Top-contacting molecular monolayers using single crystalline Au microplate electrodes† Radha Boya, Deepak Jayaraj and Giridhar U. Kulkarni * Integrating molecules in electronic devices to exploit their unique properties requires efficient methods to bring about their electrical contact in large arrays. In this study, chemically synthesized single crystalline Au microplates have been employed as top-contact electrodes in a micro-sandwich device where molecules could be sandwiched between the bottom Au film and the top microplate in capacitor geometry. The device has been tested employing many alkanemono- and -dithiols not only in as-adsorbed conditions but also under dynamic loading. Further, encapsulation using PDMS was carried out which enhanced its stability and shelf-life. Introduction Transcending Moore's law, molecules are the choice of future nanoelectronics, as they represent eventual miniaturized active elements. 1 Following the seminal work by Aviram and Ratner in 1974, 2 there have been many reports on molecules in elec- tronics. A wide variety of molecules, from simple alkanethiols to conjugated monolayers, have been investigated, both theoreti- cally and experimentally, for applications in interconnects, diodes, transistors, logic circuits, photovoltaics, and lubricants as well as for memory applications. 3 In this context, several nanofabrication methods 4 and device architectures 5 have been explored as molecular test beds. 6 For contacting molecules, generally a densely packed self-assembled monolayer (SAM) of molecules is rst formed on a substrate, followed by deposition of a noble or a semi-noble metal onto the SAM, 7 so as to form a at top electrode with surface roughness at the molecular length scale (<1 nm), as is generally achievable with the bottom electrode itself. Unfortunately, this approach leads to electrical shorts through defect areas in the SAM resulting in low (<1%) device throughput. 8 Many alternatives have been tried, such as cold evaporation of the top metal 9 and nanopore models for the top electrode, 10 but it is rather difficult to completely eliminate possible electrical leakage. Scanning probe methods, 11 hanging mercury electrodes, 12 cross wire junctions, 13 break junctions, 3 self-assembled nanogaps formed by nanorods coupled to molecules, 14 multi-layer edge devices where molecules are bridged vertically, 4 surface diffusion mediated so contact deposition, 15 nanotransfer printing 9 etc., are other alternative methods, which deal with either small electrode areas or curved surfaces. Large area at Au electrodes supported by PEDOT:PSS 16 or graphene 17 interlayers beneath have also been tried in order to prevent metal leakage. While the above mentioned device architectures are useful for studying molecular conduction processes, the molecules may not be amenable to external inuences, say in chemical sensing. An open architecture with a simple, easy-to-fabricate method for top- contacting an assembly of molecules is still a challenge, and is the focus of the present work. For this purpose, single crystalline, highly (111) oriented Au microplates, synthesized by a novel method developed in our laboratory, 18,19 were chosen as elec- trodes instead of the conventional polycrystalline Au. The nanometric roughness 19 achievable with the microplate surfaces prompted us to use them as top electrodes for molecules. Indeed, the Au microplates have served as top electrodes for vertically grown InAs nanowires establishing ohmic contacts by electrical activation. 20 Encouraged by the results, the present study tran- scends the idea to a much ner length scale, namely molecules in SAMs. The molecules chosen for the study are alkanemono- and -dithiols, as these are considered perfect models for any new test bed. 21 Further, we have carried out dynamic thermal and mechanical analyses of the molecular devices. The proposed device promises an unprecedented synergic combination of versatility and off-the-shelf utility. Results and discussion Fig. 1(a) schematically shows the fabrication steps of the proposed micro-sandwich molecular device (details in experi- mental section). The device works in the capacitive geometry Chemistry and Physics of Materials Unit and DST Unit on Nanoscience, Jawaharlal Nehru Centre for Advanced Scientic Research, Jakkur P. O., Bangalore 560 064, India. E-mail: kulkarni@jncasr.ac.in † Electronic supplementary information (ESI) available: Detailed materials and methods; surface roughness measurements of Au microplate electrode; resistance of a single molecule plotted versus the number of carbons of the alkanethiol and dithiol molecules probed in the molecular junction device; Table S1 showing b values typically observed in various methods of probing molecular junctions; I–V and J–V plots of molecular junctions in linear scale. See DOI: 10.1039/c3sc00058c Cite this: Chem. Sci., 2013, 4, 2530 Received 8th January 2013 Accepted 1st April 2013 DOI: 10.1039/c3sc00058c www.rsc.org/chemicalscience 2530 | Chem. Sci., 2013, 4, 2530–2535 This journal is ª The Royal Society of Chemistry 2013 Chemical Science EDGE ARTICLE