Nanogap Electrodes towards Solid State Single‐Molecule Transistors

Abstract

With the establishment of complementary metal-oxide-semiconductor (CMOS)-based integrated circuit technology, it has become more difficult to follow Moore's law to further downscale the size of electronic components. Devices based on various nanostructures were constructed to continue the trend in the minimization of electronics, and molecular devices are among the most promising candidates. Compared with other candidates, molecular devices show unique superiorities, and intensive studies on molecular devices have been carried out both experimentally and theoretically at the present time. Compared to two-terminal molecular devices, three-terminal devices, namely single-molecule transistors, show unique advantages both in fundamental research and application and are considered to be an essential part of integrated circuits based on molecular devices. However, it is very difficult to construct them using the traditional microfabrication techniques directly, thus new fabrication strategies are developed. This review aims to provide an exclusive way of manufacturing solid state gated nanogap electrodes, the foundation of constructing transistors of single or a few molecules. Such single-molecule transistors have the potential to be used to build integrated circuits.

Massively parallel fabrication of crack-defined gold break junctions featuring sub-3 nm gaps for molecular devices

“…When data was only collected for positive bias voltages, as was the case for all the junctions not used in the molecular junction experiments in our study, we found that assuming a symmetric barrier (φ L = φ R ) produced better fits. While both symmetric and asymmetric barrier could be fitted to the I-V data to produce fits of visually similar quality (see Junction 3,7,8,13,and 22 in the data series presented in Supplementary Note 1), the values for barrier height for the case of symmetric barrier were more reasonable; when an asymmetric barrier was assumed, the two barrier heights were found to be comparable in most cases, but were very different in a few cases (e.g., 0.6 and 3.9 eV or 0.05 and 2.8 eV). The gap widths did not vary by more than 0.1 nm between the two barrier models unless the barrier heights were very different for the left and right electrodes like in the cases mentioned above.…”

“…P ractical molecular electronics based on solid-state devices will require the integration of arrays of interconnected molecular junctions into circuits and systems [1][2][3][4][5] . Before this becomes possible, new methodologies have to be developed for scalable and reproducible fabrication of nanogap electrodes featuring sub-3 nm wide gaps [6][7][8][9][10] . Mechanically controllable break junctions (MCBJs) 4,6,8,9,11,12 , scanning tunneling microscopy based break junctions (STM-BJ) 13,14 and electromigration breakdown junctions (EBJs) 15,16 made of gold are currently the most widespread nanogap electrodes used to realize molecular junctions.…”

“…Before this becomes possible, new methodologies have to be developed for scalable and reproducible fabrication of nanogap electrodes featuring sub-3 nm wide gaps [6][7][8][9][10] . Mechanically controllable break junctions (MCBJs) 4,6,8,9,11,12 , scanning tunneling microscopy based break junctions (STM-BJ) 13,14 and electromigration breakdown junctions (EBJs) 15,16 made of gold are currently the most widespread nanogap electrodes used to realize molecular junctions. For fundamental investigation of molecular junctions, reconfigurable nanogaps with sub-nm precision can be achieved using MCBJs and STM-BJs.…”

Sub‐5 nm Metal Nanogaps: Physical Properties, Fabrication Methods, and Device Applications

“…Previously, metal nanogaps have been reviewed with different specific focuses, such as on fabrication methods based on physical [39] or chemical methods, [40] various applications in specific areas, including electrodes, [41,42] molecular devices, [43,44] Compared with the relatively mature fabrication methods for nanogaps, sub-5 nm is a critical gap size that requires special methods to achieve. Moreover, many important properties and applications can only be achieved with sub-5 nm nanogaps, and the corresponding fabrication and devices are more challenging; thus, this area deserves more attention.…”

“…Previously, metal nanogaps have been reviewed with different specific focuses, such as on fabrication methods based on physical or chemical methods, various applications in specific areas, including electrodes, molecular devices, or plasmonic devices, and fabrication techniques for massive production . These reviews offer very good references for researchers and practitioners from a very specific perspective or from a broad view of metal nanogaps.…”