A method to build large areas of semiconductive material that is two molecules thick and 4.4nm tall has been devised by a Japanese team.
The films function as thin film transistors and according to the team from the University of Tokyo (UTokyo), have potential future applications in flexible electronics or chemical detectors.
These thin film transistors are said to be the first example of semiconductive single molecular bilayers created with liquid solution processing.
"We want to give electronic devices the features of real cell membranes: flexible, strong, sensitive, and super thin,” explained first author, assistant professor Shunto Arai.
“We found a novel way to design semiconductive single molecular bilayers that allows us to manufacture large surface areas, up to 100cm2.”
Geometric frustration led to the breakthrough – a concept that uses a molecular shape which makes it difficult for molecules to settle in multiple layers on top of each other.
According to the researchers, the film is transparent, but the forces of attraction and repulsion between the molecules create an organised, repeated herringbone pattern when the film is viewed from above through a microscope. The overall molecular structure of the bilayer is “highly stable” and the team claimed it should be possible to build the same structure out of different molecules with different functionalities.
The individual molecules used in the current film are divided into two regions: a head and a tail. The head of one molecule stacks on top of another, with their tails pointing in opposite directions so the molecules form a vertical line. These two molecules are surrounded by identical head-to-head pairs of molecules, which all together form a sandwich called a molecular bilayer.
The team said they discovered additional bilayers could be prevented from stacking on top, by building the bilayer out of molecules with different length tails. This meant the surfaces of the bilayer were rough and naturally discouraged stacking.
Standard methods of creating semiconductive molecular bilayers cannot control the thickness without causing cracks or an irregular surface, the researchers explained. But, the geometric frustration of different length tails has allowed the researchers to avoid these pitfalls and build a 10cm by 10cm square film using solution processing.
This single molecular bilayer created is much faster than amorphous silicon thin film transistors, the UTokyo team added.
Looking to the future, UTokyo said it will continue to investigate the properties of geometrically frustrated single molecular bilayers and potential applications for chemical detection.