Selective CW Laser Synthesis of MoS 2 and Mixture of MoS 2 and MoO 2 from (NH 4 ) 2 MoS 4 Film.

Very recently, the synthesis of 2D MoS 2 and WS 2 through pulsed laser-directed thermolysis can achieve wafer-scale and large-area structures, in ambient conditions. In this paper, we report the synthesis of MoS 2 and MoS 2 oxides from (NH 4 ) 2 MoS 4 film using a visible continuous-wave (CW) laser at 532 nm, instead of the infrared pulsed laser for the laser-directed thermolysis. The (NH 4 ) 2 MoS 4 film is prepared by dissolving its crystal powder in DI water, sonicating the solution, and dip-coating onto a glass slide. We observed a laser intensity threshold for the laser synthesis of MoS 2 , however, it occurred in a narrow laser intensity range. Above that range, a mixture of MoS 2 and MoO 2 is formed, which can be used for a memristor device, as demonstrated by other research groups. We did not observe a mixture of MoS 2 and MoO 3 in the laser thermolysis of (NH 4 ) 2 MoS 4 . The laser synthesis of MoS 2 in a line pattern is also achieved through laser scanning. Due to of the ease of CW beam steering and the fine control of laser intensities, this study can lead toward the CW laser-directed thermolysis of (NH 4 ) 2 MoS 4 film for the fast, non-vacuum, patternable, and wafer-scale synthesis of 2D MoS 2 .