STEM EELS Spectrum Imaging

Spectrum line scan across interface (50 spectra) Each ach spectrum was taken with 0.5s exposure at <20pA 0pA Useful when insufficient beam current to acquire full image
Original
Hypothetic STEM Images
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STEM EELS and EFTEM Spectrum Imaging
Decimation
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Binning
Advanced STEM SI – Sub‐pixel scanning …..
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STEM EELS and EFTEM Spectrum Imaging
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STEM EELS SI – Visualization example
Spectrum-image Spectrum image is displayed as an xy plane over a specified energy
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STEM spectrum image acquisition

Acquired by stepping a focused electron probe from one pixel to the next
EDX STEM


Spectrum image data cube is filled one spectrum column at a time STEM allows collecting any combination of EELS, x‐ray, and CL spectra p simultaneously y DF or SE signal permits spatial drift correction during acquisition
20 nm
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STEM EELS and EFTEM Spectrum Imaging
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Advanced STEM SI – Sub‐pixel scanning
Sub-pixel scanning Rasters beam at each SI-pixel during acquisition Prevents under-sampling when probe is smaller than pixel spacing Frequent condition with FEG instruments
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STEM EELS ad EFTEM Spectrum Imaging
analytical TEM
digital imaging
specimen preparation
TEM specimen holders
SEM products
Can be acquired with high resolution – limited to probe size / delocalisation

Spectral information can be acquired with high spectral resolution
o
o
Verify S/N for acq time OK ‐ Ex. ~100‐200e‐/ch at O‐edge For EELS, verify energy region and alignment ‐ Ex: [70‐1008]eV, E=0.7eV

Setup desired corrections Start acquisition
Spectral resolution the same as conventional EELS
Scanning probe limits sample damage and contamination compared with fixed probe approach
‐ Cons Acquisition times can be lengthy for high number of pixels Requires STEM capability Spatial resolution limited to minimum probe size (not good for LaB6)
Original Image 416x256 6 Sub-Pixel Scanning Off
Sub-Pixel Scanning On
5 52x32
20 20 nm nm
8x Binning
20 20 nm nm
26x x16
20 20 nm nm
16x Binning
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‐ Ex: 100x50 pixels, 2.3nm/pixel

Setup spectroscopy parameters
Select acquisition time per pixel
‐ Ex: 16ms / spectrum; 80s total
View test spectra from around ROI
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EELS SI – Example processing elemental maps

Use EELS quantification tools on an extracted spectrum
Select edges of interest Apply processing to parent spectrum t i image Generates elemental maps, and optionally p y error information Optionally combine elemental maps to understand spatial relationship
Al
10 nm
nm
60
80
Al K
50 400 600 800 1000 1200 1400 1600 1800 2000 0 10 20
200
Si K
40 30
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STEM EELS and EFTEM Spectrum Imaging
Move the size and position of the extraction region to view changes in spectrum, including the effect of processing
EELS and EFTEM Training School
STEM EELS and EFTEM Spectrum Imaging

EELS and EFTEM Training School
STEM EELS and EFTEM Spectrum Imaging
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Spectrum Imaging – 2 Principle Acquisition Modes
E
y
x
STEM SI Parallel spectrum acquisition with scanned probe at position (x,y) S i l image-pixel Serial i i l acquisition i iti by b changing (x,y) EFTEM SI Parallel image acquisition with filter at energy-loss E Serial spectral acquisition by changing E
STEM EELS and EFTEM Spectrum Imaging
E
y
x
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STEM Spectrum Imaging
EELS and EFTEM Training School
STEM EELS and EFTEM Spectrum Imaging
20 20 nm nm
STEM EELS and EFTEM Spectrum Imaging
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Advantages and disadvantages of EELS‐SI
+ Pros Spatial information acquired in addition to spectral information
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Advanced STEM SI – Simultaneous EELS / ADF
ADF Image recorded at each point of STEM SI Allows exact correlation with image features Allows advanced quantification tifi ti and d correction

DF survey image El Elemental t l Composition C iti Profile P fil EELS-SI Line-scan
Relative compositio R on (%) 100 80 60 40 20 0 -20 Al Si O
SiO2
Spectrum Image
x y
Specimen