Van der Waals forces play unexpected role in thin-film properties
These forces could be used to tune the physical and electronic properties of ferroelectric thin films.
Research undertaken by scientists at North Carolina State University, USA, has found lattice matching combined with van der Waals forces can affect the thickness, strain state and domain structure of the epitaxial material studied.
To reach their conclusions, the team deposited a film of tin selenide (SnSe) on a monolayer of molybdenum disulphide (MoS2). The latter because it can be easily integrated into electronic devices and the former because it is widely studied in ferroelectric research.
'Epitaxy is when you deposit a crystalline layer of material on top of another crystalline layer of material,' says Assistant Professor Yin Liu. 'When you are doing this with thin films, and the two layers are chemically bonded, the structure of those two layers have to match. However, if the two layers are bonded using van der Waals forces, the layers can have different orientations.
'We wanted to see whether the relative strength or weakness of the van der Waals force influences the physical and electrical properties of an epitaxial material.
'We also chose these materials because MoS2 has very close lattice matching with SnSe – meaning the crystalline structures are closely aligned,” says Liu.
The role that van der Waals forces play in influencing the material’s physical and electronic properties suggests it could provide a valuable tool for engineering materials in electronic devices.
Their study also found that using a monolayer of MoS2 as a substrate enables them to grow larger thin films of SnSe than has been previously demonstrated on other substrates, and that the thin films are higher quality with fewer defects.
For more like this...
