Formation of Domain Pattern in Near‐Congruent Lithium Tantalate Crystals by Electron Beam Irradiation

We study the domain structure evolution induced by e‐beam irradiation in monodomain and polydomain samples of near‐congruent lithium tantalate covered by photoresist layer. The dot e‐beam irradiation is carried on Z‐ polar surface. The polydomain state is created by partial polarization reversal of the sample with photoresist layer. Irradiation results in formation of rounded domains with backswitched smaller domains: irregularly shaped randomly distributed micron‐size domains and quasi‐regular circular nanodomain arrays. The formation of the micron‐size domains is due to the depolarization field after irradiation and subsequent relaxation of the injected charge. The lower concentration of such domains in the polydomain state is attributed to interaction with existing domains. The appearance of nanodomain arrays is reported for the first time to the authors knowledge. Four concentric regions with different patterns are distinguished: nanodomains in the central region, nanodomain arrays arranged in spiral and randomly oriented chains, and an external part without nanodomains. The appearance of these domains is attributed to the field produced by charges localized in bulk near the irradiated surface. The concentric regions with different domain patterns are related to the field values and gradients. These findings are important for high‐pitch periodical domain poling for creation of nonlinear optical devices.