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Mauro Sardela Editor Practical Materials Characterization Practical Materials Characterization Mauro Sardela Editor Practical Materials Characterization Editor MauroSardela UniversityofIllinois-UrbanaChampaign Urbana,IL,USA ISBN978-1-4614-9280-1 ISBN978-1-4614-9281-8(eBook) DOI10.1007/978-1-4614-9281-8 SpringerNewYorkHeidelbergDordrechtLondon LibraryofCongressControlNumber:2014941610 ©SpringerScience+BusinessMediaNewYork2014 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped.Exemptedfromthislegalreservationarebriefexcerpts inconnectionwithreviewsorscholarlyanalysisormaterialsuppliedspecificallyforthepurposeofbeing enteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthework.Duplication ofthispublicationorpartsthereofispermittedonlyundertheprovisionsoftheCopyrightLawofthe Publisher’s location, in its current version, and permission for use must always be obtained from Springer.PermissionsforusemaybeobtainedthroughRightsLinkattheCopyrightClearanceCenter. ViolationsareliabletoprosecutionundertherespectiveCopyrightLaw. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexempt fromtherelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface Materials characterization is an ever-growing field in science since it plays a key role in the screening of electronic, mechanical, optical, and thermo properties of materialsbeingincorporatedinvariousindustrialproductsthataffectourdailylife. Inaddition,analyticalmethodsarebeingdevelopedormodifiedinresponsetonew demands for improved spatial resolution, detection limits of contents and impuri- ties,atomicimagingcontrast,deviceminiaturization,etc. Rather than attempting to survey the hundreds of analytical methods currently being employed in various research fields, in this book we focus on five major analyticalmethodsandtheirderivations.Themethodspresentedhereoffernotonly general applicability to most types of materials (ranging from hard coatings for toolstonovelbiologicalmaterialsandnanoscaleddevices)butalsooffersufficient complexity that data analysis and interpretation can be far from trivial in many cases.Inthisaspect,werecruitedcontributorstothisbookwhohavedemonstrated extensivehands-on experience with each of the techniques coveredin the various chapters. All the authors in this book have 20+ years of experience in their respective field as materials analysts, with extensive exposure to industrial, academic,andadvancedresearchenvironment. The analytical methods presented here are based on interactions of ions, electrons,orphotons(includingvisiblelightandX-rays)withthematter.Thosespecies interact with the analyzed material and produce secondary ions, electrons, or photons through scattering processes. A multitude of material properties can be evaluated by studying those scattering processes under the proper environment (in some cases including vacuum systems) and the use of advanced instrument designanddetectiontechnologies. X-ray analysis methods (including diffraction and reflectometry) described in Chap.1arethemostwidelyusedtoolsfortheidentificationofcrystallineproperties of materials, in addition to materials strain, texture, stress, density, and surface roughness—properties that are key parameters for various industrial applications. Chapter2coversawiderangeofopticalcharacterizationtechniqueswithfocuson ellipsometry,Ramanscattering,Fouriertransforminfraredspectroscopy,andspec- trophotometry. Those methods, covering a wide range of photon energy and laser v vi Preface technology, are broadly applied in academic and industrial laboratories to study many different material properties. They involve distinct physical phenomena driving the interaction between the photons and the material and here they are systematicallycomparedwithrelevancetotheirstrengthsandlimitations.Chapters 3 and 4 are devoted to mainstream surface analysis techniques. Chapter 3 covers X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), whichprobechemicalstatesandchemicalpropertiesofmaterials.Alargenumber of examples are presented where the same set of samples was analyzed by both techniques andcomparativeresultsarediscussed.Chapter4covers secondaryion mass spectrometry (SIMS) and its variations. This is a technique with extreme sensitivityandverylowdetectionlimitsinmanymaterials(inmanycases,partsper billion). Combined with depth profiling, SIMS is a powerfulmethod in the inves- tigation of composition and impurity contents as a function of depth in complex multilayeredmaterialsused,forexample,intheoptoelectronicindustry.Finally,in Chap.5recentadvancesintransmissionelectronmicroscopyarepresentedbyone of the world-class experts in the field. Various methods and strategies for sample preparation,smartproceduresininstrumentationsetup(suchastheproperchoiceof lenses and apertures) are discussed with several examples involving novel materials. The foundations of the most spectacular developments in the area, such as sub-Angstrom spatial resolution and aberration correction microscopy are discussedwithemphasisonbasicprinciples. Our foremost goal in this book was to produce a direct, modern review of selected, major analytical techniques of wide, general applicability in a textbook withemphasisonpracticalapplications.Abriefoverviewofthephysicalprinciples behind each technique is given but the emphasis is on modern, recent metrology advances. The complementarity of the various techniques became obvious as we reviewedtheresolutionandsensitivitylimitsofeachtechnique.Whileaparticular techniqueisusefulinordertoprovideveryhigh-resolutioninformationoncrystal- linelatticedistortionsoverlargesamplevolumes(X-raydiffraction),othermethods excel in probing small volumes at extremely high spatial resolution (transmission electron microscopy). Even when comparing two related surface analysis techniques,differencesandcomplementarityareevident:forinstance,XPScanprovide moreaccurateinformationonthechemicalstateofnear-surfacespeciesthanSIMS, but if the research problem requires ultrahigh detection limits to species, SIMS is nearly unbeatable. In some cases, the same information can be probed by two competingtechniquesbutthechoiceofthebettermethodmaydependonthedetails ofthematerial.Thicknessmeasurementsofultrathinlayersofelectronicmaterials canbedone,forinstance,byX-rayreflectivityorellipsometry.However,whilethe first method (X-ray reflectivity) is limited to layers with relativelysmall interface roughness,ellipsometrymightalsorequireextensivemodelingandseveralassump- tions on the optical properties of the materialbeing investigated. It is thus crucial for the materials scientist to being able to understand the strength and potential artifactsofeachmetrologybeingemployed. Urbana,IL,USA MauroSardela Contents 1 X-RayDiffractionandReflectivity. . . . . . . . . . . . . . . . . . . . . . . . . . 