Impact of friction-induced microdefects on the surface properties of MoS₂

The rapid evolution of the high-end equipment manufacturing industry, from traditional manual Methods to advanced digital intelligent manufacturing, has significantly improved production precision and contributed to technological advancements across various sectors. As the demand for the reliability and durability of critical components in aerospace, semiconductor manufacturing, and other industries continues to rise, there is an increasing focus on understanding microscale defects caused by friction. These friction-induced microdefects, including microcracks and phase transitions, present significant challenges. Although these defects are often subtle and not easily observed under standard conditions, their cumulative effects can significantly impact material performance. Currently, systematic investigations into the influence of friction-induced defects on the optical properties of semiconducting materials remain limited.

This research addresses this gap by focusing on monolayer molybdenum disulfide (MoS₂), a widely studied two-dimensional (2D) material known for its exceptional electronic and optical properties. Monolayer MoS₂ samples, free of defects, were prepared through the mechanical exfoliation method. Microscale friction-induced defects were introduced via atomic force microscopy under controlled loading conditions to ensure reproducibility and minimize significant structural damage. After defect introduction, the optical properties were analyzed via photoluminescence (PL) spectroscopy and Raman microscopy.

The experimental results showed that friction-induced defects generated new defect energy levels within the MoS₂ structure. These defect states served as non-radiative recombination centers, leading to a substantial reduction in PL intensity and exciton lifetime. Steady-state PL measurements showed a significant decrease in fluorescence intensity in defect-affected regions compared with pristine regions. Time-resolved PL spectroscopy further quantified the reduction in exciton lifetime, from 0.198 ns in pristine regions to 0.128 ns in defected regions, confirming that defects introduced non-radiative dissipation channels for excitons. Raman spectroscopic analysis confirmed the structural integrity of the samples after friction, with observable shifts in vibrational modes indicating the presence of localized stress fields and defect-induced modifications. Temperature-dependent PL studies highlighted the pronounced impact of friction defects at low temperatures. As the temperature decreased, defect-induced PL peaks became dominant in the spectral profile, particularly below 60 K; this behavior is attributed to the enhanced capture of excitons by defect states owing to reduced thermal activation at lower temperatures. Moreover, the defect-induced spectral features became more prominent with higher excitation powers, highlighting the influence of the features on carrier dynamics and non-radiative recombination pathways. These results emphasize the critical role of defect management in optimizing the performance of MoS₂-based optoelectronic devices.

The presence of friction-induced defects not only reduces PL efficiency but also shortens exciton lifetimes, posing challenges for applications that require high quantum yield and stable emission properties. Therefore, strategies to mitigate defect formation during manufacturing and operational processes are crucial for improving device reliability and efficiency. This study elucidates the physical mechanisms driving defect-induced alterations in the optical properties of 2D materials, offering a foundation for improved material design and device engineering. Future research will focus on extending these findings to other 2D materials, such as WS₂ and BN, and incorporating advanced characterization techniques, such as electron microscopy and first-principles calculations, to investigate defect formation at the atomic scale. By addressing these challenges, this research plays a key role in advancing the development of next-generation, high-performance optoelectronic devices suited for demanding industrial applications.