Microstructured Optical Fibers as New Nanotemplates for High Pressure CVD
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Microstructured Optical Fibers as New Nanotemplates for High Pressure CVD Neil Baril1, John Badding1, Pier Savio2, Venkatraman Gopalan3, Dong-Jin Won3, Thomas Scheidemantel4, Chris Finlayson2, Adrian Amezcua-Correa2, and Bryan Jackson3 1 Chemistry, Penn State University, University Park, PA, 16802 2 University of Southampton, Southampton, SO17 1BJ, United Kingdom 3 Materials Science and Engineering, Penn State University, University Park, PA, 16802 4 Physics, Penn State University, University Park, PA, 16802
ABSTRACT Solid state chemists have long been interested in templated growth of materials using many approaches. The resulting materials have been useful in areas as diverse as photonics and catalysis. Microstructured optical fibers (MOFs) form a new class of nanotemplates that can have sub 20 nm pores that are meters to kilometers long. We have developed a high-pressure microfluidic chemical process that allows for conformal deposition of materials within MOFs to form the most extreme aspect ratio semiconductor nanowires known. The wires can be spatially organized with respect to each other at dimensions down to the nanoscale because the MOF templates can be designed with almost any desired periodic or aperiodic pattern. Many if not most of the chemistries used for conventional chemical vapor deposition (CVD) can be adapted for this process. The resulting materials should enable a large range of scientific and technological applications. INTRODUCTION Advanced devices and materials are enabled by hierarchal organization at length scales less than 10 to 100 nm. Nanoparticle superlattices, for example, may open the door to a wide range of new materials properties [1]. Chemists have long employed templates such as anodic alumina [2], mesoporous silica [3], and polycarbonate membranes [4] for growth of materials organized down to nanoscale dimensions. Here we report on our progress in using microstructured optical fibers (MOFs) as templates for the synthesis of new photonic and electronic materials. MOFs are drawn from silica performs in a manner similar to that used for conventional optical fibers. However, MOF preforms can be designed to have patterns of holes of arbitrary geometry that are scalably reproducible upon drawing down to dimensions of 10 nm [5]. They are thus versatile new nanotemplates that have a number of attractive features beyond the design flexibility in the patterns of holes. They are typically produced from silica giving them exceptional optical transparency, high strength, and the potential for 10% elastic deformation. Such elasticity should enable strain-tuning materials deposited within the MOFs. The walls of the capillaries within MOFs have a roughness of 1 angstrom RMS providing an ideal surface for the deposition [6].
EXPERIMENTAL We have developed a technique for infiltrating the capillaries of MOFs with semiconductor materials [7]. High-pressure gases carry chemical vapor deposition (CVD) precursors through the capillaries of the MOFs. The fibers are then heated to tempe
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