Investigation on Nonlinear Optical Properties of MoS2 Nanoflake, Grown on Silicon and Quartz Substrates

Two-dimensional (2D) materials like molybdenum disulfide (MoS2) are attracting substantial interest because of having optical and electronic properties and unique nonlinear optical response. Bulk or multilayer MoS2 is a... [ view full abstract ]

Two-dimensional (2D) materials like molybdenum disulfide (MoS₂) are attracting substantial interest because of having optical and electronic properties and unique nonlinear optical response. Bulk or multilayer MoS₂ is a semiconductor with an indirect band gap of 1/2 eV. However, single-layer MoS₂ shows a direct band gap of 1/9 eV . This decreasing of the layers has been attracted attention of optics community like saturable absorption, nonlinear absorption, nonlinear scattering and nonlinear refraction . In this study, MoS₂ was directly synthesized by chemical vapor deposition (CVD), on different substrates including Si/SiO₂ and quartz, using MoO₃ and sulfide powders as precursor. The X-Ray diffraction patterns demonstrate the high crystallinity of MoS₂ on Si/SiO₂ and quartz substrates as seen in Fig 1. Scanning electron microscopy confirmed the formation of MoS₂ grown on both substrates as seen in Fig 2. According to line width and frequency difference between the E¹_2g and A_1g in Raman spectroscopy, it is inferred that the MoS₂ grown on Si/SiO₂ substrate is monolayer (frequency difference between two peaks: 20 Cm^-1) and the MoS₂ grown on quartz substrate is multilayer (frequency difference between two peaks: 25 Cm^-1) as seen in Fig 3. Moreover, by assessment of MoS₂ nanoflake band gap via UV-visible analysis, it verified the formation of few layer structures. In addition, the open-aperture and close-aperture Z-scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the synthesized MoS₂. All experiments were performed using a diode laser with a wavelength of 532 nm as light source. The monolayer MoS₂ synthesized on Si/SiO₂, display considerable two-photon absorption. However, the multilayer MoS₂ synthesized on quartz displayed saturable absorption (SA) as seen in Fig 4. It is noticeable that both samples demonstrate obvious self-defocusing behavior. In general, few layered MoS₂ would be useful for the development of nanophotonic devices like optical limiters, optical switchers, etc.