- Nano Electronics
- Nano-scale Sensors and Measurement
- Dip-pen Nanolithography and Nanoprinting
- Carbon Nanotube-based Integrated Circuit
- As the miniaturization of microelectronics approaches technical and economical limits, extensive effort has been given to develop alternative electronic devices based on synthetic nanowires such as carbon nanotube. In this new architecture, often called "bottom-up" approach, nanowires synthesized on a solution or powder form are assembled onto the substrate to build functional devices. However, the lack of a massive assembly method has plagued the nanowire-based electronics since its invention, and the new architecture is not yet seriously considered as alternatives to microelectronics. Here we research the ultimate form of a "bottom-up" method for CNT circuit fabrication, where individual CNTs recognize the configuration of organic molecular patterns on the substrate and self-assemble to form pre-designed circuits. Utilizing this method, we demonstrated the wafer-scale assembly of millions of CNT-based circuit structures with single-CNT-level precision.
- "Lens" Effect in Directed Assembly of Nanowires
- We report a new phenomenon, named here as the ¡°lens¡± effect, in the directed-assembly process of nanowires (NWs) on self-assembled monolayer (SAM) patterns. In this process, the adsorption of NWs is focused in the nanoscale regions at the center of microscale SAM patterns with gradient surface molecular density just like an optical lens focuses light. As a proof of concepts, we successfully demonstrated the massive assembly of V2O5 NWs and single-walled carbon nanotubes (swCNTs) with a nanoscale resolution using only microscale molecular patterning methods. This work provides us with important insights about the directed-assembly process, and from a practical point of view, it allows us to generate nanoscale patterns of NWs over a large area for mass fabrication of NW-based devices.
- Nanowire-based Integrated Circuit
We present a method for assembling silicon nanowires (Si-NWs) in virtually general shape patterns using only conventional microfabrication facilities. In this method, silicon nanowires were functionalized with amine groups and dispersed in deionized water. The functionalized Si-NWs exhibited positive surface charges in the suspensions, and they were selectively adsorbed and aligned onto negatively charged surface regions on solid substrates. As a proof of concepts, we demonstrated transistors based on individual Si-NWs and long networks of Si-NWs.
- Pristine Vanadium Oxide Nanowire-Based Devices
- Nanowires have been drawing a tremendous attention due to their potential applications for various nanoscale devices. However, one major bottleneck for their practical applications is a lack of a high-yield mass-production method for such devices. Herein, we report a method named ¡°surface-programmed assembly¡± for high-precision assembly and alignment of a large number of pristine vanadium oxide nanowires on solid substrates. In this method, positively-charged surface molecular patterns guide the ¡®assembly¡¯ and ¡®alignment¡¯ of negatively-charged vanadium oxide nanowires on solid substrates. Using this method, we demonstrated massive assembly of vanadium oxide nanowire-based transistors and confirmed their gating effects.
- Current Research Results - I. Textured Network Devices
Transistors based on swCNTnetworks usually have a poor on?off ratio due to metallic swCNTs in the network channels. Furthermore, nanotube/nanowire network-based devices in general exhibit low mobility and conductivity with nanoscale channel width due to the poor scaling behavior of percolated network channels. We presented a strategy to solve these fundamental problems simply by controlling the connectivity of swCNT/nanowire networks. In this strategy,'textured' network channels were prepared via the directed assembly method and they were utilized to fabricate high-performance network-based devices. Using this strategy, we significantly improved the yield of swCNT network-based FETs with a large on?off ratio without removing metallic swCNTs.
Current Research Results - II. Vertically suspended and stretched CNT network junctions
Vertically suspended and stretched carbon nanotube network junctions were fabricated in large quantity via the directed assembly strategy using only conventional microfabrication facilities. In this process, surface molecular patterns on the side-wall of the Al structures were utilized to guide the assembly and alignment of carbon nanotubes in the solution. We also performed extensive experimental (electrical and mechanical) analysis and theoretical simulation about the vertically suspended single-walled carbon nanotube network junctions. Furthermore, we demonstrated gas sensing and electromechanical sensing using these devices.