Practical Materials Characterization

242 Pages·2014·8.309 MB·English

by  Mauro Sardela (eds.)

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
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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, aca-
demic,andadvancedresearchenvironment.
The analytical methods presented here are based on interactions of ions, elec-
trons,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 mate-
rials. 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 tech-
niques,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 con-
cepts 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).