1. Signature (unit, name, etc.) Transmissions electron microscopy Basic principles Sample preparation Imaging aberrations (Spherical, Chromatic, Astigmatism) contrast (Mass-thickness, Diffraction, Phase)

2. Signature (unit, name, etc.) Project report Report due Monday May 11, 14.00 Project presentation and oral ”exam” Friday May 15 Possible report outline: –Introduction about the material and motivation –Experimental methods used –Results and discussion –Conlusions –References

3. Signature (unit, name, etc.) Basic principles, first TEM Electrons are deflected by both electrostatic and magnetic fields Force from an electrostatic field F= -e E Force from a magnetic field F= -e (v x B) Wave length of electrons:200kV: λ= 0.00251 nm (v/c= 0.6953, m/m 0 = 1.3914) a)The first electron microscope built by Knoll and Ruska in 1933, b) The first commercial electron microscope built by Siemens in 1939. Ernst Ruska: Nobel Prize in physics 1986

4. Signature (unit, name, etc.) Basic TEM Electron gun Vacuum requirements: - Avoid scattering from residual gas in the column. - Thermal and chemical stability of the gun during operation. - Reduce beam-induced contamination of the sample. LaB 6 : 10 -7 torr FEG: 10 -10 torr Cold trap Electron source: ●Tungsten, W ● LaB 6 ● FEG Sample position

5. Signature (unit, name, etc.) The lenses in a TEM Sample Filament Anode 1. and 2. condenser lenses Objective lens Intermediate lenses Projector lens Compared to the lenses in an optical microscope they are very poor! The point resolution in a TEM is limited by the aberrations of the lenses. The diffraction limit on resolution is given by the Raleigh criterion: δ d =0.61λ/μsinα, μ=1, sinα~ α - Spherical - Chromatic - Astigmatism

6. Signature (unit, name, etc.) Spherical aberrations Spherical aberration coefficient d s = 0.5MC s α 3 M: magnification C s :Spherical aberration coefficient α: angular aperture/ angular deviation from optical axis 2000FX: C s = 2.3 mm 2010F: C s = 0.5 nm r1r1 r2r2 Disk of least confusion α r1r1 r2r2 α

7. Signature (unit, name, etc.) Chromatic aberration v v - Δ v d c = C c α ((ΔU/U) 2 + (2ΔI/I) 2 + (ΔE/E) 2 ) 0.5 C c : Chromatic aberration coefficient α: angular divergence of the beam U: acceleration voltage I: Current in the windings of the objective lens E: Energy of the electrons 2000FX: C c = 2.2 mm 2010F: C c = 1.0 mm Chromatic aberration coefficient: Thermally emitted electrons: ΔE/E=kT/eU Force from a magnetic field: F= -e (v x B) Disk of least confusion

8. Signature (unit, name, etc.) Lens astigmatism Loss of axial asymmetry y-focus x-focus y x This astigmatism can not be prevented, but it can be corrected!

9. Signature (unit, name, etc.) Resolution limit YearResolution 1940s ~10nm 1950s ~0.5-2nm 1960s 0.3nm (transmission) ~15-20nm (scanning) 1970s 0.2nm (transmission) 7nm (standard scanning) 1980s 0.15nm (transmission) 5nm (scanning at 1kV) 1990s 0.1nm (transmission) 3nm (scanning at 1kV) 2000s <0.1 nm (Cs correctors) http://www.sfc.fr/Material/hrst.mit.edu/hrs/materials/public/ElecMicr.htm

10. Signature (unit, name, etc.) Technical data of different sources TungstenLaB 6 Cold FEG SchottkyHeated FEG Brightness (A/m2/sr) (0.3-2)10 9 10 11 -10 14 Temperature (K) 2500-30001400-20003001800 Work function (eV) 4.62.74.62.84.6 Source size (μm) 20-5010-20<0.01 Energy spread (eV) 3.01.50.30.80.5 H.B. Groen et al., Phil. Mag. A, 79, p 2083, 1999 http://dissertations.ub.rug.nl/FILES/faculties/science/1999/h.b.groen/c1.pdf

11. Signature (unit, name, etc.) Sample preparation for TEM Samples need to be ~100 nm thick. How? –Crushing –Cutting –saw, diamond pen, ultrasonic drill, FIB –Mechanical thinning Grinding, dimpling –Electrochemical thinning –Ion milling –Coating –Replica methods Plane view or cross section sample? Is your material brittle or ductile? Is it a conductor or insulator? Is it a multi layered material?

