Dynamics of Single-Molecule Dissociation by Selective Excitation of Molecular Phonons

Probing surface properties of organic molecular layers by scanning tunneling microscopy

In view of the relevance of organic thin layers in many fields, the fundamentals, growth mechanisms, and dynamics of thin organic layers, in particular thiol-based self-assembled monolayers (SAMs) on Au(111) are systematically elaborated. From both theoretical and practical perspectives, dynamical and structural features of the SAMs are of great intrigue. Scanning tunneling microscopy (STM) is a remarkably powerful technique employed in the characterization of SAMs. Numerous research examples of investigation about the structural and dynamical properties of SAMs using STM, sometimes combined with other techniques, are listed in the review. Advanced options to enhance the time resolution of STM are discussed. Additionally, we elaborate on the extremely diverse dynamics of various SAMs, such as phase transitions and structural changes at the molecular level. In brief, the current review is expected to supply a better understanding and novel insights regarding the dynamical events happening in organic SAMs and how to characterize these processes.

Universal Zigzag Edge Reconstruction of an α-Phase Puckered Monolayer and Its Resulting Robust Spatial Charge Separation

Edges are important, because they dictate the stability and properties of nanoribbons. Here, we reveal a universal reconstruction of the ZZ edge into a (2 × 1) tubed [ZZ(Tube)] edge, enabling an ultimate narrow nanotube to terminate nanoribbons for α-puckered group-V elemental and compound monolayers (GeS/Se and SnS/Se). The reconstructed edge formations are confirmed by CALYPSO. The ZZ(Tube) edge forms easily, is highly stable, and is semiconducting. Remarkably, the ZZ(Tube) edge always exhibits a type-II band structure and robust spatial charge separation. For a compound monolayer monochalcogenide, mild (2 × 1) ZZ(S-R) occurs at the chalcogenide-terminated edge. TDDFT simulations indicate that charge separation occurs only at 672 fs, while the lifetime is over 5 ns, thus facilitating robust spatial charge accumulation. These remarkable features of ZZ(Tube) edge-terminated α-puckered nanoribbons are ideal for optoelectronic and photocatalytic applications.

Unraveling current-induced dissociation mechanisms in single-molecule junctions

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.

Quantum algorithm for simulating molecular vibrational excitations

We introduce a quantum algorithm for simulating molecular vibrational excitations during vibronic transitions. The algorithm is used to simulate vibrational excitations of pyrrole and butane during photochemical and mechanochemical excitations.