Familirization with XPS Familirization with XPS method and techniquemethod and technique

by Dr. Dmitry A. Zatsepinby Dr. Dmitry A. Zatsepin**

Institute of Physics PAS, Al. LotnikInstitute of Physics PAS, Al. Lotnikóów 32/46w 32/46PLPL--0202--668 Warsaw, POLAND668 Warsaw, POLAND

*on temporary leave from Institute of Metal Physics *on temporary leave from Institute of Metal Physics –– Russian Academy of Sciences,Russian Academy of Sciences,Laboratory of XLaboratory of X--ray Spectroscopy, S.Kovalevskoj Str. 18, 620990 Yekaterinburg ray Spectroscopy, S.Kovalevskoj Str. 18, 620990 Yekaterinburg

SciSci. Ed. made by Prof. Dr. Kurmaev E.Z., Russian Academy of Science. Ed. made by Prof. Dr. Kurmaev E.Z., Russian Academy of Sciences s –– Institute of Metal PhysicsInstitute of Metal Physics

UsefulUseful comments: comments: Prof.DrProf.Dr. Krystyna Jablonska (IP. Krystyna Jablonska (IP-- PAS, PAS, PolandPoland) and Dr. Rolf Berger (Uppsala ) and Dr. Rolf Berger (Uppsala UnivUniv., Sweden) ., Sweden)

Warsaw Warsaw ©© 20142014

The scope of lecture:The scope of lecture:

1.1. What is inside XPS What is inside XPS physicsphysics ? ? ((the description of physical phenomena used in XPSthe description of physical phenomena used in XPS))

2.2. Why XWhy X--ray Photoelectron Spectroscopy ?ray Photoelectron Spectroscopy ? ((a brief review ofa brief review of XPS method featuresXPS method features))

3.3. XPS InstrumentationXPS Instrumentation ((main parts and XPS tricks for Xmain parts and XPS tricks for XPS PS beginnersbeginners) )

4. UPS technique4. UPS technique ((UPS method features and examplesUPS method features and examples))

Part 3. XPS InstrumentationXPS Instrumentation

33--1. XPS Instrumentation 1. XPS Instrumentation –– Main PartsMain Parts

Typical Typical XX--ray ray photoelectronphotoelectron spectromemterspectromemter -- simplified schemesimplified scheme

Based on ThermoFisher Scientific XPS EscaLab 250 Xi Based on ThermoFisher Scientific XPS EscaLab 250 Xi ©© 2010 ThermoFisher Scientific2010 ThermoFisher Scientific

33--2. XPS Instrumentation 2. XPS Instrumentation –– Main PartsMain Parts

•• XPS tricks for the XXPS tricks for the X--ray Sourceray Source::

Stable vacuum Stable coolant flow At least 10 min. of idle-cycle before XPS Stable filament current and accelerating

voltage (!!!) Avoid long-time previously used e--target

zone Always use the most possible „soft”

Power Mode for X-ray Source

Stable XStable X--ray Source = Precise XPS Dataray Source = Precise XPS Data

Typical XTypical X--ray DUAL Source Parametersray DUAL Source Parameters

XPS XXPS X--ray Sourceray Source

33--3. XPS Instrumentation 3. XPS Instrumentation –– Main PartsMain Parts

Different types of monochromators : Different types of monochromators : CzernyCzerny--Turner typeTurner type(plane multilayers) and (plane multilayers) and RowlandRowland typetype (curved (curved multilayers)multilayers).. The latter can be build using different XThe latter can be build using different X--ray ray „„focusingfocusing”” schemes. Hischemes. Hi--End XPS systems haveEnd XPS systems haveadjustable dispersersadjustable dispersers or or multiplying dispersersmultiplying dispersers for for obtaining highobtaining high--brilliance Xbrilliance X--ray Source.ray Source.

XPS XXPS X--ray Monochromatorray Monochromator

XPS tricks for the XXPS tricks for the X--ray Monochromator ray Monochromator : :

Avoid XAvoid X--ray Sourceray Source intencity decrease or/and distortion due to improper intencity decrease or/and distortion due to improper monochromatizationmonochromatization (if (if handhand--tuningtuning availableavailable) while using different X) while using different X--ray sources (Al, Mg, Zr, . . . )ray sources (Al, Mg, Zr, . . . )

Perfect XPerfect X--ray Monochromatization = Precise XPS Data !ray Monochromatization = Precise XPS Data !

