# Nanofabrication Techniques in Large-Area Molecular Electronic Devices
## 2 Fabrication of Molecular Films, Deposition Techniques
### The Self-Assembly Technique
These seminal works served to set the basis of the methods to measure the electrical properties of both single-molecules and ensembles of molecules and also to demonstrate the viability of using molecules as basic elements in circuitry. However, the Au-S bond is fluxional and not very stable, which explains some of the reproducibility problems encountered in the literature [92; 109]. Additionally, other drawbacks to the thiol on gold SA technique have been reported, such as the tendency of organic thiols to oxidize to disulfides; this problem can be overcome by using protected thiols, but the incorporation of extraneous material within the system when in situ deprotection steps are involved may also affect the final electrical properties of the system [180]. The chemical reactivity and thermal stability of these systems in ambient and aqueous solutions have also been reported to seriously limit the technological applications of thiol and dithiol monolayers on gold [161]. Moreover, a recent contribution has revealed that SAMs prepared from the solution deposition of dithiols do not have a chemisorbed character [181]. For these reasons, many other anchor groups have been studied in the last two decades on different substrates (SiO\({}_{2}\), Cu, Ag, Au, WO\({}_{3}\), and ITO-indium tin oxide-among others), including selenols [94], amines [110; 111], cyanides and isocyanides [95; 96], isothi cyanates [182], trimethylsilyl group [183; 184], acetylenes [185; 107; 112; 124; 186], thiophenes [132; 186], trichlorosilanes [133], trimethoxysilanes [97; 142], phosphonate [98; 105] terminated molecules, perylenes [187], and fullerenes [106; 188; 189]. Recently, [PERSON] et al. [106] reported the spontaneous formation of molecular junctions of glycol ether functionalized fullerenes on Au\({}^{\text{TS}}\), which resulted in the large stability and robustness of the SAMs. As it was mentioned before in the introduction section of this review, much interest has been paid recently to the use of SAMs incorporating multidentated anchor groups [190] that are expected to provide additional robustness to the molecular junction, lower fluctuation defects, more efficient electronic coupling, and enhanced electrical performance [26; 170]. In this context dithiols [100; 122], carboxylic acids [103], dithiocarbamates [123; 191], carbodithiolates [75], dithiocarboxylic acids [93], tetrathialfulvalenes [131], phosphonic acids [101; 102; 192] and cathecols [136] terminal groups have been assembled in SAMs and their electrical response evaluated. Some of these multidentated anchor groups have been demonstrated to exhibit superior electrical properties. For instance, dithiocarbamates on gold result in improved stable and low contact resistance junctions in comparison to thiol contacts, with a drop in the contact resistance by ca. 2 orders of magnitude [123]. Multiposal platforms also provide firm coupling between the molecule and the electrode through individual anchor points, and are also receiving increasing interest. Examples include tripodal [134; 135; 193] and tetrapodal [194] platforms incorporated onto SAMs which, allow to make a strong contact and to enforce an orientation of the molecules at a fixed distance from the surface [190]. Additionally, a selection of the bulky tripodal platform guaranties an effective separation with the metal surface, avoiding the quenching of the excited state caused by the metal surface in a photoisomerization process, allowing to develop optoelectronic devices of great interest in the electronic industry [82]. Construction of multilayer films using multipodal molecules by hydrogen-bond formation through pH control has also been used to demonstrate long-range electronic transport [192]. Other relevant properties in multipodal platforms have also been found, including attenuation of tunnel currents more effectively than do the corresponding monodentate SAMs, which may be useful in future applications for gate dielectric modification in organic thin-film devices [101].