Nanotech 2011

Laser Writing of Metallic Nanostructures in a Polymer Matrix with Applications to Metamaterials

S. Shukla, X. Vidal, E.P. Furlani, M.T. Swihart, P.N. Prasad
Harvard University, US

Keywords: fabrication, laser lithography


We present a novel laser-based method for directly writing metallic nanostructures in a polymer matrix with sub-wavelength resolution [1]. The method involves two-photon lithography (TPL) in which a femtosecond-pulsed laser induces two-photon initiated in situ reduction of a metal salt and simultaneous polymerization of a negative photoresist. Interest in TPL has grown dramatically in recent years, especially for applications that require fabrication of three-dimensional microstructures with subwavelenth resolution. Conventional lithographic techniques are not well suited to this, as they are inherently limited to two-dimensional processing. However, three-dimensional TPL using photopolymers overcomes these limitations and has found broad application in micro/nanofluidics, biotechnology and photonics, particularly optical data storage and photonic crystal structures. In this presentation, we demonstrate the use of TPL to write gold nanoparticle-doped polymeric lines from a gold salt and SU-8 photoresist (Fig. 1). Structures with line widths from 150 nm to over 1000 nm have been prepared and characterized using scanning electron microscopy and confocal optical microscopy. The individual in situ generated metallic nanoparticles are a few nanometers in diameter and metallic structures formed from continuous arrays of these particles have features as small as 50 nm. The quasi-continuous metallic structures formed in this fashion exhibit good effective conductivity and plasmon resonance absorption at a wavelength consistent with the plasmonic behavior of the constituent gold nanoparticles. This method is well suited for the fabrication of micro- and nanoscale features because it is based on the initiation of a photochemical process in a small (sub-wavelength) focal volume. The ability to write three-dimensional metallic structures in a polymeric matrix holds potential for disruptive advances in emerging fields such as nanophotonics, flexible electronics, metamaterials and plasmonics. We present various fabricated functional structures and corresponding simulations of their electromagnetic performance (Fig. 2)

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