Uniform growth of MoS2 films using ultra-low MoO3 precursor in one-step heating chemical vapor deposition

•The effect of ultra-low mass MoO3 to the growth of MoS2 films is studied.•The formation of MoO3-xSy cluster act as nucleation points in the MoS2 growth process.•The optimized grown MoS2 films are uniform (∼50 mm2) and ∼6 layers thick.•A growth model of MoS2 films is proposed. In chemical vapor deposition (CVD), homogeneous molybdenum vapor concentration is important in synthesizing uniform thickness and large coverage of two-dimensional molybdenum disulfide (2D-MoS2) films. Here, we synthesize few-layer MoS2 films with uniform thickness and adequate coverage over 50 mm2 size area using ultra-low molybdenum trioxide (MoO3) precursor placed directly under a face-down silicon dioxide/silicon (SiO2/Si) substrate in one-step heating CVD. The precursor mass is controlled by dispersing MoO3 powder in ethanol (C2H5OH) and varying the volume of MoO3/C2H5OH solution coated on SiO2/Si substrates into 10, 20 and 25 µL. Field emission scanning electron microscopy images reveal that 20 µL MoO3/C2H5OH solution produces ∼93% area coverage of 2D-MoS2 films. The average Raman spectra show the typical presence of MoS2 peaks around 378.8 cm−1 and 404 cm−1 referring to the E12g and A1g modes, respectively. The difference between the two Raman modes for all samples is ∼25 cm−1, indicating few-layer MoS2 films. The thickness of MoS2 films is estimated at around 2.8 ± 0.44 nm and 3.2 ± 0.43 nm (∼6 layers) using atomic force microscopy analysis. These findings suggest that ultra-low MoO3 precursor is useful to produce uniform thickness and high coverage few-layer MoS2 films using one-step heating CVD.