How does adding lithium affect the characteristics of thin MoS2 films?

Molybdenum disulfide (MoS₂) is a frequently studied material due to its layered structure, exceptional properties, and applicability in electronics, optoelectronics, and lithium batteries. In our research, we have shown how the addition of lithium affects the properties of ultrathin MoS₂.

The layered structure of MoS2 allows the intercalation of foreign atoms into the van der Waals gaps between the individual layers, which can affect the electronic structure as well as the electrical and optical properties of the material. Our colleagues investigated intercalation of few-layers MoS₂ with lithium. The initial few-layers MoS₂ were prepared using two different techniques – thermally assisted conversion (TAC) and pulsed laser deposition (PLD). We used a mixture of sulfur and Li₂S powders as a source of lithium, which was heated to a high temperature together with MoS₂. Through diffusion, lithium entered the space between the MoS₂ layers. The presence of lithium in the samples was confirmed using synchrotron radiation photoelectron spectroscopy. We did not observe any structural changes or changes in the optical properties of the layers after intercalation. However, the electrical resistance of the samples with lithium content increased significantly. By measuring the temperature dependence of resistance, we found that carrier transport in our layers is best described by Efros-Shklovskii variable range hopping, typical for a disordered semiconductor. Since the resistance of the layers increased significantly with increasing lithium content, we can conclude that lithium introduced new disorder into our layers, resulting in increased resistance. Even if lithium donated electrons to the MoS₂ layers, this effect remained hidden due to the prevailing disorder effect.

Image: The electrical resistance dependence on temperature, x in LixMoS_2, refers to Li content in MoS₂ layers.

More: https://doi.org/10.1063/5.0191046

Authors: J. Hrdá, M. Moško, I. Píš, T. Vojteková, L. Pribusová Slušná, P. Hutár, M. Precner, E. Dobročka, M. Španková, M. Hulman, Š. Chromik, P. Siffalovic, F. Bondino and M. Sojková