Porous Aluminum Oxide: Templates for Industrial Scale Production of Highly Ordered Metallic Nanowires
Graham Young, Kevin Nguyen, Alan Rassolkhani, Syed Mubeen*
Department of Chemical and Biochemical Engineering
University of Iowa, Iowa City, IA - 52242
One-dimensional (1-D) nanostructures exhibit unique optoelectronic, catalytic, and interfacial properties that are of both fundamental and technological importance. The past decade has seen revolutionary advances in our ability to design, tailor and control these properties for technological implications. However for wide scale industrial adoption, the scale-up science associated with device, system and process level are still poorly understood. The objective of this project was to demonstrate a manufacturably scalable and sustainable method for nanowire production with controlled orientation and device architecture.
Conventionally, the procedures to fabricate 1-D nanostructures in desired device configuration requires expensive electron beam lithography or spatially limited photolithographic techniques. Herein we overcome this challenge by using inexpensive ordered alumina oxide membranes, which acts as a growth template and a structure directing agent for nanowire growth. Aluminum was chosen as a base for nanowire templates because of its low cost, (0.80 dollars per m2)  and material availability.
A modified anodization procedure [2,3,4] was used for generation of high density hexagonally ordered homogeneous nanopore arrays with tunable pore diameters, interpore distance and pore lengths. Pore diameters were controllably tuned from 30 to 80nm. Pore diameter ranges are dependent on pore density, which is determined by anodization conditions. Pore diameter growth rate was calculated to be 5.4nm per minute and pore length growth was optimized and found to be 1μm per 12 minutes. Collectively, enabling us to create high density nanostructures with aspect ratios (L/D) ranging from 33 to 12.5. Pore densities were calculated to be 14.6 billion pores per cm2, with interpore distances of 96nm. Scanning electron microscope (SEM) techniques were used to characterize pore diameter, pore density and interpore distance. Methods of electrodeposition of silver and other semiconducting materials with desired functionalities are currently being investigated 
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