Ultrasmooth and Photoresist‐Free Micropore‐Based EGaIn Molecular Junctions: Fabrication and How Roughness Determines Voltage Response

Abstract

In molecular electronics, it is critical to minimize the sources that can result in defective electrodes, such as contaminations related to the fabrication process (photoresist and organic residues) or roughening of the electrode during etching, because these defects hamper the formation of well‐organized molecular structures. Junctions based on micropores are desirable as they are scalable, but micropores are not fabricated on ultrasmooth template‐stripped electrodes, and may suffer from stray capacitances and leakage currents across the insulating matrix. A method is reported to fabricate micropores in AlOx on template‐stripped Au based on a two‐step etch process so that the Au surface is not in direct contact with photoresistance during the fabrication process. These junctions do not suffer from stray capacitances or leakage currents, enable temperature variable measurements down to 8.5 K, have excellent current retention characteristics, and are stable for at least 2 months. By analyzing the normalized differential conductance curves and detailed comparison against junctions with cone‐shaped tips of EGaIn and EGaIn stabilized in a through‐hole in polydimethylsiloxane, how the surface roughness of top electrodes affects the effective contact area, influences the symmetry of the response of the junctions, and how the electrical characteristics scale with molecular length are established.

A Single Atom Change Turns Insulating Saturated Wires into Molecular Conductors

“…69 In this framework, the distance dependence of the conductance is related to a thickness-dependent barrier akin to the one inherent to the Simmons model. 68,70 In their model, however, the barrier arises from the presence of localized charge traps along the path of charge migration leading to a non-linear potential drop between the macroscopic leads. Figure 6f shows the linear relation of the double-log plot of β vs. ' with a slope of -0.82 which is lower than the expected -0.5 from the model by Berlin et al 69 , but note that a change in the contact resistance or further changes in the barrier shape are not taken into consideration in this model.…”

Nanofabrication Techniques in Large-Area Molecular Electronic Devices

“…Finally, the sample is placed in a vacuum chamber to thermally deposit the bottom metal (Au) electrode. Recently, large-area junctions based on SAMs deposited in AlO x micropores fabricated on ultraflat template stripped bottom electrodes of gold (Au TS ) have been fabricated with high mechanical stability [378]. The construction of a nanowell is more simplified, and occurs in a planar device in contrast with the nanopore.…”

Photoswitching Molecular Junctions: Platforms and Electrical Properties

“…The construction of ensemble molecular junctions is more robust for ensuring well‐defined electrical conductance because of the nature of ensembled molecules; furthermore, it is more practical in terms of reproducibility, yield, and mass production because of the large‐scale bottom and top configuration. To construct ensemble molecular junctions, large‐area junctions, [48–51] conductive atomic force microscopy (C‐AFM) junctions, [52–54] liquid metal junctions, [46,72–74] crosswire junctions, [75,76] and nanoparticle network junctions [34,55] have been proposed. In contrast to the single molecule junctions, ensemble molecule junctions with well‐ordered self‐assembled monolayers (SAMs) offer a more robust electrical conductance and a more straightforward junction fabrication process.…”

“…However, it is challenging to control the number of molecules at the contact because of the curvature of the wires. Liquid metal junctions have been exploited extensively in the area of molecular electronics because of their high device yield and easy settlement of junctions [46,72–74] . In addition, the liquid metal technique is unlikely to create defects in the SAMs.…”