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TEM
- 1. Transmission electron microscopy By Sri. M.Ragu Assistant Professor Department of Chemistry Vivekananda College Madurai, Tamil Nadu
- 2. AdvancedMaterialsCharacterization Workshop Transmission Electron Microscopy J.G. Wen, C.H. Lei, M. Marshall W. Swiech, J. Mabon, I. Petrov Supportedby the U.S. Departmentof Energy under grantsDEFG02-07-ER46453and DEFG02-07-ER46471 © 2008 University of Illinois Board of Trustees. All rightsreserved. Outline 1. Introduction to TEM 2. Basic Concepts 3. Basic TEM techniques Diffraction contrast imaging High-resolution TEM imaging Diffraction 4. Scanning-TEM techniques 5. Spectroscopy X-ray Energy Dispersive Spectroscopy Electron Energy-Loss Spectroscopy 6. Advanced TEM techniques Spectrum imaging Energy-filtered TEM 7. Other TEM techniques Low-dose; in-situ; etc. 8. Summary
- 3. Why Use Transmission Electron Microscope? AN is 0.95 with air up to 1.5 with oil Transmission Electron Microscope (TEM) Optical Microscope Resolution limit: 200 nm 100k eV electrons : 0.037 Å Sample thickness requirement: Thinner than 500 nm High quality image: <20 nm Resolution record by TEM 0.63 Å GaN [211] Thin foil, thin edge, or nanoparticles < 500nm =0.66(Cs3)1/4 Basic Structure of a TEM Gun and Illumination partGun: LaB6, FEG 100, 200,300keV Mode selection and Magnification part View screen TEM Sample Objective lens part
- 4. How does a TEM get Image and Diffraction? TEM Conjugated planes Sample Objective Lens Back Focal Plane Incident Electrons < 500nm First Image Plane Back Focal Plane View Screen First Image Plane u v u v f Object Image 1_+ 1_= _1 Structural info Morphology Specimen magnetic prism Inelastically scattered electrons Incoherent beam Diffracted beam Coherent beam Transmitted beam Basic Concepts High energy electron – sample interaction Incident high-kV beam 1. Transmitted electron (beam) 2. Diffracted electrons (beams) Bragg Diffraction 3. Coherent beams 4. Incoherent beams 5. Elastically scattered electrons 6. Inelastically scattered electrons TEM X-rays
- 5. d Bragg’s Law 2 d sin = n Zero-order Laue Zone (ZOLZ) First-order Laue Zone (FOLZ) …. High-order Laue Zone (HOLZ) Diffraction Electron Diffraction I SOLZ FOLZ ZOLZ Wavelength X-ray: about 1A Electrons: 0.037A is small, Ewald sphere (1/) is almost flat EwaldSphere 002 022 50 nm Polycrystal Lattice parameter, space group, orientation relationship Diffraction Electron Diffraction II Diffraction patterns from single grain and multiple grains Tilting sample to obtain 3-D structure of a crystal To identify new phases, TEM has advantages: 1) Small amount of materials 2) No need to be single phases 3) determining composition by EDS or EELSAmorphous
- 6. Major Imaging Contrast Mechanisms: 1. Mass-thickness contrast 2. Diffraction contrast 3. Phase contrast 4. Z-contrast Imaging Major Imaging Techniques 1) Imaging techniques in TEM mode a) Bright-Field TEM (Diff. contrast) b) Dark-Field TEM (Diff. contrast) Weak-beam imaging hollow-cone dark-field imaging a) Lattice image (Phase) b) High-resolution Electron Microscopy (Phase) Simulation and interpretation 2) Imaging techniques in scanning transmission electron microscopic (STEM) mode 1) Z-contrast imaging (Dark-field) 2) Bright-field STEM imaging 3) High-resolution Z-contrast imaging (Bright- & Dark-field) 3) Spectrum imaging 1) Energy-filtered TEM (TEM mode) 2) EELS mapping (STEM mode) 3) EDS mapping (STEM mode) Mass-thickness contrast Diffraction Contrast Image Kikuchi Map TEM Imaging Techniques I. Diffraction Contrast Image: Contrast related to crystal orientation [111] [110] [112] [001] Application: Morphology, defects, grain boundary, strain field, precipitates Two-beam condition [001] Many-beam condition Transmitted beam Diffracted beam
- 7. ObjectiveLens Aperture Back Focal Plane DiffractionPattern First ImagePlane Bright-field Image Dark-field Image Sample Sample T D Diffraction ContrastImage TEM Imaging Techniques II. Diffraction Contrast Image: Bright-field & Dark-field Imaging Two-beam condition Bright-field Dark-field Bright-field thickness B Increasing S S=0 B S=0 Increasing S S<0 t /g g Extinction distance 0 g Excitation error S = g Thickness fringes Bending contour To distinguish them from intrinsic defects inside sample: Tilting sample or beamslightly dz g g Sd0 = i exp{2isz} Diffraction ContrastImage TEM Imaging Techniques III. Thickness fringes and bending contour Electron Wave B Howie-Whelan equation S>0 S>0 s -g 0 g I
