Atomic mapping of Li:ZnO thin films and its spectroscopic analysis

Lithium detection in materials is often crucial even with sophisticated compositional analysis techniques, like Energy Dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). The present work focuses on the three-dimensional compositional mapping of Li in Li-doped ZnO films using atom probe tomography (APT). A syringe pump spray pyrolysis (SSP) technique was prosperously used to synthesize undoped and Li doped zinc oxide (ZnO) thin films with Li concentration range from 0 to 8 at.%. onto glass substrates. The chemical reagents used for this experiment are Zinc acetate (Znfacach) and lithium acetate (Li (acac)(2)) under atmospheric conditions. Spectroscopic analyses of the films using Raman and Fourier transform infra-red (FTIR) spectroscopic techniques were done to confirm phase formation. Diffuse but strong absorption peaks within 400 - 600 cm(-1) in FTIR spectra confirm compound formation while the existence of E-2(High) and E-1 (LO) vibration modes in Raman spectra confirms the hexagonal wurtzite nature of ZnO films. Structure evolution of the films were ascertained using scanning electron microscopy (SEM). The stoichiometric ratio of Zn and O was estimated using EDX while their chemical state was probed using XPS. XPS also gives a qualitative account of Li with its probable chemical state. The latter is quantitatively estimated and mapped with atomic resolution using APT, where Li concentration was found to be similar to 7.5%, which is very close to the concentration introduced in the solution. APT confirms a uniform dispersion of Li, Zn and O along the film surface with no significant segregation or concentration fluctuation even at the atomic scale.

Automated summary

This study focuses on the three-dimensional compositional mapping of Li in Li-doped ZnO films using atom probe tomography, and confirms the phase formation of the films through spectroscopic analyses. Scanning electron microscopy was used to determine the structure evolution of the films, while EDX and XPS were employed to estimate the stoichiometric ratio of Zn and O and probe their chemical state. APT was then used to quantitatively estimate and map the distribution of Li, Zn, and O on the film surface.