Domain patterning in ion-sliced LiNbO3 films by atomic force microscopy

Abstract

Photonic structures denoted as LNOI (LiNbO3-on-insulator) are of considerable interest for integrated optics due to a high refractive-index contrast provided by the interface LiNbO3/insulator. A topical problem for LNOI-based optical waveguides is optical-frequency conversion, in particular realized on ferroelectric domains on the basis of quasi phase-matching principle. This paper presents extended studies on the fabrication of domain patterns by atomic force microscopy (AFM) methods (raster lithography, piezo-force microscopy, conductive AFM) in single-crystal ion-sliced LiNbO3 films forming LNOI sandwiches. A body of data obtained on writing characteristics of domains and specified 1D and 2D domain patterns permitted us to manipulate the domain sizes and shapes. Of special importance is the stability of created patterns, which persist with no degradation during observation times of months. The domain coalescence leading to the transformation of a discrete domain pattern to a continuous one was investigated. This specific effect—found in thin LiNbO3 layers for the first time—was attributed to the grounding of space-charges accumulated on domain walls. Observations of an enhanced static conduction at domain walls exceeding that in surrounding areas by not less than by five orders of magnitude supports this assumption. AFM domain writing in ion-sliced films serves as a basis for studies in nonlinear photonic crystals in integrated optical schemes.