EELS Measurement of Palladium (Pd)
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Table 3425 lists the comparison of EELS and EDS measurements on thin TEM samples with Pd elements. The comparisons are based on the same data acquisition condition, consequently the same electron dose used.

Table 3425. Comparison of EELS and EDS measurements on TEM samples with Pd elements.
Measurement Signal Energy Signal ranking
EELS M4,5-edges 335 eV Very strong signal and highest contrast, often used
EELS L2,3-edges 3170 eV Sufficient signal, can be used for analysis if needed
EDS Lα lines 2.84 kV Often used in EDS measurement, but it is worse than M4,5-edges in EELS

Pearson et al. [1] experimentally and theoretically (based on one-electron Hartree-Slater calculations) found that the intensities of L2,3 white lines for most of the 3d and 4d transition metals decreased nearly linearly with increasing atomic number, reflecting the filling of the d states. Figure 3425a shows the deconvoluted and background-subtracted L2,3 energy-loss spectra for the 4d transition metals. The edge energies are not shown in order to present all the spectra on the same figure, while the intensities of the white lines are scaled simultaneously for all elements.

The deconvoluted and background-subtracted L2,3 energy-loss spectra for the 4d transition metals.

Figure 3425a. The deconvoluted and background-subtracted L2,3 energy-loss spectra for the 4d transition metals. [1]

If transitions between all of the filled and unfilled states of Pd were allowed, the interband transitions may be expected to produce numerous energy losses distributed over a wide range of energies in the EELS profile.

Figure 3425b shows the plasmon and low-energy core-loss peaks of yttrium (Y) and palladium (Pd). For the case of Y, the plasmon and core-loss peak can well be separated by spectra fitting with a polynomial function, while for the case of Pd with completed d shells its plasmon peak (~8 eV) is accompanied by a number of other features and their separation can hardly be achieved unambiguously. Those features of Pd probably correspond to different excitations of the composite outer shell consisting of different 4d+5s+5p electronic configurations [2]. Therefore, this interpretation suggests that the number of valence electrons per atom involved in plasmon scattering is larger than number of electrons taking part in chemical reactions.

plasmon and low-energy core-loss peaks of yttrium (Y) and palladium (Pd)

Figure 3425b. Two representative examples (for Y and Pd) of separating the plasmon and low-energy core-loss contributions in the EEL spectra. [2]

Figure 3425c shows an EEL spectrum, presenting Pd-M4,5 edge at 335 eV, taken from a Pd nanoparticle on holey carbon (C) film. Both the C and Pd signals are clear. In order to extract the Pd signal, the energy window for background subtraction is selected before the C K edge but not immediately before the Pd-M4 edge onset since there is uncertainty which is induced by the carbon peak.

EEL spectrum taken from a Pd nanoparticle on holey carbon film

Figure 3425c. EEL spectrum taken from a Pd nanoparticle on holey carbon film. Adapted from [3]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[1] D. H. Pearson, C. C. Ahn, and B.Fultz, White lines and d-electron occupancies for the 3d and 4d transition metals, Physical Review B, 47(14), (1993) 8471-8478.
[2] Konstantin Iakoubovskii, Kazutaka Mitsuishi,Yoshiko Nakayama, and Kazuo Furuya, Mean free path of inelastic electron scattering in elemental solids and oxides using transmission electron microscopy: Atomic number dependent oscillatory behavior, Physical Review B 77, 104102 (2008).
[3] R. Esparza, Amado F. García-Ruiz, J. J. Velázquez Salazar, R. Pérez, and M. José-Yacamán, Structural characterization of Pt–Pd core–shell nanoparticles by Cs-corrected STEM, J Nanopart Res. 2012 Dec; 15(1342).

 

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