Collective effects in charge transfer within a hybrid organic-inorganic system

Surface Strain-Induced Collective Switching of Ensembles of Molecules on Metal Surfaces

A central difficulty in the design of molecular electronics is poor control of the contact state between the molecule and metal electrode, which may induce instability and noise in logic and memory devices and even destroy the intrinsic functionality of the device. Here, we theoretically propose a simple and effective strategy for realizing full control of the contact state of organic molecules coated on the metal surface by applying homogeneous surface strain. As exemplified by pyrazine molecules on Cu(111), application of compressive (tensile) strain causes the molecules to uniformly adopt the physisorbed (chemisorbed) state. Within the framework of non-equilibrium Green's function calculations, we show that the two distinct contact states yield simultaneous rectification and switching behaviors. Because the contact states of all surface-bound molecules are transformed uniformly via surface strain perturbations, fully controlled collective switching and rectification effects can be simultaneously achieved in this contact system.

Photonics and spectroscopy in nanojunctions: a theoretical insight

Green function methods for photonics and spectroscopy in nanojunctions.

Controlling avalanche criticality in 2D nano arrays

Many physical systems respond to slowly changing external force through avalanches spanning broad range of sizes. Some systems crackle even without apparent external force, such as bursts of neuronal activity or charge transfer avalanches in 2D molecular layers. Advanced development of theoretical models describing disorder-induced critical phenomena calls for experiments probing the dynamics upon tuneable disorder. Here we show that isomeric structural transitions in 2D organic self-assembled monolayer (SAM) exhibit critical dynamics with experimentally tuneable disorder. The system consists of field effect transistor coupled through SAM to illuminated semiconducting nanocrystals (NCs). Charges photoinduced in NCs are transferred through SAM to the transistor surface and modulate its conductivity. Avalanches of isomeric structural transitions are revealed by measuring the current noise I(t) of the transistor. Accumulated surface traps charges reduce dipole moments of the molecules, decrease their coupling, and thus decrease the critical disorder of the SAM enabling its tuning during experiments.

The Chemical Problem of Energy Change: Multi-Electron Processes

This special issue is focussed on arguably the most important fundamental question in contemporary chemical research: how to efficiently and economically convert abundant and thermodynamically stable molecules, such as H2O, CO2, and N2 into useable fuel and food sources. The 3 billion year evolutionary experiment of nature has provided a blueprint for the answer: multi-electron catalysis. However, unlike one-electron transfer, we have no refined theories for multi-electron processes. This is despite its centrality to much of chemistry, particularly in catalysis and biology. In this article we highlight recent research developments relevant to this theme with emphasis on the key physical concepts and premises: (i) multi-electron processes as stepwise single-electron transfer events; (ii) proton-coupled electron transfer; (iii) stimulated, concerted, and co-operative phenomena; (iv) feedback mechanisms that may enhance electron transfer rates by minimizing activation barriers; and (v) non-linearity and far-from-equilibrium considerations. The aim of our discussion is to provide inspiration for new directions in chemical research, in the context of an urgent contemporary issue.