1 introduction - electron microscopy and diffraction
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Do Minh Nghiep
Materials Science Center
Electron MicroscopyElectron Microscopyand Diffractionand Diffraction
1. Introduction1. Introduction
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ContactContact
Lecturer: Minh Nghip
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Tel. 38691332
e-mail: n hie mail.hut.edu.vn Class time: Mon 14:50-17:20
Class room: D6-106
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ourse ou comesourse ou comes
n erstan ng o mage orma on y g ass anelectromagnetic lenses.
.
Understanding of the construction of various types of
electron microscopes, the function of the variousparts and methods of image formation.
Understanding of methods ofsample preparation for
. Ability to utilize EDS and WDS results forelemental
(microchemical) analysis.
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on enon en
Introduction to EM Electron optics
Electron source and vacuum system
Electron-matter interaction SEM
TEM
Electron diffraction
EDS and WDS
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Lab worksLab works
1. Preparation of an alloy specimen to observeits microstructure by SEM
2. Determination and imaging of chemicalcomposition of the alloy specimen by SEMand EDS
. repara on o an spec men o mageits microstructure and to analyze ED pattern
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ea ngea ng
Textbook: Handouts
References:1. D. B. Williams and C. B. Carter, Transmission electron microscopy, Books
1 to 4, Plenum Press, 1996
2. P. Hirsch, et al.; Electron microscopy of thin crystals; Huntington, N. Y., R.. . .,
3. Elizabeth M. Slayter, Henry S. Slayter; Light and electron microscopy;Cambridge (England), New York, Cambridge University Press, 1992
.formation and microanalysis; Berlin, New York, Springer-Verlag, 1993
5. John M. Cowley; Diffraction physics; Amsterdam, New York: North-HollandPub. Co., New York: Sole distributors for the U.S.A. and Canada, ElsevierNorth-Holland, 1981
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ra ngra ng
The weighting factors used to determinet e na gra e:
Lab work and reports: 20 % Mid-term test and final exam: 70 %
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Week 1 Why electron microscope - a brief history
Week 2 Electron sources, Vacuum
Week 3 Electron optics, Electromagnetic lenses, Resolution limits
Week 4 Electron beam -specimen interactions
Week 5 Mid-term test
Week 6 SEM: Scanning system, Detectors, SE image,
Backscattered image, Resolution - , ,
Diffraction, Phase)
Week 8 Microprobe analysis: Detection systems (EDS, WDS), Qualitative
and quantitative analysis
Week 9 Practical lab for SEM, EDS
Week 10 Electron diffraction, Diffraction patterns
Week 11 Practical lab for TEM, ED
Week 12 Final exam
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IntroductionIntroduction
a er a s c arac er za ona er a s c arac er za on
HistoryHistory Why EM ?Why EM ?
Overview of SEM and TEMOverview of SEM and TEM
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characterizationcharacterization mean?mean?
Character: a sum of qualities that make a person / thing different fromothers
Characterize: to indicate / describe / investigate / express the characterof a person / thing (action)
Materials characterization:
- in specifying the internal microstructure of an engineering materials
including the chemistry, the crystallography, the structural morphology- in terms of engineering properties of materials, and reflects the need toknow the physical, chemical and mechanical properties of the materialsbefore we can design an engineering system or manufacture its components
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characterization is important?characterization is important?
It is believed that optimization of material properties through control of
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.
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structure and propertiesstructure and properties
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Atomic level: Physics and Chemistry
Microscopic level: Chemistry and Materials Sci..
Macroscopic level: Mechanical and Materials Eng.
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of materialsof materials
Mechanical properties
em ca proper es
Physical properties- Thermal property
- Optical property
- Electrical property- Magnetic property
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EquipmentsEquipments
analysisanalysis
molecular levels)molecular levels)
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EquipmentsEquipments
analysisanalysislevels)levels)
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HistorHistor
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Optical/light microscope (OM): visible light limits magnification of max1000-2000X and resolution of 0,2 mm. Electron microscope (EM) is
developed for overcoming these limitations. 1932 - 1938:
- The first TEM (1932, idea of EM, Max Knoll and Ernst Ruska,Germany)
- The first SEM (1938, laterSTEM - TEM with scanning coil, Knoll and,
1940 -1952:- The first SEM for thick sample (1942, Zworykin et al., RCA
a ora or es . . , reso u on mm.- The first Field Emission electron source (1942, FE Gun)- The SEM with resolution of 50 nm (1952, Oatley and McMullan,
ng an
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1959-1967:
- SEM with stereoscan (Wells)- Performance of SE detector (1960, Everhart and
Thornley)- The first commercial EM (1965)- Electron-channeling contrast for crystal orientations
(1967)
[Oatley (1982), J. Appl. Phys. 53, R1]
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1932 theory of EMAntonie van Leeuwenhoek,
th
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1986 Nobel Prize winners.,
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James Hillier
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EM19401938 - First SEM is produced
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The prototype of thefirst Stereoscansupplied by the
Company to theduPont Company,
U.S.A. (Stewart and
McMullans originalmicroscope
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Wh EM ?Wh EM ?
