Polariton-enhanced near field lithography and imaging with infrared light
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Polariton-enhanced near field lithography and imaging with infrared light
Gennady Shvets and Yaroslav A. Urzhumov The University of Texas at Austin, Department of Physics, Austin TX 78712, USA ABSTRACT A novel approach to making a material with negative index of refraction in the infrared frequency band is described. Materials with negative dielectric permittivity ² are utilized in this approach. Those could be either plasmonic (metals) or polaritonic (semiconductors) in nature. A sub-wavelength plasmonic crystal (SPC), with the period much smaller than the wavelength of light, consisting of nearly-touching metallic cylinders is shown to support waves with negative group velocity. The usage of such waves for sub-wavelength resolution imaging is demonstrated in a numerical double-slit experiment. Another application of the negative-epsilon materials is laser-driven near field nanolithography. Any plasmonic or polaritonic material with negative ² = −²d sandwiched between dielectric layers with ²d > 0 can be used to significantly decrease the feature size. It is shown that a thin slab of SiC is capable of focusing the midIR radiation of a CO2 laser to several hundred nanometers, thus paving the way for a new nano-lithographic technique: Phonon Enhanced Near Field Lithography in Infrared (PENFIL). Although an essentially near-field effect, this resolution enhancement can be quantified using far-field measurements. Numerical simulations supporting such experiments are presented. 1. INTRODUCTION The wave nature of light places a stringent limit, known as the Abbe resolution limit,1 on the resolution of a microscope: the minimal feature size that can be detected by any conventional (far-field) optical system, with acceptance angle α, immersed in a host medium with dielectric √ permittivity ²h , is ∆ = 1.22λ/(2 ²h sin α), where λ is the wavelength of light. While resolution can be enhanced beyond the canonical λ/2 limit by using high-²h materials (as it is done in liquid or solid immersion microscopy2 ), the truly impressive gains in resolution may require unconventional materials and approaches. One example of such meta-materials are the so-called double-negative (or ”left-handed”) materials.3, 4 The possibility of accessing the sub-wavelength resolution using the so-called ”super-lens” 3, 5 is the most challenging and technologically rewarding application of the left-handed materials (LHMs). Two approaches to making a ”perfect” lens have been immediately identified: (i) constructing a composite material with both negative dielectric permittivity ²ef f < 0 and magnetic permeability µef f < 0, and (ii) using occurring in nature non-magnetic materials with ² < 0 to significantly enhance near-field imaging. There has been significant theoretical and experimental progress in developing LHMs in the microwave frequency range, where periodic structures consisting of metallic wires and split-ring resonators spaced by the period d ¿ λ have been designed and tested. Making such intricate sub-wavelength periodic structures i
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