12. Signature (unit, name, etc.) TEM sample preparation: Thin films Top view Grind down/ dimple Cross section or Cut out a cylinder and glue it in a Cu-tube Grind down and glue on Cu-rings Cut a slice of the cylinder and grind it down / dimple Ion beam thinning Cut out cylinder Ion beam thinning Cut out slices Glue the interface of interest face to face together with support material Cut off excess material Focused Ion Beam (FIB)

13. Signature (unit, name, etc.) Imaging / microscopy 200 nm Si SiO 2 TiO 2 Pt BiFeO 3 Glue TEM - High resolution (HREM) - Bright field (BF) - Dark field (DF) - Shadow imaging (SAD+DF+BF) STEM - Z-contrast (HAADF) - Elemental mapping (EDS and EELS) GIF - Energy filtering Holography – Map magnetic domains – Map electrostatic potential – Enhance resolution

14. Signature (unit, name, etc.) Apertures Selected area aperture Condenser aperture Objective aperture

15. Signature (unit, name, etc.) Simplified ray diagram MENA3100 V08 Objective lense Diffraction plane (back focal plane) Image plane Sample Parallel incoming electron beam Si 1,1 nm 3,8 Å Objective aperture Selected area aperture

16. Signature (unit, name, etc.) Use of apertures Condenser aperture: Limits the number of electrons hitting the sample (reducing the intensity), Reducing the diameter of the discs in the convergent electron diffraction pattern. Selected area aperture: Allows only electrons going through an area on the sample that is limited by the SAD aperture to contribute to the diffraction pattern (SAD pattern). Objective aperture: Allows certain reflections to contribute to the image. Increases the contrast in the image. Bright field imaging (central beam, 000), Dark field imaging (one reflection, g), High resolution Images (several reflections from a zone axis).

17. Signature (unit, name, etc.) Objective aperture: Contrast enhancement All electrons contribute to the image. A small aperture allows only electrons in the central spot in the back focal plane to contribute to the image. Intensity: Thickness and density dependence Mass-thickness contrast Si Ag and Pb glue (light elements) hole 50 nm One grain seen along a low index zone axis. Diffraction contrast (Amplitude contrast)

18. Signature (unit, name, etc.) Diffraction contrast: Bright field (BF), dark field (DF) and weak-beam (WB) BF image Objective aperture DF imageWeak-beam Dissociation of pure screw dislocation In Ni 3 Al, Meng and Preston, J. Mater. Scicence, 35, p. 821-828, 2000.

19. Signature (unit, name, etc.) Bending contours BF image DF image Obj. aperture Obj. lens sample

20. Signature (unit, name, etc.) Thickness fringes, bright and dark field images Sample DF image BF image

21. Signature (unit, name, etc.) Phase contrast: HREM and Moiré fringes 2 nm http://www.mathematik.com/Moire/ A Moiré pattern is an interference pattern created, for example, when two grids are overlaid at an angle, or when they have slightly different mesh sizes (rotational and parallel Moire’ patterns). HREM image Long-Wei Yin et al., Materials Letters, 52, p.187-191 200-400 kV TEMs are most commonly used for HREM Interference pattern

22. Signature (unit, name, etc.) Moire’ fringe spacing Parallel Moire’ spacing d moire’ = 1 / IΔgI = 1 / Ig 1 -g 2 I = d 1 d 2 /Id 1 -d 2 I Rotational Moire’ spacing d moire’ = 1 / IΔgI = 1 / Ig 1 -g 2 I ~1/gβ = d/β Parallel and rotational Moire’ spacing d moire’ = d 1 d 2 /((d 1 -d 2 ) 2 + d 1 d 2 β 2 ) 0.5 β g1g1 g2g2 ΔgΔg g1g1 g2g2 ΔgΔg

23. Signature (unit, name, etc.) HREM of boundaries