33--4. XPS Instrumentation 4. XPS Instrumentation –– Main PartsMain Parts

There are There are twotwo principally different typesprincipally different types of Energy of Energy Analysers in electron Analysers in electron spectroscopyspectroscopy : : hemispherical hemispherical (HA(HA--type)type) and and cylindrical (CAcylindrical (CA--type)type) energy analyser.energy analyser.Actually for XPS the Actually for XPS the HAHA--type is used, because of type is used, because of adequate brilliance within the different electron energy adequate brilliance within the different electron energy range, no BE position distortion (highrange, no BE position distortion (high--prescision), prescision), possibility to made ARXPS.possibility to made ARXPS.

Hemispherical Energy Analyser Hemispherical Energy Analyser –– main ideamain idea

XPS tricks for the hemispherical Energy Analyser XPS tricks for the hemispherical Energy Analyser : : The lower pass energy The lower pass energy EE00 –– usuallyusually the the betterbetter resolution of XPS, but improper values resolution of XPS, but improper values of pass energy and inputof pass energy and input--output slits result in spectrum shape distortionoutput slits result in spectrum shape distortion Made test XPS recording for wellMade test XPS recording for well--known material and verify the obtained spectral known material and verify the obtained spectral parameters with published data parameters with published data

Correct Correct settingssettings forfor Energy AnalyserEnergy Analyser and XPS DATA verification = Precise XPS Data !and XPS DATA verification = Precise XPS Data !

33--5. XPS Instrumentation 5. XPS Instrumentation –– Main PartsMain Parts

Hemispherical Energy Analyser Hemispherical Energy Analyser –– howhow it is inside XPS system ?it is inside XPS system ?

Reproduced from technical presentation for University of PennsylReproduced from technical presentation for University of Pennsylvania, USA, vania, USA, ©© University of PennsylvaniaUniversity of Pennsylvania

33--6. XPS Instrumentation 6. XPS Instrumentation –– Main PartsMain PartsCylindrical Energy Analyser Cylindrical Energy Analyser –– main ideamain idea

XPS tricks for the Cylindrical Energy XPS tricks for the Cylindrical Energy Analyser Analyser : : Pass energy Pass energy –– the same trick as for the same trick as for HA systemsHA systems AcceptanceAcceptance and and EntranceEntrance Angles Angles add one more additional limitation to add one more additional limitation to XPS with CMA: no ARPS is possible XPS with CMA: no ARPS is possible Highly suitable to collect Auger data Highly suitable to collect Auger data

Correct choise of Energy Analysing SystemCorrect choise of Energy Analysing System = Extended possibilities for XPS != Extended possibilities for XPS !

33--7. XPS Instrumentation 7. XPS Instrumentation –– Main PartsMain PartsEnergy Analysers Energy Analysers –– example of Analyser Pass Energy Influence on XPS lineexample of Analyser Pass Energy Influence on XPS line--shape resolutionshape resolution

Advice Advice ::

From the very beginnig made From the very beginnig made XPSXPS--test linetest line--shape recording, shape recording, and then compare Your XPSand then compare Your XPS--data with Hand Book of XPS data with Hand Book of XPS spectrocsopy or Official XPS spectrocsopy or Official XPS Database, but donDatabase, but don’’t forget t forget about:about:

PET XPS C 1PET XPS C 1ss spectra were obtained by ULVACspectra were obtained by ULVAC--PHI Analytical Scientists and used only as example PHI Analytical Scientists and used only as example ©© ULVACULVAC--PHI, USA PHI, USA

Absolute Absolute spectral spectral resolutionresolution::

ΔΔEE = FWHM or = FWHM or 2 2 ΔΔEE = = EEbasebase

RelativeRelative spectral spectral resolutionresolution::

RR = = ΔΔEE//EE00

33--8. XPS Instrumentation 8. XPS Instrumentation –– Main PartsMain Parts

The The most important characteristicmost important characteristic for XPS for XPS Energy Analyser, because it isEnergy Analyser, because it is

Represents the efficiency of concrete Energy Represents the efficiency of concrete Energy Analyser to transfer XPS electrons via analyser Analyser to transfer XPS electrons via analyser to XPS Solid State Detector or to XPS Solid State Detector or real real ””XPS XPS signalsignal”” deviations from deviations from ””perfectly perfectly transferred synthetic XPS transferred synthetic XPS signalsignal””

It is used by Central XPS Data Processing It is used by Central XPS Data Processing Unit to correct the XPS spectrum ;Unit to correct the XPS spectrum ;

The type of Energy Analyser is selected (if The type of Energy Analyser is selected (if possible) from possible) from the most frequently XPS tasks to the most frequently XPS tasks to be performed be performed

Energy Analysers Energy Analysers –– Transmission Function Transmission Function

The modified and supplemented figure is reproduced from R. PayntThe modified and supplemented figure is reproduced from R. Paynter review er review ©© 2004, INRS2004, INRS--Energie, Quebec, Canada Energie, Quebec, Canada

