2 September 2009 Experimental investigation of Fang's Ag superlens suitable for integration
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Abstract
We report on experimental realization of the Fang Ag superlens structure [1] suitable for further processing and integration in bio-chips by replacing PMMA with a highly chemical resistant cyclo-olefin copolymer, mr-I T85 (Micro Resist Technology, Berlin, Germany). The superlens was able to resolve 80 nm half-pitch gratings when operating at a free space wavelength of 365 nm. Fang et al. used PMMA since it enables the presence of surface plasmons at the PMMA/Ag interface at 365 nm and because it planarizes the quartz/chrome mask. If the superlens is to be integrated into a device where further processing is needed involving various organic polar solvents, PMMA cannot be used. We propose to use mr-I T85, which is highly chemically resistant to acids and polar solvents. Our superlens stack consists of a quartz/chrome grating mask, a 40 nm layer of mr-I T85, 35 nm Ag, and finally 70 nm of the negative photoresist mr-UVL 6000 (Micro Resist). A 50 nm layer of aluminium on top of the quartz/chrome mask reflected all light that did not penetrate through the mask openings thereby reducing waveguiding in the top resist layer. The exposures took place in a UV-aligner at 365 nm corresponding to the excitation wavelength of the surface plasmons at the mr-I T85/Ag interface. Supporting COMSOL simulations illustrate the field intensity distribution inside the resist as well as the presence of surface plasmons at the mr-I T85/Ag boundary. AFM scans of the exposed structure revealed 80 nm gratings.
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Claus Jeppesen, Claus Jeppesen, Rasmus B. Nielsen, Rasmus B. Nielsen, Sanshui Xiao, Sanshui Xiao, Niels Asger Mortensen, Niels Asger Mortensen, Alexandra Boltasseva, Alexandra Boltasseva, Anders Kristensen, Anders Kristensen, "Experimental investigation of Fang's Ag superlens suitable for integration", Proc. SPIE 7395, Plasmonics: Nanoimaging, Nanofabrication, and their Applications V, 73951I (2 September 2009); doi: 10.1117/12.825940; https://doi.org/10.1117/12.825940
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