Self-Formed Nano Junctions for Optical and Molecular Detection

We present self-formed nanojunction device architecture based on unique hybrid nanostructures fabricated using SiGe nanowires (NWs). The hybrids, termed, Nanoflora, feature a metallic nanoshell cap, which functions as nano electrodes. The active junction is formed between the edge of the nano electrode and a macroscopic counter electrode, overall having small contact area owing to the unique nanowire geometry. The fabrication process is robust, using simple lithographic methods (top-down) for the micron-scale parts of the device, and bottom-up methods for the nanoscale elements. The device architecture results in a versatile platform that can be utilized in several applications. (I) Self-formed molecular junction for electrical detection where the gap size is adjustable according to the trapped molecule. Transport measurements performed before and after the introduction of molecules and quantum dots into the nanogap corresponded to the expected molecular details, allowing probing their band structure and energy gap in the measured I-V curves in ambient conditions.

(II) The same device architecture is demonstrated as a sensitive photo detector extending to the NIR. Where the gold nanoshell cap acts as a plasmonic metastructure, located at the active junction. This gold cap allows an enhancement of the photoresponse and its extension to the NIR regime. In addition, the existence of hot spots, generated by the irregular shape of the metallic cap results in SERS enhancement of adsorbed molecules.

Overall, the presented device platform delivers fast and scalable realization of nano-molecular junctions coupled to plasmonic metastructure using crude techniques, thus alleviating the need for using serial, costly techniques such as advanced e-beam lithography, ion-beam milling or complex systems such as STM or mechanically controlled break junctions.