Measuring nanoscale thermal gradients in suspended MoS2 with STEM-EELS.

Transition metal dichalcogenides such as molybdenum disulfide (MoS₂) may see service in the heart of next-generation nanoelectronic devices, where highly localized power dissipation can produce nontrivial temperature gradients over nanometer-scale distances. Here, we demonstrate that MoS₂ is a promising target for plasmon energy expansion thermometry (PEET), a high-spatial resolution temperature mapping technique employed in a scanning transmission electron microscope (STEM) equipped with electron energy loss spectroscopy (EELS). We first use a calibrated, commercial MEMS-style TEM sample heater chip to measure the temperature dependence of the MoS₂ bulk plasmon. We corroborate the chip's temperature calibration with Raman thermometry and determine the bulk thermal expansion coefficient (TEC) of MoS₂ in the temperature range of 300–1100 K. Applying this TEC value to PEET measurements on a suspended MoS₂ flake, we map 70–90 K/μm temperature gradients with a submicrometer spatial resolution. [ABSTRACT FROM AUTHOR]