Thermal Force Imaging of Hot Electrons in Operando Nanodevices

The relentless pursuit of smaller, faster nanoelectronics concentrates intense heat at nanometer scales, threatening performance and reliability. Yet directly mapping this heat from nonequilibrium hot electrons has remained elusive. Here we introduce the non-contact force technique that directly images hot-electron temperature distributions in operando devices. Using a bimodal atomic force microscope with sideband modulation, we harness frequency mixing to greatly boost sensitivity to hot-electron forces while suppressing parasitic electrostatic signals. This enables a thermal force microscope that visualizes hot electrons in the nanoconstriction of a silicon channel. Quantitative analysis reveals that thermal-fluctuation-induced force from hot electrons (Δ Tₑ ~ 700\,K) significantly exceed indirect effects from lattice heating (Δ TL ~ 3\,K) or permittivity changes. At a 5 nm tip–sample gap, this pressure reaches ~3 bar, sufficient to drive substantial electro-thermo-mechanical effects. These results open a powerful route to probing hot-electron dynamics in working nanodevices and inform electro–thermal co-design strategies for post-Moore nanoelectronics. The authors demonstrate a non-contact approach for detecting nanoscale hot electrons by sensing thermal Casimir forces, enabling direct operando mapping of nonequilibrium hot-electron distributions in semiconductor nanodevices.