2DCC User Research Highlight

The synthesis of high-quality SnSe is plagued with difficulties in controlling the film thickness to the single layer limit and challenges in maintaining the correct stoichiometry throughout the film. Controlling layered growth in 2D materials is, however, critical for the emergence of unique properties like the proposed thermoelectricity, piezoelectricity, and ferroelectricity of Pnma SnSe. This work investigates the stabilization of SnSe during MBE growth both from an experimental and a theory standpoint.

Quantum anomalous Hall (QAH) insulators are a realization of the Chern insulator, first envisioned by Nobel prize winner Duncan Haldane. In a QAH insulator, the Hall effect is precisely quantized and the longitudinal resistance vanishes at zero magnetic field. Like the integer quantum Hall effect, the QAH effect is protected against local perturbations and independent of sample details. This insensitivity makes the microscopic details of the local current distribution inaccessible to global transport measurements.

Intercalation is the process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on the intercalation of metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains challenging. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface.

Intercalation forms heterostructures, and over 25 elements and compounds are intercalated into graphene, but the mechanism for this process is not well understood. Here, the de-intercalation of 2D Ag and Ga metals sandwiched between bilayer graphene and SiC are followed using photoemission electron microscopy (PEEM) and atomistic-scale reactive molecular dynamics simulations. By PEEM, de-intercalation “windows” (or defects) are observed in both systems, but the processes follow distinctly different dynamics.

Project Summary: To assess the potential of transition metal dichalcogenides (TMDs) for future circuits, it is important to study the variation in key device parameters across a large number of devices.

Project Summary: Molybdenum trioxide (a-MoO3) is a wide bandgap 2D layered oxide (Eg~3 eV) that is of interest for resistive switching-based nonvolatile memory devices.  It is difficult to produce large-area monolayer MoO3 through exfoliation of bulk crystals or other techniques. This study demonstrates a facile route to obtain wafer-scale monolayer amorphous MoO3 using monolayer 2D MoS2 grown by metalorganic chemical vapor deposition (MOCVD) as a starting material, following by UV-ozone oxidate at substrate temperatures as low as 120oC.

Project Summary: A multi-dimensional optical imaging technique that combines scattering  was developed to map subdiffractional distributions of doping and strain in MoS2 and MoS2/graphene vertical heterostructures.

Project Summary: Quasi-two-dimensional transition-metal dichalcogenides are a key platform for exploring emergent nanoscale phenomena arising from complex interactions. Access to the underlying degrees-of-freedom on their natural time scales motivates the use of advanced ultrafast probes sensitive to self-organized atomic-scale patterns.

Project Summary: Transition metal dichalcogenides (TMDCs) with van der Waals gaps (vdW) have been a subject under extensive studies, since 2D thin layers of these materials exhibit a plethora of technologically useful properties, e.g. large direct band gap and high

Project Summary: The topological Hall effect (THE) is a phenomenon that is a consequence of a Berry phase created by spin textures in real space. Interfacing a topological insulator with a magnetic insulator provides a model platform for studying this phenomenon in a well-controlled manner. This papers reports the first clear evidence for the THE in heterostructures that combine a model topological insulator (Bi2Se3) with a ferromagnetic insulator (BaFe12O19).