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PHOTOELECTRON SPECTROSCOPY (XPS)
PRINCIPLES AND APPLICATIONS
Prof. Nizam M. El-Ashgar
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Photoelectron Spectroscopy XPS
• What is XPS?
• Aim of XPS Analysis.
• General Theory
• How can we identify elements and compounds?
• Instrumentation for XPS
• Examples of materials analysis with XPS
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What is XPS?• X-ray Photoelectron Spectroscopy (XPS), also
known as Electron Spectroscopy for ChemicalAnalysis (ESCA) is a widely used technique toinvestigate the chemical composition ofsurfaces.
• Sample is illuminated with soft (1.5kV) X-rayradiation in an ultrahigh vacuum.
• The photoelectric effect leads to the productionof photoelectrons, the energy spectrum of whichcan be determined in a beta-ray spectrometer.
XX--rayray PhotoelectronPhotoelectron spectroscopy,spectroscopy, basedbased ononthethe photoelectricphotoelectric effect,effect,11,,22 waswas developeddeveloped ininthethe midmid--19601960’s’s byby KaiKai SiegbahnSiegbahn andand hishisresearchresearch groupgroup atat thethe UniversityUniversity ofof Uppsala,Uppsala,SwedenSweden..33
1. H. Hertz, Ann. Physik 31,983 (1887).
2. A. Einstein, Ann. Physik 17,132 (1905). 1921 Nobel Prize in Physics.
3. K. Siegbahn, Et. Al.,Nova Acta Regiae Soc.Sci., Ser. IV, Vol. 20 (1967). 1981 Nobel Prize in Physics.
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The Atom and the X-Ray
Core electrons
Valence electrons
X-RayFree electron
proton
neutron
electron
electron vacancy
The core electrons respond very well to the X-Ray energy
X-Rays on the Surface
Atoms layers
e- top layer
e- lower layer
with collisions
e- lower layer
but no collisionsX-Rays
Outer surface
Inner surface
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X-Rays on the Surface
• The X-Rays will penetrate to the core e- of theatoms in the sample.
• Some e-s are going to be released without anyproblem giving the Kinetic Energies (KE)characteristic of their elements.
• Other e-s will come from inner layers and collidewith other e-s of upper layers– These e- will be lower in lower energy.– They will contribute to the noise signal of the
spectrum.
X-Rays and the ElectronsX-RayElectron without collision
Electron with collision
The noise signalcomes from theelectrons that collidewith other electronsof different layers.The collisions causea decrease in energyof the electron and itno longer willcontribute to thecharacteristic energyof the element.
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Aim of XPS Analysis• Identification of elements at surfaces (depth:
10 nm).• Identification of functional groups and redox
states.• Concentration and depth profiling.• Estimation of over layer thickness.• Comparison of bulk and surface composition.• Surface homogeneity/heterogeneity• Possible surface morphology of adlayers.
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Physical Bases• Based upon photon in/electron out process.• Photon E (Einstein ): E= hνwhere: h - Planck constant ( 6.62 x 10 -34 J s ).
ν - frequency (Hz) of the radiation.• In XPS the photon is absorbed by an atom in a
molecule or solid, leading to ionization and theemission of a core (inner shell) electron.
• If the photon interacts with valence levels(ionization by lost of one of them) the technique isdifferent and called UPS, Ultraviolet photoelectronspectroscopy .
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Photoelectrıc effect
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Introduction to the Solid State
In solids, atomic and molecular energylevels broaden into bands that in principlecontain as many states as there areatoms/molecules in the solid.
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Process of Photoionization
A + h ν A+ + e-
E(A) + h ν = E(A+ ) + E(e-)KE = h ν – [ E(A+ ) - E(A) ]• The difference in energy between the
ionized and neutral atoms, is generallycalled the binding energy (BE) of theelectron:
KE = h ν - BE
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nn XPSXPS spectralspectral lineslines areareidentifiedidentified byby thethe shellshellfromfrom whichwhich thethe electronelectronwaswas ejectedejected ((11s,s, 22s,s, 22p,p,etcetc..))..
nn TheThe ejectedejectedphotoelectronphotoelectron hashas kinetickineticenergyenergy::KEKE == hvhv –– BEBE -- φφ
nn FollowingFollowing thisthis process,process,thethe atomatom willwill releasereleaseenergyenergy byby thethe emissionemissionofof anan AugerAuger ElectronElectron..
