Surface zenithal anchoring of nematic on holographic gratings

We study the zenithal anchoring strength of the nematic 5CB on holographic gratings of different amplitudes and a period Λ=0.5 μm. The surface monostable planar anchoring can be broken by short external electric pulses after which the director displays bistable textures: uniform and half-turn twisted. The measured threshold of the surface anchoring breaking is about 6 V/μm and is independent from the grating amplitude.