Integrated Study of Emerging 2D Materials and Interfaces
Abstract
As in the early stages of group III-V research, the growth of wafer-scale monolayers of various two-dimensional (2D) materials is central to the exploration and exploitation of optoelectronic applications. Our decades of research on the group III-V heterojunction systems provide an opportunity to apply our expertise to 2D emergent materials. Recently a novel growth technique has been developed for the wafer-scale growth of monolayer (ML) transition-metal dichalcogenides (TMDs), such as MoS2 and WS2, using metal-organic chemical vapor deposition (MOCVD). The monolayer films show excellent structural and electrical uniformity over the whole wafer. Vertically aligned 2D TMDs possess many of the favorable attributes of epitaxial graphene including high mechanical strength, high electrical conductivity, and high electrical conductivity but boast the advantage of an intrinsic electronic band gap. The latter property makes them inherently more useful for optoelectronic applications. The TMD systems are relatively new, but it is of technological interest as theoretical investigations indicate that it has an intrinsic band gap in stark contrast to graphene, as well as intriguing valley physics. Since graphene is a centrosymmetric crystal; external perturbations can be applied to break the inversion symmetry, giving rise to a finite bandgap and valley-contrasting Berry curvature. In TMD systems, the valley Hall effect has been demonstrated using optoelectronic measurements, in which valley-polarized electrons and holes are injected through optical excitations by employing the valley optical selection rules. With the population imbalance between the valleys, the valley Hall effect manifests as a charge Hall current that changes sign with the polarization of the excitation laser. The proposed work explores approaches to the growth, characterization, processing, and modeling of emerging 2D materials and interfaces. The emerging 2D materials include the boron nitride (BN), TMDs (such as MoS2, WS2, TiS2, TaS2, and ZrS2), graphyne, silicene and germanene, phosphorene, as well as two-dimensional polymers systems into membranes for technological applications. The proposed study involves the characterization of electron density-of-states for hetero-interfaces. Electron and ion spectroscopies will be used to characterize the growth morphology, structure, topology, and the work function of membranes. The spectroscopies available include ultraviolet photoemission spectroscopy (UPS) for probing valence states and shallow core levels, Auger and X-ray photoemission spectroscopies (XPS) of deep core levels for binding energies, band offsets, and stoichiometry. Our newly acquired secondary ion mass spectrometry (SIMS) system will provide information on species migration and interfacial abruptness. The evolution of electronic properties of heterointerfaces as a function of the applied electric bias will be investigated using combined experimental UPS measurements and theoretical density functional theory (DFT)calculations. Significant control of the low-energy electronic states of emerging 2D materials can be accomplished by tuning interactions in hetero-interfaces.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 04, 2019
- Source ID
- W911NF1810481
Entities
People
- M. D. Williams
Organizations
- Army Contracting Command
- Clark Atlanta University
- Office of the Secretary of Defense