Identifying core–shell pseudo-single-crystals in MoS2 monolayers via visible light dark-field microscopy imaging

Synthetic molybdenum disulfide (MoS2) with uniform electrical properties has emerged as a promising semiconductor in the advanced 2D transistor and integrated circuit (IC) processes. Focusing on the core–shell structure pseudo-single-crystal issue in the chemical vapor deposition-grown MoS2, and induced performance deterioration risks in MoS2 electronics, this work presents an efficient optical characterization technique based on dark-field (DF) microscopy imaging. We discover that the invisible pseudo-single-crystals in bright-field microscopy imaging can be clearly discriminated using DF imaging. By conducting theoretical analysis, a fourth-power signal amplification relation between the DF imaging intensity contrast and the local roughness of MoS2 surface is quantified. The angstrom-scale MoS2 roughness perturbations can be substantially amplified to identifiable scattered light signals within the visible light wavelength band. This scattering model fundamentally indicates a precise, rapid, low-cost, and nondestructive characterization tool suitable for identifying hidden inferior domains in 2D material-on-wafer specimens. The visible light DF microscopy imaging exhibits the potential for integration into standard semiconductor IC techniques, and may thus promote future developments of 2D electronics and ICs.