C, Ni and Si nanowires formation by local CVD and SLS mechanisms
C. Wang, L. Taherabadi, K. Malladi and M. Madou
University Of California, Irvine, US
C-MEMS, carbon nanofiber, Ni nanowire, Si nanowire, local CVD, SLS
For microbattery and DNA array applications, one important issue is the selection of suitable current collectors materials and contact leads. We have developed two and even three level C-MEMS processes to fabricate low resistance contacts to C-MEMS features and to make very high aspect ration structures (> 40). In the case we used the more familiar Ti/Au combination as contact material, the Au layer melted and changed to a multitude of Au balls at the high pyrolysis temperature, distorting the C-MEMS features in the layer above. An interesting discovery was made though: using SEM and TEM investigation, carbon fibers were observed near the Au balls. Unlike conventional CVD methods for growing nanotubes in which a gaseous carbon source, such as CH4, is commonly used, in our study the only carbon source is photoresist. Therefore we suggest that the process involves a local CVD mechanism in which the pyrolyzing resist provides the gaseous carbon source. Switching to Ni as a catalyst in the C-MEMS process, two kinds of Ni nanowires, short irregular structured nanowires and high aspect ratio long wires, are formed in very high quantities. In the absence of photoresist---the carbon source, Si nanowires are successfully grown. A modified solid-liquid-solid (SLS) mechanism is invoked to explain these results. The presence of carbon poisons the formation of Si wire and Ni wire growth dominates. A detailed microscopic investigation and analysis was performed and will be presented in this talk. We will also demonstrate that we can switch at will from carbon fibrous material to Ni or Si wires.
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Nanotech 2005 Conference Program Abstract