Conduction BandConduction Band
Valence BandValence Band
LL22,L,L33LL11
KK
FermiFermi
LevelLevel
Free Free
Electron LevelElectron Level
Incident XIncident X--rayrayEjected PhotoelectronEjected Photoelectron
11ss
22ss22pp
The Photoelectric Process
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The BE is a direct measure of the energy required to justremove the electron concerned from its initial level to thevacuum level and the KE of the photoelectron is againgiven by :
KE = h ν - BENOTE - the binding energies (BE) of energy levels in
solids are conventionally measured with respect to theFermi-level of the solid, rather than the vacuum level.
This involves a small correction to the equation givenabove in order to account for the work function (φ) ofthe solid, but for the purposes of the discussion belowthis correction will be neglected.
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Binding Energy (BE)vThe Binding Energy (BE) is characteristic of the core electrons for
each element.
vThe BE is determined by the attraction of the electrons to the nucleus.
vIf an electron with energy x is pulled away from the nucleus, theattraction between the electron and the nucleus decreases and theBE decreases.
vEventually, there will be a point when the electron will be free of thenucleus.
These electrons areattracted to the protonwith certain bindingenergy x
This is the point with 0 energyof attraction between theelectron and the nucleus. Atthis point the electron is freefrom the atom.0
x
p+
B.E.
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Why the Core Electrons?• An electron near the Fermi level is far from the nucleus,
moving in different directions all over the place, and will notcarry information about any single atom.– Fermi level is the highest energy level occupied by an
electron in a neutral solid at absolute 0 temperature.– Electron binding energy (BE) is calculated with respect to
the Fermi level.
• The core e-s are local close to the nucleus and have bindingenergies characteristic of their particular element.
• The core e-s have a higher probability of matching theenergies of AlKα and MgKα X rays.
Core e-
Valence e-
Atom
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XPS Spectra1- Characteristic binding energy associated with each
core atomic orbital i.e. each element will give rise to acharacteristic set of peaks in the photoelectronspectrum at kinetic energies determined by thephoton energy and the respective binding energies.
2- The presence of peaks at particular energiestherefore indicates the presence of a specific elementin the sample under study.
3- The intensity of the peaks is related to theconcentration of the element within the sampledregion. (quantitative analysis of the surfacecomposition).
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KE versus BE
E E E
KE can be plotteddepending on BE.
Each peak represents theamount of e-s at a certainenergy that ischaracteristic of someelement.
1000 eV 0 eV
BE increase from right to left
KE increase from left to right
Binding energy
# of
ele
ctro
ns
(eV)
KE = hv – BE - Ø
XPS Spectrum• The XPS peaks are sharp.
• In a XPS graph it is possible to see Augerelectron peaks.
• The Auger peaks are usually wider peaks in aXPS spectrum.
• Aluminum foil is used as an example on thenext slide.
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XPS Spectrum
O 1s
O because
of Mg source
CAl
Al
O 2s
O Auger
Identification of XPS Peaks
• The plot has characteristic peaks for eachelement found in the surface of the sample.
• There are tables with the KE and BE alreadyassigned to each element.
• After the spectrum is plotted you can look forthe designated value of the peak energy fromthe graph and find the element present on thesurface.
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X-rays vs. e- Beam
• X-Rays– Hit all sample area simultaneously permitting
data acquisition that will give an idea of theaverage composition of the whole surface.
• Electron Beam– It can be focused on a particular area of the
sample to determine the composition ofselected areas of the sample surface.
