View
13
Download
0
Category
Preview:
Citation preview
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
A Shimadzu Group CompanyA Shimadzu Group Company Monochromated vsnon-monochromated X-ray source
Monochromated Al Kα excited Ag spectrum
Non-monochromated Mg Kα excited Ag spectrum
FWHM 0.97 eV
FWHM 0.46 eV
satell
ite
A Shimadzu Group CompanyA Shimadzu Group Company
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
A Shimadzu Group CompanyA Shimadzu Group Company
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
A Shimadzu Group CompanyA Shimadzu Group CompanyValence band Spectroscopy
Stereo isomersof PBMA only difference inValence band
Only 5minacquisition time
A Shimadzu Group CompanyA Shimadzu Group Company Angular Dependence of XPS
0 deg (bulk sensitive)
60 degrees
45 degrees
75 degrees(surface sensitive)
A Shimadzu Group CompanyA Shimadzu Group Company Quantitative XPS images combined with small spot analysis
Pt 1(SiO2) Pt2 (SiN)
A Shimadzu Group CompanyA Shimadzu Group Company Quantitative XPS images
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)
A Shimadzu Group CompanyA Shimadzu Group Company AXIS Components - magnetic lens
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
A Shimadzu Group CompanyA Shimadzu Group CompanyX-ray Monochromator -
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
A Shimadzu Group CompanyA Shimadzu Group Company AXIS Magnetic Lens
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
A Shimadzu Group CompanyA Shimadzu Group Company
• 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:
A Shimadzu Group CompanyA Shimadzu Group Company AXIS Charge Neutralisation
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.
A Shimadzu Group CompanyA Shimadzu Group CompanySources of charge neutralisation
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
A Shimadzu Group CompanyA Shimadzu Group Company AXIS Electron Optics : Selected Area
Selected area apertures
Angle defining iris
110µm analysis area 27µm analysis area
Analyser entrance slit
A Shimadzu Group CompanyA Shimadzu Group Company
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
A Shimadzu Group CompanyA Shimadzu Group Company Detector Technology
Time
∆τx
MCP
‘x’ delay line
A Shimadzu Group CompanyA Shimadzu Group Company Delay line detector schematic
A Shimadzu Group CompanyA Shimadzu Group Company Snap shot mode
A Shimadzu Group CompanyA Shimadzu Group Company Snapshot modes of operation
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
A Shimadzu Group CompanyA Shimadzu Group Company Snapshot mode with spot size and PE
Au 4f 500um
Au 4f 55µm Au 4f 15µm
A Shimadzu Group CompanyA Shimadzu Group Company Ultra DLD Spectroscopy Mode
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
A Shimadzu Group CompanyA Shimadzu Group Company
Imaging Mode
• 2 delay-line anodes arranged orthogonally.
• Position of photoelectron event defined in 2 dimensions.
• Full pulse counting photoelectron imaging.
A Shimadzu Group CompanyA Shimadzu Group Company
DLD
Ultra DLD Imaging Mode
Image ModeStandard input lensElectrons pass through ‘outer’ hemisphere into SMA & back to detector planeParallel image maintainedFast, real time image
A Shimadzu Group CompanyA Shimadzu Group Company Imaging Performance of the SMA
• 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
A Shimadzu Group CompanyA Shimadzu Group CompanyVariable Field of View - Real Time Imaging of Au grid
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
A Shimadzu Group CompanyA Shimadzu Group Company XPS Imaging of 5 µm Cu Bars
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
A Shimadzu Group CompanyA Shimadzu Group Company Examples:Cu grid
• 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!!
A Shimadzu Group CompanyA Shimadzu Group Company XPS Imaging of Layered Materials
• 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
A Shimadzu Group CompanyA Shimadzu Group Company Analysis of surface oxides
• 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
A Shimadzu Group CompanyA Shimadzu Group Company Elemental imagesTi 2p image
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.
A Shimadzu Group CompanyA Shimadzu Group Company Elemental & Chemical State Imaging
O 1s image at FeOx binding energy (531.8eV)
O 1s image atTiOx binding energy (529.7eV)
Fe 2p elemental Ti 2p elemental
A Shimadzu Group CompanyA Shimadzu Group Company Small spot XPS
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
A Shimadzu Group CompanyA Shimadzu Group Company O1s images variable FOV
O 1s parallel images acquired at predefined fields of view
A Shimadzu Group CompanyA Shimadzu Group Company Chemical state images
• 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.
A Shimadzu Group CompanyA Shimadzu Group Company C1s chemical state imageCH, CC hydrocarbon
C-O bonding
55µm analysis area
A Shimadzu Group CompanyA Shimadzu Group Company C fibre electrode
• 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.
A Shimadzu Group CompanyA Shimadzu Group Company Large area analysis : 300x700µm
A Shimadzu Group CompanyA Shimadzu Group Company Large area analysis
• 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
A Shimadzu Group CompanyA Shimadzu Group Company Chemical state images
F 1s image
C 1s image corresponding to C-FC 1s image corresponding to C-H
Uncovered fibres
Resin coating
A Shimadzu Group CompanyA Shimadzu Group Company Chemical state images
• 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
A Shimadzu Group CompanyA Shimadzu Group CompanySpectroscopy from fibres - 5µm Spectra
from Images
Spectrum from uncoated 5 µm fibre
Spectrum from coated 5 µm fibre
CC photoelectron image C-F photoelectron image
A Shimadzu Group CompanyA Shimadzu Group Company Summary
• 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!
A Shimadzu Group CompanyA Shimadzu Group Company Bond pad contamination
Al 2p photoelectron image
Optical image of Al padsin-situ
Al pad
Si substrate structure
Cross section of sample
A Shimadzu Group CompanyA Shimadzu Group Company Bond pad contamination
• 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
A Shimadzu Group CompanyA Shimadzu Group Company Al 2p and F 1s images
F 1s image showsdistribution of F on pads
Al 2p image
F 1s image
A Shimadzu Group CompanyA Shimadzu Group Company Small spot spectroscopy
55µm spectra showAl / F on pad
A Shimadzu Group CompanyA Shimadzu Group Company Photoelectron images
F 1s and Al 2p imagesshow uneven distribution of F across bond pad
A Shimadzu Group CompanyA Shimadzu Group CompanyApplications of photoelectron imaging to
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
A Shimadzu Group CompanyA Shimadzu Group Company µ-CP process
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
A Shimadzu Group CompanyA Shimadzu Group Company PAA on Au films
Au 4f photoelectron image
Attenuation of Au substrategives contrast mechanism for the image.
Au substrate
PAA layer
alkyl amine
A Shimadzu Group CompanyA Shimadzu Group Company C 1s spectra - 27µ m analysis area
PAA
C 1s from PAA layer
A Shimadzu Group CompanyA Shimadzu Group Company Au 4f & C 1s image
Excellent correlation shown between C 1s and Au 4f images.
A Shimadzu Group CompanyA Shimadzu Group Company High Resolution Imaging
< 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.
A Shimadzu Group CompanyA Shimadzu Group Company Fluorinated PAA on PE
PE-COOCOR
Experiment repeated usingPE substrate with PAA layer being fluorinated
A Shimadzu Group CompanyA Shimadzu Group Company C 1s Selected Area Spectra & Images
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
Recommended