Event Date
Two-dimensional (2D) semiconductors offer promising pathways beyond the scaling limits of silicon electronics, but their wafer-scale synthesis and direct integration into functional devices remain significant challenges. In the first part of this talk, I will present a wafer-scale, conformal strategy for growing continuous mono- to few-layer metal sulfides. Demonstrated across six compounds and multiple polytypes, the method uses spin-coated, single-source organosulfur precursors derived from dithioacids. Molybdenum ethyl xanthate, for example, decomposes below 200 °C to form a metastable, sulfur-rich amorphous intermediate that governs the nucleation and growth of MoS2 during annealing. In situ spectroscopy and microscopy, reactive molecular dynamics, and density functional theory reveal how precursor chemistry controls crystallization, thickness, grain size, and defect formation. The resulting monolayers exhibit optical properties comparable to exfoliated materials and conformally coat high-aspect-ratio structures. The reactive intermediate also enables substrate-selective growth, seed-free integration of atomic-layer-deposited dielectrics, transfer-free superlattice fabrication, and substitutional doping through precursor co-formulation. The films support reliable field-effect transistors and vertical memristors exhibiting nanosecond spike-timing-dependent plasticity. This general chemistry provides a scalable route toward manufacturable 2D electronics. The second part of my talk will describe a selective-area method for tuning the work function and carrier density of monolayer graphene. Sub-monolayer gallium is precipitated beneath graphene from an ion-implanted diamond-like carbon film. Controlling the annealing temperature enables spatially precise, ambient-stable ambipolar doping, with carrier densities ranging from approximately 1.8 × 1010 cm-2 hole-doped to 7 × 1013 cm-2 electron-doped. Theory and experiments confirm that interfacial gallium governs charge transfer to the graphene. Extending this approach to other elements that can be implanted into diamond-like carbon offers a versatile platform for investigating highly doped 2D materials and emerging heterostructures.