Other imaging techniques Ps: I put things on the comment block below so please make sure you are in edit status Fan Ziyi

Before we introduced methods using diffraction contrast, phase contrast to characterize specimens. However, there are variations to the standard ways in which we can extract more information from a TEM image Today we are going to talk about other imaging techniques

TOPICS STEREO MICROSCOPY 2.5D MICROSCOPY MICROSCOPY CONCERNING MAGNETIC SPECIMENS Lorentz microscopy magnetic correction CHEMICALLY SENSITIVE IMAGES IMAGING WITH DIFFUSELY SCATTERED ELECTRONS SURFACE IMAGING Reflection Electron Microscopy Topographic Contrast HIGH-ORDER BF IMAGING SECONDARY-ELECTRON IMAGING &BACKSCATTERED-ELECTRON IMAGING CHARGE-COLLECTION MICROSCOPY ELECTRON HOLOGRAPHY IN-SITU TEM: DYNAMIC EXPERIMENTS FLUCTUATION MICROSCOPY

STEREO MICROSCOPY Present 3d image

Function: record images from more than one direction to give a 3D view of the sample. why it work: your brain gauges depth by simultaneously interpreting signals from both your eyes, which view the same scene from slightly different angles (about 5°), giving a parallax shift. How it works: 1.Select the region of interest, making sure that the specimen is eucentric. 2.Record an image (normally BF). 3.Tilt the specimen by at least 5° 4. Record another image. 5.Develop or display the images and observe them under a stereo viewer

2.5D MICROSCOPY

Function: separating close spaced diffraction spots Why it works: view two DF images taken at different focus through a stereo viewer, you see features at different apparent depths. It’s 2.5D because it’s not a true depth, it’s just a depth your brain feel and easy to separate some diffraction spots. How it works( just go underfocus and overfocus) 1.Select the area of interest making sure the specimen is eucentric. 2.Tilt the beam so that the several diffraction spots cluster around the optic axis; center the objective aperture around this group of spots. 3.Return to image mode and underfocus the objective lens until you see the clarity of the image begin to degrade; then overfocus one click back to maintain focus. 4.Record an image. 5.Overfocus the objective lens until the image begins to lose clarity again, then underfocus back one click. 6.Record another image. 7.Develop or display the images and view them in a stereo viewer.

B,C Show ”depth” difference of those two spots Close spaced diffraction spots, hard to separate

MICROSCOPY CONCERNING MAGNETIC SPECIMENS

The Magnetic Correction If your specimen is magnetic, its magnetic field will deviate the electron beam. All your images will be severely aberrated and shift when you try to focus them. Two topics The Magnetic Correction Lorentz microscopy: showing showing domains and domain walls. Here we are going to introduce methods that can minimize the effect and also how to obtain information from magnetic specimens such as image showing domains.

Magnetic correction Function: correct the aberrations caused by magnetic materials. Most important step: make the magnetic part of your specimen as thin and small as possible to reduce its total magnetic field strength.

Lorentz microscopy Function: see magnetic domains and domain walls why it work: diffraction spots got splitted due to the magnetic field. This is a form of phase-contrast microscopy Two images: Foucault Images: can see domain walls or domains Fresnel Images: can only see domain walls

Splitted spots Domain wall domains

CHEMICALLY SENSITIVE IMAGES

How it works: Form DP images and compare. Function: study the composition of the materials. especially GaAs and the other III–V compound semiconductors. why it work: structure factor F varies from different composition of materials. How it works: Form DP images and compare. many materials have the structure factor, F, for some reflections sensitive to the difference between the atomic-scattering amplitudes of the constituents.

Function: record images from more than one direction to give a 3D view of the sample. why it work: your brain gauges depth by simultaneously interpreting signals from both your eyes, which view the same scene from slightly different angles (about 5°), giving a parallax shift. How it works: 1.Select the region of interest, making sure that the specimen is eucentric. 2.Record an image (normally BF). 3.Tilt the specimen by at least 5° 4. Record another image. 5.Develop or display the images and observe them under a stereo viewer

IMAGING WITH DIFFUSELY SCATTERED ELECTRONS

Function: to see non-crystalline regions why it work: non-crystalline regions scatter electrons into a different region of reciprocal space away from the diffracted beams, then the non-crystalline regions can be seen in strong contrast. How it works:Form a dark field(DF)image.

SURFACE IMAGING

Reflection Electron Microscopy Topographic Contrast Two ways Reflection Electron Microscopy Topographic Contrast Surface imaging is used to obtain surface information. There are several ways of doing it. We only introduce two ways: REM and topographic contrast

Function: obtain surface information. REM Function: obtain surface information. Why it works: electrons are scattered by different angles based on the surface. How it works: you mount your specimen in the holder ,so the beam hits at a glancing angle REM images showing surface steps on a cleaved single crystal of GaAs.

Function: obtain surface images. Topographic Contrast Function: obtain surface images. Most important step: displacing the objective aperture until its shadow is visible across the region of the image that you’re looking at. topographic contrast from Fe3O4 particles on a carbon film.

HIGH-ORDER BF IMAGING

Function: lower the contrast and see details of defects.

BACKSCATTERED-ELECTRON IMAGING SECONDARY-ELECTRON And BACKSCATTERED-ELECTRON IMAGING

Function: reveal the surface topography Secondary-electron imaging Backscattered-electron imaging

CHARGE-COLLECTION MICROSCOPY

Function: characterization of semiconductors in the SEM why it works: incident beam generates electron-hole pairs which are swept apart by the internal field of the p-n junction and not allowed to recombine.

ELECTRON HOLOGRAPHY

Function: create a 3D image of an object. why it works: it records both the intensity and the phase information of the waves emitted or scattered by the object.

IN-SITU TEM: DYNAMIC EXPERIMENTS

Function: record dynamic changes in the microstructure during the experiment. Image of reaction front of a Ge/Ag/Ge trilayer during the heating.

FLUCTUATION MICROSCOPY

Function: to study medium-range order ( 0 Function: to study medium-range order ( 0.5–2 nm) in amorphous materials, such as glasses, amorphous silicon and carbon. why it work: More random structures give gray regions; more ordered structures give locally brighter or darker regions depending on whether the local electron scatter is on axis or off axis more ordered: black and white Random-give gray

references

Reference Wiiliams,D.B.,&Barry Carter,C.,(1996).transmission electron microscopy.new york: Springer ScienceþBusiness Media

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