# Nanofabrication Techniques in Large-Area Molecular Electronic Devices
## 2 Fabrication of Molecular Films, Deposition Techniques
### The Electrografiting Technique  
Electrografiting (EG) is a well-known approach for surface functionalization or modification, in which an electrochemical reaction takes place between the conductive substrate and organic material [312]. This methodology has two main and powerful advantages:  
* The formation of a direct covalent bond between the electrically active molecule (s) and the electrode, resulting in stable and robust molecular junctions. Carbonaceous electrodes (in addition to other conductive substrates, such as metals, metal oxides, polymers, and semiconductors) are relatively easy to functionalize. The use of carbon-based electrodes represents a growing trend today in the development of sustainable technology able to manufacture electronic devices free of expensive and contaminant materials [313]. Nevertheless, the main drawback associated with this methodology is the tendency to form non-ordered multi-layered systems, due to the extremely high reactivity of free-radicals involved in the electrografting process. Several strategies have been successfully used in order to avoid such a multilayer growing. These approaches include molecular functionalization with bulky groups or the use of redox mediators or inhibitors [314; 315]. EG covers reductive and oxidative processes, depending on the organic compound, as was comprehensively described before by [PERSON] and [PERSON] [312]. Since this methodology was developed [316], different functional groups have been used for surface modification, including aliphatic amines [99], aromatic amines [317], or diazonium salts [314; 315]. In the field of molecular electronics, widespread research concerns the modification of a bottom electrode (metals, carbon-based electrodes, hydrogenated silicon surfaces, etc.) by electrografting of diazonium salt derivatives [314; 315; 318; 319]. One of the preferred methodologies to generate diazonium cations is the in situ diazotization of aromatic amines, as illustrated in Figure 4[320]. As a general procedure, the diazotization step is followed by the electrochemical reduction, where highly active aryl radicals are produced. Subsequently, these radical intermediates covalently bind to the surface [128]. Numerous examples can be found in the literature reporting molecular electronic devices based on the electrografting of diazonium salts. Here, it is noteworthy the pioneering work done in the group of [PERSON] [321; 322], that reported the first all-carbon based molecular tunnel junctions. This group also developed methodologies for the grafting of diazonium salts onto a pyrolyzed photoresist film (PPF) [323] and has recently reported an all-carbon molecular electronic device constructed on flexible or semi-transparent substrates [33]. These methodologies and materials pave the way for applications in which molecular electronics and photonics are combined. Additionally, the [PERSON] group also launched the first commercialized molecular electronic device, in which a molecular rectifier composed of a molecular layer sandwiched between two carbon-based electrodes is used for audio processing applications [72]. A different and emerging family of suitable molecules for indirect or direct electrografting are iodonium salts [130]. Concerning the direct grafting, [PERSON] et al. [324] have reported the surface functionalization of a gold substrate by UV-light grafting of the 3,5-bis (trifluoromethyl)phenyl)iodonium salt. [PERSON] et al. [325] recently described the fabrication of electrografted films by oxidation of anitrophenylbutyrate derivative (NO\({}_{2}\)Ph(CH\({}_{2}\))\({}_{3}\)COO\({}^{-}\)) exploring the influence of different supporting electrolyte ions on the film formation. [PERSON] et al. [326] used a two-phase bipolar grafting system to simultaneously functionalize gold bipolar electrodes with diazonium salts and primary amines or thiophenes.