Controlled synthesis of templated vertical carbon nanotube structures
Single-walled and double-walled carbon nanotubes (SWNTs and DWNTs, respectively) possess excellent electronic and thermal transport properties while offering high strength. As such, they have been identified as excellent electronic candidates for applications including electronics, thermal management, radiation sources, and biological sensors. SWNTs and DWNTs have commercial potential in electron emitters for flat panel displays, gas and biological sensors, metallic electrical interconnects, and semiconducting channels for field effect transistors. While "proof of concept" experiments and prototypes have verified the performance of SWNTs in these applications, full utilization of their potential has been hindered by the lack of a reliable platform upon which to manufacture devices and a lack of synthesis control. Many prototype devices (such as field effect transistors) rely on dispensing CNTs in solution upon functionalized substrates to bridge one or more CNTs across electrical contacts. Other applications, such as electron emission devices and electrical interconnects, often rely on largely uncontrolled growth of dense CNTs mats. The objective of this research is the development of a controllable method for the production of vertical SWNT and DWNT-based electronic devices utilizing technology that is readily available in the semiconductor industry. The ideal device structure will preferentially yield SWNTs and/or DWNTs and will allow for easy integration of post-synthesis processing techniques, such as contact metallization to individual CNTs, to customize the device for various applications. ^ This thesis details the development of a modified porous anodic alumina template (PAA) containing a thin CNT catalyst layer directly embedded into the pore walls. CNT synthesis using; the template selectively catalyzes SWNTs and DWNTs from the embedded catalyst layer to the top PAA surface, creating a vertical CNT channel within the pores. Subsequent processing allows for easy contact metallization and adaptable functionalization of the CNTs and template for a myriad of applications. Equally important is the optimization of the PECVD synthesis conditions used to grow individual vertical SWNTs, which is described in detail in this dissertation. Finally, a post-processing technique used to create a simple two-terminal CNT device from the template is described in detail, and more complicated device structures based on the structure are proposed. ^
Timothy S. Fisher, Purdue University.
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