Oxygen Plasma Surface‐Activated Lithium Niobate for Controlling Protons Diffusion Rate

Lithium niobate (LN) is one of the key materials in modern instrument engineering. Currently, photonic devices based on thin films have great potential for use. That is why the role of the surfaces in technological operations strongly increases. Herein, the powerful effect of modifying the surface of LN in oxygen plasma at low pressures on the diffusion coefficient of hydrogen ions is demonstrated. Plasma activation of LN surface leads to changes in chemical composition, found by X‐Ray photoelectron spectroscopy (XPS), Raman, and IR spectroscopy methods that the part of niobium relative to oxygen on the surface of LN decreases. During proton exchange (PE), the deformations of the crystal lattice and the change of refractive index are sharply reduced. No surface damage of LN is observed at direct PE. For the first time, it is possible to form an intermediate phase at low PE temperatures and without annealing. This was previously considered impossible. An explanation is proposed for the adsorption of benzoic acid on the surface of lithium niobate. This effect can be used in ridge waveguides and diffuse optical waveguide technology, nonlinear optical applications, and lab on chip.