- 8. Dislocation loop Diffraction contrast images of typical defects Dislocations Stacking faults dz g g d0 = i exp{2i(sz+g.R)} Howie-Whelan equation g 1 2 3 3-Each staking fault changes phase 2 Sample Diffraction ContrastImage TEM Imaging Techniques II. Diffraction Contrast Image Two-beam condition for defects Dislocations Use g.b = 0 to determine Burgers vector b Stacking faults Phase = 2 g • R Diffraction ContrastImage Weak-beam Dark-field imaging High-resolution dark-field imaging Dislocations can be imaged as 1.5 nm narrowlinesBright-field Weak-beam C.H. Lei g g Planes do not satisfy Possible planes satisfy Bragg diffraction Bragg diffraction S Weak-beam means Large excitationerror Exact Bragg condition “Near Bragg Condition” “Away from Bragg Condition” Taken by I. Petrov 1g 2g 3g Experimental weak-beam
- 9. Lattice imaging Two-beam condition Phase Contrast Image C.H. LeiM. Marshall Many-beam condition [001] Phase Contrast Image Lattice imaging Delocalization effect from a field-emission gun (FEG) From a LaB6 Gun Field-Emission Gun Lattice image of film on substrates
- 10. Weak-phase-object approximation (WPOA) srsch = 0.66 C 4 4 1 Scherzer Defocus: Positive phase contrast “black atoms” 2 Scherzer Defocus: ("2nd Passband" defocus). Contrast Transfer Function is positive Negative phase contrast ("white atoms") fsch fsch Phase Contrast Image High-resolution Electron Microscopy (HREM) Simulation of images Software: Web-EMAPS (UIUC) MacTempas f(x,y) = exp(iVt(x,y)) ~1 + i Vt(x,y) Vt(x,y): projected potential Indirect imaging Depends on defocus Scherzerdefocus 1 fsch = - 1.2(Cs)2 Resolution limit 1 3 J.G. WenContrast transfer function Selected-area electron diffraction (SAD) Example of SAD and dark-field imaging Selected-area aperture High-contrast aperture Diffraction Major Diffraction Techniques 1) Selected-area Diffraction 2) Nanobeam Diffraction 3) Convergent-beam electron diffraction Objective aperture SAD aperture A. Ehiasrian, J.G. Wen, I. Petrov
- 11. Diffraction Electron Nanodiffraction 5 m condenser aperture 30 nm M. Gao, J.M. Zuo, R.D. Twesten, I. Petrov, L.A. Nagahara & R. Zhang, Appl. Phys. Lett. 82, 2703 (2003) J.M. Zuo, I. Vartanyants, M. Gao, R. Zhang and L.A. Nagahara, Science, 300, 1419 (2003) This technique was developed by CMM Back FocalPlane Sample Sample Large-angle bright-field CBED Bright-disk Dark-disk Whole-pattern 4. Defects 5. Chemical bonding SAD CBED 1. Point and space group 2. Lattice parameter (3-D) strain field 3. Thickness Diffraction Convergent-beam electron diffraction (CBED) Parallel beam Convergent-beam
- 12. Diffraction Convergent-beam electron diffraction Quantitative Analysis of Local Strain Relaxation a b c d e f g h i CoSi2 C. W. Lim, C.-S. Shin, D. Gall, M. Sardela, R. D. Twesten, J. M. Zuo, I. Petrov and J. E. Greene Use High-order Laue zone (HOLZ) lines to measure strain field secondary electrons <50 eV Auger electrons backscattered electrons characteristic& Bremsstrahlung x-rays 1 m Scanning electron microscopy (SEM) 1O primary e-beam 0.5-30 keV Scanning transmission electron microscopy (STEM) primary e-beam 100-300 keV characteristic & Bremsstrahlung x-rays Probe size 0.18 nm SEM vs STEM Thickness <100 nm STEM “Coherent” Scattering (i.e. Interference) “Incoherent” Scattering i.e. Rutherford Dark-field Detector Bright-field
- 13. 5 nm 5 nm ADF-STEM Ir nanoparticles TEM 10nm Z-contrast image TEM vs STEM Ge quantum dots on Si substrate 1. STEM imaging gives better contrast 2. STEM images show Z- contrast STEM L. LongJ.G. Wen Annular dark-field (ADF) detector I Z2 Z-contrast imaging Z HRTEM vs STEM STEM 3 3 3BaTiO /SrTiO /CaTiO superlattice 1. Contrast • High-resolution TEM (HRTEM) image is a phase contrast image (indirect image). The contrast depends on defocus. • STEM image is a direct atomic column image (average Z-contrast in the column). From Pennycook’s group J.G. Wen 2. DelocalizationEffect • High-resolution TEM image from FEG has delocalization effect. • STEM image has no such an effect.
