Terahertz Near-Field Scanning Noise Microscopy of Nonequilibrium Hot Electrons

Measuring the energy of charge carriers is essential for understanding transport, dissipation, and reliability in modern electronic and photonic structures, yet optical thermometry based on spontaneous photon emission inevitably averages over sub-wavelength features. Scanning Noise Microscopy (SNoiM) in the terahertz (THz) frequency has emerged as a promising candidate for contact-free nanoscale thermometry by detecting intrinsic THz evanescent electromagnetic fields near surfaces. We describe the SNoiM detection architecture and a compact signal model linking the measured signal to the local near-field energy density, and present representative measurements at the nanoscale that reveal nontrivial hot-electron dissipation phenomena in operating devices. Because SNoiM shares a similar near-field scattering geometry with well-established scattering-type scanning near-field optical microscopy (s-SNOM), yet probes fundamentally different physical quantities, we further clarify its distinction from illumination-driven s-SNOM. Together, these results position SNoiM as a practical candidate for noninvasive nanothermometer with broad relevance to nonequilibrium carrier physics and reliability metrology.