Photo-induced Ag deposition on periodically poled lithium niobate: Concentration and intensity dependence

This research focuses on the formation of Ag nanopatterns on periodically poled lithium niobate (PPLN). The photo-induced process employs UV-light exposure while the PPLN is immersed in a AgNO₃ solution. The Ag deposition was consistent with previous results, showing preferential deposition along the domain boundary as well as an increased density of particles on the positive domain surface in comparison to the negative domain. By tuning the chemical solution concentration and the UV-light intensity, the Ag⁺ ion flux and the electron flux are varied and the deposition pattern could be controlled to either enhance the nanowire-like structures along the domain boundary or create a more uniform deposition pattern over the positive and negative domains. To understand the deposition process, we investigated the relationship between the Ag⁺ ion flux because of diffusion and the electron flux initiated by the UV exposure of the ferroelectric surface. The subsequent results suggest that this relationship is responsible for the different deposition patterns. The observed variation of boundary-enhanced or boundary-depressed deposition is explained by consideration of the electric field distribution and the ratio of the Ag⁺ ion and photon flux. The results establish that the ratio can be controlled by varying the solution concentration and/or UV-light intensity to generate enhanced nanowire-like structures along the domain boundary or a more uniform deposition pattern over the positive and negative surface. Moreover, the specific value of the Ag ⁺/photon flux ratio where the pattern changes is dependent on other factors including the nucleation limited growth mechanism and the Stern layer on the lithium niobate.