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14 May 2010 Self induced patterning of PDMS structures by surface-charge lithography driven by photorefractive effect
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Direct patterning of Polydimethylsiloxane (PDMS) thin film is demonstrated. A procedure is implemented to induce PDMS self-patterning in one and two dimensional geometries based on surface-charge lithography by means of the photorefractive properties of iron doped Lithium Niobate (LN) crystal. Linear periodic and radial arrays of microchannels are fabricated by changing the wettability on the LN crystal surface. The substrate is x-cut Fe+ doped LN crystal, the covering substance is PDMS. Fabrication process is divided in three stages: PDMS spinning on the substrate, PDMS reshaping and PDMS curing. After spinning step the sample is inserted in an optical setup. We employ an Argon laser whose wavelength is 514nm. Light passes trough an amplitude grating that is imaged by a lens. The sample is positioned in the conjugate plane of the grating. Light impinging on the lower LN surface is spatially inhomogenous and excites the charge carriers inside the crystal. The space-charge field generate inside the material modulate the refractive index via electro-optic effect and cause lateral forces near the upper surface able to manipulate and trap liquids. PDMS moves on the crystal surface trapping itself and gathering up in stripes to form geometries with the same period of the phase grating written inside the crystal. While the light source generate the PDMS structure, a thermal treatment applied to the crystal, induces the cross-linking of the PDMS, leading to a stable and reliable PDMS pattern. We propose an alternative one step patterning process based on light driven self assembly.
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L. Miccio, M. Paturzo, and P. Ferraro "Self induced patterning of PDMS structures by surface-charge lithography driven by photorefractive effect", Proc. SPIE 7716, Micro-Optics 2010, 77162M (14 May 2010);

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