Electron Diffraction Techniques and Applications. Stavros Nicolopoulos. NanoMEGAS SPRL, Blvd Edmond Machtnens, B-1080 Brussels Belgium.

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1 Electron Diffraction Techniques and Applications Stavros Nicolopoulos NanoMEGAS SPRL, Blvd Edmond Machtnens, B-1080 Brussels Belgium Edgar Rauch SIMAP laboratory, CNRS-Grenoble INP, BP rue de la Physique, Saint Martin d Hères, France Muriel Veron SIMAP laboratory, CNRS-Grenoble INP, BP rue de la Physique, Saint Martin d Hères, France Amith Darbal, JK Weiss AppFive LLC 1095 W Rio Salado Parkway Tempe, Arizona 85281, United States ABSTRACT Precession Electron Diffraction technique (PED) has been key to obtain reliable orientation and phase maps at 1-3 nm resolution (in case of FEG-TEM) for a variety of materials (metals, alloys, oxides etc..).the technique is very similar to EBSD-SEM, but in our case is based on collection of several PED patterns on an crystalline area and template matching with theoretically generated templates. TEM orientation imaging can be applied for in-situ TEM strain applications where is important to analyze crystal / grain size textures at different deformation cycles. PED has also been recently successfully applied to obtain strain mapping analysis of several semiconductor materials at 1-4 nm resolution (in case of FEG-TEM, sensitivity 0.02%), based on comparison of NBD patterns from strained /reference un-strained areas. The technique is very easy to use at any TEM and provides very fast and accurate data (same order of magnitude as dark field holography) without any need to index diffraction patterns. Free transnational access to the most advanced TEM equipment and skilled operators for HR(S)TEM, EELS, EDX, Tomography, Holography and various in-situ state-of-the-art experiments 2 SME partcipate CEOS NanoMEGAS

2 PRECESSION ELECTRON DIFFRACTION NEW structure analysis technique for TEM > 150 articles in 8 years > 80 installations world-wide in TEM

3 PRECESSION DIFFRACTION Chris Own, PhD Dissertation, 2004 Scan Scan lens Specimen De-scan De-scan lens Nonprecessed (Diffracted amplitudes) THE UNIVERSITY OF TEXAS AT AUSTIN Courtesy Northwestern Univ USA (ref. C.S.Own, L.Marks) Precessed Conventional Precession Diffraction Pattern Texture materials characterization at nm scale from 50 nm EBSD-SEM to 1 nm EBSD -like TEM 10 nm

4 ASTAR (Orientation and phase imaging in TEM) NO precession precession Using precession diffraction the number of ED spots observed increases ( almost double ) ; correlation index map becomes much more reliable when compared with templates Orientation map Scanning the TEM beam in precession mode Step size 0.1 nm -100 nm Dedicated CCD with > 100 frames /sec Typical area 5 x 5 microns Scanning times (typical) 5-10 min Procedure : beam is scanned over the sample ( eg. 10 µ x 10 µ ) spot electron diffraction patterns are collected ( NOT sensitive to stress/ strain or surface sample preparation like in EBSD-SEM ) Beam scanning performed by spinning star unit / no STEM need Thousands of experimental spot ED patterns are acquired by a very fast optical CCD camera attached to TEM screen ( 180 patterns/sec ) Slow scan CCD can also be used ( but slow : 5-10 patterns/sec ) Thousands of theoretical ED patterns are generated ( templates ) from.cif files or commercial databases for all known phases in a sample Template matching is used ( by cross-correlation of all experimental ED patterns with all templates ) to generate most probable orientation of every scanned position in the sample.

