp(2#ikr)

r


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White Fresnel Fringe = Under Focus

Black Fresnel Fringe =Over Focus

B O W U


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Magnification = CRT Display Size / Area Swept by Beam on Sample

The scanning process is the mechanism whichThe scanning process is the mechanism whichallows us to use small probes to form images of large areas.allows us to use small probes to form images of large areas.


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Abbe (Diffraction) Limit:

Defines the minimum resolvable distance between theimage of two point objects using a perfect lens.

In any magnifying system a point object (i.e. zero dimension)cannot be imaged as a point but is imaged as a distribution ofintensity having a finite width.

R esolution of an imaging system= =0.61

sin ( )

"= wavelength of the imaging radiation#= index of refraction of the lens!= illumination semi-angle

What Limits Resolution?What Limits Resolution?

This ASSUMES a Perfect LensEx: 100 kV electrons !~ 100 mR =>(= 0.23


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What limits our ability to perfectly focus?What limits our ability to perfectly focus?

Lens Aberrations


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Prespecimen Aberrations


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Aberrations and Probe Size Related ParametersAberrations and Probe Size Related Parameters

Aberration Correction also increases usable probe current


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Aberration Correction also increases usableprobe current

Can we see aberrations ? Yes if you look for them


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Can we see aberrations ? Yes if you look for them.

150 !m 70 !m 30 !m

70 !m Clean 100 !m Dirty 100 !m Dirty


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60 nm

12 nm

6 nm


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PostSpecimen

Aberrations

i h S i l l i i


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TEM-High Spatial Resolution ImagingTEM-High Spatial Resolution Imaging


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Aberrations and Image ResolutionAberrations and Image Resolution

B.B. KabiusKabius - ANL- ANL


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Light Microscope

Electron

Microscope

Resolution

()

0.1

1

10

100

1000

104

105

1800 1840 1880 1920 1960 2000 2040

Aberration-corrected EM

d ()

point res.

uncorrected

Cscorrected

TEAM Project Phase 1 :TEAM Project Phase 1 : Ultra High Resolution ImagingUltra High Resolution Imaging

Requirements:Requirements:


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)f = -257 nm; R= 1.4 nm )f = -68 nm; R = 4.4 nm )f = -12 nm; R = 0.1 nm

SiSi

CoSiCoSi22CoSiCoSi

22

SiSi

2 nm2 nm

Uncorrected : CUncorrected : Css= 1.2 mm= 1.2 mm

CoSiCoSi22

1 nm1 nm

SiSi

Corrected :Corrected :

CCss= 0.05 mm= 0.05 mm

B. Kabius, S. MantlArgonne, Juelich: ~1997CM200

focus of least confusion Scherzer defocus Scherzer defocus (AFI)

Aberration Free ImagingAberration Free ImagingInfluence of Contrast DelocalizationInfluence of Contrast Delocalization

Delocalization : R = | CDelocalization : R = | C55""55gg55+ C+ C

33""33gg33 ++ ""CC

11g |g |

maxmax


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TEAM 0.5

Examples of Environmental Artifacts


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Aperiodic - Vibrational

Periodic - EM Fields User-Acoustic

User-Mechanical

p


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Sub-ngstrom Microscopy and Microanalysis LaboratorySub-ngstrom Microscopy and Microanalysis Laboratory

Temp:Temp: ++0.1 F0.1 F

EMF: < 0.01mGEMF: < 0.01mG

Acoustics: < 40 dBAcoustics: < 40 dB

Air Flow: < 1 cm/minAir Flow: < 1 cm/min

Vibrations: < 0.25 !m PkVibrations: < 0.25 !m Pk

Best -> Worse

Environmental Conditions

zaluzec 1 instrumentation.ppt

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