XPS Technology• Consider as non-
destructive.– because it produces
soft x-rays to inducephotoelectronemission from thesample surface
• Provide information aboutsurface layers or thin filmstructures
• Applications in theindustry:– Polymer surface– Catalyst– Corrosion– Adhesion– Semiconductors– Dielectric materials– Electronics packaging– Magnetic media– Thin film coatings
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How Does XPS Technology Work?• A monoenergetic x-ray beam emits photoelectrons from the from
the surface of the sample.
• The penetration of the x-ray photons about a micrometer of thesample
• The XPS spectrum contains information only about the top 10 -100 Ǻ of the sample.
• Ultrahigh vacuum environment to eliminate excessive surfacecontamination.
• Cylindrical Mirror Analyzer (CMA) or hemispherical sector analyzer (HSA) measure the KE of emitted e-s.
• The spectrum plotted by the computer from the analyzer signal.
• The binding energies can be determined from the peak positionsand the elements present in the sample identified.
Instrumentation:COMPONENTS OF XPS
vA source of X-raysvAn ultra high vacuum (UHV) vAn electron energy analyzervmagnetic field shieldingvAn electron detector systemvA set of stage manipulators
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The basic requirements:• A source of fixed-energy radiation (an x-ray
source).
• An electron energy analyzer (which can dispersethe emitted electrons according to their kineticenergy, and thereby measure the flux of emittedelectrons of a particular energy).
• A high vacuum environment (to enable theemitted photoelectrons to be analyzed withoutinterference from gas phase collisions).
XPS Instrument
X-Ray Source
Ion Source
SIMS Analyzer
Sample introduction
Chamber
Secondary ion mass spectrometry (SIMS)
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X-ray Photoelectron Spectrometer
Diagram of the Side View of XPS SystemX-Ray source
Ion source
Axial Electron Gun
Detector
CMA
sample
SIMS Analyzer
Sample introduction Chamber
Sample Holder
Ion PumpRoughing Pump Slits
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Schematic Diagram of XPS
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Energy of Light
Wavelength
(λ)106µm 103µm 1 µm 10-3µm 10-6µm
Energy
(E)
Bro
ad-c
ast
Shor
t wav
e ra
dio
X-ra
y
1 MeV1 KeV1 eV10-3eV10-6eV
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X-Ray Sources• Irradiate the sample surface, hitting the core electrons
(e-) of the atoms.• The X-Rays penetrate the sample to a depth on the
order of a micrometer.• Useful e- signal is obtained only from a depth of around
10 to 100 Å on the surface.• Normally, the sample will be radiated with photons of a
single energy (MgKα or AlKα).• This is known as a monoenergetic X-Ray beam.• The X-Ray source produces photons with certain
energies:– MgKα photon with an energy: hν = 1253.6 eV– AlKα photon with an energy :h ν = 1486.6 eV
The emitted photoelectrons will therefore have kineticenergies in the range of ca. 0 - 1250 eV or 0 - 1480 eV
X-ray Source Requirements• 1. High X-ray flux at sample• 2. Narrow X-ray line width• 3. Multiple-anode capability• 4. Ability to move the X-ray source (X-Y)
and retract it (Z)• 5. Long anode and filament lifetime
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The X-ray source for XPS:• In contrast to the electron source, the X-ray
source energy depends on the choice of theanode material, resulting in the availability of anumber of discrete energies rather than acontinuous variation of the energy, as exists forelectron and ion guns.
• The photon energy must be sufficiently high toexcite intense photoelectron peaks from allelements of the periodic table.
• For XPS analysis, it is very important toconsider the energy resolution of the primary X-rays.
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X-ray tubeEarly x-ray source
Standard lab X-ray source is byvery high energy ebeam hitting theanode.
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X-ray spectrum from x-ray tube
Characteristic lines from the X ray fluorescence process (XRF) and a broad background (Bremsstrahlung), which is strongly depends on the energy of the electron
Monochromatic X-ray
1. Narrow peak width2. Reduced background3. No satellite & Ghost
peaks
Goal to achieve
SampleSample
XX--ray Anoderay Anode
Energy Energy
AnalyzerAnalyzer Quartz Quartz
Crystal DisperserCrystal Disperseree--
Rowland CircleRowland Circle
nλ=2dsinθ
For quartz (1010)surface, d=0.42 nm and78.5 degree for Al Kα0.93 nm
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Synchrotron RadiationThe synchrotron storage ring is a tubular vacuum chamber made to:
Hold an electron beam travelling through it at nearly the speed of light.Maintain the high energy of the electron beam. As the accelerating electronscircle the ring at relativistic velocities, they give off intense beams of lightincluding x-rays. By using a monochromator the light will beMonochromatic.
