In the quest to harness the unique properties of two-dimensional materials for advanced energy applications, a team of researchers led by Paolo Canepa from the University of Genoa’s OptMatLab has uncovered crucial insights into the behavior of tungsten disulfide (WS₂) flakes. Their study, published in the Journal of Physics: Materials, sheds light on how defects in these atomically thin materials can significantly influence their mechanical and optical properties, paving the way for more efficient and reliable micro- and nanomechanical devices.
WS₂, a member of the transition metal dichalcogenides (TMDs) family, has garnered considerable attention for its potential use in energy storage, photovoltaics, and flexible electronics. However, the presence of defects, such as atomic vacancies, can greatly affect its performance. Canepa and his team set out to understand how these defects impact the material’s adhesion, friction, and optical properties, with a view to optimizing its use in practical applications.
Using chemical vapor deposition (CVD), the researchers grew monolayer WS₂ flakes and identified two distinct domains, named α and β, with markedly different mechanical and optical properties. “The α-domains exhibit high photoluminescence and strong Raman response, indicating a high quality and pristine-like behavior,” Canepa explains. “In contrast, the β-domains show very low photoluminescence, weak Raman response, and significantly higher friction.”
The team attributed these differences to the varying densities of sulfur and tungsten atomic vacancies in the two domains. “The tungsten vacancies in the β-domains not only mediate non-radiative recombination processes but also drive a prominent friction enhancement,” Canepa notes. This friction enhancement could be due to an increase in the amplitude and disorder of the WS₂ potential energy surface or an impact on the stress distribution within the growing flakes.
The findings have significant implications for the energy sector, where TMDs like WS₂ are being explored for use in solar cells, batteries, and other energy storage devices. By understanding and controlling the defect structure of these materials, researchers can optimize their performance and reliability. “Our results help identify the type of defects and mechanisms that most significantly affect the properties of TMD monolayer flakes prepared by scalable production routes,” Canepa says.
The research also highlights the importance of characterizing the nanoscale properties of two-dimensional materials, as these can greatly influence their macroscopic behavior. As the field of TMDs continues to evolve, such insights will be crucial in guiding the development of new materials and devices for energy applications.
In the broader context, this work underscores the need for a comprehensive understanding of the relationship between defects, optical properties, and mechanical behavior in two-dimensional materials. As Canepa and his colleagues continue to unravel these complexities, they bring us one step closer to realizing the full potential of TMDs in the energy sector and beyond. The study, titled “Adhesion and friction patterns of CVD-grown monolayer flakes induced by vacancy-rich defect domains,” was published in the Journal of Physics: Materials, which is known in English as the Journal of Physics: Materials.