3D EDX MICROANALYSIS IN A FIB/SEM

3D EDX MICROANALYSIS IN A FIB/SEM:WHAT CAN WE EXPECT, WHERE ARE THE LIMITS.?Marco Cantoni, Pierre BurdetCentre Interdisciplinaire de Microscopie Electronique(EPFL-CIME)CIMESince August 2008: Nvision 40e‐beam: ZEISS Gemini1‐30kV, 1nm @ 30kV, 2.5nm @1 kVIon‐beam: 1‐30kV, 4nm @ 30kVEDS X‐MAX (SDD) 80mm2 detectorKleindiek micromanipulator (TEM prep)2‐3 Ga Sources / yearFIB Applications @ CIME Materials Science:––––– TEM Lamellae preparationcross-sectioning, SE/BSE imaging, EDX3D reconstruction3D EDX (in collaboration with ZEISS andOXFORD INSTRUMENTS)3D reconstruction of biocompatible materialsLife Science:–Serial sectioning of Brain tissue:SUPER-STACKS

outline 3D Microstructure Analysis by FIB/SEMvolume reconstruction 3D Analytics review– 3D EBSD– 3D EDX with Si(Li) detectors, first steps EDX limitations– Speed– Geometry– ZAF Example ConclusionFIB-NT compared with other 3D-techniques Voxel size 5‐10nmDwell time 10µsec.1 slice, image / min.HT: 1‐2kVEscape depth of signal (BSE) 5nm3D‐EDX of NiTi/Stainless steelPierre Burdet, Marco CantoniNew possibilities in3D-microscopy:Combination with quantitativeanalytical SEM techniques:EBSD, EDX

3D EBSDS. Zaefferer:EMAS 2009, Gdansk, Poland speed 10-100 points/sec.20-30min./slicecurrent and hardware limited2011: 600Hz ( 1.6msec dwell time)o Stage movement necessary (rotation)overhead for image recognition anddrift correctionA 3D‐EBSD map from a thin film Nickel sample with a grainsize of about 1 micron. The map is 51x32x24 voxels, eachvoxel is 20nm wide (OXFORD INSTRUMENTS)o high voltages: 15‐20kVLimits: “overhead”: tilt or rotation, image recognition acquisition speed(100Hz 10msec./pixel)(600Hz 1.6msec/pixel)

3D EDX with Si(Li) detectors, first steps@ 20 keV: 100 electrons generateSignals 50‐75 SE 30‐50 BSE 0.7 X‐raysMethodsignal requireddetection solid anglebottleneck3D FIB/SEM256 grey levels of BSEsmallcurrent in small probeEBSD320x240 pixel imagebigcamera speedEDXspectrum 1000 countssmall (getting bigger)detection speedThe “Si(Li) age”Quantitative Chemical Analysis 3D EDX‐microanalysis1. Sl2. Sl3. Sl2D Ca maps4. Sl5. Sl3D reconstruction Separate volume of interest from the bulk Cut the sample slice by slice with the I-beam Map each cross-section with the e-beam andEDXS Reconstruct 3D-model from 2D maps[1] Kotula et al, . Microsc. Microanal. 12 (2006), 36-48[2] Schaffer et al, Ultramicroscopy 43 (2007), 587-597Courtesy: Miroslava Schaffer

Fully automated 3D‐FIB EDXS experimentOverview SEM ImagesDetail SEM Images and EDXS Maps[2] Schaffer et al, Ultramicroscopy 43 (2007), 587-597(Ca)MgTiOx ceramic9Fully automated 3D-FIB EDXS experiment3D Ca distribution3D Mg distribution3D void distribution(reconstr. from BSE images)3D Ti distribution3D Si distribution[2] Schaffer et al, Ultramicroscopy 43 (2007), 587‐597

F. A. Lasagni: EMAS 2009, Gdansk, Poland30min.‐ 40 min. per slice/map310 nm voxel dimension (z)The “SDD age”New detectors speed up the acquisition !dreaming of 1M counts/sec.50-100k counts/sec. are more realistic at the moment

