Synthesis of Large-Area Highly Crystalline Monolayer Molybdenum Disulfide with Tunable Grain Size in a H2 Atmosphere

Large-area and highly crystalline monolayer molybdenum disulfide (MoS2) with a tunable grain size was synthesized in a H-2 atmosphere. The influence of introduced H-2 on MoS2 growth and grain size, as well as the corresponding mechanism, was tentatively explored by controlling the H-2 flow rate. The as-grown monolayer MoS2 displays excellent uniformity and high crystallinity evidenced by Raman and high-resolution transmission electron microscopy. The Raman results also give an indication that the quality of the monolayer MoS2 synthesized in a H-2 atmosphere is comparable to that synthesized by using seed or mechanical exfoliation. In addition, the electronic properties and dielectric inhomogeneity of MoS2 monolayers were also detected in situ via scanning microwave microscopy, with measurements on impedance and differential capacitance (dC/dV). Back-gated field-effect transistors based on highly crystalline monolayer MoS2 shows a field-effect mobility of similar to 13.07 cm(2) V-1 s(-1) and an I-on/I-off ratio of similar to 1.1 x 10(7), indicating that the synthesis of large-area and high-quality monolayer MoS2 with H-2 is a viable method for electronic and optoelectronic applications.