2025 Theses Doctoral

Pristine Gold-Tape Exfoliation of Transition Metal Dichalcogenide Monolayers

Olsen, Nicholas Michael

Transition metal dichalcogenides (TMD) monolayers have proven to be a premier class of two-dimensional semiconductor due to their chemical simplicity, suitable carrier mobilities, and desirable band gaps. However, popular fabrication methods fail to produce TMD monolayers with both suitable sizes and quality. The metal-assisted “gold-tape” method enables the deterministic exfoliation of macroscopic TMD monolayers from bulk single crystals, overcoming the size limitations of the widely used “Scotch-tape” method.

However, concerns regarding the quality of gold-exfoliated TMD monolayers have limited the technique’s adoption. This thesis discusses the quality and cleanliness of gold-tape exfoliated TMD monolayers from furnace to device. A substantial population of free charges is observed for photoexcited TMD monolayers, unless exfoliated from state-of-the-art flux grown crystals, highlighting the importance of parent crystal quality.

Furthermore, the discovery of a previously unknown irreversibly adsorbed polyvinylpyrrolidone (PVP) residue layer is chronicled, and a critical Ar/O2 reactive ion etch (RIE) step is introduced to eliminate it. Gold-tape exfoliation is shown to produce pristine, millimeter-scale, TMD monolayers which exhibit defect density, charge carrier mobility, and excitonic properties intrinsic to the parent crystal. Finally, post-process patterning and stacking are explored.