Orientation Of 5CB Liquid Crystal On Zinc Oxide And Enhancement Of Interfacial Electric Field

With the coming of the information age,display technology and photonic devices have been greatly developed,and the preparation of excellent performance of display devices and photonic devices has gradually become a research hotspot.Liquid crystal is widely used in various display devices because of its unique physical properties.In this thesis,the vertical orientation of Zn O（Zn S）films to 5CB liquid crystal（4,4-n-pentylcyanobiphenyl）is theoretically analyzed by ab initio.Liquid crystal cell samples based on Zn O were prepared,and their orientation was verified with crossed-polarized system.The rapid response characteristic of the prepared liquid crystal cell sample was investigated by two-wave-coupling experiments.The modification of Zn O by 5CB liquid crystal and the charge accumulation at the interface of 5CB liquid crystal-Zn O were analyzed theoretically,and the physical mechanism of diffraction enhancement induced by interface of 5CB liquid crystal-Zn O was explored.This thesis provides a reference for the preparation of adjustable surface plasmon polaritons（SPPs）photonic devices.Firstly,the orientation of the 5CB liquid crystals on the Zn O and Zn S substrates was studied with ab initio.It was found that the liquid crystals arranged vertically on the surface of the Zn O substrate due to the unilateral anchoring of unsaturated zinc atoms to 5CB molecules and the formation of’surface suspension bonds’.In order to further push the universality of this orientation forⅡ-Ⅵsemiconductors,a similar study has been carried out on Zn S and similar results have been obtained.Secondly,the vertical orientation of the Zn O substrate to the 5CB liquid crystal was verified by the experiments,and the liquid crystal cell samples with rapid response were prepared.The liquid crystal cells were prepared by sputtering Zn O film on the surface of Indium Tin Oxide（ITO）glass substrate as the oriented layer.The orientation of the liquid crystal cell was detected by a crossed-polarized system.The results show that the liquid crystal cell samples are with excellent vertical orientation.Therefore,the vertical orientation of the Zn O substrate to the 5CB liquid crystal is verified experimentally.Besides,in the two-wave-coupling experiment,it is found that the response speed of the liquid crystal cell increases with increasing applied voltage,and the fastest response speed of the liquid crystal cell in the experiment reaches 20 ms.Finally,the charge accumulation at the interface of 5CB liquid-Zn O was analyzed by the Thomas-Fermi screening model,and the physical mechanism of the diffraction enhancement of the liquid crystal cell sample was explaind.The Thomas-Fermi screening model was used to calculate the charge accumulation density at the interface of the 5CB liquid crystal and Zn O.The results show that the charge accumulation of Zn O near the interface reache as high as 10²⁸ orders of magnitude.This high charge accumulation density changes the permittivity of Zn O and the phase grating formed by liquid crystal photorefractive effect leads to the excitation of SPPs.Due to the excitation of SPPs,the diffraction efficiency of the liquid crystal cell samples is enhanced.When the applied voltage changes,the electric field changes inside the liquid crystal cell result in the charge redistribution at the interface of 5CB liquid crystal and Zn O,which leads to the change of high-order diffraction spots.The response speed of the liquid crystal cell sample prepared by us is less than 20ms,which is of great significance for the research of holographic color stereoscopic real-time display.At the same time,the research of this paper can offer an opptunity in the research of adjustable SPP components.