Halogen-Mediated Polymer-Free Recovery of Pristine MoS₂ Monolayers From Gold-Assisted Exfoliation

Metal-assisted mechanical exfoliation has recently emerged as a powerful strategy for producing large-area monolayers of two-dimensional (2D) transition-metal dichalcogenides (TMDs) with near-intrinsic crystalline quality. The strong adhesion between the TMD monolayer and the metallic adhesion layer poses a significant challenge for device integration, as it generally requires polymer-assisted transfer processes that introduce contamination, mechanical strain, and structural defects. Here we report a halogen-mediated biphasic etching strategy that enables the polymer-free recovery of TMD monolayers directly from gold-assisted exfoliation substrates. Sequential iodine vapor exposure followed by liquid-phase iodine etching weakens the Au-TMD interfacial interaction and subsequently removes the gold adhesion layer while preserving the structural integrity of the monolayer. Spectroscopic characterization, time-resolved morphological analysis, and first-principles calculations reveal that iodine adsorption modifies the electronic structure of the Au surface and reduces its binding strength to the TMD layer. MoS₂ monolayers recovered using this approach exhibit significantly reduced strain, lower charge doping, and suppressed wrinkle formation compared with polymer-transferred counterparts. Optoelectronic devices fabricated from these monolayers demonstrate enhanced photocurrent and improved operational stability. These findings establish halogen-mediated biphasic etching as a scalable route for integrating pristine 2D semiconductors with technologically relevant substrates and provide a promising pathway toward high-performance 2D optoelectronic devices.