Standing growth mechanism and ultrafast nonlinear absorption properties of WS2 films

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Tungsten disulfide (WS2) films were successfully prepared by magnetron sputtering. The structure, morphology and standing growth mechanism of WS2 films under different sputtering conditions (sputtering time and substrate temperature) were studied. The scanning electron microscopy (SEM) showed that the sputtering time reached 1.5 h or the substrate temperature reached 250 °C, the morphology of WS2 reveal a “sickle” texture on the surface. The standing growth mechanism was demonstrated by SEM results. X-ray diffraction (XRD) patterns showed that only (101) diffraction peak existed in WS2 films. The nonlinear absorption in WS2 films were characterized by Z-scan technique in the femtosecond regimes at 800 nm. The results showed that the WS2 films have two-photon absorption process, and the transition from saturable absorption to reverse saturable absorption was observed. The nonlinear absorption coefficients of the WS2 films at different sputtering time were 6.386 × 10−10 (for 2 h), 9.704 × 10−10 (for 1.5 h) and −9.759 × 10−10 m/W (for 1 h), respectively. The nonlinear absorption coefficients of the WS2 films at different substrate temperature were −6.275 × 10−10 (for 250 °C), 5.430 × 10−9 (for 300 °C) and 3.899 × 10−9 m/W (for 350 °C), respectively. The standing WS2 films have excellent nonlinear optical performance and simple synthesis route, which provide a good prospect for the application of two-dimensional materials in nonlinear optics.