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AXIS Supra
Getting Started Guide39-341
Supplied by: Kratos Analytical Ltd.
Wharfside, Trafford Wharf Road,
Manchester, M17 1GP, UK
Photoelectric effectPhotoelectric effect
Einstein, Nobel Prize 1921
Photoemission as an analytical tool
Kai Siegbahn, Nobel Prize 1981
Introduction
XPS X-ray Photoelectron SpectroscopyESCA Electron Spectroscopy for Chemical AnalysisUPS Ultraviolet Photoelectron SpectroscopyPES Photoemission Spectroscopy
XPS, also known as ESCA, is the most widely used surface analysis technique because of its relative simplicity in use and data interpretation.
1s
2s2p
3s
VB
Ef
Ev
Photoelectron
0
BindingEnergy
0
KineticEnergy
Photonhν
φ
Analytical Methods Analytical Methods
KE = hν - (EB+ϕ)
— Elemental identification and chemical state of element
— Relative composition of the constituents in the surface region
— Valence band structure
------ XX--ray Photoelectron Spectroscopy (XPS)ray Photoelectron Spectroscopy (XPS)
XPS spectrum:Intensities of photoelectrons versus EB or KE
B.E. = h - K.E. - .F specν φ
e-
Vacuum level
Fermi level
core level
Fermi level
Vacuum level
φsample
φspec
K.E. = h -B.E. -ν φ.F sample
B.E.F
K.E. = h -B.E. - - ( )
= h -B.E. -
ν φφ φ
ν φ
.F sample
spec sample
.F spec
-Binding Energy Reference
Instrumentation• Electron energy analyzer• X-ray source• Ar ion gun• Neutralizer• Vacuum system• Electronic controls• Computer system
Ultrahigh vacuum system< 10-9 Torr (< 10-7 Pa)• Detection of electrons• Avoid surface reactions/
contaminations
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Monochromated Al Kα excited Ag spectrum
Non-monochromated Mg Kα excited Ag spectrum
FWHM 0.97 eV
FWHM 0.46 eV
satell
ite
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XPS Spectra Showing the Chemical State of Si
Si elemental
Si oxide
Si oxide Si elemental Two samples with different SiO2film thicknesses on Si substrate.
-note large chemical shift between elemental Si and silicon dioxide peaks.
d d
Si elemental
Si oxide
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Quantitative Surface Analysis of Poly(ethylenetetraphthalate) - PET
C 1s region O 1s regionO(1) 530.8eV 51 at% O(2) 532.1eV 49 at%
C(1) 285.0eV 65 at%C(2) 286.5eV 23 at%C(3) 289.2eV 12 at%
C3C2
C1 O1O2
-(-O-C- -C-O-CH2-CH2-)-= =
O On
2223
1
32
1
1
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Stereo isomersof PBMA only difference inValence band
Only 5minacquisition time
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0 deg (bulk sensitive)
60 degrees
45 degrees
75 degrees(surface sensitive)
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Pt 1(SiO2) Pt2 (SiN)
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SiN
Silicate fibres
A Shimadzu Group CompanyA Shimadzu Group Company AXIS UltraDLD
• Primary features:– 165mm hemispherical analyzer (HSA)– Concentric Spherical Mirror Analyzer (SMA)– 128 channel DLD detector for spectroscopy and
imaging– Magnetic immersion lens– Co-axial charge neutralization– Monochromatic and Achromatic X-ray sources– Automated sample manipulator– Multi-technique capability (XPS, FE-Auger, SIMS,
ISS)
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Co-axial chargeneutraliser(Kratos PatentEP 0 458 498 B1)
Magnetic lens(Kratos Patent EP 0 243 060 B1)
Iris
Aperture
AXIS
AXIS Ultra is designed around the established co-axial technology
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The Rowland circle geometry
Energy dispersion ∆E ~ Rowland circle diam.
For 500 mm ~ 0.625 eVmm-1
250 mm ~ 1.25 eVmm-1
Fixed mono spotEnergy dispersivedirection, ∆E
Toroidal quartz backplane
Electron gun & x-ray anode
Rowland circle diameter
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Charge Neutraliser Magnetic Lens
Sample
Scan Plates
Spot size apertures
ElectrostaticLens
Analyser entrance slit plate
Projector Lens
Objective Lens
Angle defining iris
sample
iris
aperture
Magnetic flux lines
photoelectrons
The magnetic immersion lens of the ‘snorkel’ type is positioned below the sample and focuses photoelectrons onto the spot size aperture.
Kratos Patent: EP 0 243 060 B1
See diagram to right
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• High collection efficiency– large solid angle of collection– low spherical aberration therefore high magnification
(ca. x10) in both spectroscopy and imaging
• High small spot spectroscopy sensitivity
AXIS Magnetic Lens (III)
The magnetic snorkel lens focuses photoelectrons onto the spot size aperture. A set of electrostatic deflection plates enables the position of the analysis spot to be moved to a static point on the sample, or scanned to produce an image. The electrostatic lens can be used independently or in combination with the magnetic lens.
