Observing Weak Interchain Coupling in 1D vdWs Ternary Mo₆Se₂I₈ to Achieve Probe Exfoliation of Ultrathin Molecular Chains

van der Waals (vdWs) interchain coupling is a unique feature of 1D vdWs materials, where strong vdWs coupling in 1D vdWs materials leads to the thickness-dependent physical properties, while weak vdWs coupling can preserve the single-chain property even in their thick counterparts. Different from 2D vdWs materials, due to their nanoscale widths, identifying and producing ultrathin 1D molecular chains are challenging, severely limit their device applications. Thus, looking for novel 1D vdWs materials with weak interchain coupling is crucial. In this paper, the authors report that the 1D ternary vdWs material, Mo₆Se₂I₈ with non-centrosymmetric characteristic and strong optical anisotropy, exhibits weak interchain coupling. On one hand, the density functional theory (DFT) calculations theoretically demonstrate its thickness-independent electronic structure, negligible interchain differential charge density, and weak cleavage energy as low as 0.256 J m⁻². On the other hand, the thickness-independent work function and low first-order temperature coefficient of −0.0030 cm⁻¹ K⁻¹ further experimentally confirm its weak interchain coupling. Moreover, taking advantage of this weak vdWs coupling characteristic, the in situ exfoliation of the Mo₆Se₂I₈ nanowires is achieved by using a nanoprobe in a scanning electron microscope (SEM), obtaining ultrathin molecular chains with a thickness of ≈1.2 nm.