Electron microscopy
 
Comparison between EFTEM and EELS Mapping
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  EFTEM EELS Mapping
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Electron beam

Large, parallel, and fixed-beam illumination in TEM mode

A focused beam is scanned across the area of interest of the specimen in STEM mode
Acquired data

Acquires energy-selected images with spectral information integrated over a specific energy-loss range as defined by an energy-selecting slit

Acquires spectral data at each pixel in a serial manner
EFTEM
EELS Mapping
Spatial information
Is recorded in a parallel manner

Builds up in a serial manner
Illumination angle
Small: similar to CTEM Large in order to optimize the probe size and current
Collection angle
Small: similar to CTEM Large in order to optimize the collection efficiency
Spatial resolution
With delocalization effects providing the fundamental limiting factor
Lower because both the illumination and EELS collection angles are small Considerably higher because both the illumination and EELS collection angles are large
Aberration effect
More aberration effects In the STEM, the EELS collection optics does not focus the electrons into an image and thus is much less affected by aberrations [1]
Spectral information
Is probed serially by acquiring a number of images separated in energy loss
Acquires spectral data at each pixel in a serial manner
Acquisition efficiency
Less efficient since only the energy region defined by the energy-selecting slit is recorded More efficient since the information at each pixel is recorded
Specimen damage
More radiation damage since the total electron dose is more Less radiation damage since the total electron dose is less
Data acquisition time

Short since the recording time is almost independent of the number of pixels due to spatially parallel nature and larger total electron dose

Long due to non-negligible readout time per spectrum
Dose-rate-dependent specimen damage
Minimized There are such damages, e.g. hole-drilling and movement of segregants

 

 

 

 

 

 

[1] Stephen J. Pennycook, Peter D. Nellist, Scanning Transmission Electron Microscopy Imaging and Analysis, 2011.

 

 

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