5 ASTAR : diffraction pattern adquisition 1 µm Example :Severely deformed 7075 Aluminium Alloy Any TEM FEG/LaB6 may work with ASTAR TEM orientation imaging technique ΤΕΜ$ Control D.A. Board Computer Beam Control Camera Frame Grabber Image Processing Phase /orientation maps generation (off-line) Capture of ED patterns by ultrafast (> 180 frames/sec) dedicated CCD camera Beam scanning Dedicated precession unit «Spinning Star» -DigiSTAR ASTAR : Automatic Crystal Orientation and phase mapping hardware /software package for TEM

6 DiffGen : Template generator Features: Any crystallographic structure Laue class adapted to the space group Structure generator (space group, structure factor equ.) Crystallographic orientation identification Pre-calculated templates Template generation of all possible simulated orientations (every1º) within stereographic triangle for given crystal lattice(s) and symmetry m Q(i) ~ P(x j,y j ) T i (x j,y j ) j=1 Correlation index Acquired pattern Degree of matching between experimental patterns and simulated templates is given by a correlation index ; highest value corresponds to the adequate orientation/phase Stereographic projection 1-11 (example,cubic)2000 ~ simulated patterns

7 TEM orientation imaging Pattern matching by image cross- correlation Corrected intensity profile Measured intensity profile Template Template Measured intensity profile Correlation index Image treatment Cross-correlation comparison of all acquired ED patterns with all simulated templates to deduce correct pattern index; degree of matching between experimental patterns and simulated templates is given by a correlation index where highest value corresponds to the adequate orientation/phase. Identification example : nanocrystalline Cu Diffraction pattern ( copper ( nanocrystalline cubic correlation index = 585 Correlation index map For a given ED pattern, the correlation index map is calculated for all possible template orientations and plotted on a map that represents a portion of the stereographic projection (reduced to a double standard triangle). That resulting map reveals the most probable orientation for every experimental spot ED pattern ( in this case ED pattern is found to be close to 110 ZA orientation )

8 ASTAR : ultra-fast TEM orientation map Sample : severely deformed copper 250 x 200 pixel data adquisition 5 min Typical software data analysis time ( for cubic ) 5-15 min ( hexagonal, tetragonal ) Orientation map x 3-4 more time NBD step 20 nm TEM orientation imaging techniques TEM nm orientation mapping TEM nm phase mapping orientation /phase maps with precession

9 Examples of TEM orientation maps Microstructure of a 200 nm thick Al film deformed in tension. (courtesy of S. Godet, Université libre de Bruxelles, Brussels, Belgium) Collected on a Philips CM20 LaB6 Grain growth can be observed in the necking area 8 nm resolution Power of the TEM orientation imaging technique 10 nm ASTAR :Orientation analysis from Pt ~100 particles ~6 nm in size 1 nm resolution for orientation map Data courtesy Prof. P.Ferreira, J.Ganesh Univ Texas at Austin USA JEOL 2010 FEG THE UNIVERSITY OF TEXAS AT AUSTIN

10 Phase identification Al TiN multilayers Credits: D. Bhattacharyya, LANL, Los Alamos NM Data acquired at Deakin Univ. JEOL 2100 FEG Correlation Index (spot size and step size: 0.5 nm) Phases Al TiN Two cubic phases with lattice parameters 4% apart Orientation HAADF-STEM image (D. Bhattacharyya et al, Acta Mater. 59 (2011) Appl. Phys. Lett. 96, ) 1 nm TiN layer Orientation + Correlation Index TEM orientation imaging applications TEM nm orientation mapping TEM nm phase mapping orientation /phase maps with precession

11 TEM orientation imaging Performance comparison LaB6-FEG microscope example Libra Libra 200 FE Orthorhombique Cubic ASTAR - Jeol 2100F : Titanium alloy orientation map VBF X Y Z (courtesy Prof. Dong, Deakin University) TEM bright field image

12 TEM orientation imaging: Phase maps for nanoparticles example : TWO POSSIBLE PHASES Sample : Replica sample extracted from 430 stainless steel contain lot of precipitates NOT possible to distinguish between them from size M23C6 carbides cubic fcc a = A Cr2N nitrides hexagonal a = 4.83, c = 4.51 A carbides TEM nitrides ASTAR crystal phase map, step 22 nm TEM orientation imaging - Thin films analysis W on Si and Encapsulated with SiO2 200 nm Bright Field TEM image. Circular area indicated in red approximately depicts the area mapped for orientation analysis Orientation Map of the selected area on the bright field TEM image Sample: 40 nm thick W Film sputter deposited on Si and encapsulated with 20 nm of amorphous SiO2 followed by annealing :Data courtesy Prof. C.Barmak Carneggie Mellon University USA

