CC BY
14LP-PS-4
Laser synthesis of the LiCoO2 thin films
L. Parshina1, O. Novodvorsky1, O. Khramova1
1ILIT RAS - Branch of the FSRC «Crystallography and Photonics» RAS, Laboratory of nanostructures and thin films, Shatura, Russian Federation
The LiCoO2 solid-state thin-film electrolytes are ideal candidates for the fabrication of all-solidstate electrochromic devices and thin-film batteries [1, 2]. The use of the solid-state electrolyte in an electrochromic device will greatly simplify the fabrication technique, reduce the coloration time and ensure functioning at lower temperatures, which will increase the durability and reliability of the device [3]. Currently, investigations of the LiCoO2 solid-state thin-film electrolytes are making in order to improve their ionic conductivity and optical transparency.
The LiCoO2 thin films on the c - sapphire and high-conductive silicon substrates were produced at the substrate temperature of 25 to 500 °C by the pulsed laser deposition. The film synthesis was from the LiCoO2: Li2O ceramic targets. The targets were produced from the LiCoO2 and Li2O powders by pressing and annealing at the temperature of 1200 °C for two hours. The Li2O concentration in the target was 5 %. Ablation of the targets was performed by the excimer KrF-laser radiation with the wavelength of 248 nm at the energy density on the target of at least 3 J/cm2 and the oxygen pressure of 100 mtorr in the vacuum chamber during the film growth. The optical, electrical properties and the surface morphology of the produced films with the thickness of 2040 nm were investigated depending on the type and the substrate temperature. By the AFM and SEM methods it was established that the films produced on both types of the substrate at room temperature had a granular surface structure. The size of the granules was several hundred nanometers. It was found that with an increase in the substrate temperature during the growth of the LiCoO2 film, its surface roughness decreased to 10 nm for the film produced at 500 °C on the c-sapphire substrate. The study of the transmission spectra of the LiCoO2 films produced on the c-sapphire substrate showed that with a change in the substrate temperature from 25 to 500 °C, the transparency of the films increased by 30 % in the whole of the spectral range under study. It was established that the LiCoO2 films produced on the c-sapphire substrate, regardless of its temperature, were dielectrics. The LiCoO2 films deposited at room temperature on the silicon substrates with the resistivity of M0-3 Ohm-cm became highly conductive with the resistivity of about 2.5-10-7 Ohm-cm.
This work was supported by the Ministry of Science and Higher Education within the State assignment FSRC «Crystallography and Photonics» RAS in part of «the thin films synthesis» and the Russian Foundation for Basic Research (Project № 19-29-03032, 17-07-00615, 16-29-05385) in part of «analysis of the thin films».
References
[1] A. Yano et al., Journal of The Electrochemical Society, 165, A3221 (2018).
[2] Sh.-Ch. Wang et al., Thin Solid Films, 520, 1454 (2011).
[3] K. J. Patel et al., J. Solid State Electrochem., 21, 337 (2017).
