Chemical Fabrication of Heterometallic Nanogaps for Molecular Transport Junctions

• Published in: Nano letters Vol. 9; no. 12; pp. 3974 - 3979
• Main Authors: Chen, Xiaodong, Yeganeh, Sina, Qin, Lidong, Li, Shuzhou, Xue, Can, Braunschweig, Adam B, Schatz, George C, Ratner, Mark A, Mirkin, Chad A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-12-2009
• Subjects: Cross-disciplinary physics: materials science; rheology; Crystallization - methods; Electric Conductivity; Electrochemistry - methods; Electron Transport; Exact sciences and technology; Gold - chemistry; Macromolecular Substances - chemistry; Materials science; Materials Testing; Methods of nanofabrication; Microelectrodes; Molecular Conformation; Nanocrystalline materials; Nanolithography; Nanoscale materials and structures: fabrication and characterization; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanotechnology - methods; Nanotubes; Particle Size; Physics; Platinum - chemistry; Quantum wires; Semiconductors; Surface Properties; Gold; Molecular form; Work functions; Thiols; Lithography; Gallium phosphide; Raman spectroscopy; Diodes; Nanowires; Arrays; Sulfur; Molecular junction; Nanorod; Nanostructured materials
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl9018726

We report a simple and reproducible method for fabricating heterometallic nanogaps, which are made of two different metal nanorods separated by a nanometer-sized gap. The method is based upon on-wire lithography, which is a chemically enabled technique used to synthesize a wide variety of nanowire-based structures (e.g., nanogaps and disk arrays). This method can be used to fabricate pairs of metallic electrodes, which exhibit distinct work functions and are separated by gaps as small as 2 nm. Furthermore, we demonstrate that a symmetric thiol-terminated molecule can be assembled into such heterometallic nanogaps to form molecular transport junctions (MTJs) that exhibit molecular diode behavior. Theoretical calculations demonstrate that the coupling strength between gold and sulfur (Au−S) is 2.5 times stronger than that of Pt−S. In addition, the structures form Raman hot spots in the gap, allowing the spectroscopic characterization of the molecules that make up the MTJs.