Low-cost Micro- and Nano-structures in Porous Nanomaterials Realized by Direct Imprinting of Porous Substrates
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Low-cost Micro- and Nano-structures in Porous Nanomaterials Realized by Direct Imprinting of Porous Substrates Judson D. Ryckman1, Marco Liscidini2, J. E. Sipe3, and S. M. Weiss1 1 Department of Electrical Engineering and Computer Science, Vanderbilt University Nashville, TN 37235, USA 2 Dipartimento di Fisica “A. Volta”, Università degli Studi di Pavia, via Bassi 6, 27100 Pavia, Italy 3 Department of Physics and Institute for Optical Sciences, University of Toronto 60 St. George St. Toronto M5S 1A7 Ontario, Canada ABSTRACT We present a simple one-step methodology for direct structuring of porous nanomaterials on the micro- and nano-scale. Our technique, direct imprinting of porous substrates (DIPS), relies on the application of a pre-patterned and reusable stamp to directly imprint porous substrates. DIPS is performed at room temperature and pressure in less than one minute, and circumvents the conventional requirement for resist processing and etching procedures. It is shown that arbitrarily shaped patterns and structures can be transferred to porous nanomaterials with a very high (sub-100nm) feature resolution that is primarily limited by the pore dimensions of the substrate material. DIPS is demonstrated on a wide variety of porous nanomaterials including metals, semiconductors, and insulators. Furthermore, DIPS can be utilized to locally modify material properties including pore dimensions, density, dielectric function, and surface roughness. Lastly, example structures fabricated by DIPS are discussed for their relevance to important applications ranging from drug delivery and imaging, to solar energy conversion, and biosensing. INTRODUCTION Porous nanomaterials exhibit many unique electrical, chemical, optical, and mechanical properties arising from their nanoscopic heterogeneous composition. Importantly, the production of porous nanomaterials is often self-organizing and can be achieved through straightforward techniques capable of yielding desirable nanoscopic qualities over very large areas (~cm2) and at low-cost [1-4]. In order to implement these nanomaterials and enhance their functionality in useful devices, for example in applications ranging from drug delivery and imaging [5,6], to chemical and biological sensing [7,8], plasmonics [9], and solar energy conversion [10,11], it often becomes imperative to precisely structure or pattern them on the micro- and nano-scale. One approach for patterning porous nanomaterials is to apply conventional lithographic techniques such as photolithography or electron-beam lithography followed by wet or dry etching. However, the cost and complexity of such processes are not complimentary to the lowcost and straightforward production of porous nanomaterials. Moreover, conventional lithographic techniques are limited by a prohibitive trade-off between resolution and throughput. For porous materials, wet etching is not always an option due to chemical incompatibilities, and dry-etching techniques are expensive and require specific chemistries that must be appropriately char
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