This challenge in nanomanufacturing is crucial for the integration of nanostructures into existing silicon technologies and the incorporation of functional complexity. Methods for precise alignment and positioning are necessary for reproducibly interfacing nanowires to micro or macro components with reliable electrical contact. Complex structures including the cross-junction of nanowires are also needed to create heterostructures to perform logic functions and energy conversion, thus enabling higher-order operations from a small set of building blocks. Hierarchy assembly techniques must consequently be able to facilitate complex arrangements with both site-specific positioning and nanowire–nanowire junctions.
In our recent work, we demonstrated hierarchy assembly of nanowires using sequential alignments and radial field gradients. In sequential alignments, deposited nanowires were found to behave as ferromagnetic electrodes for subsequent nanowire alignments, resulting in both cross-junction and T-junction formation with excellent control over nanowire direction. Microfabricated ferromagnetic electrodes were also utilized for additional control, dominating dipole interactions among nanowires for an addressable nanowire assemblage.
Maturation of this technology could have significant implications for applications diverse as cell manipulation, sensors, spintronics and nano-electronics. Current efforts by the Nano Electrochemical Systems Laboratory at University of California, Riverside, include synthesis and assembly of multi-functional nanowires for bio and gas sensors, spintronics and thermoelectrics.