A Beginners' Guide to Scanning Electron Microscopy

421 Pages·2018·14.421 MB·English

by  Anwar Ul-Hamid

Anwar Ul-Hamid
A Beginners’ Guide
to Scanning Electron
Microscopy
’
A Beginners Guide to Scanning Electron
Microscopy

Anwar Ul-Hamid
’
A Beginners Guide to
Scanning Electron
Microscopy
AnwarUl-Hamid
CenterforEngineeringResearch
KingFahdUniversityofPetroleum&Minerals
Dhahran,SaudiArabia
ISBN978-3-319-98481-0 ISBN978-3-319-98482-7 (eBook)
https://doi.org/10.1007/978-3-319-98482-7
LibraryofCongressControlNumber:2018953310
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To my wife
Preface
Theabilityofthescanningelectronmicroscope(SEM)tocharacterizematerialshas
increased tremendously since its inception on a commercial basis at Cambridge,
UnitedKingdom,in1965.Thetremendousprospectsofferedbythisinventionhave
been consistently built upon, thanks to steady advances in instrumentation and
computer technology in the past few decades. Presently, surface morphology of
materials ranging from biological, polymers, alloys to minerals, ceramics, and
corrosion deposits is routinely studied from micrometer to nanometer scale. The
SEM has emerged as a vital, powerful, and versatile tool in the advancement of
modern day nanotechnology by contributing to the area of characterization of
nanostructured materials. Its ease of use, typically prompt sample preparation and
straightforwardimageinterpretationcombinedwithhighresolutionandhighdepth
of field as well as the ability to undertake microchemical and crystallographic
analysis, has made it one ofthe most popular techniques used for characterization.
Presently, the SEM is being used by professionals with a diverse technical back-
ground,suchaslifescience,materialsscience,engineering,forensics,andmineral-
ogy,invarioussectorsofthegovernment,industry,andacademia.
A significant number of in-depth and specialized accounts of the scanning
electron microscopy are available to interested readers. This book is meant to
serve as a concise and brief guide tothe practice of scanning electron microscopy.
In this treatment, the material has been developed with the goal of providing an
easilyunderstoodtextforthoseSEMuserswhohavelittleornobackgroundinthis
area. It provides a solid introduction to the subject for the uninitiated. The instru-
mentation and working and image interpretation have been explained in a succinct
practical guide to the SEM. The aim is to provide all useful information regarding
SEM operation, applications, and sample preparation to the readers without them
having to go through extensive reference material. Essential theory of specimen-
beaminteractionandimageformationistreatedinamannerthatcanbeeffortlessly
comprehended by the readers. The SEM technique is described in simple terms to
helpoperatorsandusersoftheSEMtogetthebestimagingresultspossiblefortheir
materialsofinterest.ThecapabilitiesandlimitationsoftheSEMarealsodescribed
to enable students, engineers, and materials scientists to identify and apply this
techniquefortheirwork.
vii
viii Preface
NecessarybackgroundtotheSEMisdevelopedinChap.1.Primaryandsecond-
ary components of the instrument are introduced in Chap. 2. Basic concepts of
electronbeam-specimeninteractionandcontrastformationaredescribedinChap.3.
Chapter 4 elaborates on the mechanisms of image formation in the SEM. The
working of the SEM is introduced, and the factors affecting the quality of images
are discussed. Specialized SEM techniques are described briefly in Chap. 5.
Chapters6and7elaboratethecharacteristicsofx-raysandprinciplesofEDS/WDS
microchemical analysis, respectively. Chapter 8 includes sample preparation
techniques used for various classes of materials. Images, illustrations, and
photographs are used to explain concepts, provide information, and aid in data
interpretation.Theeffect ofvariousimagingconditionsonthequality ofimagesis
describedtohelpusersgetthebestresultsfortheirmaterialsofinterest.Thebookis
structuredinawaythatcanhelpanovicefindnecessaryinformationquickly.
The support of the King Fahd University of Petroleum & Minerals (KFUPM),
Dhahran, through project number BW161001 is gratefully acknowledged. I am
utterly indebted to Mr. Abuduliken Bake for drawing with great skill almost all of
theillustrationsappearinginthisbook.Inaddition,hehastakenanumberofSEM
imagesandphotographs.Hishelphasbeeninstrumentalinthetimelycompletionof
themanuscript.Iamalsogratefultopersonnelworkinginvariousorganizationswho
permittedtheuseofrelevantmaterial.IespeciallythankMr.TanTeckSiongfrom
JEOL Asia Pte Ltd. for providing me with a number of wonderful images. I also
extendmyappreciationtomycolleagues attheMaterialsCharacterizationLabora-
tory,CenterforEngineeringResearch,KFUPM,fortheircontinuedsupport.
Intheend,Iamgratefultohavebeenblessedwithfamilyandfriendswhomake
lifetrulyworthwhile.
King Fahd University of Petroleum & AnwarUl-Hamid
Minerals,Dhahran,SaudiArabia
Contents
1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 WhatIstheSEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 ImageResolutionintheSEM. . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 ImageFormationintheSEM. . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 InformationObtainedUsingtheSEM. . . . . . . . . . . . . . . . . . . . 4
