Towards the Fabrication of the Top-Contact Electrode in Molecular Junctions by Photoreduction of a Metal Precursor

Langmuir films of 4-{[4-({4-[(trimethylsilyl)ethynyl]phenyl}ethynyl)phenyl]ethynyl} benzenaminium chloride ([1 H]Cl) undergo anion metathesis when assembled on an aqueous auric acid (HAuCl4) subphase. Subsequent transfer to solid supports gives well-formed Langmuir–Blodgett (LB) monolayers of [1 H]AuCl4 in which the trimethylsilyl group serves as the surface contacting group. Photoreduction of the aurate on these monolayers leads to the formation of metallic gold nanoislands, which were distributed over the surface of the film. Electrical properties of these nascent devices were determined by recording current–voltage (I–V) curves with conductive atomic force microscopy (c-AFM) using the PeakForce tunneling AFM (PF-TUNA) mode. This gives consistent sigmoidal I–V curves that are indicative of well-behaved junctions free of metallic filaments and short circuits. The photoreduction of a metal precursor incorporated onto monomolecular films is therefore proposed as an effective method for the fabrication of molecular junctions.