Key properties of synchrotron radiation:high intensity
tunability in wide range
near-coherenceمتماسكة
polarized.
pulsed
well collimated NUS has such a source in Singapore!
Sample charging effectsThe light for XPS always charges surface positively (shifting ofspectrum to higher binding energy) and leads to general instability(spectral noise).For the metal sample, which can be grounded and the charges canbe quickly gone.However, for insulator, this effects are serious and need to betreated.
C 1s shifts due to the charging
For XPS (even For XPS (even AES) never forget AES) never forget ground the ground the sample !!!sample !!!
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Inhomogeneous Surface ChargingCharging can even change the line shape due to InhomogeneousSurface Charging, which have different positive voltage on thesurface.
In a lot of cases,there is onlyspectral shift due tocharging, which canbe determined bycomparison withknown elementalXPS lines, forexample C 1s.
Vacuum System
• The instrument usesdifferent pump systemsto reach the goal of anUltra High Vacuum(UHV) environment.
• The Ultra High Vacuumenvironment willprevent contaminationof the surface and aidan accurate analysis ofthe sample.
University of Texas at El Paso, Physics Department
Side view of the Phi 560 XPS/AES/SIMS UHV System
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UHV for Surface Analysis? Why
XPS AnalyzerAnalyzer Requirements1. Precision energy measurement across a
wide energy range2. High-energy resolution capability3. Ability to define the analysis area and, if
possible, to change it4. High dynamic range and low noise
detector
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Instrumentation (analyzers)
Analyzer:
Most essential part of any electron spectroscopy,its characteristic are: energy range, energyresolution, sensitivity and acceptance angle.
Normally its functions involve: retarding اعاقة ofthe incoming electron, selection of the electronswith right kinetic energy (pass energy), detectingof the electrons (channeltron)
Detection of electron energy (Analyzers)
• Mainly two types of detectors are used in AES and XPSsystems: The cylindrical mirror analyser (CMA) and thehemispherical sector analyzer (HSA).
• In the past, the CMA was preferred for AES systems merely forgeometrical reasons and for its high analyzer transmissionfunction, and the HSA analyzer for XPS for its superior energyresolution.
• More and more, however, depending on the constructor and onthe requirements of the customer, the HSA detector is alsoused in AES systems.
• A multifunctional AES-XPS system is evidently operated byonly one electron detector, and mostly a HSA type is chosen.
• Yet, it is important to mention that not all of the requirementsimposed by the type of analysis coincide for XPS and AES .
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The hemispherical sector analyzers (HSA• All constructors use HSA detectors for electron dispersion
analysis in XPS.• A typical configuration is shown in Fig. bellow.• The HSA is designed to have a constant and as high as
possible energy resolution for the detection ofphotoelectrons.
• The best energy resolution in XPS is 0.4 eV,corresponding to the line width of the monochromator.
• In order to reduce the size of the analyzer, it is standardpractice to retard the kinetic energies of thephotoelectrons either to a user-selected analyzer energy,called pass energy, or by a user-selected ratio.
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Mode of fixed analyzer transmission mode (FAT)• Also known as the constant analyzer energy mode (CAE).• In this mode of operation, which is applied for the detection of
photoelectrons, a constant voltage is applied across the hemispheresallowing electrons of a particular energy to pass between them.
• The most important characteristic in this case is a constant energyresolution in the spectrum as a function of the energy, in contrast tothe CMA analyser where a relative energy resolution is obtained.
• The electrons are emitted from the specimen and transferred to thefocal point of the analyzer by the lens assembly.
• At this point they are retarded electrostatically before entering theanalyzer itself.
