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Speaker : Prof. Kwabena Bediako Affiliation : College of Chimistry at UC Berkeley Region : Americas Year : 2022 Language : English Van der Waals materials provide atomic-level control in stacking layers with widely varying material properties. Unlike epitaxial growth processes, the weak interplane bonding allows unlimited possibilities for each successive layer during vertical stacking. Thus, precise and complex heterostructures can be assembled. The most precise modern methods for lateral patterning such as electron beam lithography (EBL), rely on polymer-based lithographic processes. These polymers limit the spatial resolution of patterning due to proximity effects and introduce significant residue. The residue often introduces enough disorder to destroy fragile quantum electronic states such as the fractional quantum Hall effect, Wigner crystallization, and other emergent phases in strongly correlated electron systems. We exploit the metastable structural phases of van der Waals materials to perform polymer-free nanopatterning of MoS2. We use a 30 kV electron beam to selectively convert 2H-MoS2 into its metallic 1T phase, which physically corresponds to the gliding of one S-plane and destroys the mirror symmetry of the 2H phase. Features with dimensions less than the diameter of the electron beam can be written since metallic regions nucleate at a point and grow as the material is locally dosed with higher electron concentrations. This technique unlocks the possibility of using a single material to create various electronic devices such as patterned electrostatic gates, field-effect transistors, Schottky diodes, quantum dots, and nanowires. We characterize this transition in many-layer flakes of MoS2 through electrical transport measurements and atomic force (AFM) and Kelvin probe force microscopy (KPFM). KPFM measurements demonstrate an increase in the work function of over 100 meV. AFM measurements also indicate reduction in flake thickness, suggesting a significant variation in interlayer spacing.