33--9. XPS Instrumentation 9. XPS Instrumentation –– Main Parts Main Parts →→

XPS Data XPS Data Acquisition UnitAcquisition Unit –– XPS Signal Intensity (theory)XPS Signal Intensity (theory)

33--10. XPS Instrumentation 10. XPS Instrumentation –– Main PartsMain Parts

Dual type of XPS electron release from the Dual type of XPS electron release from the samplesample::

„„cleanclean”” (without collisions) –– actual XPS dataactual XPS data ;interactedinteracted with energy losswith energy loss –– XPS backgroundXPS background.

InteractionsInteractions areare elasticelastic andand inelasticinelastic →→ attenuationattenuation →→ IFMP IFMP curvecurve

XPS Data XPS Data AcquisitionAcquisition – XPS XPS SignalSignal Attenuation EffectAttenuation Effect

Interacting electronsInteracting electrons XX--Ray FluxRay Flux

„„CleanClean”” electronselectrons

XPS tricksXPS tricks ::

Better to record spectrum under XBetter to record spectrum under X--ray LPM (i.e. 50 W instead of 200 W), but ray LPM (i.e. 50 W instead of 200 W), but to collect XPS data from to collect XPS data from multiplemultiple pointspointsof the surface of the surface samplesample with summationwith summation, than to use only 1 XPS scan under HPM , than to use only 1 XPS scan under HPM

ALWAYS use Background ALWAYS use Background RemovalRemoval Software to Software to removeremove inelasticinelastic contribution from XPS Datacontribution from XPS Data

Correct XPS Data AcquisitionCorrect XPS Data Acquisition = Precise XPS Data != Precise XPS Data !

33--11. XPS Instrumentation 11. XPS Instrumentation –– Main PartsMain Parts

XPS tricksXPS tricks ::

Multipoint and relatively not high PM of XMultipoint and relatively not high PM of X--ray Source Modes allow also to control the ray Source Modes allow also to control the homogeneity of the homogeneity of the samplesample under strudy under strudy

Multiple experimental data selection ALWAYS reduce experimental Multiple experimental data selection ALWAYS reduce experimental error contribution error contribution

Atomic layers

e- top layer

e- lower layer with collisions

e- lower layer but no collisionsX-Rays

Outer surface

Inner surface

XPS Data Collecting = Precise XPS Data !XPS Data Collecting = Precise XPS Data !

XPS Data XPS Data Acquisition UnitAcquisition Unit –– Multipoint AquizitionMultipoint Aquizition

33--12. XPS Instrumentation 12. XPS Instrumentation –– Main PartsMain Parts

The most dissimilar situations:The most dissimilar situations:

a (exactly surface)a (exactly surface) : XPS electrons actually are not scattered : XPS electrons actually are not scattered →→ very low contribution to the very low contribution to the BGBG--tailtail

d (exactly d (exactly ””bulkbulk””)) : maximum collisions of XPS electrons : maximum collisions of XPS electrons →→ the highest contribution to the the highest contribution to the BGBG--tailtail

This phenomena was found, studied and reported by Sven Tougaard,This phenomena was found, studied and reported by Sven Tougaard, in J. in J. VacVac. . SciSci. . TechnolTechnol. A, . A, 1414, 1415 (1996)., 1415 (1996).

XPS Data XPS Data Acquisition Unit Acquisition Unit –– example of depth morphologyexample of depth morphology

Can be used as quick reference of depth probing (software Can be used as quick reference of depth probing (software atat www.quases.com) www.quases.com)

33--13. XPS Instrumentation 13. XPS Instrumentation –– Main PartsMain Parts

XPS tricks for Charge Neutralization XPS tricks for Charge Neutralization : :

Try to reduce the actual acquisition time for Try to reduce the actual acquisition time for widewide--gap insulators as well as the Power gap insulators as well as the Power Mode of XMode of X--ray source, the longer acquisition ray source, the longer acquisition and higher Power of the Xand higher Power of the X--ray Source ray Source –– the the stronger surface charge ;stronger surface charge ; Better to apply short timeBetter to apply short time--range but range but multipointmultipoint XPS Data collection way instead of XPS Data collection way instead of XX--ray HP Mode and short timeray HP Mode and short time--range range acquisition acquisition →→ avoidance of Neutralizer Limitavoidance of Neutralizer Limit(depends on Neutralizer model)(depends on Neutralizer model) Always made 10Always made 10--15 min. Idle 15 min. Idle CycleCycle for for Charge Neutralizing UnitCharge Neutralizing Unit before XPS before XPS acquisition acquisition →→ stable charge stable charge compensationcompensationparametersparameters Always control FWHM of the XPS Always control FWHM of the XPS obtainedobtained ((especially for coreespecially for core--level XPSlevel XPS) ) →→FWHM broadening may be a signature of FWHM broadening may be a signature of improper neutralizing improper neutralizing modemode SometimesSometimes it is possible to apply it is possible to apply CarbonCarbon or or GoldGold spray onto the frame of the widespray onto the frame of the wide--gap gap insulatorinsulator samplesample for stable charge for stable charge leakingleaking

