Synthesis of nanoscale electronic device by molecular place exchange reaction in the nanoparticle nanoelectrode bridge platform. : Synthesis of nanoscale electronic device by molecular place exchange reaction in the nanoparticle-nanoelectrodebridge platform

• For reducing the size and power consumption of electronic devices, building components with molecules is one alternative1. This has not been a success yet due to difficulty in creating stable molecular junctions2, 3. In efforts of creating molecular devices, we have developed the nanoparticle-nanoelectrode-molecule-bridge platform4  which has been employed to prepare 1,8 octanedithiol based molecular devices with stable metal molecule junctions5 and enabled us to observe the vibrational signals from inelastic electron tunneling spectroscopy (IETS) measurements6. The platform is electrically and mechanically stable over periods of months7.Nanoparticle-nanoelectrode-molecule bridge platform is fabricated by the standard cleanroom techniques; where 150 nm wide patterns are developed using combination of Electron beam lithography and Photolithography. Gold is deposited using standard resistive evaporation. A very fine cut is made in the gold line using Focused Beam of Gallium ions that results in less than 20 nm separation (nanogap) between the electrodes. Gold nanoparticles (AuNPs) coated with stopper ligands and alkane thiols are synthesized by wet chemistry. Proportions of stoppers and alkane monothiols is controlled and nano particles with 5% to 10% stopper coverage (90% to 95% monothiols)  are synthesized and used in present work. These functionalized AuNPs are trapped in the nanogaps using dielectrophoretic trapping technique. Here we present fabrication of molecular electronic nano devices based on biphenyl-4,4′-dithiol  and TBTs by molecular place exchange reaction in nano sized devices. The devices are prepared by replacing the stopper ligand attached to the surface of the AuNPs with the active molecules, using ligand exchange reaction which is carried out in inert atmosphere by placing trapped nanogaps in solution of target molecules. The reaction can take upto 100 hours to reach equilibrium. Electrical characterization before and after ligand exchange shows resistance change of more than 2 orders of magnitude which is considered as a clear signature of success of formation of molecular electronic device. 

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