Controlling the direction of rectification in a molecular diode

Abstract

A challenge in molecular electronics is to control the strength of the molecule-electrode coupling to optimize device performance. Here we show that non-covalent contacts between the active molecular component (in this case, ferrocenyl of a ferrocenyl-alkanethiol self-assembled monolayer (SAM)) and the electrodes allow for robust coupling with minimal energy broadening of the molecular level, precisely what is required to maximize the rectification ratio of a molecular diode. In contrast, strong chemisorbed contacts through the ferrocenyl result in large energy broadening, leakage currents and poor device performance. By gradually shifting the ferrocenyl from the top to the bottom of the SAM, we map the shape of the electrostatic potential profile across the molecules and we are able to control the direction of rectification by tuning the ferrocenyl-electrode coupling parameters. Our demonstrated control of the molecule-electrode coupling is important for rational design of materials that rely on charge transport across organic-inorganic interfaces.

Model of self assembled monolayer based molecular diodes made of ferrocenyl-alkanethiols

“…In order to improve the understanding, we consider the specific case of a 11-(ferrocenyl)-1-undecane-thiol (HSC 11 Fc) based molecular diode. As it is depicted in Figures 1(a) and 1(b), we consider a self-assembled monolayer (SAM) of SC 11 Fc sandwiched between two electrodes, forming a Metal-SAM-Metal diode.…”

“…As it is depicted in Figures 1(a) and 1(b), we consider a self-assembled monolayer (SAM) of SC 11 Fc sandwiched between two electrodes, forming a Metal-SAM-Metal diode. The first electrode is made of silver (Ag).…”

“…Nijhuis, Reus, and Whitesides 10 and Yuan et al 11 obtained RR greater than 100 using ferrocenyl-alkanethiol based molecular diodes in which both electrodes exhibited similar work functions. In this case, the rectification process was not governed by the work function difference between the electrodes but was due to the intrinsic rectifying properties of ferrocenyl-alkanethiols.…”

“…In this case, the rectification process was not governed by the work function difference between the electrodes but was due to the intrinsic rectifying properties of ferrocenyl-alkanethiols. Furthermore, Yuan et al 11 experimentally showed very recently that a control of the direction of rectification is possible by placing the Fc units of ferrocenyl-alkanethiols (HSC i FcC 13Ài ) at different positions within the alkyl chain. In this study, we develop a multiband quantum transport model based on a matrix formulation 12 in which we consider both the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) levels and examine the electrical properties of the molecular junctions made of ferrocenyl-alkanethiols.…”

“…After this introduction, Section II of the paper is devoted to the description of the model developed to study the electrical properties of the molecular diodes. Section III is dedicated to the simulation of the electrical properties of HSC 9 Fc and HSC 11 Fc based molecular diodes. We investigate a) david.duche@im2np.fr the influence of the HOMO and the LUMO energy bands of the ferrocene moiety and the alkyl chain length on the electrical properties of the diodes.…”