1 MauroR.SardelaJr. 2 IntroductiontoOpticalCharacterizationofMaterials. . . . . . . . . . . 43 JulioA.N.T.Soares 3 X-RayPhotoelectronSpectroscopy(XPS)andAuger ElectronSpectroscopy(AES). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 RichardT.Haasch 4 SecondaryIonMassSpectrometry. . . . . . . . . . . . . . . . . . . . . . . . . . 133 JudithE.Baker 5 TransmissionElectronMicroscopy. . . . . . . . . . . . . . . . . . . . . . . . . . 189 JianGuoWen Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 vii Chapter 1 X-Ray Diffraction and Reflectivity MauroR.SardelaJr. 1.1 Introduction X-rays are photons with energy ~125 eV–125 keV (wavelength λ~0.01–10 nm). The X-ray analysis techniques—X-ray diffraction (XRD) and reflectometry (XRR)—discussed in this chapter involve processes of X-rays in and out of the sample. When X-rays impinge on a material several interaction processes are possible. X-rays can be elastically or inelastically scattered by electrons in a material(X-rayscatteringbythenucleusisvirtuallynegligible).Elasticscattering, responsible for the diffraction process (and also known as Thompson scattering) correspondstothecasewheretheenergyoftheincomingandoutgoingphotonsare equal. Inelastic or Compton scattering refers to the case where the energy of the emitted photon is lower than the energy of the incoming photon. The energy differenceistransferredtothescatteringelectron(whichcanrecoilandbeejected fromtheatom).Elasticandinelasticscatteringareusedinanalysisofmaterials. One additional process of interest is fluorescence where the incoming X-ray photon is used to eject an electron(called“photoelectron”) fromthe inner atomic shells;thisprocesscreatesaholewhichisfilledbyanelectronfromtheoutershells. The energy excess is then emitted as characteristic photon. X-ray fluorescence analysis uses this photon energy to identify the various elements present in a material with detection limits down to parts per million in some cases. A related process resulting from the photon/electron interaction is the Auger electron emis- sion(discussedindetailselsewhereinthisbook). In this chapter we will focus on X-ray diffraction processes for the analysis of materials.XRDissensitivetocrystallinephasesdownto0.1–1wt%.Conventional XRD instruments use monochromatic (that is, with a well defined wavelength) X-rayradiationfromCu,Cr,MoorAgsources.Cu,inparticularwiththeK-αline M.R.SardelaJr.(*) UniversityofIllinois,Champaign,Urbana,IL,USA e-mail:[email protected] M.Sardela(ed.),PracticalMaterialsCharacterization, 1 DOI10.1007/978-1-4614-9281-8_1,©SpringerScience+BusinessMediaNewYork2014 2 M.R.SardelaJr. (which is the specific electronic transition in Cu used to generate a wavelength 0.15418nm,energy8.05keV),isthemostcommonlyusedradiationinlaboratory sources.CrisnormallyusedforapplicationsinvolvingFeandsteelmaterials,and MoandAgareusedforapplicationswheredeeperX-raypenetrationisrequired. TypicalprobedvolumeinasampleduringXRDanalysisdependsontheX-ray penetration depth, which is a function of the X-ray energy, sample material and angle ofincidenceofthe primaryX-ray beam relative tothe surface.When using Curadiation,thepenetrationdepthinmostofthematerialswillbeseveraltensof microns (but it may be less for heavy materials such as Pb). The probed volume ofthetechniquealsodependsonthelateralspatialresolution,whichdependsonthe incident X-ray beam shape and collimation, and on the angle of incidence. For conventionalX-raydiffractometers,lateralresolutioncanbefrom1to2mm(high angle of incidence relative to the sample surface) to a few cm’s (low angle of incidence). Microdiffraction primary optics can focus the X-ray beam from typi- cally 10 to 500 μm [1]. The above discussion refers to conventional lab source instruments,whicharemorecommonandarethesubjectofthischapter.Synchro- tronradiationsourcescanprovideamuchwidervarietyofwavelengths,penetration depthandbeamcoherence. 1.2 Basics of Diffraction Bragg’s law is one of the cornerstones in XRD analysis, and it is related to concepts such interspacing between atomic planes (“d-spacing”) and reciprocal lattice. Bragg’s law, which can be mathematically demonstrated using both concepts of waves interference in real space and wavevectors in reciprocal space, statesthattheinterplanarspacingdcanbedeterminedbymeasuringtheangle2θ betweentheincidentanddiffracteddirectionsoftheradiationwithwavelengthλin amaterial[2,3]: 2dsinθ¼λ ð1:1Þ The simplicity of this relationship probably played a major role in the devel- opment of analytical techniques based on diffraction. It basically allows the determination of a microscopy entity (atomic inter planar spacing) by merely measuringtheanglefromtheoutgoingdiffractedbeamrelativetoafixedincident direction.Fromthemeasuredangular2θpositionofthevariousdiffractionpeaks observed in a material, the corresponding d spacing can be determined. The specific set of values of d’s can be used as unique fingerprints to identify not onlythechemistryofthematerial(suchastheelements andcompoundspresent) butalsotheparticularpolymorphicphase.Forinstancethetechniquecanidentify in a titanium-oxide material not only the presence of Ti and O, but also the stoichiometric form (for example, TiO2) and the particular phase (rutile, anatase or brookite forms of TiO2).