Nanosphere Lithography: Self-Assembled Photonic and Magnetic Materials
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Nanosphere Lithography: Self-Assembled Photonic and Magnetic Materials Amanda J. Haes, Christy L. Haynes, Richard P. Van Duyne Department of Chemistry, Northwestern University Evanston, IL 60208-3113, U.S.A. ABSTRACT Early work with size-tunable periodic particle arrays (PPAs) fabricated by nanosphere lithography (NSL) demonstrated that the localized surface plasmon resonance (LSPR) could be tuned throughout the visible region of the spectrum. Further developments of the NSL technique have produced a myriad of nanoparticle configurations. Presented in this paper are several array types and examples of their utility in current applications. Both the sensitivity and tunability of the LSPR have been firmly established using single layer PPAs. Magnetic force microscopy (MFM) has been used to show that double layer PPAs act as single domain magnets and give strong MFM contrast. Angle-resolved NSL has produced nanogap and nano-overlap structures with manipulation resolution of one nanometer. Nanowell structures extend the original twodimensional structure into the third dimension. Exploitation of this flexible, materials-general NSL technique allows for investigation of the catalytic, electrochemical, magnetic, optical and thermodynamic properties of nanoparticles. INTRODUCTION Nanoparticles composed of metals and semiconductors exhibit distinct size-dependent chemical and physical properties that differ from their bulk material counterparts. Understanding these properties and developing low cost, high-efficiency production methods are motivating factors in this line of research. Several standard lithographic methods are routinely used to create nanostrutures with controlled size, shape, and spacing. UV photolithography [1,2] is a widely used method; however, its feature sizes are limited by its diffraction-limit of λ/2. Electron beam lithography [2] is characterized by low sample output, high sample cost, modest feature shape control, and excellent feature size control. X-ray lithography [3] is characterized by initially high capital costs but high sample throughput. Additional lithographic techniques are in development. Among these methods are scanning tunneling microscopy [4] and atomic force microscopy [5] lithographic techniques. As a consequence of the aforementioned limitations, alternative, parallel nanolithographic techniques are being explored including (1) diffusion-controlled aggregation at surfaces [6]; (2) laser focused atom deposition [7]; (3) chemical synthesis of metal-cluster compounds and semiconductor nanocrystals [8]; and (4) "natural lithography" [9,10]. The work presented here is an extension of Deckman’s "natural lithography," hereafter renamed nanosphere lithography (NSL) [11]. NSL is inexpensive (less than $1 per sample), inherently parallel, high-throughput, and materials general technique. Consequently, NSL is capable of producing well-ordered, 2D periodic arrays of nanoparticles from a wide variety of materials on many substrates. In this paper, demonstrations of multiple NSL structures will b
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