# Nanofabrication Techniques in Large-Area Molecular Electronic Devices
## 2 Fabrication of Molecular Films, Deposition Techniques
### The Self-Assembly Technique
More examples of both multidentate [74; 81; 195] and multipodal [196; 197; 198] platforms have been studied at the single molecular level, though the extension of these investigations to large-area ensembles is a topic of growing interest. The incorporation of compounds with different molecular lengths has been recently explored as a tool to tune the electronic interaction between neighbor molecules in these mixed SAMs, which results in changes in the quantum tunneling performance of the devices [199; 200]. This result opens the door to the exploration of new functionalities taking advantage of the lateral supramolecular organization of the molecules in SAMs. Whilst, the incorporation of photochromic moieties to fabricate switching molecular electronics devices, where it is possible to control the on/off state by external stimuli, is also a topic of interest [201]. In addition to the standard SA method, the combination of SA capabilities with other techniques, such as electrochemistry results in the electrically assisted self-assembly methodology [202; 203; 204; 205; 206; 207] that may result in a significant decrease in the deposition time and an improve in the quality of the monolayer. Self-assembly strategies in which molecules are located onto a gold electrode by forming covalent Au-C \(\sigma\)-bonds [208] have resulted in SAMs with a significantly higher conductance than those with the above-described conventional anchoring groups [76; 209; 210; 211]; electrically transmissive monolayers with Au-C junctions have also been reported [112]. These results are attributable to the creation of exceptionally stable SAMs (\(\sim\)4 eV) and strong electronic coupling because of an uninterrupted conjugation between the electrode and the molecule [107; 212]. These investigations have been extended to other interfaces, including various metal-C and C (from the electrode)-C (from the molecule) [212], as well as silicon-C junctions [34]. Ultrastable SAMs with high thermal, hydrolytic, chemical, oxidative, and electrochemical stabilities of N-heterocyclic carbenes (NHCs) on gold have also been demonstrated [213]. Proteins are basic elements that work as building blocks in bioelectronics devices, including protein-based transistors or sensing applications (monitoring bio-molecular interactions between target molecules and proteins). In this context, an important body of research in the field of molecular electronics is being done with proteins both at a single-molecule level [214; 215; 216; 217; 218] and thin-films comprising a monolayer or a short number of layers [219; 220; 221; 222; 223]. Additionally, it has been experimentally and theoretically proved that it is possible to tune molecular electron transfer rates in electron transfer proteins (ETpr's) through (i) chemical modifications and changes in the redox center, as well as the locations of the donor, the acceptor, and the bridge moieties within the ETpr's structure [220; 224; 225; 226; 227; 228] (ii) modifying the solvent environment [229], and importantly, (iii) orientation relative to the electrode and changing the strength of the protein-electrode coupling [230; 231; 232]. The study of large-area protein-based molecular electronic devices has been carried out mainly by the self-assembly method [148; 149] via an appropriate linker. DNA has also focused the interest of researchers in the molecular electronics community due to several reasons, including (i) superior self-assembly properties [233; 234]; (ii) its unique electrical properties [235], and (iii) its potential use in bioelectronics devices. Additionally, a combination of self-assembly and dielectrophoresis (DEP) methodologies has been pointed out as an efficient tool in the construction of nanodevices [236]. Relative large materials in the field of molecular electronics, including proteins, DNA, carbon nanotubes, graphene oxide, nanoparticles, etc., can be assembled onto an electrode by means of DEP [148; 223; 237; 238; 239; 240; 241; 242; 243].