EMALEMAL U of M The Transmission Electron Microscope: A Tool for Diffraction & Imaging in Materials Science & Engineering John Mansfield North Campus Electron Microbeam Analysis Laboratory University of Michigan 417 SRB, 2455 Hayward, Ann Arbor MI Phone: (734) FAX (734) URL: people/jfmjfm/jfmjfm.htmlEMALEMAL U of M

EMALEMAL John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan In a typical TEM a static beam of electrons at kV accelerating voltage illuminate a region of an electron transparent specimen (~10nm to ~500nm) which is immersed in the objective lens of the microscope. Transmitted and diffracted electrons are recombined by the objective lens to form a diffraction pattern in the back focal plane of that lens and a magnified image of the sample in its image plane. A number of intermediate lenses are used to project either the image or the diffraction pattern onto a fluorescent screen for observation. The screen is usually lifted and the image formed on photographic film for recording purposes. What is a TEM?

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan JEOL 2010F Electron gun Probe forming lenses - Cond. Specimen holder Magnifying lenses - Int. & Proj. Objective Lens HAADF Detector Viewing Chamber Camera Chamber STEM Detector &/or EELS XEDS Detector Basic features of an analytical electron microscope What is a TEM? Explanation of features.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Electron Beam Source W Filament - Current density ~10A/cm 2, probe size ~5.0nm LaB 6 - Current density ~10 3 A/cm 2, probe size ~1.5nm FEG - Current density ~10 5 A/cm 2, probe size ~<1.0nm

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Schematic of the Optics of a Transmission Electron Microscope

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan l Schematic Diagram of Crude Electron Lens. Remember from basic physics: a moving charge in a magnetic field experiences a force, the direction of which can be determined by Fleming ’ s Left Hand Rule. l Can use electrostatic lenses too, but magnetic are more common. l Although we draw ray diagrams and talk about electron beams as if they were like rays of light they cannot be focussed by glass lenses!

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Philips Tecnai F20 Modern TEMs JEOL 2010F JEOL 2000FX

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Resolution! For light From consideration of Rayleigh ’ s Criterion and simple diffraction theory it can be shown that: r=d/2=0.61 /  sin  where: is the wavelength of light.  is the refractive index of the medium through which the light is propagating.  is the semi-angle that the microscope aperture subtends at the specimen.  sin  is usually termed the numerical aperture or NA. Why Electrons?

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Resolution! For electrons In the expression for the resolution: r=d/2=0.61 /  sin   is effectively 1 no medium in electron lenses  is very small -> sin  ->  and so r~0.61  Compare light to electrons Green light200kV Electrons  ~ 400nm ~ nm sin  can be made large~1sin  ->  ~ 0.1 radians  ~ 1.7 (oil immersion)  ~ 1 (vacuum) r max ~ 150nm (0.15  m)r max ~ 0.02nm (1/10th the size of an atom!) UNREALISTIC! WHY? Why Electrons?

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Resolution limited by lens aberrations With out going into details, electron lenses are frequently likened to Coke bottle bottoms when compared with light optics! Actual resolution limit is ~ 0.1nm

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Imaging in the TEM l Two principal kinds: l Diffraction contrast imaging. Use either an non-diffracted or diffracted beam and remove all other beams from the image by the use of an objective aperture. l Phase contrast or high resolution imaging. Use all of the diffracted and non-diffracted beams (by using a large objective aperture or none at all) and add them back together, phase and intensity to form a phase contrast image

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Silicon zone axis pattern. Recorded with Gatan 673 wide-angle CCD TV camera Selected Area Diffraction

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan JEOL 2010F Electron gun Probe forming lenses - Cond. Specimen holder Magnifying lenses - Int. & Proj. Objective Lens Viewing Chamber Camera Chamber Basic features of an analytical electron microscope Intermediate Aperture Or Selected Area Aperture Selected Area Diffraction

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Selected Area Diffraction Selected area aperture inserted in image plane, not specimen plane. Minimum area limited by lens aberrations to ~1 µ m diameter.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Title Selected Area Electron Diffraction Pattern recorded from both BN film & Si substrate. Si 111 type Si 002 type Hex BN 0002 type -EMALEMAL U of M “ Normal ” transmission electron microscopy imaging forms an image from one of these spots (diffraction contrast imaging)

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Si Si3%Ge g= nm Cross sectionnal TEM image of a Si-3%Ge alloy grown on a silicon substrate. Alloy grown by CVD with a rotating substrate holder. The fringes visible in the alloy are due to compositional variations in the alloy layer. Example of Cross sectional TEM. Dislocations

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Defect Imaging In the TEM Optimal imaging of dislocations, faults and grain boundaries is performed by setting the sample just off a strong diffracting condition and allowing the lattice distortion around the defects to the bring them into the strong diffracting condition and hence appear dark.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan l Extensive dislocations between the matrix and this sample of M 23 X 6 in an austenitic 316 steel. l One set on the top surface and one on the bottom. l Feature on left is precipitate on a grain boundary. 0.3µm g=200 Matrix Precipitate Matrix

