Unraveling current-induced dissociation mechanisms in single-molecule junctions

TL;DR

This paper investigates how current induces bond breaking in single-molecule junctions using a quantum mechanical approach, revealing three distinct dissociation mechanisms across various transport regimes.

Contribution

It introduces a comprehensive quantum mechanical analysis of dissociation mechanisms in molecular junctions, covering diverse transport and vibronic coupling regimes.

Findings

Stepwise vibrational ladder climbing dominates at weak and intermediate vibronic coupling.

Multi-quantum vibrational excitations induce dissociation at strong vibronic coupling.

Vibrational relaxation influences dissociation dynamics and stability strategies.

Abstract

Understanding current-induced bond rupture in single-molecule junctions is both of fundamental interest and a prerequisite for the design of molecular junctions, which are stable at higher bias voltages. In this work, we use a fully quantum mechanical method based on the hierarchical quantum master equation approach to analyze the dissociation mechanisms in molecular junctions. Considering a wide range of transport regimes, from off-resonant to resonant, non-adiabatic to adiabatic transport, and weak to strong vibronic coupling, our systematic study identifies three dissociation mechanisms. In the weak and intermediate vibronic coupling regime, the dominant dissociation mechanism is stepwise vibrational ladder climbing. For strong vibronic coupling, dissociation is induced via multi-quantum vibrational excitations triggered either by a single electronic transition at high bias voltages or by multiple electronic transitions at low biases. Furthermore, the influence of vibrational relaxation on the dissociation dynamics is analyzed and strategies for improving the stability of molecular junctions are discussed.