Reducing the width of atomically thin 2D devices will be crucial for applications that can compete with silicon, which can already be reduced to just a few nanometres in size, explains team member Yimo Han of Cornell University in New York. Until now, researchers have mainly made 2D heterostructure devices by lithographically patterning the 2D layer of one material and then growing a layer of another 2D material on top of the first one in the patterned areas.

Although this technique allows the size of the material to be controlled to below 100 nm or so, the lithographic patterning process itself creates atomic defects and contamination. The atomic junctions in these heterostructures thus contain electronic defects states, which adversely affect the final electronic properties of the device.

The team, led by David Muller of Cornell University, has now come up with a new approach to make coherent 1D channels within 2D heterostructures. These channels are less than 2 nm wide and their sidewalls are free of dislocations and dangling bonds.

The researchers began by making a lateral interface between two 2D transition metal dichalcogenide materials, MoS2 and WSe2. They then introduced precursor molecules into the ensemble that provide a high chemical potential for the channel material (MoS2). The core of the misfit dislocation is more reactive than its surroundings, which allows the channel atoms (Mo and S) to be inserted into the dislocation core. This pushes the dislocations away from the original interface between the MoS2 and WSe2, and the process creates 1D MoS2 channels in a trail behind the core.

“This dislocation-catalysed growth technique is rather like replacing a white thread in a silk sheet with a red one,” explains Han. “This essentially produces a 1D red wire in 2D white silk. It can also be thought of as being the flat analogue of semiconductor nanowire growth from seeded catalysts – a process that has played a crucial role in semiconductor nanoscience,” he adds.

Dislocation- and dangling-bond-free

“According to our density-functional calculations, the 1D MoS2 wires have extraordinary electronic properties, such as quantum confinement and type II band alignment – two properties that could come in very useful for future device applications,” he tells

The researchers say that their technique might easily be extended to other 2D materials.

The team, which includes researchers from King Abdullah University of Science and Technology in Thuwal, Academia Sinica in Taipei, MIT and Texas Tech University, says it will now be looking at how to better control and design the 1D wires. “Ultimately, we would like to pattern them in 2D materials and stack these patterned 2D films to make highly integrated flexible and transparent circuits,” says Han.

The sub-nanometre channels are described in Nature Materials doi:10.1038/nmat5038.