- 14. Spatial resolution ~1 nm A r eaMapping A B 2-D mapping HAADF voids Au Ti Mo Si Al Ga Liang Wang Au Ti Mo B Line scan Spectroscopy X-ray Energy-Dispersive Spectroscopy (EDS) 1) TEM mode spot, area 2) STEM mode spot, line-scan and 2-D mapping A A. Ehiasrian, I. Petrov Ti0.85Nb0.15 metal ion etch Creates a mixed amorphised surface layer ~ 6 nm Electron Energy-loss Spectroscopy (EELS) ZLP Low-loss Spectroscopy ZLP Low-loss t = ln( ℓ ) I I0 I0 Iℓ Mean free path Post-column In-column EELS spectrum: 1. Zero-loss Peak (ZLP) 2. Low-loss spectrum (<50eV) Interacted with weakly bound outer-shell electrons Plasmon peaks Inter- & Intra-Band transition Application: Thickness measurement Elemental mapping
- 15. Low-loss Ti O Mn La Edges 1. Plasmon imaging 2. Edge imaging e M 1. ZLP imaging 2. Plasmon imaging 3. Edge imaging TEM mod Diamond Nanoparticle bonding Amorphous carbon bonding Edge Peaks in EELS Spectroscopy ZLP Low-loss Ti O Mn La x100 Edge peak position 3. High-loss spectrum Interacted with tightly bound inn-shell electrons Edge peaks Application: Elements identification Chemistry Edge peak shape J.G. Wen Spectrum imaging Energy-filtered TE TEM mode ZLP Image atE1 Image atE2 Image atE3 Image at En E x y Energy-filtered TEM •Fill in data cube by taking one image at each energy STEM mode •Fill in data cube by taking one spectrum at each location S Spectrum imaging
- 16. Low-loss Spectrum imaging Energy-Filtered TEM (EFTEM) EFTEM - Zero-Loss Peak imaging Only elastic electrons contribute to image – remove the “inelastic fog” 1. Improve contrast (especially good for medium thick samples) 2. Z<12, the inelastic cross-section is larger than elastic cross-section ZLP A B A B WAl Spectrum imaging EFTEM – Plasmon Peak imaging Spectrum image (20 images) Al mapping image W mapping image J.G. Wen 30 nm
- 17. Three-window method Jump ratio EFTEM – Edge Peak imaging Image Ti SiTi EELS spectrum Spectrum imaging J.G. Wen convergence angle ~ 10mrad scan coils incident probe probe size ~ 0.2 nm specimen Z-contrast image HAADF detector magnetic prism Spectrum imaging STEM + EELS Spectroscopy LaMnO3 SrTiO3 LaMnO3 SrTiO3 Z-contrast image Ti O Mn La EELS spectrum
- 18. Spectrum imaging STEM + EELS Spectroscopy Z-contrast image shows where columns of atoms are and EELS spectrum identify chemical components Electronic structure changes are observed in the fine structure of O K-edge Electron Energy-Loss Spectrum n iot di re c S c a n Z-contrast Image E O K edge La M4,5 O KMnL2, 3 Ti L2,3 La M4,5 2nm STO SMO STO 3LMO STO 2LMO STO 2LMO STO LMO STO STMO STO STMO J.G. Wen, Amish, J.M. Zuo Ti O Mn La New TEM: Cs-corrected Analytical STEM/TEM Sound Isolation Low Airflow Vibrationdecoupling CEOS Corrector Ω-Filter Remote operation With this setup we can achieve a probe-size of <0.1nm JEOL 2010F, Cs = 1.0 mm JEOL 2200FS, Cs < 5 m Cs-corrected Ronchigram
- 19. Small probe size for high-resolution scanning transmission electron microscopic images 1.36Å Si [110] Zone Axis JEOL 2010F, Cs = 1 mm (2nd smallestProbe) JEOL 2200FS with probe forming Cs Corrector La atom Mn atom La atom Sr atom Ti atom Sr atom 2 x 2 LaMnO3-SrTiO3 superlattice Dec. 2006 June 2007 Dec. 2007 Thick specimen Same specimen Thin Specimen