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e n one n on
Microscope - A device with a lens or series of lensesthat enlarge (magnify) the appearance of an object.
Image - Perception of an object using your eyes (vision).
One can sense an object without vision (touch, etc..).Requires visible light.
Lens - A lens is an optical componentwhich is used to
.made of a glassy material, whereas non-uniformelectromagnetic fields are used as lens for electrons.
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Ma nification - The ratio between ima e size to the
object size. Can be varied by changing the distancebetween the object and the final lens (of the eye) or by.
Wavelength - Distance between peaks of the waveform.
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Resolution
- RP is the smallest
points at which two or moreobjects can be
distin uished as se arate.
- Resolution is the abilityofa lens to distinguish
at infinity, when they areviewed in the image plane.
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In 1870, Ernst Abbe (1840-1905) derived mathematical
RP (1/2)
expression for resolution of microscope: Resolution is
limited to 0.5 the wavelength of illuminating source.
, RP= ----------------
NA = n.sin
- . -n - index of refraction - half angle of illumination
increasing the half angle of illumination, b) increasing the refractiveindex of the lens by using Crown glass, and c) decreasing the
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Increase sin decr. workin distance incr. size of the lens :
Increase refractive index n (oil refractive index ishigher than air)
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Replacing visible lightReplacing visible lightby electron beamby electron beam
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e sma est stance etween two po nts t at can e
resolved by
uman eye: . - . mm
Light microscope: 0.2 m
SEM: 1-2 nm
TEM: 2
This high resolution is achieved by TEM thanks to theuse of a high energy electron beam (small wavelength).
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ew ng op onsew ng op ons
Sample
thickness
Sampleenvironment
Resolution[m]MagnificationInstrument
crye
ThickAir15-1002-10
Magnifying
glass
ThickAir or Oil0.2200-1300Optical
microscope
cacuum.-
ThinVacuum0.00014103-1.5X106TEM
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ElectronElectron-- dual (wavedual (wave--particle) character:particle) character:Light particlesLight particles -- Matter wavesMatter waves
Hermann Busch (1924): Axial magnetic fields refract electrons
h - Planck constant (6.624 X 10-27 erg/s)
v- electron velocity (p = mv: momentum)V- accelerating voltagemo - rest electron mass
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- re a v s c e ec ron mass . x - gram = o pro on
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1/2
e ro g e re at ons pe ro g e re at ons p
Resolution limit of light microscope:
- can ecrease o nm- n.sin is limited to 1.6- Thus the maximum resolution is about 200 nm
Cannot go beyond this even with better optics.Solution ? Use illumination ofshorter wavelength
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eso u on o m croscopeseso u on o m croscopes
Resolution of electron microscope:
- can decrease to 10-3 nm- n.sin is very small, because n 1 and 0.1 radians
- ,of 0.0389 and a theoretical resolution of 0.0195 !
- But in practice most TEMs will only have an actual
resolution 2.4 at 100 kV
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refraction/bendingrefraction/bending
on a ray of illumination entering amedium of differing density causing
.
In the vacuum environment of an electron microsco e the indexof refraction is 1.0 and thereforeNA depends solely on the half
angle of illumination.
In electron microscopy therefractive index cannot exceed
Refractive index:
n = tani/tanr
. , e a ang e s very sma ,and thus the only thing that can beadjusted is decreasing the
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en ng y ensesen ng y enses
Converging (convex/positive) lens: bendsrays toward the axis. It has a positive focallength. Forms a real inverted image of anobject placed to the left of the first focal pointand an erect virtual image of an object placedbetween the first focal point and the lens.
Diverging (concave/negative) lens: bendsthe light rays away from the axis. It has anegative focal length. An object placed
in an erect virtual image. It is not possible toconstruct a negative magnetic lens althoughnegative electrostatic lenses can be made.
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Glass lenses (curved glassor mirror) forvisible light
concaveconcave convexconvex
Electromagnetic lenses(solenoid/coil) for
(electron, protons,positrons)
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Equipments for structural analysisEquipments for structural analysis
m croscop c eve sm croscop c eve s
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ScanningScanning ElectronElectron MicroscopesMicroscopes - SEMVersions: Environmental (ESEM) / Low Voltage (LVSEM) /
ar e ressure eva e ressure ,Field Emission (FESEM)
-Versions: High Resolution (HRTEM), Scanning- (STEM),Field Emission (FETEM), Energy Filtering (EFTEM)
AnalyticalAnalytical ElectronElectron MicroscopeMicroscope - AEMVersions: SEM-EDS/WDS, STEM-EDS-EELS
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Overview of EMsOverview of EMs
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nnin El r nnnin El r nMicroscopeMicroscope -- SEMSEM
SEM is an instrument using electron light to image andcontrol the material sample in very fine scale.