2008 (“SDD age”)installation of Nvision 40 @ CIMEuse the full potential of the machineo3D‐EDXStack of 269 EDX mapsoooooPierre Burdet: Ph.D. Thesis in collaboration with ZEISSGoal: FIB Nano‐Tomography based on EDX‐elemental mapsnew generation of EDX detectors (SDD)Develop algorithms do “deconvolute” the interaction volume ofcharacteristic X‐rayHigh tension : 5kVVoxel size : 20 x 20 x 40 nmPixel per map : 256 x 192 (x 269)Time per slice : 4 1 minutesTime of acquisition : 24 hoursIon beamSample: Al/Zn, Jonathan Friedli, STI‐LSMXEDX geometrical limitations3D EDX is not like FIB/SEM Tomography“The detector doesn’t see everything” Not all X-rays reach the detectordminh30 mI‐beamEDXe‐beam

EDX limitations“The detector sees everything .”BSE– Parasitic X‐rays generated by :X‐ray BSE hitting the trench walls X‐rays hitting the trench walls(Fluorescence)EDX limitationsParasitic X-ray sNb3Sn (no Cu) in Cu matrix Parasitic signal of CuUp to 7% at (@ HT 7 kV)Up to 20% at (@ HT 20kV)Depends on position on the face10 m3.77.7NbCu [% atm]NbNb3SnCuCuSiTaSnCuNb02SnTaNbO4602Sn4keV630 m

EDX limitations– Parasitic X‐ray signal depends on: Geometry and composition of surrounding Detector position– Solutions Bigger trenchesRemove VOI out of surrounding : Block lift‐outMove the wall facing detector further awayEdge geometry (similar to3D‐EBSD)Complete lift‐outEDX resolutionResolution limit:Interaction volume Lower the high tension as much as possible Big voxels Small voxels: “convolution” problem– Delocalisation (metrology !)– Quantification (inhomogeneities, interfaces,multiple phases)15kV

EDX resolutionevaluation of delocalisation: Model systemIntensity80090 %600Al Ka40050 %Zn La200100 nmZnposition nm 20010 %Al- 200- 1000100– Simulated linescan across the interface normal to y Signal is shifted towards Al because of the incident angle Positions of threshold (10 %, 50 % and 90 %) are used to compare with othergeometriesEDX resolutionmodel system: AlZn– Stack of 269 EDX maps Acquisition parameters–––––yHigh tension : 5kVVoxel size : 20 x 20 x 40 nmPixel per map : 256 x 192 (x 269)Times per map : 4 1 minutesTime of acquisition : 24 hours Al K elemental map, x/y aligned,smoothing filter (median 3D), surfacereconstruction with a single threshold– Study of the delocalisation of interface(normal to main axes)3.7 m9.4 mxz5.2 m

EDX resolutionDelocalisation of interfacesRelativerel. errorerror% % – Implication of delocalizationBSE, volumeAl Ka, volumeZn La, volumeBSE, surfaceAl Ka, surfaceZn La, surface30Relative error % Cubic Al precipitates in Zn matrix(edge 400nm) Errors in volume and surface v.s. edgelength of the precipitates2010200400600800Particle Size (cube)Improving 3D quantification : Idea– When interaction volume is bigger than voxel size Each spectrum contains a contribution of neighboring voxels Standard quantification inappropriate for voxels close to GB Possibility of quantification enhancementScan through x and zof a grain boundaryRecorded nAl12!!!!!3Zn!ZnMaterial AMaterial BAlAlAl012301230123012301231000 nm

Improving 3D quantification : IdeaThesis: Pierre BurdetAlgorithm to enhance 3D EDXquantificationGrain boundary and voxels in depthRecursive relationComposition of a voxel depends also onthe subsequent voxels (along z)Sample considered as stratifiedf function: Thin film ( z)quantification*Recursive relationz index (layer)CiA f (k-ratiosi,Ci-1 , Ci-2 , )Element index*Pouchou, J. Analytica Chimica Acta 283(1), pp. 81–97 November (1993).Application: enhanced quantification– Geometry of acquisition : tilt of 36 Interaction volume delocalized in y– Ci-z weighted mean of neighbors in y Mean electron y-distribution per z-layer Simulated from pure materialRecursive relationz index (layer)CiA f (k-ratiosi,Ci-1 , Ci-2 , )Element indexElectron distributionin the i-2 layer

