Chemical Self-Assembly Strategies for Designing Molecular Electronic Circuits: Demonstration of Concept

Abstract

The design of molecular electronic circuits will require the development of strategies for making controlled interconnections between nanoelectrodes. The simplest example of a molecular electronic component consists of aryl rings with para-anchoring functionalities, commonly isocyanide or thiol groups. In particular, 1,4-phenylene diisocyanobenzene (1,4-PDI) has been shown to form conductive one-dimensional, oligomeric chains that are composed of alternating gold and 1,4-PDI units in which a gold adatom is linked to two trans isocyanide groups. Density functional theory (DFT) calculations of the oligomerization pathway reveal that growth occurs via a vertical, mobile Au-PDI adatom complex that forms by binding to the gold substrate and oligomerizes by the gold adatom attaching to the isocyanide terminus of a growing chain. In this case, the gold atoms in the oligomer derive from the gold substrate. In principle, bridging between adjacent electrodes could be tuned by controlling the 1,4-PDI dose. However, because both nucleation of the adatom complex and the subsequent oligomerization reactions occur at the periphery of gold nanoparticles, it is postulated that oligomer growth is inherently self-limiting. An analytical model is developed for this process that demonstrates the existence of self-limiting growth. This is modeled in greater detail using kinetic Monte Carlo simulations with the energy parameters derived from DFT calculation on gold that confirm that the growth is self-limiting and predicts that bridging between nanoelectrodes should only occur for spacings less than 12 nm.