Vibrational Energy Dissipation in Non-Contact Single-Molecule Junctions Governed by Local Geometry and Electronic Structure

Abstract

The vibrational dynamics of adsorbate molecules in single-molecule junctions depend critically on the geometric structure and electronic interactions between molecule and substrate. Vibrations, excited mechanochemically or by external stimuli, dissipate energy into substrate electrons and phonons. Energy dissipation leads to the broadening of spectral lines, vibrational lifetimes, and the coupling between molecular and substrate phonons. It affects molecular manipulation, giving rise to nanoscale friction, and contributes to scanning probe and surface spectroscopy signals. We present an approach to disentangle adsorbate vibrational dynamics in non-contact junctions by employing density functional theory, machine learning, and non-adiabatic molecular dynamics. Focusing on the CO-functionalised Cu surfaces representing a single-molecule junction, a widely studied system in scanning probe and energy dissipation experiments, we reveal strong vibrational mode specificity governed by the interplay of electron-phonon and phonon-phonon coupling. Electron-phonon relaxation rates vary by two orders of magnitude between modes and sensitively depend on the tip-substrate geometry. We find evidence of a weak non-additive effect between both energy dissipation channels, where electron-phonon coupling enhances phonon-phonon coupling. Our predicted vibrational lifetimes agree with infrared spectroscopy and helium scattering experiments. Finally, we outline how our findings can inform and enhance scanning probe experiments.

References in corpus (9)

• CO adsorption on close-packed transition and noble metal surfaces: Trends from ab-initio calculations
• The shortcomings of semi-local and hybrid functionals: what we can learn from surface science studies
• The origin of high-resolution IETS-STM images of organic molecules with functionalized tips
• Density-functional model for van der Waals interactions: Unifying many-body atomic approaches with nonlocal functionals
• CO adsorption on Cu(111) and Cu(001) surfaces: improving site preference in DFT calculations
• Ab-initio tensorial electronic friction for molecules on metal surfaces: nonadiabatic vibrational relaxation
• Mode specific electronic friction in dissociative chemisorption on metal surfaces: H${}_2$ on Ag(111)
• Electron-mediated phonon-phonon coupling drives the vibrational relaxation of CO on Cu(100)
• Dynamic friction unraveled using an atomically defined model system