Temperature Measurement by a Nanoscale Electron Probe using Energy Gain and Loss Spectroscopy*

Heat dissipation in integrated nanoscale devices is a major issue that requires the development of nanoscale temperature probes. Here, we report the implementation of a method that combines electron energy gain and loss spectroscopy to provide a direct measurement of the local temperature of BN nano-flakes. We find that a BN optical phonon presents a linear red shift behavior (towards lower energies) as the sample is heated up, from 50 to 1300 °C. First-principles calculations reveal that the shift is due to lattice thermal expansion and anharmonic phonon scattering, with the latter being the dominant factor to reduce the energy of the phonon as the temperature increases. The gain peak exhibits an increase of intensity as a function of temperature, in accordance with the occupation probability theory. The experiments and theory presented here open the doors to the study of anharmonic effects in materials by directly probing phonons in the electron microscope.