Nanoscale and Element-Specific Lattice Temperature Measurements using Core-Loss Electron Energy-Loss Spectroscopy

TL;DR

This paper demonstrates that core-loss electron energy-loss spectroscopy can be used for nanoscale, element-specific temperature measurements in semiconductors, offering advantages over plasmon-based thermometry especially in complex, multi-component systems.

Contribution

It introduces a new method for nanoscale, element-specific lattice temperature measurement using core-loss EELS, validated through ab initio modeling and comparison with plasmon thermometry.

Findings

Core-loss redshift is due to bandgap reduction from electron-phonon interactions.

Core-loss thermometry can be more accurate than PEET with spectral denoising.

It enables nanoscale thermal measurements in complex, multi-component materials.

Abstract

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 occurs due to bandgap reduction from electron-phonon renormalization. Our results indicate that despite lower core-loss signal intensity compared to plasmon features, core-loss thermometry has key advantages and can be more accurate through standard spectral denoising. Specifically, we show that the Varshni equation easily interprets the core-loss redshift for semiconductors, which avoids plasmon spectral convolution for PEET in complex junctions and interfaces. We also find that core-loss thermometry is more accurate than PEET at modeling thermal lattice expansion in semiconductors, unless the specimen's temperature-dependent dielectric properties are fully characterized. 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.