Versatile electrochemical approaches towards the fabrication of molecular electronic devices

The concept of molecular electronic devices (MEDs) has evolved since the first theoretical report was published in 1974. This theoretical article laid the foundation for understanding charge-transport phenomena by utilizing either a single molecule or numerous molecules sandwiched between two electrical conductors. Since then, many research groups have engaged in molecular junction fabrication using a variety of molecules including organic, inorganic, and organometallic molecules, polymers, and biomolecules that can mimic the electronic functions of traditional silicon-based devices. To date, most of these molecular junctions have been constructed using well-explored molecular assemblies of thiolated derivatives adsorbed mostly on Au substrates. However, the Au-S bond is not considered to be a true covalent bond in view of its surface bond energy, which is ∼1.9 eV, much less than pure covalent bond energy. Additionally, Au-S interfaces suffer from poor reactivity and instability over time; thus, they are not suitable for real world applications. Therefore, an alternative approach for the fabrication of molecular electronic junctions must be envisioned to address all the difficulties mentioned above. Herein, we summarize the most recent experiential outcomes to demonstrate how electrochemical techniques can be employed to form robust molecular layers on various substrates including Au, ZnO, SnO₂, H-terminated Si, and conductive carbon electrodes that are suitable for the fabrication of reliable molecular electronics devices for charge-transport studies. This fascinating electrochemical technique is appropriate for producing not only homostructure but also heterostructure molecular layers with desired thicknesses. We also discuss the pros and cons of the electrochemical process for growing molecular layers in the Conclusion and outlook section.