13 TEM orientation imaging VBF index reliability VBF index reliability ASTAR (EBSD -TEM) orientation maps : Nanotwins in Cu CBD mode Jeol 3010 microscope TEMdpa : Virtual Bright Field on-line construction Orientation map Bright field

14 ASTAR : Reliability Stereographic projection Templates for copper Superimposed diffraction patterns at a grain bounday Q 2 Q1 Q 1 > Q 2 R = 100 (1- Q 2 /Q 1 ) Reliability Deconvolution of superimposed Diffraction patterns Reliability index (%) Reliability index (%) Reliability Misorientation Reliability Misorientation Position (nm) Position (nm) Misorientation ( ) 2 µm Grain 1 Grain 2

15 TEM orientation imaging applications TEM nm orientation mapping TEM nm phase mapping orientation /phase maps with precession 0º 0.5º 1º As the precession angle increases from 0º to 3º, the diffraction pattern goes to higher resolution (i.e. more diffraction spots are seen). 2º 3º

16 Precession adds a value to TEM orientation imaging : ED patterns acquired with precession contain less dynamical effects, more spots and when compared with templates give much better correlation-reability than ED patterns without precession Correlation index for many reflections highly increases even at small precession angles ( eg 0.2 º -0.5º ) Orientation maps for several materials are of much better quality with precession Phase maps for several materials are of much better quality with precession ( much less artifacts or ambiguities ) In orientation-phase maps 180º ambiguity for cubic crystals can be solved using precession ASTAR : combine scanning with precession NO precession precession Using precession diffraction the number of ED spots observed increases ( almost double ) ; correlation index map becomes much more reliable when compared with templates Orientation map In this example (right) a metal particle gives wrong correlation index without precession due to presence of Kikuchi lines; after applying precession (right lower image), index gets correct value as ED quality improves and Kikuchi lines dissapear

17 TEM orientation maps with and without beam precession orientation map, NO precession beam scanning step 28 nm VBF In this example three different cubic mayenite crystals Ca12Al14O33 are analyzed with ASTAR ; orientation map generated without precession results in inconsistent index over areas that must have uniform orientation. On the contrary, orientation maps generated with small precession angle present true uniform orientation over individual grains orientation map precession angle 0.25º CONCLUSION Orientation maps are more precise with precession TEM orientation imaging : Phase maps with and without precession 3 existing phases: only possible to distinguish by precession Orientation map crystal phase map VBF When stacking faults cross themselves, they produce locally α martensite structure (a= 2.87 A) Austenitic matrix with γ fcc structure (a=3.58 A) Stacking faults with ε hexagonal structure (a=2.57 c= 4.08 A) NO precession precession 0.4º

18 Al2O3 sample ASTAR- Tecnai F20, no precession applied VBF ORZ Reliability ASTAR- Tecnai F20, 0.5 deg precession applied (courtesy M.Cantoni EPFL Lausanne, S.Lartigue Thiais Paris) Nanoparticle ( 50 nm ) phase identification cubic 8.32 A Fd3m Magnetite or maghemite?? Fe 3 O 4 P cubic 8.32 A γ-fe 2 O 3 ALL Nanoparticles REVEALED AS magnetite (RED ) Orientation map precession 0.3º PHASE map precession 0.3º

