Large Area Transition Metal Dichalcogenide Monolayers with Intrinsic Physics Properties

Transition metal dichalcogenides (TMDs) have proven to be a premier class of two-dimensional semiconductor due to their chemical simplicity, suitable carrier mobilities, and desirable band gaps. Stacking TMD monolayers to form moiré structures with small twist angles has provided a tunable platform for the investigation of a myriad of quantum phases. While the Scotch tape method has been widely adopted in TMD sample fabrication, its stochastic nature results in a low yield of small-area monolayers, limiting sample sizes, and preventing the method from scaling outside laboratory settings. Bottom-up growth methods, such as chemical vapor deposition (CVD), ameliorate the scalability issues, but the resulting TMD monolayers are limited by large defect densities and grain boundaries. Recently, metal assisted exfoliation, particularly the “gold-tape” method, was discovered as a top-down approach to deterministically exfoliate large TMD monolayers from bulk crystals. However, this method has not seen wide spread application due to concerns with monolayer quality, strain, and cleanliness. Here, we improve the “gold-tape” method to produce TMD monolayers with macroscopic dimensions and, more importantly, with electronic properties intrinsic to the starting crystal. Utilizing scanning tunneling microscopy and hyperspectral mapping to characterize monolayers at length scales spanning six orders of magnitude, we demonstrate that, gold-tape exfoliation deterministically produces millimeter-scale TMD monolayers with the same intrinsic defect density, exciton properties, and charge carrier mobility as those from the state-of-art Scotch tape methods. This demonstration opens the door to broader application of the “gold-tape” method for the fabrication of TMD based devices.