Controlled sputtering time growth, ultrafast nonlinear absorption and carrier dynamics properties of vertically WSe2 films under photoexcitation

Abstract

In this work, the vertically-grown-WSe2-films were successfully prepared using the RF magnetron sputtering. Their structure, morphology, growth mechanism and nonlinear optical properties were investigated by adjusting the growth time. The special "worm-like" structure was characterized by scanning electron microscopy, attributing to the two growth orientations in C-axis type I (C//) and type II (C⊥). The X-ray diffraction results confirmed the preferential growing on (002) and (008). The nonlinear optical properties were studied by femtosecond Z-scan to reveal the nonlinear absorption mechanism. WSe2 films exhibited the nonlinear optical process from saturable absorption to reverse saturable absorption with the growing time. The NA coefficient for WSe2 films is ∼10−9 m/W. The carrier relaxation time was determined by femtosecond transient absorption spectroscopy. This proposed WSe2 films will be an excellent candidate for developing optoelectronic devices due to the excellent nonlinear optical properties.