Nanoparticle-and-Dye-Doped Liquid-Crystal Phase Grating with Multistable and Dynamic Modes

We developed a phase grating composed of a nematic liquid crystal (LC) doped with silica nanoparticles and azo dyes, which exhibits both multistable and dynamic operational modes. The integration of photoalignment techniques curtailed the electrophoretic movement of silica nanoparticles within the hybrid aligned nematic (HAN) LC cell, thereby preserving the LCs' vertical orientation throughout the electrical operation. This effect was achieved through the adsorption of azo dyes onto the silica networks within the homogeneously aligned section of the sample, facilitating the formation of two distinct LC structures that constitute the grating. By applying a precise DC pulse voltage, the silica nanoparticles were induced to migrate and cluster on the substrate surface that exhibits homogeneous alignment. This process effectively stabilized the homeotropic orientation of LCs, thereby enabling the grating to achieve multistable diffraction efficiencies. In its dynamic mode, the application of a low AC voltage allowed for the modulation of the grating's diffraction efficiency, demonstrating the system's versatile performance capabilities.