Nanoscale View of Engineered Massive Dirac Quasiparticles in Lithographic Superstructures.

Massive Dirac fermions are low-energy electronic excitations characterized by a hyperbolic band dispersion. They play a central role in several emerging physical phenomena such as topological phase transitions, anomalous Hall effects, and superconductivity. This work demonstrates that massive Dirac fermions can be controllably induced by lithographically patterning superstructures of nanoscale holes in a graphene device.

Long-term stability and tree-ring oxidation of WSe using phase-contrast AFM.

In this work, we use atomic force microscopy (AFM) to investigate the long-term evolution of oxidative defects of tungsten diselenide (WSe) in ambient conditions over a period of 75 months, which is the longest such study performed on any layered material. In particular, we find that phase-imaging AFM of mechanically exfoliated WSe crystals provides convenient, direct identification of exposed and covered step-edges, and together with topographic thickness measurements allows complete determination of the layer arrangement in a multilayer flake. Step-edges with low or no phase-contrast consistently exhibit long-term stability in ambient conditions, indicating that they are covered and effectively protected by above-lying WSe layers.

Super-Resolution Nanolithography of Two-Dimensional Materials by Anisotropic Etching.

Nanostructuring allows altering of the electronic and photonic properties of two-dimensional (2D) materials. The efficiency, flexibility, and convenience of top-down lithography processes are, however, compromised by nanometer-scale edge roughness and resolution variability issues, which especially affect the performance of 2D materials. Here, we study how dry anisotropic etching of multilayer 2D materials with sulfur hexafluoride (SF) may overcome some of these issues, showing results for hexagonal boron nitride (hBN), tungsten disulfide (WS), tungsten diselenide (WSe), molybdenum disulfide (MoS), and molybdenum ditelluride (MoTe).