  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 nm-scale edge
roughness and resolution variability issues, which especially affects the
performance of 2D materials. Here we study how dry anisotropic etching of
multilayer 2D materials with sulfur hexafluoride (SF6) may overcome some of
these issues, showing results for hexagonal boron nitride (hBN), tungsten
disulfide (WS2), tungsten diselenide (WSe2), molybdenum disulfide (MoS2),
molybdenum ditelluride (MoTe2). Scanning and transmission electron microscopy
reveal that etching leads to anisotropic hexagonal features in the studied
transition metal dichalcogenides, with the relative degree of anisotropy ranked
as: WS2 > WSe2 > MoTe2 / MoS2. Etched holes are terminated by zigzag edges
while etched dots (protrusions) are terminated by armchair edges. This can be
explained by Wulff constructions, taking the relative stabilities of the edges
and the AA stacking order into account. Patterns in WS2 are transferred to an
underlying graphite layer, demonstrating a possible use for creating sub-10 nm
features. In contrast, multilayer hBN exhibits no lateral anisotropy, but shows
consistent vertical etch angles, independent of crystal orientation. This is
used to create super-resolution lithographic patterns with ultra-sharp corners
at the base of the hBN crystal, which are transferred into an underlying
graphite crystal. We find that the anisotropic SF6 reactive ion etching process
makes it possible to downsize nanostructures to obtain smooth edges, sharp
corners, and feature sizes significantly below the resolution limit of electron
beam lithography. The nanostructured 2D materials can be used themselves or as
etch-masks to pattern other nanomaterials.
