# Nanofabrication Techniques in Large-Area Molecular Electronic Devices
## 3 Fabrication of the Top Contact Electrode
Meanwhile, soft top-contacts for the non-destructive fabrication of molecular junctions using floating-processed ultrathin graphene films [384], or transferred onto the layer via poly(methyl methacrylate) (PMMA)-mediated transfer [388], have also been implemented. Nanoscale gaps in SWNTs with precise control are fabricated by lithography-defined oxidative cutting [389], resulting in SWNT-molecule single-molecule junctions, which could be easily extended to industrial mass production since all of the operations in the process are compatible with conventional micro- and nanofabrication techniques [9]. Meanwhile, using dash-line lithography [390], robust single-molecule junctions with a high yield, based on indented graphene point electrodes can be created. This methodology provides a large control regarding the size of the nanogaps through the regulation of the etching process. Electron beam evaporation of carbon (e-C) to create soft top-contact electrodes onto monolayers has been used successfully with a high yield, excellent reproducibility, and thermal stability [33; 391; 392; 393; 331; 332; 333; 334; 335; 336; 337; 338; 339]. The fabrication of amorphous carbon top-contact electrodes (with well-defined shape, thickness, and precise positioning on the film) from a naphthalene precursor using a focused electron beam induced deposition (FEBID) technique has been recently employed to create molecular junctions with a high yield and stability [117]. Once the top-contact electrode is fabricated to close the circuit, the typical way to verify that these molecular junctions, created with a given structure, are reliable is to statistically investigate the electrical characteristics of these devices. Conducting-atomic force microscope (C-AFM) and scanning tunneling microscope (STM) are the techniques usually used to address the electron transport properties of these devices by registering current-voltage (_I-V_) curves (or density current-voltage (_J-V_) curves). A detailed analysis of these curves together with temperature-varying measurements allow to rule out the presence of short circuits; also to determine conductance through the fabricated molecular junctions, as well as establish the mechanisms that govern the charge transport; in addition, it is possible to elucidate energy level alignments through a spectroscopic analysis (by the transition voltage spectroscopy, TVS, method). Theoretical models are also employed to better understand the charge transport mechanisms through the molecular junctions. Whilst, the shape of the obtained conductance histograms for the molecular junctions is an efficient technique to determine the interaction energy between adjacent molecules, one of the key parameters to understand and optimize the performances of these large-area molecular electronic devices. Additionally, inelastic electron tunneling spectroscopy (IETS) can be utilized to investigate the vibrational modes in the molecular junctions. In addition,the thermoelectricity of the molecular junction, which measures the induced voltage drop or the induced current across the junctions between two electrodes at different temperatures, helps our understanding of the mechanism of the thermoelectric effect, and therefore, may serve to improve the technologies for converting wasted heat into useful electrical energy. Finally, the determination of durability and operational stability of the device is crucial for the practical application of these devices in the actual industry.