Two-dimensional structures of ferroelectric domain inversion in LiNbO3 by direct electron beam lithography

We report on the fabrication of domain-reversed structures in LiNbO3 by means of direct electron beam lithography at room temperature without any static bias. The LiNbO3 crystals were chemically etched after exposure of the electron beam, and then the patterns of domain inversion were characterized by atomic force microscopy (AFM). In our experiment, an interesting phenomenon occurred when the electron beam wrote a one-dimensional grating on the negative c face: a two-dimensional (2D) dotted array was observed on the positive c face, which is significant for its potential to produce 2D and three-dimensional photonic crystals. Furthermore, we also obtained 2D ferroelectric domain inversion in the whole LiNbO3 crystal by writing the 2D square pattern on the negative c face. Such a structure may be utilized to fabricate 2D nonlinear photonic crystal. AFM demonstrates that a 2D domain-reversed structure has been achieved not only on the negative c face of the crystal, but also across the whole thickness of the crystal.