• Those electrons with energies matching the pass energy of theanalyser are transmitted, detected and counted by the electrondetector.
• The retarding field potential is then ramped, and so the electrons arecounted as function of energy.٥٠
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Improving Sensitivity of HSA• To improve the sensitivity of the HSA, the electron
detection is done by a multichannel detectorsystem.
• Depending on the type of system, the number ofelectron multipliers may go up to 16.
• This parallel electron detection is especiallyuseful when a monochromator is used due to theloss of intensity of the primary X-rays.
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Sample Preparation & Surface Damage in XPS1. Any Sample that is vacuum stable can be analyzed
by XPS.2. Sample containing volatile components can be
cooled to low temp. to avoid devolatilization3. Normally, Solid materials, such as metals ceramics
& polymer, are fairly stable under X-ray irradiationand damage caused by X-ray is minimal during atypical XPS experiment
4. Films, plaques الواح or powders can be mounted ona sample holder with a double-sided sticky tape
الصق شریط of low volatility first and then examined asbulk samples.
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5. Certain Polymer & Biological samples wouldundergo some chemical changes under prolongedX-ray exposures in an XPS experiment.
Examples are: PTFE, PVC, PVA, especially., whenthe materials are in thin films.
6. To minimize the damage, the exposure timeshould be as short as possible, and the samplesare cooled to low temperatures.
7. The causes for the XPS induced damage include:secondary electrons generated at X-ray source &impinging on the polymer or biological samplesurface.
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XPS Instrument
The XPS is controlled byusing a computer system.
The computer system willcontrol the X-Ray typeand prepare theinstrument for analysis.
University of Texas at El Paso, Physics Department
Front view of the Phi 560 XPS/AES/SIMS UHV System and the computer system that controls the XPS.
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Where do Binding Energy Shifts Come From? Or element or compound identification.
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Elemental Shifts
Elemental Shifts
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Binding Energy Determination
The photoelectron’s binding energy will be based on the element’s final-state configuration.
Conduction BandConduction Band
Valence BandValence Band
FermiFermi
LevelLevel
Free Free
ElectonElecton
LevelLevel Conduction BandConduction Band
Valence BandValence Band
11ss
22ss
22pp
Initial StateInitial State Final StateFinal State
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Electronic EffectSpin-Orbit Splitting or Spin-Orbit Coupling• Some electronic levels (most obviously 3p and 3d ) give
rise to a closely spaced doublet, Which appear whenspectra expanded.
• Permitted J values = L ± S• Coupling between L: The Angular Q.N., S: Unpaired
Spin• The lowest energy final state is the one with maximum J• The relative intensities of the two peaks reflects the
degeneracies of the final states (gJ = 2J + 1),• 2D 5/2: gJ = 2x{5/2}+1 = 6 (lower B.E)• 2D 3/2: gJ = 2x{3/2}+1 = 4 (higher B.E)• These two values determines the probability of transition
to such a state during photoionization.
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s-Orbital
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p-Orbital
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d-Orbital
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f-Orbital
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Chemical ShiftsThe exact binding energy of an electron depends notonly upon the level from which photoemission isoccurring, but also upon :
1) The formal oxidation state of the atom.2) The local chemical and physical environment.
Changes in either (1) or (2) give rise to small shifts in thepeak positions in the spectrum - so-called chemical shifts .
Atoms of a higher positive oxidation state exhibit ahigher binding energy due to the extra coulombicinteraction between the photo-emitted electron and theion core.
• The shifts are typically a few to 10 eV or more, andtherefore detectors with a high energy resolution are used.
• To subtract chemical information , it is imperative todetermine peak positions as accurately as possible.
• The line of interest is preferentially evoked by ایضاح meansof a monochromatic X-ray source, and recorded with thehighest possible energy resolution.
• When dealing with small chemical shifts, overlapping peaksmay anyway occur in the spectra.
• Peak deconvolution التداخل فك and peak fitting tools areavailable in the commercial data handling systems.٦٨
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• The capability to distinguish between different chemical statesis the main characteristic of XPS.