1.5 StrengthsandLimitationsoftheSEM. . . . . . . . . . . . . . . . . . . . 8
1.6 BriefHistoryoftheSEMDevelopment. . . . . . . . . . . . . . . . . . . 11
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 ComponentsoftheSEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 ElectronColumn. . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . .. . 15
2.1.1 ElectronGun. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 ThermionicEmissionElectronGuns. . . . . . . . . . . . . . . . . . . . . 20
2.2.1 TungstenFilamentGun. . . . . . . . . . . . . . . . . . . . . . . . 22
2.2.2 LanthanumHexaboride(LaB )Emitter. . . . . . . . . . . . . 28
6
2.3 FieldEmissionElectronGuns. . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.1 WorkingPrinciple. . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3.2 Advantages/Drawbacks. . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.3 ColdFieldEmitter(ColdFEG). . . . . . . . . . . . . . . . . . . 32
2.3.4 SchottkyFieldEmitter. . . . . . . . . . . . . . . . . . . . . . . . . 34
2.3.5 RecentAdvances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.4 ElectromagneticLenses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.4.1 CondenserLens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.4.2 Apertures. . . . .. . . .. . . .. . . .. . . .. . . .. . . . .. . . .. 41
2.4.3 ObjectiveLens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.4.4 LensAberrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.4.5 ScanCoils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.4.6 Magnification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.5 SpecimenChamber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.5.1 SpecimenStage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.5.2 InfraredCamera. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.6 Detectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2.6.1 Everhart-ThornleyDetector. . . . . . .. . . . . . .. . . . . . .. 59
ix
x Contents
2.6.2 Through-the-Lens(TTL)Detector. . . . . . . . . . . . . . . . . 64
2.6.3 BackscatteredElectronDetector. . . . . . . . . . . . . . . . . . 66
2.7 MiscellaneousComponents. . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.7.1 ComputerControlSystem. . . .. . . . . . . . .. . . . . . . . .. 71
2.7.2 VacuumSystem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
2.7.3 High-VoltagePowerSupply(HTTank). . . . . . . . . . . . . 74
2.7.4 WaterChiller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
2.7.5 Heater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
2.7.6 Anti-vibrationPlatform. .. . . . .. . . . . .. . . . .. . . . . .. 75
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3 ContrastFormationintheSEM. . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.1 ImageFormation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.1.1 DigitalImaging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.1.2 RelationshipBetweenPictureElementandPixel. . . . . . 80
3.1.3 Signal-to-NoiseRatio(SNR). . . . . . . . . . . . . . . . . . . . . 82
3.1.4 ContrastFormation. . . . . . . . . . . . . . . . . . . . . . . . . . . 85
3.2 Beam-SpecimenInteraction. . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.2.1 AtomModel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.2.2 ElasticScattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.2.3 InelasticScattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.2.4 EffectofElectronScattering. . . . . . . . . . . . . . . . . . . . . 89
3.2.5 InteractionVolume. . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.2.6 ElectronRange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.3 OriginofBackscatteredandSecondaryElectrons. . . . . . . . . . . . 95
3.3.1 OriginofBackscatteredElectrons(BSE). . . . . . . . . . . . 95
3.3.2 OriginofSecondaryElectrons(SE). . . . . . . . . . . . . . . . 95
3.4 TypesofContrast. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3.4.1 CompositionalorAtomicNumber(Z)Contrast
(BackscatteredElectronImaging). . . . . . . . . . . . . . . . . 97
3.4.2 TopographicContrast(SecondaryElectronImaging). . . 113
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4 ImagingwiththeSEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4.1 Resolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4.1.1 CriteriaofSpatialResolutionLimit. . . . . . . . . . . . . . . . 131
4.1.2 ImagingParametersThatControltheSpatialResolution. 134
4.1.3 GuidelinesforHigh-ResolutionImaging. . . . . . . . . . . . 138
4.1.4 FactorsthatLimitSpatialResolution. . . . . . . . . . . . . . . 140
4.2 DepthofField. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
4.3 InfluenceofOperationalParametersonSEMImages. . . . . . . .. . 146
4.3.1 EffectofAcceleratingVoltage(BeamEnergy). . . . . . . . 146
4.3.2 EffectofProbeCurrent/SpotSize. . . . . . . . . . . . . . . . . 147
4.3.3 EffectofWorkingDistance. . . . . . . . . . . . . . . . . . . . . 151
4.3.4 EffectofObjectiveAperture. . . . . . . . . . . . . . . . . . . . . 154