Download - Machine learning tools in analytical TEM
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Machine learning tools in analytical TEM C.HébertEPFL&HuiChenLausanne
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Analytical STEM: EELS & EDX
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• Starting material: a synthetic pyrolite glass doped with Nd, Sm, Hf, Lu, and U (0.3 wt.% for each).
• Samples were first compressed in symmetrical diamond anvil cells (DAC) at 46 Gpa and melted by double-sided laser heating, and then slowly cooled down be low the so l idus temperature before quenching.
Sample used as an example:
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From materials to TEM sample
FIBsamplepreparation(1DACexp=1TEMsample)
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x
y
E Spectrum=backgroundsignal+setsofGaussianpeaks(eachspecificelementinthesampleyieldsauniquesetofGaussianpeaks,likeasignatureinEaxis)+noise
• TheintegratedEDSspectrum
• ArepresentativesinglepixelEDSspectrum
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EDSmapsofthesubsolidusregionfromEspritsoftware
Fp
Brg
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First use of PCA in analytical TEM
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HyperMap data processing: the "0 eV peak"
• WithrawdatacubePCAgivescomponent(s)withregularpatternsofintensity• Thisisthe0eVpeak,whoseintegratedsignalshowsregularfringes• MustberemovedforPCAtowork
GuillaumeLucasandDuncanAlexander,LSME&CIME
• Everydatacubehasitsown0eVpeakpatternWhat is it?Solution:cutof“zeroeVpeak”andmoveon
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EDX HyperMap data processing: non-random noise components in low signal regions
• PCAdecompositiongivesscreeplotwhichdoesnottaperoffrapidly
• “Physical”componentsappearmixedupwithnoisecomponents
• Noisecomponentsseemtoshowstrong,non-randomspeckle
• =>Non-random(e.g.non-Poissonian)noise-readoutnoise?
PCAloading
PCAscore
AvoidholesandlowintensityEDXregion(ormaskthemoutfortreatment),andmoveon
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• “Raw”spectrumimagedata:examplesinglepxspectra:
EELS is not spared…
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Low-loss:
High-loss:
• Spectra look correct.!
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Dual EELS: camera response
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Scree:low-loss Scree:high-loss
• PerformMSA;screeplotslookcorrect• Howevermanycomponentsshowdistinctdifferencebetweenthetwodetectorquadrantsacrosswhichthespectrumhasbeenrecorded,bothforlow-lossandcore-loss
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Dual EELS: camera response
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Low-lossloadings:1 2
3 4
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MSA facts
• PCAisdamngoodatspottingdetectorsartifacts…
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Dataunmixing:PCAanalysis
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MSA facts
• PCAisdamngoodatspottingdetectorsartifacts…• PCAdo*not*givecomponentswithphysicalmeaning
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IndependentComponentAnalysis
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MSA facts
• PCAisdamngoodatspottingdetectorsartifacts…• PCAdo*not*givecomponentswithphysicalmeaning• ICAmightgivecomponentwithphysicalmeaning
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q NonNegativeMatrixFactorization
NMF#1
(b)
(d)
NMF#0
NoSi
NMF#0
NMF#1
(a)
(c)
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MSA facts
• PCAisdamngoodatspottingdetectorsartifacts…• PCAdo*not*givecomponentswithphysicalmeaning• ICAmightgivecomponentwithphysicalmeaning• NMFgiveEDXcomponentsthatlooksliketheyhaveaphysicalmeaning
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q BrgphasesegmentationviaNMFmask
NdLα SmLα
Fig. (a) mask of the pure Brg area generated via NMF#1 thresholding; (b) segmented pure Brg phase; (c) EDS spectrum of a selected Brg area; (d) EDS spectral comparison of a selected Brg area and the masked Brg area.
(b)
(d)
(a)
(c)
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Fe Mg Si Al Ca Nd Sm O
NMF#0 0.17 9.3 24 2.2 1.1 0.066 0.071 63
NMF#1 8.2 40.5 0.0 0.87 0.076 0.0 0.0 50
Brgmask 1.7 15 19 2.0 0.93 0.048 0.070 60
Quantificationofthespectra
- NMFgivescomponentswhichareclosetobephysical,butarenot.Thisisevenworse(andmoredangerous)
- Whyisthismethodcalled“machinelearning”ifwecannotteachthemachine?
- Needtomovetosupervisedlearning.Themicroscopistshasalotof“knowledge”thatcanbetransferredtothemachine
- Wecaneasilydetect<0.1%dopants
- Challenge:ifthereisasmallparticleinonecornerofthesample
Conclusion