Transition Metals Dichalcogenide (TMDC) materials have attracted the scientific community due to their unique optical, mechanical, and electronic properties. Molybdenum disulfide (MoS2), an emerging 2D material, exhibit a tunable band gap that strongly depends on the numbers of layers, which makes MoS2 an attractive candidate for optoelectronic applications. However, recent reports have shown that engineering a monolayer using laser thinning can be an effective method without oxide formation, which can be a promising technique for various applications. Here, we investigate this laser thinning process using Raman spectroscopy, µ-XPS, and AFM measurements. Our results show that laser thinned multilayer MoS2 exhibit a large oxide on the surface of the nanosheet, contrary to previous reports. This oxide cannot be detected using µ-Raman spectroscopy. We also show that monolayer and bilayer MoS2 nanosheets exhibit distinctive phonon behavior compared to multilayer MoS2 nanosheets after prolonged laser treatments. This behavior is reflected on the steep intensity decrease for E2g mode, while the intensity of A1g mode slightly changes. This behavior can be interpreted as localized non-equilibrium temperature change due to the formation of anomalous particles on the surface of monolayer and bilayer MoS2 nanosheets. We show that these anomalous particles have a significant effect on the measured Raman properties of pristine monolayer and bilayer MoS2 nanosheets, unlike multilayer MoS2 nanosheets. Our results shed some light on the behavior of MoS2 nanosheets when laser treated for future photodetector applications.
Moh Amer, Frank DelRio, Fadhel Alsaffar, and Abdullah Alrasheed, "Laser treated molybdenum disulfide nanosheets: towards engineering better 2D photodetectors (Conference Presentation)," Proc. SPIE 10349, Low-Dimensional Materials and Devices 2017, 1034908 (Presented at SPIE Nanoscience + Engineering: August 09, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2274582.5581155604001.
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