The new material they call Janus sulphur molybdenum selenium (SMoSe) has a crystalline construction the researchers claim can host an intrinsic electric field and that also shows promise for catalytic production of hydrogen.
"This type of two-faced structure has long been predicted theoretically but very rarely realised," said materials scientist Jun Lou. "The break of symmetry in the out-of-plane direction of 2D TMDs could lead to many applications, such as a basal-plane active 2D catalyst, robust piezoelectricity-enabled sensors and actuators at the 2D limit."
The two-faced material is technically two-dimensional, but like molybdenum diselenide it consists of three stacked layers of atoms arranged in a grid.
According to the researchers, tight control of the conditions in a typical chemical vapor deposition furnace – 800°C at atmospheric pressure – allowed the sulphur to interact with only the top layer of selenium atoms and leave the bottom untouched.
The researchers claim the presence of sulphur gave the material a larger band gap than molybdenum diselenide.