19 LiFePO 4 /FePO 4 : Samples LiFePO 4 /FePO 4 (LFP/FP) powder for lithium-ion batteries Par$cle(size:(30/200(nm( Understanding of the Li insertion/extraction mechanisms 1 µm! Are(the(par$cles(fully(lithiated(/delithiated(or(mixed(?(! Three%samples:%! Single%phase%LiFePO 4 %(LFP)%sample%! Single%phase%FePO 4 %(FP)%sample% LFP FP " Phase identification Valida$on(of(the(phase(recogni$on(method(! Par7ally%charged%sample%(77%%FePO 4,%23%%FePO 4 %@%X@ray)% Phase(recogni$on( Courtesy G.Brunneti et al LiFePO 4 /FePO 4 : Structures Quadratic structure a([nm]( b([nm]( c([nm]( α,(β,(γ([ ]( LiFePO 4( 1.033% 0.601% 0.469% 90% FePO 4 ( 0.981% 0.579% 0.478% 90% Maximum difference: 5% Kinematical simulated diffraction patterns along [100] LiFePO 4 No precession FePO 4 LiFePO 4 + FePO 4 Precession (0.96 ) LiFePO 4 FePO 4 Necessity to work with PED Association of Precession Electron Diffraction and NanoBeam Electron Diffraction for phase mapping Courtesy G.Brunneti et al

20 Validation on pure FePO 4 sample Acquisition of series of diffraction patterns! Phase%iden7fica7on%considering%%two%libraries%(LFP%and%FP%libraries)% %%! #(The(best(correla$on(index(Q(determines(the(phase.(((! Example(of(phase(iden$fica$on((Pure(FP(sample)( Precession%angle:%0.96 % Q:%correla7on%index% LiFePO 4! Phase(mapping:( Q=554 Q=658 LiFePO 4 FePO 4 FePO 4 FePO 4 Phase%maps% Q>200% R>5% 100 nm Courtesy G.Brunneti et al Partially charged sample Six phase maps (Spot size 2.7 nm, 500x500 nm², step size 5 nm) The(par$cles(are(either(fully( lithiated(or(fully((delithiated( 100 nm 100 nm " Confirma$on(of(domino(cascade(model 1 ( for(li(inser$on/extrac$on(mechanisms% Checked%by%HRTEM,%EFTEM/EELS% %published%at%%chemistry%of%materials% 100 nm 100 nm 1 C. Delmas et al., Nature Mater. 7 (2008) 665. LiFePO 4 FePO 4 Phase%map,%Q>200,%R>5% Courtesy G.Brunneti et al

21 TEM orientation imaging on organic structures Organic matter : [Fe(Htrz) 2 (trz)].bf 4 Jeol 3010, 100fps, spot 25nm, condenseur 2 Credits:Sebastien Pillet, France Strain in semiconductor devices Strain measurement is critical to monitor designed and unintended strain distributions Desired: Strain introduced in Si to enhance electron mobility in the channel Unintended: Stress concentration in devices leads to failure Strain measurement applications in semiconductor and materials science require high spatial resolution and high precision.

22 Strained Silicon Transistors pmosfet Requirements Desired spatial resolution ~ 1 nm Strain sensitivity << 0.1% Highly automated Thompson et al., IEEE Trans. On Electron Devices, VOL. 51, NO. 11, 2004 Electron Diffraction and Strain Measurement SEM EBSD Not enough spatial resolution CBED Needs the sample to be relatively thick (>150 nm) Sample needs to be oriented away from a low index axis. Very sensitive to strain relaxation Dark field holography Experimental difficulties of off-axis holography - biprism, sample alignment, etc.; Requires strain and unstrained regions close by. High resolution imaging Limited field of view Stringent requirements on specimen quality

23 Conventional Nano-Beam Diffraction Strain determined by measuring shift in spot positions Advantage High spatial resolution - better than 1 nm Disadvantage Dynamical diffraction D Cooper et al., Journal of Physics: Conference Series (2011). Dynamical Diffraction and Precession Position 1 20 nm from Position 1 Single crystal Si FIB prepared sample

24 Precession Electron Diffraction Makes TEM diffraction patterns easier to interpret Can compare to kinematical patterns Not very sensitive to thickness Can automate analysis Get more diffraction spots Higher precision measurements Topspin Data Acquistion Setup

