Overcoming Contamination-Induced Barriers: Ohmic Vertical Transport in Atomically Clean MoS₂/Au Junctions

The application of two-dimensional (2D) semiconductors, such as monolayer MoS₂, is limited by high contact resistance commonly attributed to interfacial barriers at metal contacts. Furthermore, the dependence of electrical conductivity on MoS₂ thickness remains unsettled, as both increasing and decreasing trends with layer number have been reported. Using conductive atomic force microscopy (CAFM), we measure local electrical transport in MoS₂/Au junctions with contrasting interface cleanliness: pristine interfaces prepared under ultra-high vacuum (UHV) and contaminated interfaces prepared by the widely used PDMS-assisted transfer under ambient conditions. By comparing monolayer MoS₂/Au junctions prepared under these contrasting conditions, we demonstrate that an atomically clean interface enables highly conductive, ohmic transport in the vertical CAFM geometry. Measurements on mono- and multilayer regions further show that interfacial contamination introduces a substantial transport barrier and can reverse the thickness dependence of electrical transport. We rationalize these findings using electrical transport simulations based on Kirchhoff's laws, identifying the interplay between MoS₂/Au interfacial resistance and lateral current spreading within MoS₂ layers as the origin of the opposite thickness trends. Lastly, we show that local force-mediated lamination on lightly contaminated contacts can recover pristine, ohmic contacts, offering a route toward nanoscale patterning.