- 20. Å LaMnO3 SrMnO3 SrTiO3 Substrate R S interfacial ferromagnetic moment measured at 10 Kelvin is enhanced in LaMnO3 at the sharp LaMnO3-SrMnO3 interface and reduced at the rough SrMnO3-LaMnO3 interface. Sharp Interface RoughInterface Sharp Interface RoughInterface High Mag. Image Epitaxial Oxide Films Grown on SrTiO3 Polarized neutron scattering shows STEM Image of Superlattice LaMnO3 SrMnO3 Cd Se Cd Se CdSe nanoparticles View along [110] zone axis Polarity of CdSe 100 100
- 21. Zn Te Zn Te Cd Se Cd Se ZnTe CdSe Hetero-structure nanoparticle Stacking fault Grain boundary 1 nm Se Cd Quantitative STEM Imaging
- 22. 1 nm 3 11 9 10 6 Quantitative STEM Imaging Projectedpotential 3 0 0 2 5 0 2 0 0 1 5 0 1 0 0 5 0 0 x10^4 0 50 10 0 15 0 20 0 25 0 Monometallic Pt The intensity at each atomic column is proportional to numbers of atoms No defects in Pt nanoparticles Monometallic Pd Pd nanoparticles contain many defects such as twin boundaries
- 23. x10^4 200 150 100 50 0 0 50 100 150 200 250 Bimetallic Pd(core)-Pt(shell) Pd (core) – Pt (shell) structure 1 Core-shell structure of FePd nanoparticles Core: Ordered Fe/Pd structure Shell: non-ordered structure Twin in the nanoparticle Amorphous nanoparticle 1 nm Pd columns are shown as brighter spots in the core
- 24. Both TEM & STEM STEM better contrast Ultra thin carbon grid STEM better contrast Ultra thin carbon grid Only STEM Study Nanoparticles by TEM Size distribution: STEM will give better contrast > 5nm Bi-nanoparticles Au-nanoparticles 2 nm < Size < 5nm < 2 nm Composition study: EDS counts are low 2200FS EDS system detector area 2 times bigger beam 4 times brighter 200 nm 200 nm Minimum-dose in STEM mode HAADF-STEMimage Long exposure time Minimum-dose in TEM mode Search in low magnification Focus at another area Photo with minimum dose MDS + tomography will be available on 2100 Cryo-TEM soon +/- 80 degree tilt Special TEM technique Minimum-Dose for beam sensitive samples BF-STEM image Short exposuretime Z-contrast tilt-series J.G. Wen L. Menard, J.G. Wen
- 25. In-situ capabilities 1. Heating (hot stage 1000°C) 2. Cooling (liquid N2) 3. Tensile-stage 4. MEMS tensile stage 5. Universal MEMS holder 6. Wet-cell 7. Nanomanipulator 8. Environmental holder 9. Applied voltage to sample 10.Cryo transfer holder In-situ holders MEMS straining stage nanomanipulation universal MEMS holder In-situ N. Schmit liquid cell All developed at CMM Water front 30 nm CNT in water J.G. Wen List of TEMs and functions 1. CM12 (120 KeV) (S)TEM • TEM, BF, DF, CBED (good), EDS, large tilt angle, etc 2. 2010 LaB6 TEM • TEM, low dose, NBD, good for HREM, video function 3. 2100 LaB6 (Cryo-TEM) • TEM, Low dose, special cryo- shielding; high-tilt angle (+/-80) (using special retainer). 4. 2010F (S)TEM • TEM, BF, DF, NBD, CBED, EDS, STEM, EELS, EFTEM, Spectrum imaging, etc. 5. HB501 STEM • STEM, BF, DF, EDS, EELS (cold FEG), ultra-high vacuum 6. JEOL 2200FS (S)TEM • Cs-corrected probe, TEM, BF, DF, NBD, CBED, EDS, STEM, EELS, EFTEM, Spectrum imaging, etc. CM 12 2010LaB6 2100 Cryo 2010F HB501 2200FS