مقارنة بينwds andeds
TRANSCRIPT
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Apri l, 2005
Microscopic Composition Measurement at NanoscaleMicroscopic Composition Measurement at Nanoscale
DSSC Seminar
Lin Wang
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OutlineOutline
General Introduction
Energy Dispersive Spectroscopy (EDS)
Wavelength Dispersive Spectroscopy (WDS) Electron Energy Loss Spectroscopy (EELS)
Auger Electron Spectroscopy (AES)
X-Ray Photoelectron Spectroscopy (XPS) Summary
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General IntroductionGeneral Introduction
When High Energy Electron Beam Meets MaterialWhen High Energy Electron Beam Meets Material
By Analyzing Emitted X-RayEnergy Dispersive Spectroscopy (EDS) + SEM/ TEMWavelength Dispersive Spectroscopy (WDS) + SEM
By Analyzing Inelastically Scattered ElectronsElectron Energy Loss Spectroscopy (EELS) +TEM
By Analyzing Emitted Auger ElectronsAuger Electron Spectroscopy (AES)
When XWhen X--Ray Meets MaterialRay Meets Material By Analyzing Emitted Photoelectrons
X-Ray Photoelectron Spectroscopy (XPS)
AnalyticalElectronMicroscope(AEM)
SurfaceCharacterization
Take a thin TransmittingSpecimen as an example
{AEM with EDS}
(AEM with EELS)
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Principles of EDSPrinciples of EDS
EnergyEnergy DispersiveDispersive (X(X--Ray) Spectroscopy (EDS)Ray) Spectroscopy (EDS)
X-Ray counting is done by measuring the x-ray photon energies with aSi(Ni)solid state detector
Different characteristic X-Ray lines of elements represent the typesand relative amounts of elements in the sample
The number of counts of each peak may be converted to weightconcentration using standard (more accurate) or standardlesscalculations
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Energy Resolution (Peak Broadening) measured by FWHM (Full Width
at Half Maximum of the peak)
Peak overlap
Principles of EDS (cont.)Principles of EDS (cont.)
With TEMWith SEM
Gaussian Distribution
Y=AAexp{-1/2*[(EA-E)/ ]2}
FWHM=2.355
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Application Examples of EDSApplication Examples of EDS
EDS Line Profile Software automationallows simplified composition profiling atnanometer resolution using EDS.
Sample: Si80Ge20 islands grown on Si at800C followed by Si capping.
EDS Mapping - EDS Mapping allowsvisualization of the phase separationprocess, which can be coupled with point-by-point quantitative analysis.
Sample: Cu50Ag50 ball milled at 230 C
PointPoint
AnalysisAnalysis11--D ProfilingD Profiling 22--D MappingD Mapping
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Principles of WDSPrinciples of WDS
WavelengthWavelength DispersiveDispersive (X(X--Ray) Spectroscopy (WDS)Ray) Spectroscopy (WDS)
With SEM
X-Ray counting is done by using a Bragg
reflector to wavelength-filter the x-rays on their
way to the detector
Braggs Law
N
=2dsin
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Capacities of WDSCapacities of WDS
Advantages
Superior spectral resolution (X10 times better than EDS)
Can detect light element Z 4
Can detects 0.1%-several ppm More accurate
Disadvantages
The equipment is more expensive
More Time consuming
More difficult to use
Usage Identification of spectrally overlapped elements such as W or Ta in Si,
or N in Ti Detect of low concentration species (down to 100 or even 10ppm)
such as P or S in metals Analysis of Low atomic number elements such as oxidation in metals
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Comparison between EDS&WDSComparison between EDS&WDS
EDS: Normally detects Z 10(below
Na) thus typically cant be
detected O, N, C. Sometimes ifusing windowless or thin
window it can detect Z 4
Parallel technique
Can quickly scan for a widerang of possible elements
Good for use both with SEM orTEM specimen
Time of a typical run take a few
minutes
WDS: Detects Z 4
Serial technique
slow but can provide excellentresolution
Requires very high x-raygeneration rates thus TEM
samples cant provide highcount (x-ray generation) rate
Time of a typical run take hours
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Principles of EELSPrinciples of EELS
Electron Energy Loss Spectroscopy (EELS)Electron Energy Loss Spectroscopy (EELS)
With TEM
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Principles of EELS (continued)Principles of EELS (continued)
Electron Energy Loss Spectroscopy (EELS)Electron Energy Loss Spectroscopy (EELS)
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Capacities of EELSCapacities of EELS
Usage
Light element spectroscopy for concentration, electronic and chemicalstructure analysis at ultrahigh lateral resolution
Sample Requirements
Solids and specimens must be transparent to electrons with about 10-200nm thickness;
sample size: 3mm diameter thin foil
Not destructive to sample
Limitation
Range of elements: Z=3-92
Lateral resolution: 1nm-10m, depending on the diameter of the incidentelectron probe size and the thickness of the specimen
Sampling depth: with thickness of specimen 10-200nm
Detection limits:10-21g
Accuracy: with standards 1-2 at.%, without standards 10-20 at.%
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Application Examples of EELSApplication Examples of EELS
EELS Mapping - The breakdown of the Li/Ni ordering at the surfacecan be seen as changes in the EELS fine structure and Ni-to-O ratio.
