3-Dimensional Al 2 O 3 Fiber Networks using Low Temperature Atomic Layer Deposition on a Cotton Template
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3-Dimensional Al2O3 Fiber Networks using Low Temperature Atomic Layer Deposition on a Cotton Template Daisuke Hojo1, G. Kevin Hyde2, Joseph Spagnola3, and Gregory N Parsons2 1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku Univ., Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Sendai, Japan 2 Department of Chemical and Biomolecular Engineering, North Carolina State University, 911 Partners Way, Centennial Campus, Raleigh, NC, 27695 3 Department of Material Science and Engineering, North Carolina State University, 911 Partners Way, Centennial Campus, Raleigh, NC, 27695 ABSTRACT Micro-scale woven structures were replicated 3 dimensionally by conformal coating onto natural woven cotton using a binary reaction of trimethylaluminum and water at 100°C. Even after the woven cotton was removed at 450°C, the woven structures completely remained. Results demonstrate the capability of ALD to penetrate into the complex 3D network structure of natural woven cotton to form uniform coating at low temperature and give insight into general understanding of methodology to translate deposition processes from 2D surface to a 3D network to obtain a uniform coating throughout the sample network bulk. It also shows the possibility of replication of micro-scale structures from highly conformal coatings to give the unique synthesis root of hollow structures. INTRODUCTION Microtubes with precisely defined nanoscale walls can be constructed by replicating the original structures by conformal coating onto a variety of 3 dimensional (3D) templates including nanorods,[1] nanotubes,[2-4] polymer fibers,[5-11] and natural fibers such as cotton or sisal.[12-14] The template approach to fabricate these structures is one of the most popular approaches because of its ease of use and versatility. This method gives a new synthesis route of highly functional hollow structures useful for filtrations or thermal insulation. There is also a strong interest in controlling the surface properties of 3D structures, such as hydrophobicity of the surface, by coating with ALD. We have recently utilized ALD to deposit metal oxide and nitride coating on variety of fibrous surfaces including natural cotton.[12] For this study, Al2O3 thin films were coated onto natural woven cotton samples using a binary reaction of trimethylaluminum (TMA) and water at 100°C and then, the woven cotton was removed at high temperature to replicate the woven structures. Natural woven cotton has macro-scale order and each cotton fiber has nano-scale structures like another natural fibers, where Huang et al. coated TiO2 with sol-gel to modify the surface properties of paper fibers.[15] This hierarchy structure is an ideal system to verify the conformal scale from the academic view point. It will be also needed that evaluation methodology of conformal coating onto such a complex 3D structures. Unlike electrospun poly(vinyl alcohol) microfiber[6], the shape of each natural fiber like cotton is so complex that it is difficult to determine the thickness by transm
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