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

Palmer, Levi D.; Lee, Wonseok; Durham, Daniel B.; Fajardo, Javier; Liu, Yuzi; Talin, A. Alec; Gage, Thomas E.; Cushing, Scott K.

doi:10.1021/acsphyschemau.5c00044

Published November 26, 2025 | Version Published

Journal Article Open

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

1. California Institute of Technology
2. Argonne National Laboratory
3. Sandia National Laboratories California

Measuring nanoscale local temperatures, particularly in vertically integrated and multicomponent 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 L_2,3 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 L_2,3 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 multicomponent materials and stacked interfaces with elemental specificity at length scales smaller than the plasmon’s wave function.

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Acknowledgement

The authors thank Professor Ye-Jin Kim, Professor Oh-Hoon Kwon, Dr. Haihua Liu, Nicholas Heller, and Nicholas Hagopian for helpful research discussions regarding project directions and data analysis. The authors also thank Dr. Jianguo Wen for contributing to specimen preparation and microscope alignment. This research was supported as part of the Ensembles of Photosynthetic Nanoreactors, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science under Award No. DE-SC0023431. Work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. The views expressed in this article do not necessarily represent the views of the U.S. Department of Energy, National Science Foundation, or the United States Government. The computations presented here were conducted in the Resnick High Performance Computing Center, a Resnick Sustainability Institute facility at the California Institute of Technology. L.D.P. was supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1745301. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract number DE-SC0014664. W.L. acknowledges support from the Korea Foundation for Advanced Studies.

Supplemental Material

The following files are available free of charge. Analysis of beam-induced heating and precise denoising parameters, raw unsmoothed experimental data and fitting functions, Si lamella thickness mapping, overlaid comparison of calculated and experimental core-loss data, rigid redshift energy calculation, dark-field intensity differences, denoising visualization and statistics, correlation plots, analysis scripts, ground-state turboEELS and OCEAN calculations/convergence parameters, temperature-dependent theory input parameters, and example turboEELS and OCEAN input files (PDF);

Video S1, Measured STEM-EELS plasmon energy as a function of temperature (MOV);

Video S2, Average plasmon energy difference from the average 50 °C STEM-EELS measurement (MOV).

Files