Two-Dimensional Hexagonal Boron Nitride Nanosheet as the Planar-Alignment Agent in a Liquid Crystal-Based Electro-Optic Device

The planar-alignment agent in an electro-optic liquid crystal (LC) device plays an essential role for the LC’s electro-optical characteristics. Rubbed polyimide (PI) layers are conventionally used as the planar-alignment agent in traditional liquid crystal displays (LCDs). Here we experimentally demonstrate that the 2D hexagonal boron nitride (h-BN) nanosheet can serve as the planar-alignment agent in an LC cell. Two h-BN-covered indium tin oxide (ITO) glass slides are placed together to fabricate an LC cell. A nematic LC inside this h-BN-based cell exhibits uniform planar-alignment. This planar-alignment at the molecular scale is achieved due to the coherent overlay of the benzene rings of the LC molecules on the hexagonal BN lattice. This h-BN-based LC cell shows the typical electro-optical effect when an electric field is applied via ITO electrodes. The dielectric measurement across this h-BN-based electro-optic cell shows a standard Fréedericksz transition of the LC, confirming that the 2D h-BN, as the planar-alignment agent, supplies adequate anchoring energy. Finally, we show the h-BN-based LC cell exhibits more optical transparency than a regular PI alignment layer-based LC cell.