The advantages in the use of the magnetic lens include:
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Magnetic Lens Pole Piece
(2) Charge balance plate (-ve potential)
(1) Filament
(3) Low Energy Electron Trajectory in the Magnetic Field
Sample
1) Electrons are thermionically emitted from the charge neutraliser filament.
2) Negative potential of the charge balance plate forces the charge neutralisation electrons towards the sample. There is no direct line of sight of the filament with the sample.
3) The low energy electrons are confined by the magnetic field of the magnetic immersion lens, following an oscillating path between sample and charge balance plate.
4) As sample develops a positive charge, charge neutralisation electrons are attracted to the surface.
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electrons
(1) Low energy electrons thermionicallyemitted from the filament
(2) Low energy photoelectrons are over-focused and can return to the sample to provide charge compensation
Sample
e-
(2) (3) High energy photoelectrons are under-focused. Secondary electrons, created upon impact with the charge balance plates, return to the sample.
(3)
(1)
A Shimadzu Group CompanyA Shimadzu Group CompanySimple ‘Universal’ Charge Neutralisation Parameters
The charge neutralisation parameters are fully software controlled, usually operated as simple ‘on’ or ‘off’.
For > 99 % of all samples run in the applications lab the neutraliser is operated under the same conditions. Therefore, samples can be left to run unattended with complete confidence that charging will not occur during data acquisition.
Normal user operation of neutraliser
Control of parameters associated with use of neutraliser
A Shimadzu Group CompanyA Shimadzu Group CompanyNeutralisation of Rough Samples
200 microns
800 microns
Wood pulp fibres shown here in the analysis position of the spectrometer. This type of sample would traditionally be extremely difficult to neutralise, but as demonstrated by the excellent resolution on the C 1s spectrum poses no problem with the AXIS co-axial charge neutraliser.
C 1s spectrum from wood fibres
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Selected area apertures
Angle defining iris
110µm analysis area 27µm analysis area
Analyser entrance slit
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27µm analysis area
Selected area apertures
Angle defining iris
Analyser entrance slit
Beam scanning plates, x & y
AXIS Electron Optics : Selected Area and Scanned Imaging
x
yFixed x,y voltage applied to scan plates to deflect analysis position to defined position on sample.
Scanning x,y voltage applied to scan plates to deflect analysis position over defined area of sample to generate a map.
Plan view of sample
A Shimadzu Group CompanyA Shimadzu Group CompanyIntegration of the SMA into Photoelectron Spectrometer
• Objective and projector lenses operated exactly the same as image mode
• Voltages switched from outer 2 hemispheres to inner 2
x-rays
Detector
Objective lens Retarding projector lens
Sample
HSA
I1
E0
I2
Spectroscopy modeEntrance slitintroduced
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Time
∆τx
MCP
‘x’ delay line
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Pass energyeV
Energywindow
eV
Min step size Application
320 32 0.25 Full core leveleg, Cr2p, Fe 2p
160 16 0.125 Full core leveleg C1s, O1s
80 8 0.06 High resolutionat small spot
40 4 0.03 Autofocusroutine
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Au 4f 500um
Au 4f 55µm Au 4f 15µm
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DLD
Spectral ModeStandard input lensElectrons dispersed between inner and outer hemisphere, using standard spectrometerCommon detector plane
A Shimadzu Group CompanyA Shimadzu Group CompanyIntegration of the SMA into Photoelectron Spectrometer
• Objective lens produces magnified photoelectron image I1
• Projector lens produces image I2 retards to pass energy E0
• Magnification at detector variable from <5x to >100x
• Field of view on sample from >2mm to <100µm• Lateral resolution to <2µm
x-rays
MCPdetector
Objective lens Retarding projector lens
Sample
SMA
I1
E0
I2
Image mode
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Imaging Mode
• 2 delay-line anodes arranged orthogonally.
• Position of photoelectron event defined in 2 dimensions.
• Full pulse counting photoelectron imaging.
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DLD
Ultra DLD Imaging Mode
Image ModeStandard input lensElectrons pass through ‘outer’ hemisphere into SMA & back to detector planeParallel image maintainedFast, real time image
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• Fast Parallel XPS Imaging• as the sample is moved, so the photoelectron image
moves.
• Lateral Resolution specification < 3 µm• Fixed analyser transmission (FAT) mode
• energy resolution constant at all binding energies.• good energy resolution at all binding energies.
• ‘Real time’ chemical state XPS imaging• ability to differentiate between elements in different
chemical states.
…..Following slides attempt to illustrate these points
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2 mm fov 800 µm fov
400 µm fov 200 µm fov
• Au images acquired in less than 30 secs.
