Nanoscale alignment and optical nanoimaging of a birefringent liquid

Abstract

An anisotropic nanopatterning method, based on a technique of atomic forcemicroscopy (AFM) scribing of a thin polyimide film, is used to generate an alignmentlayer whose topography depends on the writing direction. Detailed experimentalmeasurements are presented for the topographical anisotropy that arises when thepolyimide alignment layer is scribed parallel and antiparallel to the AFM cantileverorientation. By means of a novel nanotomographic approach, the optical retardationδ of an alignable birefringent liquid that covers the scribed substrate is measured withunprecedented resolution of only a few tens of nanometers. In this technique a thin opticalfiber is raster-scanned at several fixed heights inside the birefringent liquid, andthe transmitted polarized light is collected downstream. The optical retardationδ from the fiber’s tip to the polyimide interface was measured as a function of positionx,y,z, with the results reflecting the spatially varying depth of the mediumdue to the polymer film surface topography. Theoretical calculations forδ are in excellent agreement with both the topographical and the high resolutionnanoimaging experimental results obtained.