# Nanofabrication Techniques in Large-Area Molecular Electronic Devices
## 1 Introduction
* The versatility of organic chemistry to produce millions of identical functional units (molecules)--estimated in \(10^{60}\) molecules with 15 atoms or fewer [51]--is expected to result in not only in low-cost manufacturing, due to self-assembly (SA) capabilities, but also in thinner and low-weight devices, lower supply-voltages [51], as well as a large variety of new and distinctive functionalities provided by molecules (optical, magnetic, thermoelectric, electromechanical, etc. ), which are often not possible by employing conventional materials [10]. * Redox-active molecular components can be addressed and'switched' through the introduction of a third 'gate' electrode [55; 56; 57; 45]. In this field, exploration of the molecular structure, ligands, inclusion of different metal clusters, control of electrochemical gating together with the potential for modular construction [58] may have relevant implications in the field of molecular electronics. * The properties of (magnetic) molecules together with control over the spin state of molecular devices by tuning the interaction of the localized orbitals of the molecule with the electronic states of the electrode also open the door to the exploration and control of spin transport phenomena and spintronic applications, e.g., switches and qubits [59; 60; 61; 62]. In addition, the study of magnetic spins on a molecule connected to a superconducting electrode represents a fascinating topic of interest today [63]. * One of the most promised envisioned applications of molecular electronics is thermoelectrics, i.e., efficient conversion of heat to electricity [64]. Fabrication of ultrahigh-efficient thermoelectric power generators as small as one molecule is possible, and could potentially be used to build ultrahigh-efficient thermoelectric power generators [64; 65; 66]. These power converters could reuse and recycle the dissipation heat produced by (molecular) electronic devices into electricity to (partially) supply the power required to operate the device, resulting in a meaningful decrease in electric power consumption [67], and also in applications for on-chip cooling in nanoscale electronic devices [68]. * The combined use of organic molecules and carbon-based or polymeric-based materials as electrodes could pave the road towards not only flexible devices [69; 33], but also to biocompatible electronics [70] and also lead to more sustainable fabrication processes, reduce e-waste and culminate in the development of electronics that self-degrade after service life [71]. Two different paradigms have attracted the interest of researchers in the field of molecular electronics. On the one hand, the study of single-molecule junctions, i.e., electrode \(|\) molecule \(|\) electrode, is of fundamental importance for the understanding of charge transport, as well as the different factors that determine the electrical properties of these junctions, Figure 1a. Thus, it is well known that the molecular structure, the anchoring groups, the presence of metal or redox moieties, etc. can strongly determine charge transport at the molecular level. However, fabrication of these single molecular junctions with our current technology is not a scalable process, which seriously hampers the incorporation of molecular electronics into the market. On the other hand, the study of large-area devices, i.e., electrode \(|\) molecular assembly \(|\) electrode, has gained attention in the last years. Here, collective effects (intermolecular forces and polarization phenomena), induced by the close packing of the molecules in the monolayer, may determine the electrical behavior of these systems, which opens the door to finding new effects and also to tune the properties of the devices by an exhaustive control of interactions between neighbor molecules, Figure 1b. Additionally, these molecular assemblies allow the manufacture of devices with a surface density of up to \(10^{15}\) molecules:cm\({}^{-2}\).