# Nanofabrication Techniques in Large-Area Molecular Electronic Devices
## 1 Introduction
Importantly, the deposition of molecules onto the electrode can be carried out using simple and scalable technologies that allow high-quality and reproducible assemblies, making possible the manufacture of thousands of devices. This potential processability and scalability in the fabrication of large-area molecular electronic devices are much more appealing for industrial processes opening the door towards industrial mass production. Here, it is encouraging to note that a molecular electronic device for audio processing has already been commercialized [72], albeit briefly. Therefore, the translation of such science to a viable technology for industrial applications is an active goal today, with a considerable number of scientific and technological challenges [73] remaining to be met, as indicated below. Such incorporation of molecules into hard electronics will probably take place, at least in a first stage, in combination with traditional silicon-based current technologies. An optimization of interface engineering has been recently named as \"the most challenging issue that hampers the development of reliable molecular junctions\" in a recent review published in Nature Reviews Physics [13]. Such technology should be able to optimize the molecule-electrode contacts oriented to mass production of high yield, robust, stable, scalable, and reproducible devices to be produced at a reasonable cost. The optimization of the electrode \(|\) molecule interface (Figure 1c) involves several aspects:  
1. Coupling of the molecule to the electrode surface through the contacting group, which plays a crucial role and has prompted an extensive search for chemical groups that can effectively serve as molecular 'anchor groups' [25; 74; 75; 76; 77; 78; 28; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88];
2. Mechanical stability of the electrode molecular junction avoiding fluxional bonds [79; 80]. Several strategies have been employed for this purpose, including the use of multidentate anchor groups [57; 81], and multipodal platforms [82];
3. Compromise between the mechanical stability and electronic coupling since a too strong interface coupling may result in the loss of electrical functionalities and also in poor gating effects in three-terminal structures. This compromise could be reached by the insertion of a spacer between the anchoring group and the conjugated skeleton within the molecular structure [13];
4. Control of the geometry of molecules to avoid fluctuations, due to different orientations (and then a different distance for the electrons tunneling between the electrodes), which can be achieved by an exhaustive control of the surface coverage and molecular packing density [83]. 5. Control of lateral interactions and aggregation effects in molecular assemblies. These lateral intermolecular interactions may have a decisive role in the electron transport properties of large-area devices based on \(\pi\)-conjugated materials [22];
6. Deposition of the top contact electrode avoiding the formation of short-circuits and/or damage of the functional organic molecules in the monolayer [84; 85]. Taking into account this scenario, consideration is now being given to device fabrication strategies (deposition of a monolayer onto the bottom electrode and deposition of the top contact electrode onto the monolayer) for the construction of large-area devices that could progress the integration of the concepts of single-molecule electronics towards viable large-area devices. The objective of this focused review, with no claims of completeness, is to describe the most widely used strategies for the deposition of a monolayer onto the bottom electrode, as well as an overview of the top-contact deposition methods explored so far.