| 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.
|
|
Philips 400ST-FEG TEM |
Hitachi, HF-3000 |
F20 TEM |
VG HB-501 STEM |
VG HB-601 STEM |
Hitachi HD-2300A [8] |
| Purpose |
|
|
|
|
|
|
4D STEM-EELS |
Acceleration voltage (kV) |
|
|
|
200 |
100 |
100 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0.3 nm and 0.5 nm |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
0.9 |
|
7.5-16 |
10 |
|
9 mrad |
|
|
11 |
|
4.76-24 |
21.5 |
|
16 mrad for low-loss & 24 mrad for core-loss |
|
|
0.1 |
0.021 |
0.1 |
|
0.01 - 0.02 |
From 70 to
1410 eV at 1.0 for Si, N, Ti, O, Co and Cu; from 10 to 115 eV at 0.1~0.2
|
Integration
time per read-out
|
|
|
|
|
|
|
|
| Detector read-out speed |
|
|
|
|
|
|
7 to 350 spectra/s |
|
|
1 or 2 |
0.08 |
|
|
0.1 |
|
Pixel time (seconds/pixel) |
|
|
|
|
|
0.05 - 0.2 |
|
| Pixel size (nm) |
|
|
|
|
|
|
3 ~ 4 |
Total acquisition time for each location (s) |
|
|
|
|
|
6 |
|
|
|
100 - 300 eV |
|
-10 to 90 |
|
|
|
|
|
100 |
|
|
|
|
|
|
|
|
100 pA |
|
|
|
60 pA (0.3 nm spot-size) to 450 pA (0.5 nm spot-
size);
low-loss SI: from 60 to 100 pA & core-loss SI: from 300 to 450 pA |
|
|
|
|
|
|
|
|
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 |
|
|
|
Gatan Enfina spectrometer |
| Drift correction |
|
|
|
|
|
|
Every 5~10
rows |
| SI image size |
|
|
|
|
|
|
72 X 48 pixel SIs
(over 213 X 142 nm) |
| Example of analyzed elements |
|
|
|
O, Co |
|
|
|
|
|
[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.
[8] Konrad Jarausch, Paul Thomas, Donovan N. Leonard, Ray Twesten, Christopher R. Booth, Four-dimensional STEM-EELS: Enabling nano-scale chemical tomography, Ultramicroscopy 109 (2009) 326–337.
|
