Large-Area, Ensemble Molecular Electronics: Motivation and Challenges

Abstract

We review charge transport across molecular monolayers, which is central to molecular electronics (MolEl), using large-area junctions (NmJ). We strive to provide a wide conceptual overview of three main subtopics. First, a broad introduction places NmJ in perspective to related fields of research and to single-molecule junctions (1mJ) in addition to a brief historical account. As charge transport presents an ultrasensitive probe for the electronic perfection of interfaces, in the second part ways to form both the monolayer and the contacts are described to construct reliable, defect-free interfaces. The last part is dedicated to understanding and analyses of current-voltage (I-V) traces across molecular junctions. Notwithstanding the original motivation of MolEl, I-V traces are often not very sensitive to molecular details and then provide a poor probe for chemical information. Instead, we focus on how to analyze the net electrical performance of molecular junctions, from a functional device perspective. Finally, we point to creation of a built-in electric field as a key to achieve functionality, including nonlinear current-voltage characteristics that originate in the molecules or their contacts to the electrodes. This review is complemented by a another review that covers metal-molecule-semiconductor junctions and their unique hybrid effects.

Anomalously Rapid Tunneling: Charge Transport across Self-Assembled Monolayers of Oligo(ethylene glycol)

“…Our XPS work, carried out with modern instruments (Thermo Scientific K-Alpha XPS) with a good signal to noise ratio, clearly indicates conformations that extend approximately perpendicular to the surface. Analysis by ellipsometry indicates thinner monolayers than expected based on calculated lengths, but accurate ellipsometry on these very thin films is difficult, 7,46 and we conclude that the values calculated by XPS are correct for our system. 22 Measurements of J(V) at forward and reverse biases (± 0.5 V and ± 1.0 V) produced nearly symmetrical profiles with rectification ratios (r = |J(+V)/J(-V)|) ≤~4 for both SAMs of alkanethiolates and SAMs of oligo(ethylene glycol)s on gold.…”

Molecular Semiconductors for Logic Operations: Dead‐End or Bright Future?

“…The fields of charge injection and contact engineering is particularly wide as different situations occur as a function of semiconductors, electrodes, and fabrication methods. Interested readers are directed toward excellent review papers . Some groups have even searched for simple, robust, and even universal strategies to reduce contact resistance and ensure ohmic injection .…”

From active plasmonic devices to plasmonic molecular electronics

“…In the following sections, we discuss these different points in the context of molecular electronics where molecular junctions are the main building blocks. A molecular junction consists of a single molecule or an ensemble of many molecules between two conducting electrodes . When the distance d between the two electrodes (or the thickness of the molecular layer) is below 5 nm, as in many single‐conjugated‐molecule devices, direct off‐resonant tunnelling through the molecule acting as a barrier is the dominant transport mechanism.…”