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Preparations, properties, and applications of periodic nano arrays using anodized aluminum oxide and di-block copolymer

Abstract

Self-ordered arrangements observed in various materials systems such as anodic aluminum oxide, polystyrene nanoparticles, and block copolymer are of great interest in terms of providing new opportunities in nanofabrication field where lithographic techniques are broadly used in general. Investigations on self-assembled nano arrays to understand how to obtain periodic nano arrays in an efficient yet inexpensive way, and how to realize advanced material and device systems thereof, can lead to significant impacts on science and technology for many forefront device applications. In this thesis, various aspects of periodic nano-arrays have been discussed including novel preparations, properties and applications of anodized aluminum oxide (AAO) and PS-b-P4VP (S4VP) di- block copolymer self-assembly. First, long-range ordered AAO arrays have been demonstrated. Nanoimprint lithography (NIL) process allowed a faithful pattern transfer of the imprint mold pattern onto Al thin film, and interesting self-healing and pattern tripling phenomena were observed, which could be applicable towards fabrication of the NIL master mold having highly dense pattern over large area, useful for fabrication of a large-area substrate for predictable positioning of arrayed devices. Second, S4VP diblock copolymer self-assembly and S4VP directed AAO self -assembly have been demonstrated in the Al thin film on Si substrate. Such a novel combination of two dissimilar self -assembly techniques demonstrated a potential as a versatile tool for nanopatterning formation on a Si substrate, capable of being integrated into Si process technology. As exemplary applications, vertically aligned Ni nanowires have been synthesized into an S4VP-guided AAO membrane on a Si substrate in addition to anti-dot structured [Co/Pd]n magnetic multilayer using S4VP self assembly. Third, a highly hexagonally ordered, vertically parallel aluminum oxide nanotube array was successfully fabricated via hard anodization technique. The Al₂O₃ nanotube arrays so fabricated exhibit a uniform and reproducible dimension, and a quite high aspect ratio of greater than ̃1,000. Such high-aspect-ratio, mechanically robust, large-surface-area nanotube array structure can be useful for many technical applications. As a potential application in biomedical research, drug storage/ controlled drug release from such AAO nanotubes was investigated, and the advantageous potential of using AAO nanotubes for biological implant surface coatings alternative to TiO₂ nanotubes has been discussed

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