MLB Methods: TEM
Eric Jones
Outline
• An introduction to TEM
– Why TEM?
– A quick look under the hood
– Electrons go in, but what comes out?
• The basics of imaging
– Scattering
– Contrast mechanisms
– Imaging modes
• Everyone likes a little spectroscopy
• Aberration correction
Why TEM?
• The diffraction limit is on
the order of the
wavelength of the
illumination
– Wavelength of light
~500nm
– Wavelength of electron (at
200 keV) ~2pm
• High energy e-beam
provides a platform for
multiple characterization
techniques
0.61 0.61


 sin 
NA
Inside a TEM
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Source
Condenser optics
Specimen
Objective optics
Projector optics
Various cameras and
detectors
Electron/sample interaction
Basics of imaging: scattering
• Elastic scattering
– Rutherford – Z dependent
– Bragg
• Inelastic scattering
– Interaction with electrons
Basics of imaging: contrast
• Mass-thickness
• Diffraction
• Phase contrast
Phase contrast
Mass-thickness
Diffraction contrast
Imaging modes: TEM vs STEM
TEM (or CTEM)
Electron beam
Specimen
Recording media
STEM
STEM not STM!
• Reduces artifacts that
arise from microscope
hardware
– Single atom imaging
• Main contrast is due to
incoherent elasticallyscattered electrons
(Rutherford)
– Z-contrast imaging
• Easily combined with
spectroscopic
techniques
Spectroscopy in TEM
• Energy dispersive X-rays (EDX)
• Cathodoluminesence (CL)
• Electron energy loss (EELS)
Aberration correction… it’s good
• Aberration correction!
– Resolutions of ~50pm now achievable
Practical considerations
• Sample preparation
– Samples must be electron transparent (> 100nm)
– Sample preparation is destructive
• Small areas of interest
• Great microscopy takes time (and really
expensive equipment)
Things going on in the world of TEM
• Vortex beams!
• Exit wave
reconstruction
• Bio-materials
imaging
• In-situ experiments
Questions?