What is imaged and controlled: Surface topography (SE: microstructure roughness) ,
and size) Composition contrast (BSE)
Elemental composition (EDS/WDS: qualitative andquantitative analysis)
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The SEM is a distinctly
image formation than is anoptical microscope and a TEM.
In the SEM, the probeexamines the object one spot at
a time, then gives out an arrayn - o e resu s rommany spots.
The optical microscope, (also
TEM) conversely, takes thesignals from simultaneously-examined spots, and gives
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em ac a a once.
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Construction of SEMConstruction of SEM
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Construction of SEMConstruction of SEM
JEOL SEM 6335F
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unc ons o ma n par sunc ons o ma n par s
Electron gun (filament/cathode, Wehnelt
cylinder, anode): generating/ emittingelectron beam
Lens system (condense and objectivelenses): focusing/linking electron beam
Scanning coil: scanning electron beamover specimen surface
Detectors: collecting electrons and/x-rays
Mearurement system (Cathode RayTube-CRT, electronic devices): dataamplifying, acquisition and processing
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ormat on o acce erate e ectron eam towar
specimen by a positive voltage (kV)
narrow beam with electromagnetic lenses andmetallic diaphragms/apertures
Focusing and scanning electron beam intospecimen surface through electromagneticlenses and scannin coil
Beam-specimen interaction Data acquisition and imaging
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In environmental SEMIn environmental SEM
Ionizing of rest gas to eliminate electric charge on- ,
- A low vacuum is used
- -avaiable
- Hydrated specimens are allowed
- Chemical composition is analyzed for onlyspecimen (without coating)
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Surface topography,
econ ary ec ron mag ng(SEI)
(BSI)
Compositional contrast
,
Scannin ElectronScannin Electron
Transmitted Electron Imaging(TEI)
Electron BackscatteredDiffraction (EBSD)
MicroscopeMicroscope(SEM)(SEM)
Internal ultrastructure Energy-Dispersive X-raySpectrometry (EDS)
Crystallographic info
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Elemental composition, mapping and linescans
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rosros strengt s :strengt s :
- Higher resolution and depth of field than that of OM (the surface of
- Allows for direct observation of surface morphology- In-situ environmental studies are possible (e.g. catalysts in an
atmosphere)- Microanalysis (composition of small areas)- Typically a low power technique, so organic material can be studied- Very good at looking at an average of sizes and arrangements in a
- Easy operation and maintenance- Negligible damage of specimen (through coating, heating during
radiation
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Pros and cons of SEMPros and cons of SEM
ConsCons (weaknesses/limitations)(weaknesses/limitations)::- Specimens must be suitable in vacuum- False/artificial outputs through sample preparation- Coating non-conductive samples is required
- The crystallinity cannot be determined
- Resolution is often not sufficient to tell all of the surface features
- Scanning process is slow and so sample may move leading to
distorted images
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Electrons path in TEM:
condenser lens(es) and
aperture sample objective lens(es) andaperture projectorlens es screen
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TEM is designed to project a
onto screen (we see only the
shadowof the specimen). Its thanks to contrast(intensity difference) of
ransm e unsca ere anforward diffracted / scattered
beam.
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--
--
Each particle image represents a 2Dprojection of the 3D object
A single projection image isplainly insufficient to infer thestructure of an ob ect.
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--
--
Watch out!
A cover slide!
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High ResolutionHigh Resolution
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High ResolutionHigh Resolution
TEMTEM -- HRTEMHRTEMContrast intensit difference on ima e lane:
Mass-thickness contrast (BF imaging)
Diffraction contrast (BF, DF imaging)
Phase contrast / HREM and Moirefringes (HR imaging)
HREM image
Interference pattern
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comparison of parameterscomparison of parameters
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TEM ca abilitiesTEM ca abilities
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TEM ca abilitiesTEM ca abilities
Electron DiffractionBright- and Dark-Field Imagingmag ng
Crystallographic info Internal ultrastructure Nanostructure dispersion Defect identification
High-ResolutionTransmission ElectronMicroscopy (HR-TEM)
Electron Energy LossSpectroscopy (EELS)
MicroscopeMicroscope
(TEM)(TEM)
Interface structure Defect structure Energy-DispersiveX-ray Spectrometry
(EDS)
Chemical composition Other bonding info
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Elemental composition, mapping and linescans
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SEMSEM High resolution for thick bulk TEMTEM High resolution (1,2-1,5 )samples: 20-50 (mostcommercial SEM) and < 10 Ao
for very thin samples (mostcommercial TEM)
- 3D-imaging due to large
depth of field Information about crystal
structure (crystal lattice ma magn ca on ava a e
as for light microscope
an or en a on,
dislocation, twinning,)
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