Proton exchange at LiNbO3 surfaces - diffusion investigations

Dörrer, Lars; Tuchel, P.S.; Schmidt, Harald GND

Proton exchange (PE) is a widely used technique to modify the surface of LiNbO3 within the region of 1 µm. The resulting Li1-nHnNbO3 layer has different optical properties (e.g. refractive index) in comparison to LiNbO3 bulk crystals. The optical properties of the standard LiNbO3 together with the possibility to modify the refractive index in a welldefined surface layer make this material to a model material for photonic and optoelectronic studies. The proton exchange process is typically done by treatment of the sample in an acid as proton source. Regardless of the technical use, the fundamental aspects of the proton exchange process are unclear up to now (“The known data on PE kinetics do not go beyond the “technological” framework ... “ [1]). The determination of the diffusion coefficients in the modified Li1-nHnNbO3 should help to extract a kinetic model to describe the process. In our investigations, we use benzoic acid with different concentrations of lithium benzoate as proton source. We determined the depth of the proton exchange area and the tracer diffusivity of deuterium in the exchanged region at 230 °C using Secondary Ion Mass Spectrometry (SIMS) and in the second case deuterated benzoic acid in addition. During further experiments we used isotope labeled 6LiNbO3 thin films as a tracer source to monitor the diffusion of lithium also by SIMS. With the information about tracer diffusivities of deuterium and lithium, it will be possible to develop a model to describe the kinetics of the proton exchange process in detail.

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Dörrer, Lars / Tuchel, P.S. / Schmidt, Harald: Proton exchange at LiNbO3 surfaces - diffusion investigations. Düren 2021. Shaker.

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