Kavli Affiliate: Scott K. Cushing
| First 5 Authors: Levi D. Palmer, Wonseok Lee, Javier Fajardo, Jr., A. Alec Talin, Thomas E. Gage
| Summary:
Measuring nanoscale local temperatures, particularly in vertically integrated
and multi-component systems, remains challenging. Spectroscopic techniques like
X-ray absorption and core-loss electron energy-loss spectroscopy (EELS) are
sensitive to lattice temperature, but understanding thermal effects is
nontrivial. This work explores the potential for nanoscale and element-specific
core-loss thermometry by comparing the Si L2,3 edge’s temperature-dependent
redshift against plasmon energy expansion thermometry (PEET) in a scanning TEM.
Using density functional theory (DFT), time-dependent DFT, and the
Bethe-Salpeter equation, we ab initio model both the Si L2,3 and plasmon
redshift. We find that the core-loss redshift is due to bandgap reduction from
electron-phonon renormalization. Our results indicate that despite lower
core-loss signal intensity and thus accuracy compared to PEET, core-loss
thermometry still has important advantages. Specifically, we show that the
Varshni equation easily interprets the core-loss redshift, which avoids plasmon
spectral convolution for PEET in complex materials. We also find that core-loss
thermometry is more accurate than PEET at modeling thermal lattice expansion
unless the temperature-dependent effective mass and dielectric constant are
known. Furthermore, core-loss thermometry has the potential to measure
nanoscale heating in multi-component materials and stacked interfaces with
elemental specificity at length scales smaller than the plasmon’s wavefunction.
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