  Single-layer MoS2 is an attractive semiconducting analogue of graphene that
combines high mechanical flexibility with a large direct bandgap of 1.8 eV. On
the other hand, bulk MoS2 is an indirect bandgap semiconductor similar to
silicon, with a gap of 1.2 eV, and therefore deterministic preparation of
single MoS2 layers is a crucial step towards exploiting the large direct
bandgap of monolayer MoS2 in electronic, optoelectronic, and photovoltaic
applications. Although mechanical and chemical exfoliation methods can be used
to obtain high quality MoS2 single-layers, the lack of control in the
thickness, shape, size, and position of the flakes limits their usefulness.
Here we present a technique for controllably thinning multilayered MoS2 down to
a single-layer two-dimensional crystal using a laser. We generate single layers
in arbitrary shapes and patterns with feature sizes down to 200 nm, and show
that the resulting two-dimensional crystals have optical and electronic
properties comparable to that of pristine exfoliated MoS2 single layers.
