2DCC In-House Research Highlight

Heterogeneous interfaces that juxtapose different materials have been known to create emergent quantum phenomena. We used molecular beam epitaxy to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic topological insulator (Cr,Bi,Sb)₂Te₃ and an antiferromagnetic metal, iron chalcogenide (FeTe). High-resolution transmission electron microscopy (HRTEM) and x-ray diffraction show the formation of heterostructures with sharp interfaces and good crystallinity.

MnBi₂Te₄ has garnered substantial scientific interest due to its status as the first intrinsic antiferromagnetic (AFM) topological insulator and its ability to host quantum anomalous Hall insulator and axion insulator states within 2D thin layers. In the bulk form, MnBi₂Te₄ has been theoretically anticipated to host an ideal time-reversal symmetry-breaking type-II Weyl semimetal (WSM) state in the ferromagnetic (FM) phase.

Nonlinear optical (NLO) crystals play a crucial role in converting laser light from one color to another using nonlinear optical processes, enabling a wide spectrum of applications such as optical communications, sensing, imaging, spectroscopy, aviation, and security. While they are mainly operational in the visible region, there are only a few crystals that work in the infrared.

Two-dimensional metals stabilized at the interface between graphene and SiC are attracting considerable interest thanks to their intriguing physical properties, providing promising material platforms for quantum technologies. However, the nanoscale picture of the ultrathin metals within the interface that represents their ultimate two-dimensional limit has not been well captured. In this work, we explore the atomic structures and electronic properties of atomically thin indium intercalated at the epitaxial graphene/SiC interface by means of cryogenic scanning tunneling microscopy.

Van der Waals epitaxy, a unique growth mechanism that relies on weak intermolecular forces between the depositing film and substrate, plays a pivotal role in the synthesis of 2D layered chalcogenides such as MoS₂, WSe₂ and related materials. By illuminating the intricacies of this growth mode using a combination of synthesis, characterization and theory/simulation, researchers affiliated with the 2D Crystal Consortium Materials Innovation Platform are enabling precise control over the nucleation and subsequent lateral growth of 2D materials.

The recent study of intrinsic antiferromagnetic topological insulator Mn(Bi,Sb)₂Te₄ has attracted a great deal of interest, since it provides access to a variety of topological quantum states such as quantum anomalous Hall insulator and axion insulator. In this work, we report systematic c-axis transport studies under high magnetic fields (up to 35T) on Mn(Bi_1-xSb_x)₂Te₄.

Epitaxial graphene (EG) plays a crucial role in the confinement and stabilization of 2D group III metals and their nitrides at the EG/SiC interface, but the mechanism of intercalation and compound formation is not well understood. Here we demonstrate the role of EG functionalization and defect engineering of EG on the synthesis of 2D Ga and GaN_x using a combination of experiments and theory. Thinner regions of graphene are chemically functionalized with O forming C=O, C-O-C and C-OH bonds, whereas thicker regions of graphene are not chemically modified during plasma treatment.

Epitaxial growth of 2D transition metal dichalcogenides (TMDs) on sapphire has emerged as a promising route to wafer-scale single crystal films for large area device applications. Mirror twins, domains with opposite 0° and 60° orientation, are commonly observed in TMD epitaxy on high symmetry substrates such as c-plane sapphire. However, steps on the sapphire act as sites for TMD nucleation and can impart a preferred domain orientation resulting in a significant reduction in mirror twins.

Transition metal dichalcogenide (TMD)/graphene vertical heterostructures are attractive for optoelectronic and energy applications. However, microstructural heterogeneities in the graphene can impact the TMD nucleation and domain growth. A detailed investigation into the effects of the stacking order and twist angle of bilayer CVD graphene on the nucleation of WSe₂ was carried out.

2D InSe is known as a moderate bandgap semiconductor with direct to indirect bandgap crossover associated with a topological band alignment in the shape of an inverse Mexican hat when reduced to the monolayer thickness. Moreover, InSe has previously shown high electron mobility exceeding the values reported for black phosphorus or TMDs. Those properties elevate InSe to a highly interesting candidate for the realization of ultra-low power, high-performance FETs and highly efficient photodetectors.