Measuring Molecular Junctions: What Is the Standard?

Abstract

Accurate measurements of electronic properties of molecular junctions are important for both fundamental and practical applications. Often the molecule-electrode contacts are poorly characterized, leading to wide variation in the measured resistance values. A new paper in this issue demonstrates the use of a reference molecule as an internal standard to compensate for the varying conditions of the molecular contact in conductive-tip atomic force microscopy measurements and yields consistent resistances relative to the reference despite variations in absolute resistance.

Transition voltages respond to synthetic reorientation of embedded dipoles in self-assembled monolayers

“…In these systems interfaces play an important role in defining the characteristics of a junction and both approaches suffer from an uncertainty—is transport dominated by molecules or by interfaces? 1 , 2 Electron transport in large-area junctions is affected by defects in self-assembled monolayers (SAMs) that can dominate transport in certain cases, 3 while single-molecule junctions exhibit background currents in which tunneling charges flow directly from one electrode to the other, by-passing the molecule in between. 4 Thus, the magnitude of J or I (current-density or current) by itself varies considerably and therefore carries little useful information on the intrinsic electronic properties of the molecules in the junction.…”

Influence of an Atom in EGaIn/Ga2O3 Tunneling Junctions Comprising Self-Assembled Monolayers

“…The minutia of their structure also become important handles for manipulating tunneling currents, if they can be successfully incorporated into devices. The use of SAMs in ME therefore reduces to a problem of finding adequate materials with which to form “top” contacts that do not damage SAMs. , Mercury drops and poly(ethylenedioxythiophene):poly(stryrenesulfonate) (PEDOT:PSS) have proven capable of this task, particularly for SAMs of alkanethiolates. The former is a liquid metal that readily conforms to the topology of the SAM, while the latter acts as a buffer layer that reduces the frequency of shorts.…”

Polarizabilities of Adsorbed and Assembled Molecules: Measuring the Conductance through Buried Contacts

“…Thus, we are able to probe the electronic connection between the switch molecules and substrate ( i.e. , the contacts − ) by measuring polarizability ( vide supra ).…”