Electric Field Control of Molecular Charge State in a Single-Component 2D Organic Nanoarray

Quantum dots (QD) with an electric-field-addressable charge state are promising for digital information storage, single-electron transistors and quantum computing. Semiconductor QDs often offer limited control on size and composition, and low potential for scalability or miniaturization. Owing to their tunability and self-assembly capability, organic molecular building blocks can be used for the synthesis of two-dimensional (2D) QD arrays. Here, we report the self-assembly of 9, 10-dicyanoanthracene (DCA) molecules on Ag(111) into periodic 2D arrays, where the molecular charge state (neutral or negative) can be altered – individually and depending on the adsorption site – by the local electric field of a scanning tunneling microscope tip. Charging is enabled by an effective DCA/Ag(111) tunneling barrier and electric-field-driven electron population of the lowest unoccupied molecular orbital (LUMO). Subtle site-dependent variations of the DCA adsorption height result in a spatial modulation of the molecular polarizability, dielectric constant and LUMO energy level alignment, giving rise to a spatially dependent likelihood of charging. Our work offers potential for high-density 2D self-assembled arrays of QDs whose charge state can be addressed individually by an electric field.