Varying Phases of Alumina Nanowires Templated by Vertically Aligned Carbon Nanotubes Grown via Atomic Layer Deposition

Typically, alumina nanowires (NWs) are synthesized via physical evaporation, templated anodized aluminum oxide (AAO), or the vapor-liquid-solid (VLS) process [1,2,3]. All of these techniques have been shown to demonstrate successful growth of alumina NWs; however, in the cases where a facile method resulting in vertically aligned NWs is desired, many of these methods are difficult to integrate into a fabrication process. Physical evaporation results in randomly aligned NWs and requires high temperatures therefore mitigating the possibility to use amorphous alumina and γ-alumina, among other low-temperature crystalline phase transitions [1]. And with the VLS process, expensive catalysts such as gold and germanium are used and the resulting alumina NWs exhibit a hierarchical organization with groups of many NWs growing from a single catalyst particle [2]. Lastly, templated AAO is a method that can provide vertically aligned NWs with high yield, however, in practice etching methods for creating structures with a high degree of physical dimension control is difficult to optimize [3]. Here, we present a method for creation of vertically aligned alumina NWs using vertically aligned carbon nanotubes (CNTs) as a template during atomic layer deposition (ALD). Post deposition, the deposited alumina can undergo crystalline phase changes via thermal processing within an oxygen-rich environment.