Instrumentation for Functionalized Two-Dimensional Nanoelectronic Heterostructures

This proposal employs atomically precise fabrication and characterization methods to understand and control the nanoelectronic properties of heterostructures based on two-dimensional materials including chemically functionalized graphene, ultrathin silicon, black phosphorus, and transition metal dichalcogenides. Specific objectives include: (1) Silicon-Based Heterostructures: Sequential deposition of carbon and silicon on Ag(111) in ultra-high vacuum will be explored to synthesize both lateral and vertical graphene-silicon heterostructures. Scanning tunneling microscopy will be used to reveal that the in-plane lateral interfaces possess atomically precise material transitions both structurally and electronically. In contrast, vertical heterostructures are expected to show non-interacting van der Waals behavior as revealed by energetically resolved scanning tunneling microscopy and Raman spectroscopy. The pristine and direct integration of graphene with two-dimensional silicon seamlessly couples two of the most studied electronic materials into a hybrid structure with promising implications for future electronics. (2) Black Phosphorus-Based Heterostructures: Exfoliated two-dimensional black phosphorus (BP) is found to chemically degrade upon exposure to ambient conditions. Atomic force microscopy, electrostatic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy will be employed to characterize the structure and chemistry of the degradation process. Atomic layer deposited AlOx overlayers will be employed to suppress ambient degradation in order to allow AlOx-encapsulated BP FETs to maintain high on/off ratios and mobilities following extended exposure to ambient conditions. (3) Transition Metal Dichalcogenide-Based Heterostructures: Single-layer MoS2 will be grown by chemical vapor deposition, incorporated into FETs, and characterized at the nanometer-scale using electrostatic force microscopy (EFM). MoS2 grain boundaries will be directly observed with EFM and are expected to significantly affect the electrostatic potential distribution in operating devices. Furthermore, gate-tunable bistable switching will be pursued in MoS2 FETs that possess grain boundaries in the channel region. The geometry of the grain boundary with respect to the FET channel will allow significant control over both the bistable switching ratio and the level of gate tunability.