Directed Nanoscale Self-Assembly of Molecular Wires Interconnecting Nodal Points Using Monte Carlo Simulations

Abstract

The influence of directing agents in the self-assembly of molecular wires to produce twodimensional electronic nanoarchitectures is studied here using a Monte Carlo approach to simulate the effect of arbitrarily locating nodal points on a surface, from which the growth of self-assembled molecular wires can be nucleated. This is compared to experimental results reported for the self-assembly of molecular wires when 1,4-phenylenediisocyanide (PDI) is adsorbed on Au(111). The latter results in the formation of (Au-PDI) n organometallic chains, which were shown to be conductive when linked between gold nanoparticles on an insulating substrate. The present study analyzes, by means of stochastic methods, the influence of variables that affect the growth and design of self-assembled conductive nano-architectures, such as the distance between nodes, coverage of the monomeric units that leads to the formation of the desired architectures and the interaction between the monomeric units. This work proposes an approach and sets the stage for the production of complex 2D nanoarchitectures using a bottom-up strategy but including the use of current state-of-the-art top-down technology as an integral part of the self-assembly strategy.

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

“…The simplest architecture for building molecular wires exploits π-conjugated systems with two terminal anchoring −SH or −NC groups to attach the molecular wire to gold nanoelectrodes; such molecules have been used as linkers for single-molecule conductivity experiments. − However, in order to design molecular-electronic circuits it is necessary to be able to make controlled electrical connections between nanoelectrodes. This can, in principle, be accomplished by designing a self-assembly strategy in which the length of a conducting molecular wire is controlled to selectively connect between gold nodes with different spacings . A possible strategy to achieve this is to use functionalized nanoparticles to provide molecular linkages between adjacent nanoelectrodes, − but this approach cannot specifically tune the interelectrode connectivity.…”

“…This can, in principle, be accomplished by designing a self-assembly strategy in which the length of a conducting molecular wire is controlled to selectively connect between gold nodes with different spacings. 24 A possible strategy to achieve this is to use functionalized nanoparticles to provide molecular linkages between adjacent nanoelectrodes, 25−27 but this approach cannot specifically tune the interelectrode connectivity. An alternative approach is to selectively self-assemble conductive electrical bridges between adjacent nanoelectrodes and this strategy is illustrated in the following using the oligomerization chemistry found for 1,4-phenylene diisocyanobenzene (1,4-PDI) on a Au(111) surface, described in greater detail below.…”

“…One concept for selectively tuning the interconnectivity between gold nanoelectrode nodes relies on carefully adjusting the dose of the gas-phase, oligomer-forming species to halt the oligomerization process when the required bridges between nodes had been formed. 24 This necessitates careful control over the dose, internode spacing, and the temperature at which the reaction is carried out (to control the various surfacereaction rates). In the following, it is demonstrated that the growth of oligomer chains nucleated on gold nanoparticles by reaction with 1,4-PDI is inherently self-limiting, thus eliminating the sensitivity of the interparticle linking process to the reactant dose.…”

“…One concept for selectively tuning the interconnectivity between gold nanoelectrode nodes relies on carefully adjusting the dose of the gas-phase, oligomer-forming species to halt the oligomerization process when the required bridges between nodes had been formed . This necessitates careful control over the dose, internode spacing, and the temperature at which the reaction is carried out (to control the various surface-reaction rates).…”