• Field of view changed by selecting predefined lens modes for a specific magnification. New f.o.v. displayed within seconds
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2.2 µm edge
25µm from centre of bars
After acquisition of the image a line scan can be generated. The line-scan can be processed to provide edge measurements, giving an indication of lateral resolution
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• Cu grid• horizontal bars 20µm • vertical bars 40µm
• Parallel images acquired in 1,5,10 & 20s
• Fast photoelectron images allow sample alignment
• As sample moves … image moves!!
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• Survey of sample in cross-section showed Ti
Ti layer 8 umAl alloy
Al/SiC matrix
A Shimadzu Group CompanyA Shimadzu Group Company Parallel images and small spot dataTi 2p image350 µm field of view
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• TiAlN sample after oxidation at >9000C in air.• XPS images shows segregation of oxide
species.• Chemical state imaging shows different oxide
species.• Confirmation of oxide segregation with small
spot XPS
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Fe 2p image Cr 2p image
Parallel images were acquired to show the elemental distribution of the oxide species at the surface of the TiAlN material.
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O 1s image at FeOx binding energy (531.8eV)
O 1s image atTiOx binding energy (529.7eV)
Fe 2p elemental Ti 2p elemental
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survey spectra acquired from 27 µm analysis area
Selected area spectra (27µm) were acquired from the sample to give a quantitative analysis of the different regions identified by parallel imaging.
A Shimadzu Group CompanyA Shimadzu Group Company Adhesive coverage on paper
• Inhomogeneous paper sample with uneven coverage of adhesive - lead to adhesive failure
• Optically - sample was homogenous - white
• XPS O1s image clearly identifies adhesive distribution
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O 1s parallel images acquired at predefined fields of view
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• C 1s image allows investigation of chemistry– small spot analysis shows variation in C-H and C-O
concentrations.
• The energy resolution of Spherical Mirror Analyser (SMA) allows chemical imaging of different C 1s species.
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C-O bonding
55µm analysis area
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• C fibre “wool” electrode from an industrial fluorination process was analysed.
• Electrode loaded with F containing epoxy base resin.
• Coverage of resin along fibres of the electrode was investigated.
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• From the large area analysis it is concluded that:– Sample inhomogeneous
• C fibre conductive• fluoro-epoxy insulating• potential differential charging removed with use of
charge neutraliser
– C 1s spectrum shows complex structure – Excellent energy resolution
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F 1s image
C 1s image corresponding to C-FC 1s image corresponding to C-H
Uncovered fibres
Resin coating
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• C-C images show uncoated fibres.• C-F images show distribution of coating.• F image overlays with C-F image.
• Overlay shows C species distribution – C-C red– C-F green
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from Images
Spectrum from uncoated 5 µm fibre
Spectrum from coated 5 µm fibre
CC photoelectron image C-F photoelectron image
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• Multi-spectral imaging used to achieve spectra from 5µm adjacent areas
• Spectra show:• graphitic C on uncoated fibre• fluoro-epoxy resin in coating
• Demonstrates:• excellent charge compensation• chemical state image on charged sample• application of MSI for 5µm areas!
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Al 2p photoelectron image
Optical image of Al padsin-situ
Al pad
Si substrate structure
Cross section of sample
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• Bad adhesion had been observed in Al bond pads.• Optical images was used to identify area of know
failure.• XPS images and small spot spectra show F
contamination• Distribution of F indicates residue from plasma
etching step in production
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F 1s image showsdistribution of F on pads
Al 2p image
F 1s image
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55µm spectra showAl / F on pad
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F 1s and Al 2p imagesshow uneven distribution of F across bond pad
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micro-contact printing
• Patterning of polymer substrate (polyethylene PE) with poly(acrylic) acid PAA.– PAA impermeable, wet and dry etch resist– PAA films easily functionalised– capped with PEG can be used for bio-applications cell growth
• Oxidised PE film is prepared• PDMS stamp (optical mask) prepared with n-alkylamine• PE “stamped” with amine to passivate PE • Unpassivated regions react with PTBA• Hydrolysis of this layer leads to PAA
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PE-COOCOR
PE-COOCOR
PE-COOCOR
i) PTBA ii) MeSO3H
alkyl amine
hyperbranchedPAA film
PDMS stamp
Oxidised PE substrate
alkyl amine
Passivated layer Unpassivated region
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Au 4f photoelectron image
Attenuation of Au substrategives contrast mechanism for the image.
Au substrate
PAA layer
alkyl amine
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PAA
C 1s from PAA layer
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Excellent correlation shown between C 1s and Au 4f images.
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< 3µm spatial resolution
Vision software allows retrospective line scans to be created from the parallel image. Here, a line scan has been generated from a thin scratch defect in the PAA layer.
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PE-COOCOR
Experiment repeated usingPE substrate with PAA layer being fluorinated
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C-Fx
C-C,C-H
Carbon chemical state overlay images.
The image is used to select the position from which the small spot spectra are acquired.
Small spot spectra