High-Resolution Probing of Molecular Junctions: Vibrational Fingerprinting and Parameter Extraction via Current Noise Spectroscopy

Abstract

The precise realization of molecular electronic devices requires a comprehensive understanding of charge transport mechanisms and the specific interplay between electronic and nuclear degrees of freedom. While average current measurements (I-V characteristics) and conventional Inelastic Electron Tunneling Spectroscopy (IETS) offer valuable insights, they are fundamentally limited by temperature-dependent line-width broadening. This study presents a high-resolution spectroscopic methodology utilizing suspended-wire molecular junctions (SWMJs) based on self-assembled monolayers (SAMs) of 1-decanethiol (C10) and 1,1',4',1''-terphenyl-4-thiol (TPT). By systematically probing the voltage-dependent current noise ($ΔI$), we demonstrate that electronic noise spectroscopy circumvents thermal degradation by probing transition rates between vibrational manifolds rather than simple additions of conductance channels, which enables sub-thermal feature mapping. Leveraging a fast-convolution-based Landauer-Büttiker transport model fitted to experimental data, we map complex vibrational manifolds, including high-energy overtones. This allows for the direct extraction of crucial nanoscale molecular parameters, including mode energies, anharmonicities ($x_e$), dissociation energies ($D_e$), and local environment reorganization energies ($E_r$). These parameter-dense noise signatures act as a unique molecular fingerprint, establishing noise spectroscopy as a highly sensitive platform for chemical sensing and discrimination in advanced quantum devices.