Surface modified solution-derived lanthanum-doped zinc oxide film for nematic liquid crystal system with free residual DC voltage

The liquid crystal (LC) alignment characteristics of the solution-derived lanthanum-doped zinc oxide (La:ZnO) film with ion-beam (IB) irradiation were investigated as a function of curing temperature. The best LC alignment state with uniform and homogeneous alignment was achieved at a curing temperature of 300 °C. To observe the effect of the IB irradiation on the La:ZnO film, physical and chemical surface analyses were conducted. Atomic-force microscopy revealed that surface roughness was increased, and the leptokurtic surface was changed to a platykurtic surface after the IB irradiation. X-ray photoelectron spectroscopy showed the breakage of the metal-oxide bonds, which induced an increase of oxygen vacancies. This caused van der Waals force, which strongly anchored LC molecules to the La:ZnO film. These results indicated that uniform and homogeneous LC alignment with the solution-derived La:ZnO films was induced by physical and chemical surface modification due to the IB irradiation. Moreover, residual DC was characterized by a capacitance-voltage hysteresis curve and nearly zero hysteresis was achieved. Therefore, IB irradiation is a useful method to achieve uniform and homogenous LC alignment, and using it with the solution-derived La:ZnO film exhibited potential for high-quality LC applications.