Enhanced Nonlinear Saturable Absorption of MoS₂/Graphene Nanocomposite Films

Abstract

MoS 2 /graphene nanocomposite films are fabricated by vacuum filtering with liquid-phase exfoliated MoS 2 / graphene suspension. The nanocomposite films are characterized by Raman spectroscopy, UV−vis spectroscopy, and atomic force microscopy, indicating the optical films with a large scale and high optical homogeneity. The enhanced saturable absorption of MoS 2 /graphene nanocomposite films compared with pristine MoS 2 film and graphene film is investigated using an open-aperture Z-scan technique with a femtosecond laser at 800 nm. The nonlinear absorption coefficient of MoS 2 /graphene nanocomposite film is ∼ −1217.8 cm/GW, which is larger than that of MoS 2 film (∼ −136.1 cm/GW) and graphene film (∼ −961.6 cm/GW) at the same condition. The imaginary part of the third-order nonlinear optical susceptibility of the nanocomposite film can reach Imχ (3) ∼ 10 −9 esu with a figure of merit ∼10 −14 esu cm, low saturable intensity (∼157.0 GW/cm 2 ), and high modulation length (∼32%). A coupling model is considered in order to understand the nonlinear absorption properties of MoS 2 /graphene nanocomposite films, which suggest the enhancement can be attributed to charge transfer between MoS 2 and graphene. The results pave the way for the design of nonlinear optical properties with two-dimensional materials for good performance of optical switches or mode lockers based on saturable absorbers.

Band Alignment of MoTe2/MoS2 Nanocomposite Films for Enhanced Nonlinear Optical Performance

“…The enhancement of NLO property from the MoTe 2 /MoS 2 heterostructure is attributed to the effect of interlayer charge transfer, which is identified by rate equations using the Runge-Kutta algorithm and the first principles calculation. Generally, the MoTe 2 /MoS 2 nanocomposite films with different filtration volumes have a linear relationship with the thickness (20,40,60,80, and 100 mL for 30, 60, 80, 100, and 120 nm, respectively). Transmission electron microscope (TEM) was used to determine the morphology of the MoTe 2 /MoS 2 nanosheet as shown in Figure 7a.…”

“…Imχ (3) and the figure of merit (FOM) show an increasing trend with the thickness when the films are thinner, while there is no significant thickness dependence of Imχ (3) and FOM, as the filtration volume is greater than 60 mL. [20] The weak thickness dependence could come from the density of localized defect states on grain boundary and interlayer coupling. These values are higher than that of MoS 2 /graphene nanocomposite film.…”

“…[20,35] The beam radius is ≈30 µm, which was measured by the scanning knife-edge technique. [20,35] The beam radius is ≈30 µm, which was measured by the scanning knife-edge technique.…”

“…An energy-level model combined with Runge-Kutta algorithm is used to understand the enhancement mechanism. [20] Meanwhile, the strong interlayer coupling between MoTe 2 and MoS 2 was observed by Zhang et al [36] The type-II heterostructures provide a new direction for nonlinear optoelectronic devices. Meanwhile, band structure of MoTe 2 /MoS 2 heterostructure is calculated by the first principles.…”

“…[17,18] Recently, there are some evidences of enhanced NLO properties by the hybridation of nanomaterials. [20] However, graphene and TMDs usually form Schottky junction, which is quite different from the heterojunction between semiconductor TMDs. [14] Zhang et al reported the enhanced nonlinear absorption coefficient of heterostructured MoS 2 /carbon nanotubes.…”