25 Strain Measurement Analysis Diffraction patterns from strained region are matched against a reference pattern. All pixels utilized, not just selected spot centers Input Non- Linear Optimization Distortion matrix In plane strain and rotation tensor Patent Pending TopSPIN PED Scanned Acquisition STEM image acquisition Virtual BF / DF via Optical CCD BF/DF via STEM detectors TEM (if available on TEM) Suite of scan modes (spot, line, area, ) Suite of image processing features

26 Results: Blanket Si-Si 1-x Ge x SiGe y A A Si x 20 nm B 20 nm B Step size: 3 nm Precession angle 0.4 A 0.85% A B B Si/SiGe multilayer: Average strain : 1.2% Precision: 0.02% (from longitudinal profile) B Sample Thickness: 37.7 nm Ge composition: 14.2% Microscopy: 200 kv Zeiss Libra PED Strain Measurement Engineered strain in a PMOS device nm nm Strain maps from the Si region of a pmos device Microscopy: 200 kv Zeiss Libra x and y-directions aligned with [220] and [002] directions in Si. Localized biaxial tensile strain close to contact edges. max strain observed (x-direction ) about ~1.5%

27 PED Strain Measurement GaN/AlGaN HEMT Measure interface strain which can lead to delamination failure For such devices, tensile strain is expected to be asymmetric on different sides of the gate, and this is seen here. Compressive strain perpendicular to the interface (x-direction ) of ~1% is seen in the AlGaN region 500 nm Microscopy: 200 kv Zeiss Libra 500 nm PED Strain Measurement Typical acquisition time: 5-10 min (150x150) Time per pixel~ ms Analysis time: 5-10 min Strain sensitivity (1 precession): 0.02% RMS deviation calculated from unstrained Si region

28 REFERENCES Botta W. J., Jorge Jr. A.M., Veron M., Rauch E. F., Ferrie E., Yavari A. R., Huot J., Leiva D. R. H-sorption properties and structural evolution of Mg processed by severe plastic deformation. Journal of Alloys and Compounds (2013) In Press ( /j.jallcom ) Idell Y., Facco G., Kulovits A., Shankar M. R., Wiezorek J. M. K. Strengthening of austenitic stainless steel by formation of nanocrystalline c-phase through severe plastic deformation during two-dimensional linear plane-strain machiningscripta Materialia 68 (2013) ( /j.scriptamat ) Galand R., Brunetti G., Arnaud L., Rouvière J.-L., Clément L., Waltz P., Wouters Y. Microstructural void environment characterization by electron imaging in 45 nm technology node to link electromigration and copper microstructure. Microelectronic Engineering 106 (2013) ( / j.mee ) Martinez M., Legros M., Signamarcheix T., Bally L., Verrun S., Di Cioccio L., Deguet C. Mechanisms of copper direct bonding observed by in-situ and quantitative transmission electron microscopy. Thin Solid Films 530 (2013) ( /j.tsf ) Ning J.-l., Courtois-Manara E., Kurmanaeva L., Ganeev A. V., Valiev R. Z., Kübel C., Y. Ivanisenko. Tensile properties and work hardening behaviors of ultrafine grained carbon steel and pure iron processed by warm high pressure torsion. Materials Science and Engineering A (2013) In Press ( /j.msea ) Amin-Ahmadi B., Idrissi H., Galceran M., Colla M.S., Raskin J.P., Pardoen T., Godet S., Schryvers D. Effect of deposition rate on the microstructure of electron beam evaporated nanocrystalline palladium thin films. Thin Solid Films 539 (2013) ( /j.tsf ) Galceran M., Albou A., Renard K., Coulombier M., Jacques P.J., Godet S. Automatic Crystallographic Characterization in a Transmission Electron Microscope: Applications to Twinning Induced Plasticity Steels and Al Thin Films. Microscopy and Microanalysis 19 (2013) ( / S )