Application Example: NiTi-SteelNiTi - steel weldingLaserJonas Vannod, EPFL-CIME /LSMX300µmNiTi– Wire welding by laserSSWelding process NiTi wire Stainless steel wire 300 mm of diameter?NiTi– Molten regionSSTernary phasediagram at 1000 C Liquid diffusion (fast) Phase formation duringsolidification– Characterization Microstructure and compositionof the different phasesN. L. Abramycheva, V. Mosko, Univ. Ser. 2: Khimiya 40 (1999) 139‐143Application ExampleExperimental: E0 and voxel size– EDX spectrum image FeLa1 2C K , Ti K , Cr K , Fe K , Ni L Fe K (6.4 kV) 10kVMax X-ray range: 500 nmVoxel size for z: 100 nmFor x, y: 100 nm (isotropic)Ni La1 2Ti La1 2Ti Ka1– SEM image SE image 12.5 nm for z For x, y: 12.5 nm (isotropic)SE escape depthEDX Spectrum at 10kVCr La1 2CKaCr Ka1Fe Ka1Ni Ka1Ti Kb1Cr Kb1Fe Kb1Si Ka101f rz ( z)234567Ni Kb18X-ray depth distribution at 10kVTi KaFe KaNi La100200300400z nm 500 nm

Application Example: NiTi-SteelExperimental : Analyzed volume– On NiTi sideSEM image of analyzed volume Phases of main interest– Analyzed volume Surface: 12.8 x 4.4 m Depth: 9.6 mNiTi– 44 EDX maps 6 min per mapSEM image ofwelding regionFIB slicingdirectionNiTiSS30 m100 mApplication Example: NiTi-SteelResults: SEM image contrast– SEM image SE (Secondary e-) contrast: no direct interpretation Mean z roughly similar (excluding TiC) low contrast for BSE (Backscatter e-)10kV SE imageNiTi10 m

Application Example: NiTi-SteelResults: EDX map–Intensity Maps(X-ray line intensity)–Quant Maps–Noise treatmentStandard EDXprocedure Ti K Fe K Ni L 5 m3D Median filter(3x3x3)at %Application ExamplePhases identification: Ternary histogramTernary phase diagram at1000 C with ternary histogram– Ternary EDX map histogram From three main EDX quantifiedmaps (noise treated) Compared to ternary phasediagram– Phase identification minA CA maxA (A Ti,Fe,Ni) minA and maxA refined with SEimage contrast

Applications: NiTi - steel welding– Segmentation based on ternary diagram Red 1: NiTi Blue 2: (Fe,Ni)Ti Green 3: Ni3TiSE image with low Fe phasesxy13Ternary diagram2zz2 mApplications: NiTi - steel welding– Segmentation based on ternary diagram Green 4: Between Ni3Ti and Fe2Ti x Red 5: Fe2Ti Blue 6: -(FeNi)SE image with high Fe phasesyTernary diagram456zz2 m

Applications: NiTi - steel welding– Small microstructure EDX phases used as mask Threshold on SE contrastxy3Ternary diagram26b6azz2 mApplications: NiTi - steel welding– Visualization523x14Ternary diagram241zy62 m563Phases visualization

Application ExamplePhase identification: other phases– Red: TiC Small black dots in SE image contrast Only bigger particles in EDX maps– Blue: TiO Identified with EDX maps Typical shape: edges and hole close to itSE image with TiO phaseSE image with TiC phase10 mMICROANALYSIS IN A FIB/SEM:EDX IN 3DWHAT CAN WE EXPECT, WHERE ARE THE LIMITS.? FIB/SEM Nano-Tomography: powerful tool formicro(structure)analysis at the nano-scale 3D-EDX: Experimental challenges: choice ofparameters, geometrical constraints 3D EDX: careful interpretation of resultsDeconvolution procedures (at least locally)Statistical treatment of data (PCA,ICA etc.)Acknowledgements:Zeiss (PhD Thesis P. Burdet)Oxford Instruments (Technical support)

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3D Analytics review – 3D EBSD – 3D EDX with Si(Li) detectors, first steps EDX limitations – Speed – Geometry – ZAF Example Conclusion FIB-NT compared with other 3D-techniques New possibilities in 3D-microscopy: Combination with quantitative analytical SEM techniques: EBSD,