XPS Data XPS Data Acquisition Unit Acquisition Unit –– Charge Neutralization with a Flood GunCharge Neutralization with a Flood Gun

Correct XPS Charge Compensation = Precise ChemicalCorrect XPS Charge Compensation = Precise Chemical--shift XPS Data !shift XPS Data !

33--14. XPS Instrumentation 14. XPS Instrumentation –– Main PartsMain Parts

1.1. SteadySteady--state Onestate One--channel and Dualchannel and Dual--channel Charge Compensators channel Charge Compensators (no dynamic charge(no dynamic charge--neutralisingneutralising) )

2. Dynamic Charge Compensators 2. Dynamic Charge Compensators ((the value of surfacethe value of surface--charge is the charge is the timetime--rangerange controlled and automatically controlled and automatically compensated by dinamically varying the electon compensated by dinamically varying the electon fluxflux density, electron energy, density, electron energy, ……. of the flood . of the flood gungun))

XPS Data XPS Data Acquisition Unit Acquisition Unit –– Charge Neutralizers typeCharge Neutralizers type

33--15. XPS Instrumentation 15. XPS Instrumentation –– Main PartsMain Parts

XPS tricks for DATA Accumulation XPS tricks for DATA Accumulation (! hardware (! hardware limitslimits !) :!) :

Avoid the saturation limit of XPS DATA Acquisition Unit, it is dAvoid the saturation limit of XPS DATA Acquisition Unit, it is different for particular Xifferent for particular X--ray Spot Size and is ray Spot Size and is individual for each XPS system ;individual for each XPS system ;

Wanna get higher CPS ? Just do the Wanna get higher CPS ? Just do the multipointmultipoint XPS and made spectra summationXPS and made spectra summation

XPS Data XPS Data Acquisition Unit Acquisition Unit –– XPS FWHM dependence on DATA accumulation XPS FWHM dependence on DATA accumulation The higher CPS The higher CPS –– allall time the time the betterbetter ??????

Using Using LinearLinear--rangerange areaarea of Data Acquisition Unit Specifications = Precise XPS Data !of Data Acquisition Unit Specifications = Precise XPS Data !

33--16. XPS Instrumentation 16. XPS Instrumentation –– Main PartsMain Parts

XPS Data XPS Data Acquisition UnitAcquisition Unit –– ARXPS (theory)ARXPS (theory)

33--17. XPS Instrumentation 17. XPS Instrumentation –– Main PartsMain Parts

XPS tricks for ARXPS XPS tricks for ARXPS :: Take an additional care for sample preparation and mounting on

sample-holder for ARXPS → possibility for shift-skewness for the ”zero-point” of normal Take-off angle → distorted XPS Data dependence on Take-off Angle

XPS Data XPS Data Acquisition Unit Acquisition Unit –– ARXPSARXPS

33--18. XPS Instrumentation 18. XPS Instrumentation –– Main PartsMain Parts

XPS Data XPS Data Acquisition UnitAcquisition Unit –– CoreCore--level and VB level and VB StandardStandard Calibration AlgorithmCalibration Algorithm

Use ASTM Calibration Use ASTM Calibration procedureprocedure (dual reference peak calibration)(dual reference peak calibration) = Presise XPS Data != Presise XPS Data !

Standard calibration algorithm offered by NSRRC, Standard calibration algorithm offered by NSRRC, TaiwanTaiwan, R.O.C., R.O.C.

33--19. XPS Instrumentation 19. XPS Instrumentation –– Main PartsMain Parts

XPS Sample ManipulationXPS Sample Manipulation Unit Unit –– Sample holders and IntroSample holders and Intro--ChamberChamber

XPS tricks XPS tricks ::

Control the sample mounting onto the sample-holder before placing it into the Intro Chamber ;

In some cases the cleaning with 99% purity alkohol can be applied before installing sample for TMP-pumping ;

Leave the sample at least 12 hours in the Intro Chamber under TMP-pumping for gaseous fraction removing → stable hi-vacuum in the Main Vacuum Chamber Unit during measurement ;

Avoid studying powder-fraction samples if no Powder Trap System → use pressed pellets instead

Proper Proper samplesample preparation and mounting = Precise XPS Data !preparation and mounting = Precise XPS Data !

