Optimization of Experimental Parameters of EELS 
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Much of analytical TEM revolves around elemental analysis based on core-shell ionization and its role in electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS). The optimized experimental parameters for EELS measurements are:

        i) Typical voltages of the primary beam of high energy electrons is between 100 and 300 keV.

        ii) Proper convergence semiangle α of the primary electron beam.

        iii) Proper beam diameter and beam current:
            Trade-off between spatial resolution and signal-to-noise ratio

        iv) Specimen thickness:
            The specimen should be sufficiently thin so that the number of collision events remains low.
            Thick specimens → multiple scattering, quantification requires deconvolution of spectrum (→ loss of information)
            However, in many cases, the specimens cannot be too thick or too thin, see page 4716.

        v) Avoid diffraction effects.

        vi) Minimize effects from carbon contamination.

        vii) For spectrum comparison, all EELS measurements should be performed at nominally the same microscope settings.

Table 4717 lists examples of experimental settings for EELS measurements.

Table 4717. Examples of experimental settings for EELS measurements.

Microscope
ZEISS EM922 OMEGA
Philips 400ST-FEG TEM
Hitachi, HF-3000
F20 TEM
VG HB-501 STEM
VG HB-601 STEM
Acceleration voltage (kV)
200
100
100
C1 aperture
2 mm
C2 aperture
200 µm
Spot size
3
Camera length
210 mm
Entrance aperture
3 mm
Convergent angle (mrad)
8.0
0.9
7.5-16
10
Collection angle (mrad)
4.3
11
4.76-24
21.5
Dispersion (eV/channel)
0.5
0.1
0.021
0.1
0.01 - 0.02
Integration time per read-out
1-3 s
Acquisition time (s)
1 or 2
0.08
0.1
Pixel time (seconds/pixel)
0.05 - 0.2
Total acquisition time for each location (s)
6
Spectrum energy range
500 - 780 eV
100 - 300 eV
-10 to 90
Beam energy (keV)
100
Beam current
6.1 nA
100 pA
Fluence rate ( eÅ−2 s−1)
5.2×103
Analyzed materials
Gold, silver and alloy anoparticles
Special application     Energy-drift correction & deconvolution
 
Energy resolution of spectrometer        
0.7
 
Energy drift        
< 0.03 eV/min
 
EELS/EFTEM system     Gatan GIF model 2002
 
Example of analyzed elements       O, Co    
Reference
[1]
[2]
[4]
[5, 7]
[6]
[3]

 

 

 

 

 

 

[1] N. Miyajima, C. Holzapfel, Y. Asahara, L. Dubrovinsky, D.J. Frost, D.C. Rubie, M. Drechsler, K. Niwa, M. Ichihara, and T. Yagi, Combining Fib milling and conventional Argon ion milling techniques to prepare high-quality site-specific TEM samples for quantitative EELS analysis of oxygen in molten iron, Journal ofMicroscopy , Vol. 238, Pt 3 2010, pp. 200–209.
[2] Laurence A. J. Garvie, Peter R. Buseck, and Peter Rez, Characterization of Beryllium–Boron-Bearing Materials by Parallel Electron Energy-Loss Spectroscopy (PEELS), Journal of Solid State Chemistry 133, 347 - 355 (1997).
[3] James W L Eccles, An Electron Energy Loss Spectroscopy Study of Metallic Nanoparticles of Gold and Silver, PhD thesis, 2010.
[4] Koji Kimoto, Kazuo Ishizuka, Teruyasu Mizoguchi, Isao Tanaka and Yoshio Matsui, The study of Al-L2,3 ELNES with resolution-enhancement software and first-principles calculation, Journal of Electron Microscopy 52(3): 299–303 (2003).
[5] Marie C. Cheynet, Simone Pokrant, Frans D. Tichelaar, and Jean-Luc Rouvière, Crystal structure and band gap determination of HfO2 thin films, Journal of Applied Physics 101, 054101 (2007).
[6] K.A. Mkhoyan, T. Babinec, S.E. Maccagnano, E.J. Kirkland, J. Silcox, Separation of bulk and surface-losses in low-loss EELS measurements in STEM, Ultramicroscopy 107 (2007) 345–355.
[7] Rosa Córdoba Castillo, Functional Nanostructures Fabricated by Focused Electron/Ion Beam Induced deposition, 2014.

 

 

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