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Title Selected Area Electron Diffraction Pattern recorded from both BN film & Si substrate. Si 111 type Si 002 type Hex BN 0002 type -EMALEMAL U of M “ Normal ” transmission electron microscopy imaging forms an image from one of these spots (diffraction contrast imaging)

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Dark Field Micrograph of a Ni8Ge8Al alloy This micrograph was recorded near a zone axis with a 100 gamma prime spot. The particles are the gamma prime precipitates present in the austenitic matrix. g=100 90nm

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Title Selected Area Electron Diffraction Pattern recorded from both BN film & Si substrate. Si 111 type Si 002 type Hex BN 0002 type -EMALEMAL U of M Phase contrast transmission electron microscopy imaging (high resolution TEM) forms an image by recombining the intensities and phases of all of the spots.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Silicon HREM Structure Image JEOL 4000EX 1.75 Å resolution. 31nm This sample is a resolution test for the HREM. It is a single crystal of silicon with a thin film of amorphous silicon oxide on the surface. The lattice spacing is 0.192nm, however the amorphous disc in the optical diffractogram (insert) reveals that the true point to point resolution is better than 0.180nm.EMALEMAL U of M

EMALEMAL 2.0nm 0.67 nm 1 nm High resolution electron microscope image a grain boundary film in a silicon nitride (Si 3 N 4 )ceramic that has been sintered with the aid of alumina and yttria Al 2 O 3 and Y 2 O 3. Research by Xiaoqing Pan of MS&E. High resolution electron microscope image a grain boundary film in a silicon nitride (Si 3 N 4 )ceramic that has been sintered with the aid of alumina and yttria Al 2 O 3 and Y 2 O 3. Research by Xiaoqing Pan of MS&E.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Summary of Diffraction and Phase Contrast Imaging

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Why are there so many spots? The Ewald Sphere

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Why are there so many spots? The Ewald Sphere

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Lecture Outline l What is a TEM? - Explanation of features. l Gun, column, lenses, specimen, viewing chamber camera. l Example instruments - JEOL & Philips. l Imaging in the TEM, why use electrons? l Two principal ways of forming an image in the TEM. l Why are there so many spots? The Ewald Sphere. l Diffraction techniques in the TEM. l Examples.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Silicon zone axis pattern. Recorded with Gatan 673 wide-angle CCD TV camera

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Diffraction pattern from M23X6 in Austenite Matrix lattice is 1/3 the size of precipitate lattice

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Title M X zone 23 6 axis pattern. Recorded at 200kV with Gatan 673 wide-angle TV camera.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Cr ZAP Cr ZAP Convergent Beam Electron Diffraction (CBED) Pattern recorded at 120kV. The ring pattern and bright spot at the centre of the direct disc are characteristic of a near critical voltage. Pattern symmetry is 6mm (projection symmetry).

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan HOLZ lines Deficit in ZOLZ Excess in HOLZ

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Direct Disc Si ZAP Direct disc of a silicon zone axis pattern (ZAP). Pattern recorded at 200kV. Sample cooled to in a liquid nitrogen cold stage to reduce the thermal diffuse scattering and sharpen the higher order Laue zone (HOLZ) line detail.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan HOLZ Example NbSe 3 CBED Pattern with multiple HOLZ rings

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Electron Diffraction Uses l Use zone axes l Can measure spot spacings to get d spacings. l Can measure angles between spots to get interplanar angles. l Can use convergent beam mode to get crystal symmetry and space group. l Can measure the HOLZ spacing to get the interplanar spacing in he beam direction. l Can measure location and movement of HOLZ lines to measure strain and/or lattice parameter. l Convergent beam patterns can be used to measure sample thicknesses.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan CBED ZAPs from Si & SiGe Alloys Si Si3%Ge Si2%Ge CBED ZAPs from Si, Si2%Ge & Si3%Ge cross section samples. Centre of direct disc. Patterns recorded at 150kV, with a beam convergence of ~8mrad. Probe diameter ~30nm. Samples were held at liquid nitrogen temperature to reduce the thermal diffuse scattering. The orthorhombic distortion of the lattice is most obvious in the Si2%Ge sample.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan [011] Er 2 O 3 m mm 2mmm m Point Group Determination ZOLZWP BF Note the dark bar in this disc, it is known as a Gjonnes- Moodie line and is a feature of the space group of this phase.

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Certain ZAPs in alloy systems are so characteristic that they may be identified merely by comparing them to a standard "fingerprint". This phase, based on a chromium carbide, exists in a great variety of compositions, however, the pattern is always characteristic enough to identify the phase. Phase Fingerprinting Example: M 23 X 6 ZAP

EMALEMAL U of M John F. Mansfield North Campus Electron Microbeam Analysis Lab., University of Michigan Two-beam convergent beam electron diffraction pattern acquired into a modified version of NIH- Image. Extra code added to the application is accessed from the custom “ Thickness ” menu. Two Beam Thickness Determination EMALEMAL U of M

EMALEMAL The Transmission Electron Microscope: A Tool for Diffraction & Imaging in Materials Science & Engineering John Mansfield North Campus Electron Microbeam Analysis Laboratory University of Michigan 417 SRB, 2455 Hayward, Ann Arbor MI Phone: (734) FAX (734) URL: people/jfmjfm/jfmjfm.htmlEMALEMAL U of M