Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

Abstract

Reflection electron energy loss spectra from some insulating materials (CaCO3, Li2CO3, and SiO2) taken at relatively high incoming electron energies (5-40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO2, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E - Egap)(1.5). For CaCO3, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li2CO3 (7.5 eV) is the first experimental estimate.

Connecting the irreversible capacity loss in Li-ion batteries with the electronic insulating properties of solid electrolyte interphase (SEI) components

“…We also have applied HSE06 hybrid functions to compute the band gaps for Li 2 CO 3 , LiF and Li 3 PO 4 , as listed inTable 2. The bandgap of Li 2 CO 3 is 7.07eV, consistent with a newly reported experiment value of 7.5eV[79]. Nevertheless, the consistent underestimation of band gap values from GGA calculations can still provide reasonable estimates of the electronic insulating behavior of the SEI, especially in the comparison of the three insulating SEI…”

On the Atomic Kinetic Energies in Ceramic Oxides

“…By combining the measured INS low [37] and high [38] phonon frequencies of v-SiO 2 at room temperature, <KE> = 63.9 meV is deduced which agrees with the average measured ECS values of α-Silica, Finally, it may be seen that Ke(X) in oxides systematically decreases with increasing mass of X. Note also that the OX bonds in oxides ( [21]. In addition, estimates of Ke(X) for pure metallic Debye solids are given in Figure 3 (see Ref.…”

A comparison of ERBS spectra of compounds with Monte Carlo simulations

“…Details about the fitting procedure and the determination of the band gap and mean kinetic energy of the atoms can be found elsewhere. For CaCO 3 , the carbonate part of the elastic peak is very similar to that in Li 2 CO 3 , but now most intensity is due to Ca near 2 eV energy loss.…”

“…The HfO 2 sample was a 60 nm thick HfO 2 layer grown by atomic layer deposition on a silicon wafer. Results of these films were published elsewhere; [8][9][10] here, the focus is on the investigation of the influence of multiple scattering on the experiment, as well as an illustration of how ERBS can be used to determine the sample composition for a wide range of samples.…”

“…Note that due to the square root dependence of the width on the mean kinetic energy (Eqn 1), a 10% increase in width causes a 20% increase in kinetic energy. The actual mean kinetic energies obtained from the experiment for the carbonates (including corrections for multiple scattering based on MC simulations and compared with theory) are given in Vos et al (2015b) [10] for the carbonates. For TiO 2 , we found, neglecting multiple scattering, a mean kinetic energy of 50 meV for Ti and 60 meV for O [9] .…”