Optical Limiting Performance of MoS2 Nanosheets Exfoliated via Liquid-Phase Sonication: Implications for Laser Shielding

The utilization of two-dimensional (2D) materials in optoelectronic devices has witnessed a surge. Production of 2D ultrathin molybdenum disulfide (MoS2) nanosheets without the use of toxic precursors and without altering the phase of the material is still a task. We developed a cost-effective liquid-phase exfoliation method that is free of additives, utilizing ultrasound to produce a significant amount of nearly single-layered MoS2 nanosheets by employing isopropyl alcohol and deionized water as a cosolvent. This work addresses the deficiencies in the current state-of-the-art studies by exploring the mechanism governing ultrasonic cavitation, resulting in MoS2 nanosheets. Various sonication durations were altered to investigate the relationship between the duration of sonication and the dimensionality of the resulting nanosheets. The findings revealed that prolonged sonication durations yielded bilayered and trilayered nanosheets. The reduction in layer thickness was confirmed by Raman modes as the sonication time increased. Size-dependent optical studies indicated that the optical properties have enhanced as the sonication time increased. An open-aperture Z-scan investigation was conducted to explore the size-dependent nonlinear optical features of MoS2 nanosheets, employing a 532 nm neodymium-doped yttrium aluminum garnet pulsed laser in a nanosecond pulsed regime. The optical limiting performance of the nanosheets sonicated at various time intervals was accessed and it was observed that as the nanosheets’ thickness decreases, the optical limiting behavior improves. Due to two-photon absorption, MoS2 nanosheets display optical limiting behaviors through reverse saturable absorption. Optical limiting thresholds as low as 2.98 × 1012 W/m2 are attained. This significant enhancement suggests that these ultrathin MoS2 nanosheets are suitable for applications in laser shielding.