6. sem - electron microscopy and diffraction

8/9/2019 6. SEM - Electron Microscopy and Diffraction

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ContentContentClassificationOperating principlesComponentsCharacteristicsImaging processApplications


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MultiformMultiform


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For research: JEOL SEM 6335FFor research: JEOL SEM 6335F


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MIRA SE for large andMIRA SE for large andnon-conductive samplesnon-conductive samples

Large chamberLarge chamberSEMSEM


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Portable Mini SEMPortable Mini SEM


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AutoEverythingAutoEverything


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Mini-SEM vs OMMini-SEM vs OM


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Mini-SEM vs SEMMini-SEM vs SEM


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Mini-SEM vs TM-1000Mini-SEM vs TM-1000


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Operating principles


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Schematic principals of SEMSchematic principals of SEM


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Construction schemaConstruction schema


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ComponentsComponents


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Principal componentsPrincipal components


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Measurement systemMeasurement system


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A number of different detectors can be incorporated

into the chamber surrounding the specimen

DetectorsDetectors


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The shadow produced in an

SEM is determined by theposition of the detector, but theview is a beams eye view asif one were looking down the

column

Side-mountedSide-mounteddetectordetector


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In-lens detectorIn-lens detector

of LEO Geminiof LEO GeminiColumnColumn

A detector placed within the column is known as an in-lensdetector and produces a very different image compared to a

conventionally located detector


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SE detectorSE detector

Side-mounted: blurredsurface

In-lens: sharf surface


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SE detectorSE detector

In-lens: sharf surfaceSide-mounted: blurredsurface


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Scanning systemScanning system

The basic premiseof an SEM is thatsignal produced

from a scannedarea of thespecimen is

displayed as an

image with theexact same scanpattern on a CRT


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Scan coilsScan coils

The scan pattern onthe specimen is

created by a set ofdeflection coils in thecolumn that move thebeam in a coordinated

X/Y pattern. This is

referred to as a scanor raster pattern.


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Scan generatorScan generator

The scan generatorcoordinates themovement of the

primary beam with the

movement of the e-gunin the back of the CRT


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Cathode Ray Tube-CRTCathode Ray Tube-CRT

Cathode Ray Tube accelerates electrons towards the phosphor coated screenwhere they produce flashes of light upon hitting the phosphor. Deflection coils

create a scan pattern forming an image in a point by point manner


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Color Cathode Ray TubeColor Cathode Ray Tube

Color CRTs usually have three separate e-guns, oneeach for red, green and blue (RGB)


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Color Cathode Ray TubeColor Cathode Ray Tube


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SEM characteristicsSEM characteristics


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MagnificationMagnification

Magnification is accomplished by scanning a progressively smallerportion of the specimen and displaying the image on the CRT. Thustotal magnification is square area of CRT divided by area scanned.


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In contrast focus is

accomplished by bringingthe beam to its crossoverpoint on the surface of thespecimen. In this wayfocus and magnificationare completely separatefrom one another in theSEM.

FocusingFocusing

andandsharfnesssharfness


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In the TEM the specimen lies very close to the objective lensresulting in a relatively large half angle of illumination. In SEM sincethe image is not formed by an objective lens the half angle can be

very small resulting in a large depth of field.

The depth of fieldThe depth of field


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10X10X

110X110X

200X200X

400X400X

4K4K

16K16K

45K45K

MagnificationMagnificationandand

sharfnesssharfness

An SEM focused at highmagnification will still be infocus at low magnification


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Strong lens:Small probe size, highresolution, short working

distance and shallowdepthof field

Weak lens:Larger probe size, lowresolution, long working

distance, and largerdepthof field

Resolution andResolution anddepth of fielddepth of field


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A smaller final lens

aperture can reduce thehalf angle and therefore

increase the depth offield. This is true on arelatively strong lens

which has a fairly shortworking distance and

therefore high resolution.

Aperture andAperture and

depth of fielddepth of field


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Imaging processImaging process


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The SEM forms animage by

generating anumber of signalsas a result of thebeam interacting

with the specimen.

Imaging signalsImaging signals


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Signal can be increased by:- Creating more beam specimen interactions

Noise can be reduced by:- Cooling electronics

- Keeping detectors settings to a minimum

Signal/noise ratio can be increased by:

- Placing detector closer to source of signal- Slowing down the scan

(collect more signal per unit time)

Image qualityImage quality


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The SEM is a probe forming (e- beam) and signal detecting device.By developing an image created in a point by point fashion an

important factor is the signal to noise (S/N) ratio. The signal being theresult of the beam interacting with the specimen and the noise being

the result of imperfections in the electronics of the detector anddisplay systems as well as spurious signal.

TheThenoisesnoises


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Although the same amount of signal is produced throughout thespecimen the topography of the surface will allow differing amounts

of signal to reach a detector placed off to the side.

Effect of sample roughnessEffect of sample roughness


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Application of SEMApplication of SEM


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Observation ofObservation ofmicrostructuremicrostructure

and topographyand topography

by SE1, SE3,by SE1, SE3,SE4, BSE (left)SE4, BSE (left)

and only SE1and only SE1

(in-lens, right)(in-lens, right)

R t lli d t i i C S


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Recrystallized twins in Cu-SnRecrystallized twins in Cu-Sn(BSE image)(BSE image)


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Test of welding cracksTest of welding cracks

SEI: topography contrast BSEI: Z contrast


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Distribution of Cu in weldedDistribution of Cu in weldedsteels (BSEI, Z contrast)steels (BSEI, Z contrast)


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ElementElementanalyzeanalyze

andandimagingimaging

EDS


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Scan lines in welding zoneScan lines in welding zone

Cu atom diffused into stell grain boundaries due to highwelding temperature and holding time.

El t i i (0 100%) fEl t i i (0 100%) f


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Element imaging (0-100%) ofElement imaging (0-100%) ofwelding zonewelding zone

El t i i (0 20%) f ldiEl t i i (0 20%) f ldi


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Element imaging (0-20%) of weldingElement imaging (0-20%) of weldingzonezone

O fOb ti f ltil


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Observation of multilayerObservation of multilayerbinding (SEI, TiN-AlN on steel)binding (SEI, TiN-AlN on steel)

50 layers ofTiN-AlN on

steel surface


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Analyze of fracture surfaceAnalyze of fracture surface

, - ,lumina in lens detector00 kX


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Brittle intergranular fracture


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Ductiledimple

fracture


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Fatigue crack


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Intragranular

ductile failure


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Techniques of surface characterizationTechniques of surface characterization

T h i f f h t i tiT h i f f h t i ti


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Techniques of surface characterizationTechniques of surface characterization


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Resolution and information depthResolution and information depth

6. sem - electron microscopy and diffraction

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