• Due to this, another acronym is in use for this technique: ESCA,which stands for ‘Electron Spectroscopy for Chemical Analysis’.
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FWHM: fullwidth at halfmax. Int.
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Chemical Shifts-Electronegativity Effects
Why Chemical Shift In AES, the situation is less promising
Ø Firstly, most AES lines are by nature broader than XPSlines.
Ø Secondly, the Auger transition involves three electrons andthe overall chemical shift is influenced by the three energylevels concerned.
• In general, similar shifts of a few eV as for XPS are to beexpected, especially when core electrons are involved in thetransition.
• Since in AES-specific equipment, detectors with lowerenergy resolution are used.
• It is clear that chemical shifts in AES are not often measuredaccurately.
• Moreover, peaks corresponding to transitions with valenceelectrons are broad and poorly defined, which makes theassignment of chemical shifts nearly impossible.
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As the samples shown before, binding energies of Al3+ is higherthan the metal atom, in the meanwhile, the binding energy ofO atom (more positive charge) is higher than the O2- ion.
The chemicalshifts due to thevariation of thedistribution of thecharges at theatom site is themain reason forthe other name ofXPS:
ESCA (Electron Spectroscopy for Chemical Analysis)
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Chemical Shifts- Electronegativity Effects
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Electronic Effects- Spin-Orbit CouplingTi MetalTi Metal Ti OxideTi Oxide
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C1s envelope has been resolved into five components of polystyrene surface exposed to an oxygen plasma.
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Final State Effects-Shake-up/ Shake-off
• Monopole transition: Only the principle quantumnumber changes. Spin and angular momentumcannot change.
• Shake-up: Relaxation energy used to exciteelectrons in valence levels to bound states(monopole excitation).
• Shake-off: Relaxation energy used to exciteelectrons in valence levels to unbound states(monopole ionization).
ResultsResults fromfrom energyenergy mademade availableavailable inin thethe relaxationrelaxation ofof thethefinalfinal statestate configurationconfiguration (due(due toto aa lossloss ofof thethe screeningscreening effecteffect ofofthethe corecore levellevel electronelectron whichwhich underwentunderwent photoemission)photoemission)..
78
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Ni MetalNi Metal Ni OxideNi Oxide
Shake-up and shake-offPhotoemission process canleave the ions in the groundstate (main peak) and alsopossibly in an excited sate(shake-up/shake-offsatellites), the latter makesthe KE of photoelectron less:higher BE.
- excitation of electron tobound state shake-upsatellite.
- excitation of electron tounbound (continuum)state shake-off satellite.
- excitation of hole stateshake-down satellite - rare.
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vThe shown is XPSspectra for Cu 2pphotoemission atdifferent chemical states.
vThe shake-up Lines doesnot exist in Cu metal, andis unique for CuO AndCuSO4
Energy loss lines
eph + esolid e*ph + e**solidPhotoelectrons travelling through the solid can interact with other electronsin the material. These interactions can result in the photoelectron exciting anelectronic transition, thus losing some of its energy (inelastic scattering).Most common are due to interband or plasmons (bulk or surface).
Surface plasmon
(bulk plasmon)
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The plasmon loss satellites are rarely sharp in insulators but veryprominent in the metals.
The main peak is normally observed at higher binding energy withseveral lines with the same energy intervals and reduced intensity, andthe interval can be not only single one due to different origins: bulk orsurface plasmons, bulk one is more prominent and interval larger (21/2
factor of the surface one).
O 1s21 eV
x4Insulating
Material
Electron Scattering EffectsPlasmon Loss Peak
Final State Effects- Multiplet Splitting
Following photoelectronemission, the remainingunpaired electron maycouple with other unpairedelectrons in the atom,resulting in an ion withseveral possible final stateconfigurations with asmany different energies.This produces a line whichis split asymmetrically intoseveral components.
