Liquid crystal quenched orientational disorder at an AFM-scribed alignment surface

Abstract

A polyimide substrate was scribed using the stylus of an atomic force microscope, then covered with a nematic liquid crystal. The fiber from a near field scanning optical microscope was immersed into the liquid crystal and rastered approximately 80 nm above the surface, thereby obviating smearing effects that occur in thicker samples. By appropriate averaging of multiple data sets, a histogram of the "frozen-in" director deviation Δφ from the average easy axis was obtained, having a full-width-half-maximum of ∼0.02 rad. Additionally, the spatial autocorrelation function of Δφ was extracted, where the primary correlation length was found to be comparable to, but larger than, the liquid crystal's extrapolation length. A secondary characteristic length scale of a few μm was observed, and is thought to be an artifact due to material ejection during the scribing process. Our results demonstrate the utility of nanoscale imaging of the interface behavior inside the liquid crystal.

Creating arbitrary arrays of two-dimensional topological defects

“…In principle, the spacing between defects can be reduced to a few micrometers when sufficiently small spacings between AFM scribed lines are used-we have achieved line spacings of 20 nm using reduced AFM stylus force to limit the displacement of the polyimide material during plowing [33]but the distance between defect cores probably cannot be made smaller than a few micrometers due to the inherent extrapolation length of the liquid crystal [21]. We should point out that other techniques can provide similar results, with some advantages and some disadvantages.…”