The illustration shows the MoS2 lattice structure (green: Mo, yellow: S). The material after cleaving is shown in the forefront, the surface is jagged, and the measured surface electronic structure is inhomogeneous (coloured map). In the back is the cleaved material after exposure to atomic hydrogen (represented by the white balls). The measured surface electronic structure, shown in the map, is more homogenous. Credit: Martin Künsting / HZB
Molybdenum disulfide (MoS₂) is an extremely adaptable substance with applications ranging from gas sensing to serving as a photocatalyst in the production of green hydrogen. Typically, the study of a material begins with its bulk crystalline form. However, in the case of MoS₂, the focus has been more on exploring its mono and few-layer nanosheets.
The few studies conducted thus far show diverse and irreproducible results for the electronic properties of cleaved bulk MoS₂ surfaces, highlighting the need for a more systematic study, which has been done now at the light source BESSY II.
Systematic Study at BESSY II
Dr. Erika Giangrisostomi and her team at HZB carried such a systematic study at the LowDosePES end-station of the BESSY II light source. They utilized X-ray photoelectron spectroscopy technique to map the core-level electron energies across extensive surface areas of MoS2 samples.
Using this method, they were able to monitor the changes in the surface electronic properties after in-situ ultra-high-vacuum cleaving, annealing, and exposure to atomic and molecular hydrogen.
Key Findings and Implications
The results from this study point to two main findings. Firstly, the study unambiguously reveals sizeable variations and instabilities in electron energies for the freshly cleaved surfaces, demonstrating how easy it is to come to diverse and irreproducible outcomes.
Secondly, the study shows that room-temperature atomic hydrogen treatment is remarkably effective in neutralizing the surface electronic inhomogeneity and instability. This is rationalized by the ability of hydrogen atoms to either accept or give away an electron and calls for further characterizations of the functional properties of the hydrogenated material.
“We hypothesize that atomic hydrogen helps to rearrange sulfur vacancies and excess of sulfur atoms yielding a more ordered structure”. Erika Giangrisostomi says.
This study marks a fundamental step in the investigation of MoS2. Due to the extensive use of MoS2 in all kinds of applications, the findings of this research have the potential to reach a wide audience in the fields of electronics, photonics, sensors, and catalysis.
Reference: “Inhomogeneity of Cleaved Bulk MoS2 and Compensation of Its Charge Imbalances by Room-Temperature Hydrogen Treatment” by Erika Giangrisostomi, Ruslan Ovsyannikov, Robert Haverkamp, Nomi L. A. N. Sorgenfrei, Stefan Neppl, Hikmet Sezen, Fredrik O. L. Johansson, Svante Svensson and Alexander Föhlisch, 31 August 2023, Advanced Materials Interfaces.
DOI: 10.1002/admi.202300392
Source: SciTechDaily
