Tailoring the Interfacial Band Offset by the Molecular Dipole Orientation for a Molecular Heterojunction Selector

Abstract

Understanding and designing interfacial band alignment in a molecular heterojunction provides a foundation for realizing its desirable electronic functionality. In this study, a tailored molecular heterojunction selector is implemented by controlling its interfacial band offset between the molecular self‐assembled monolayer with opposite dipole orientations and the 2D semiconductor (1L‐MoS2 or 1L‐WSe2). The molecular dipole moment direction determines the direction of the band bending of the 2D semiconductors, affecting the dominant transport pathways upon voltage application. Notably, in the molecular heterostructure with 1L‐WSe2, the opposite rectification direction is observed depending on the molecular dipole moment direction, which does not hold for the case with 1L‐MoS2. In addition, the nonlinearity of the molecular heterojunction selector can be significantly affected by the molecular dipole moment direction, type of 2D semiconductor, and metal work function. According to the choice of these heterojunction constituents, the nonlinearity is widely tuned from 1.0 × 101 to 3.6 × 104 for the read voltage scheme and from 0.4 × 101 to 2.0 × 105 for the half‐read voltage scheme, which can be scaled up to an ≈482 Gbit crossbar array.

Photo‐Responsive Molecular Junctions Activated by Perovskite/Graphene Heterostructure Electrode

“…However, depolarization effect did not appear to be dominant in our study in which the transport properties showed a clear dipole dependence probably due to a low packing density of phenyl-based molecule SAMs. [59,60] Moreover, a series of recent studies [61,62] have reported a critical role of dipoles in the charge transport behaviors in large area molecular junctions, which supports that the depolarization effect can be neglected in these junctions. BPT has an intrinsic dipole moment, oriented from the thiol group (δ − ) to the molecular backbone (δ + ).…”

Molecular Van Der Waals Heterojunction Photodiodes Enabling Dipole‐Induced Polarity Switching

“…This result is also consistent with that of our previous report obtained using the conductive atomic force microscopy (CAFM) technique. [32] For example, in the WSe 2 /F6H2 heterojunction, because the valence band edge is located between the bias window at V = −1.0 V, the holes only feel the molecular tunnel barrier. Consequently, the transport current is enhanced.…”

“…Two-dimensional (2D) van der Waals semiconducting transition metal dichalcogenides (TMDs) can be considered promising candidates for nanoscale heterojunction unit that vertically connects to molecular SAMs. [31][32][33] They are ultrathin optoelectronic materials, exhibiting significantly higher light absorption per unit thickness than that by typical 3D semiconductors such as Si, GaAs, and even perovskites. [34][35][36][37] Moreover, owing to their intrinsically passivated surfaces devoid of dangling bonds, 2D TMDs result in high-quality heterostructures, in which traps do not hinder the charge transport across the interface.…”

“…[38] Recent reports indicate that molecule-2D TMDs heterojunctions with various molecular species can generate useful electronic functionalities by modulating the charge transport pathways. [31][32][33] For example, depending on the molecular species and the number and types of 2D TMDs used, various electronic functionalities such as a diode, [31] selector, [32] and photo-switching behavior [33] (using photo-switchable azobenzene molecule) have been demonstrated using the scanning probe technique. Note that because the primary reason for the photo-switching behavior is the conformation change of azobenzene molecules by the light illumination, it exhibits slow photo-responsivity.…”

Temperature-Dependent Coherent Tunneling across Graphene–Ferritin Biomolecular Junctions

“…The critical role of the interface in CT across (bio)­molecular junctions has been long recognized ,,− and includes three main contributions: (i) energy alignment, (ii) molecule–electrode coupling strength (Γ, in eV), and (iii) amount of available carriers. Energy alignment dictates the energy barrier (ε 0 , in eV) between the electrode’s Fermi level and the nearest molecular level, which, in turn, depends on the vacuum position of these levels and interfacial charge rearrangement upon formation of the contacts with the electrodes and associated interface dipoles. − This interfacial charging can yield very similar ε 0 for a given (series of) molecule(s) despite large differences (even as large as 1.5 eV) in the electrode’s Fermi position .…”