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Relative Sensitivities of the Elements
0
2
4
6
8
10
12
Elemental Symbol
Rel
ativ
e S
ensi
tivity
LiBe
BC
NO
FNe
NaM
AlSi
PS
ClAr
KCa
ScTi
VCr
MFe
CoNi
CuZn
GG
AsSe
BrKrRb
SrY
ZrNb
MTc
RuRh
PdAg
CdIn
SnSb
TeIXe
CsBa
LaCe
PrNd
PSEu
GTb
DyHo
ErTYb
LuHfTa
WRe
OsIrPt
AuHg
TlPb
Bi
1s
2p
3d
4d
4f
XPS of Copper-Nickel alloy
-1100 -900 -700 -500 -300 -1000
20
40
60
80
100
120
Tho
usan
ds
Binding Energy (eV)
N(E
)/E
PeakArea
Mct-eV/sec
Rel.Sens.
AtomicConc
%Ni 2.65 4.044 49Cu 3.65 5.321 51
Cu 2p
Cu 3p
Ni 2p
Ni 3p
Ni LMM Ni
LMM Ni LMM
CuLMM
CuLMM
CuLMM
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Applications of X-ray Photoelectron
Spectroscopy (XPS)
vXPS is routinely used to analyze inorganic compounds,metals, semiconductors, polymers, ceramics, etc.
vOrganic chemicals are not routinely analyzed by XPSbecause they are readily degraded by either the energyof the X-rays or the heat from non-monochromatic X-ray sources.
Which Materials Analyzed
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ANALYSIS OF XPS
vXPS detects all elements with (Z) >3. It cannotdetect H (Z = 1) or He (Z = 2) because thediameter of these orbitals is so small, reducingthe catch probability to almost zero
vDedection unit: ppt and some conditions ppm.
For example: determination of alumınum oxide thickness wıth xps
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XPS Analysis of Pigment from Mummy Artwork
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Analysis Carbon Fiber- Polymer Composite Material by XPS
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Analysis of Materials for Solar Energy Collection by XPS Depth Profiling-The amorphous SiC/SnO /SnO2 Interface
٩٤Electron Spectroscopy for Chemical Analysis (ESCA)
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a) The C1s spectrum (resolved into component peaks) for thehardsegment polyurethane;
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(b) the O1s spectrum for the hard-segment polyurethane
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٩٧(c ) the N1s spectrum for the hard-segment polyurethane
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X-rays will penetrate deeply into asample, and stimulate electron
emission throughout thespecimen.
Only those electrons emitted fromthe surface zone that havesuffered no energy loss willcontribute to the photoemissionpeak.
Electrons emitted from the surfacezone that have lost some energydue to inelastic interactions willcontribute to the scatteringbackground.
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ESCA spectra are convolutions of the information fromeach depth within the sampling depth.
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Hydroxy groups and ethers on a surface cannot bedistinguished based upon ESCA chemical shifts. If the surfaceis reacted with trifluoroacetic anhydride, only hydroxyl groupswill pick up F. The size of the F peak in the ESCA spectrumwill be proportional to the number of reacted hydroxyl groups
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Case study of XPS
Compositional Analysis of Surfaces:
Case I: Analysis of surface treatment of a piston.
Coating Material: Fluorocarbon
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Polysiloxane Immobilized Ligand System
O
O
O
Si
CH2
CH2 C2H5
C2H5
H2N(CH2)2NH2
O
O
O
Si
CH2
CH2 NH2
NH2
C2H5OH
N
C
O
O
O
O
+
C
O
O
NH
NH
-
C
C
N
Reflux/Toluene
١٠٤
4/9/2017
53
١٠٥
١٠٦
XPS Results
NOSiCElementSystem
N1sO1sSi2pC1sCore-linePrecursor
399.5532102285
2.8541.41738.8%Composition
N1sO1sSi2pC1sCore-lineProduct
399.5532102285
9.628.719.342.4%Composition
4/9/2017
54
١٠٧
Conclusion• XPS is a powerful technique for
characterizing solid surfaces.• All types of inorganic soids can be analyzed.• Elemental (except H, He) and chemical
analyses within a depth of 10 nm.• Quantitative technique.• Extremely useful for surface treatment of
materials.
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