Sample: LiNi0.80Co0.20O2 from Li-Ion battery after aging
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Principles of AESPrinciples of AES
Auger Electron Spectroscopy (AES)Auger Electron Spectroscopy (AES)
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Capacities of AESCapacities of AES
Sample Requirements
vacuum compatible materials
no destruction except to electron beam sensitive materials and duringdepth profiling
Vacuum Requirements: 10-10 torr
Limitation
Range of elements: All except H and He
Lateral resolution: 10-30nm for Auger analysis and even less for imaging
Sampling depth: 0.5-10nm
Detection limits: 0.1-1at.% Accuracy: 30% if using published elemental sensitivity
10% if using standards that closely resemble the sample
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Applications of AESApplications of AES
Composition analysis of the 0-3nm region near the surface for allelements except H and He
Scanning Auger Microscopy
Depth-composition profiling and thin film analysis High lateral resolution surface chemical analysis and
inhomogeneity studies to determine compositional variations
Surface diffusion and segregation
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Principles of XPSPrinciples of XPS
XX--Ray Photoelectron Spectroscopy (XPS)Ray Photoelectron Spectroscopy (XPS)
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Capacities of XPSCapacities of XPS
Sample Requirements
vacuum compatible materials, flat samples preferred
no destruction except to X-ray sensitive materials and during
depth profiling
Limitation
Range of elements: All except H and He Lateral resolution: 5mm-75m
Sampling depth:0.5-5nm
Detection limits: 0.01-0.3at.%
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Applications of XPSApplications of XPS
Routinely used in industry and research whenever elemental orchemical state analysis is needed at surfaces and interfaces as well asspatial resolution requirements are not demanding (typically greaterthan 150m).
Eg.s:
examination for and identification of surface contaminations
Evaluation of materials processing steps (cleaning, plasma etching, thermal
oxidation, silicide thin-film formation etc.) Evaluation of thin-film coating or lubricants
Failure analysis for adhesion between components(air oxidation , corrosionetc.)
Tribological (or wear) activity
Effectiveness of surface treatment of polymers or plastics
Surface composition differences for alloys
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SummarySummary
All of the five methods can give both microscopic imaging functionand qualitative plus quantitative composition analysis function
Quantitative composition measurement will be more accurate withstandards esp. standards in similar composition range
For EDS, the major limitation is the peak broadening and light elementincapability
For WDS, comparing with EDS, it has high spectral resolution but ittakes longer for each run
EELS can detect light element and has a high lateral resolution
AES and XPS are surface composition detection techniques but AEShas a nm-scale lateral resolution which is much better than XPS
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ReferenceReference
J. Goldstein, D. Newbury, D. Joy, C. Lyman, P. Echlin, E. Lifshin, L,Sawyer, J. Michael, Scanning Electron Microscopy and X-RayMicroanalysis, Kluwer Academic / Plenum Publishers (2003)
C. Brundle, C. Evans, S. Wilson, L. Fitzpatrick, Encyclopedia ofMaterials Characterization, Butterworth-Heinemann (1992)
D. Williams, C. Carter, Transmission Electron Microscopy, Pledum(1996)
D. J. OConnor, B. A. Sexton, R.St. C. Smart, Surface Analysis Methods
in Materials Science, Springer (2003) http://cmm.mrl.uiuc.edu/Gallery/STEM/STEMGallery.htm