Versaprobe 500 SampleVersaprobe 500 Sample--Holders and Intro Chamber are presented as example Holders and Intro Chamber are presented as example ©© 2010 UlVAC2010 UlVAC--PHI, USAPHI, USA

33--20. XPS Instrumentation 20. XPS Instrumentation –– Main PartsMain Parts

•• HiHi--VacVac Systems that are widely used for XPSSystems that are widely used for XPS:1.1. ionion--gettergetter pumpspumps with automatic with automatic „„cutcut--offoff”” systemsystem (IGP type + IGP IGP type + IGP controllercontroller);2.2. titaniumtitanium sublimationsublimation pumpspumps with automatic with automatic „„cutcut--offoff”” systemsystem (TSP type + TSP TSP type + TSP controllercontroller);3. TitanTM ion-getter pumps with automatic with automatic „„cutcut--offoff”” systemsystem (TGP type + IGP TGP type + IGP controllercontroller);4. Combined TSP-IGP pumps

XPS Media Support Unit XPS Media Support Unit –– HiHi--Vacuum SystemVacuum System

Most Most importatntimportatnt charachteristicscharachteristics of a of a HiHi--VacVac PumpPump:

1.1. Pumping speed ;Pumping speed ;2.2. Saturation effect for absorbing plates ;Saturation effect for absorbing plates ;3.3. Pumping stability ;Pumping stability ;4.4. Starting and DropStarting and Drop--down pressures ;down pressures ;5.5. Bakeability ;Bakeability ;6.6. Contamination influence on above mentioned characteristics.Contamination influence on above mentioned characteristics.

33--21. XPS Instrumentation 21. XPS Instrumentation –– Main PartsMain Parts

According to Advanced Photonics Laboratory According to Advanced Photonics Laboratory ©© 2004, Chang Gung University2004, Chang Gung University

XPS specifications XPS specifications comparingcomparing with other techniques with other techniques

The author would like to acknowledge the following persons, who The author would like to acknowledge the following persons, who made an made an essential contribution to the field of Xessential contribution to the field of X--ray Photoelectron Spectroscopy and with ray Photoelectron Spectroscopy and with

whom it was a great honour to collaborate:whom it was a great honour to collaborate:

•• Academician Vladimir I. Nefedov, Russian Academy of Sciences, Academician Vladimir I. Nefedov, Russian Academy of Sciences, RussiaRussia

•• Prof. Dr. Ernst Z. Kurmaev, Russian Academy of Sciences Prof. Dr. Ernst Z. Kurmaev, Russian Academy of Sciences -- Ural Division, Ural Division, RussiaRussia

•• Prof. Dr. Atsushi Fujimori, Tokyo University, JapanProf. Dr. Atsushi Fujimori, Tokyo University, Japan

•• Prof. Dr. Koichi Kitazawa, The Graduate School of Science, TokyoProf. Dr. Koichi Kitazawa, The Graduate School of Science, Tokyo (now the Executive Director of the Japan (now the Executive Director of the Japan Science and Technology Agency, Japan)Science and Technology Agency, Japan)

•• Prof. Dr. Vladimir I. Anisimov, Russian Academy of Sciences Prof. Dr. Vladimir I. Anisimov, Russian Academy of Sciences -- Ural Division, Ural Division, RussiaRussia

•• Prof. Manfred Neumann, University of Osnabrueck, GermanyProf. Manfred Neumann, University of Osnabrueck, Germany

•• Dr. Dr. VadimVadim R. Galakhov, Russian Academy of Sciences R. Galakhov, Russian Academy of Sciences -- Ural Division, Ural Division, RussiaRussia

•• Prof. Dr. Joseph E. Nordgren, University of Uppsala, SwedenProf. Dr. Joseph E. Nordgren, University of Uppsala, Sweden

•• Dr. Rolf Berger, University of Uppsala, SwedenDr. Rolf Berger, University of Uppsala, Sweden

•• Prof. Dr. HansProf. Dr. Hans--J. Fitting, University of Rostok, GermanyJ. Fitting, University of Rostok, Germany

•• Dr. Wolfgang Betz, ULVACDr. Wolfgang Betz, ULVAC--PHI Inc., USAPHI Inc., USA

Thanks a lot to Thanks a lot to allall of them and to the others for their dedicated work in the fieldof them and to the others for their dedicated work in the fieldof XPS science and to You, for Your of XPS science and to You, for Your attentionattention and patience!and patience!