Nanolithographic Manipulated Cutting of Aligned Metal Oxide Nanowires
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Nanolithographic Manipulated Cutting of Aligned Metal Oxide Nanowires L.J. Campbell, Y.X. Chen, and W.L. Zhou Advanced Materials Research Institute, University of New Orleans, New Orleans, LA 70148. ABSTRACT Controlling the characteristics of nanowires in order to later construct nanoarchitecture and nanocomponents for nanodevice and nanosensor applications is essential. Metal oxide nanowires are aligned using the Langmuir-Blodgett (LB) technique to uniaxially compress the nanowires. A surfactant monolayer of metal oxide nanowires is fabricated, and then compressed on an aqueous subphase. The compression yields an array of aligned nanowires, which is transferred to a planar substrate. Cutting areas of the array are defined by electron beam nanolithography. After an etching process, it is shown that the metal oxide nanowires have been successfully cut. With further refinement of this technique, the nanowires can be used to construct basic building blocks of nanodevices and nanosensors. INTRODUCTION Recently, semiconductor nanowires, specifically ZnO, have gotten a great deal of attention in research 1-3. Many methods of synthesizing metal oxide nanowires have been used to produce uniform semiconductor nanowires 2-5. Thermal evaporation techniques have proven very effective for this purpose and have a high yield of uniform nanowires7. Being able to control the alignment and length of these nanowires is essential for the fabrication of nanocomponents and nanoarchitectures, which could be used to construct nanodevices. Various methods of aligning these nanowires have been attempted 6,8, however, the Langmuir-Blodgett (LB) technique of alignment has shown promising results 9-11. The LB technique utilizes the surface tension of a subphase with a covering layer of surfactant. The surfactant solution may contain numerous nanostructures, including nanowires. When the monolayer is compressed the wires in the surfactant become aligned. This has been called the “logs-on-a-river” approach 9 of alignment. These aligned structures can then be transferred to a planar substrate. Once this transfer is complete a number of processes can be done. In particular, a photoresist can be coated over the wires so lithography can be performed 12. In this case, electron-beam nanolithography was used to define protected areas of aligned wires. An ion milling process is used to cut the exposed wires. EXPERIMENTAL There are three main steps to process metal oxide nanowires of controlled lengths. First, the nanowires were synthesized, collected and put in solution. Next, the wires were dispersed in a LB trough and uniaxially compressed to achieve alignment. Once the wires were transferred to a silicon substrate, they were coated with a photoresist. Electron-beam nanolithography was used to pattern a “cutting” area over the nanowires. After developing, the sample was etched using ion milling for a short time. The photoresist was then removed and the sample was observed. The detail of the processing is as follows.
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Synthesis: Large q
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