Nanometal a 'challenger' to graphene

Graphene, which consists of a single layer of carbon atoms in a honeycomb lattice, has recently been dubbed the ’wonder material’ that is increasingly being used within electronic and mechanical applications, such as transistors, switches and light sources due mainly to its thermal and electrical properties.

Now, however, a research team from the UOS’s Optoelectronics Research Centre (ORC) has developed molybdenum di-sulphide (MoS2) which it says could be a potential challenger to graphene.

“The key to MoS2’s photonic properties is in the structure of its energy band gap

ORC researcher Dan Hewak

Sharing many of its properties with graphene, MoS2 differs in that it is made from a metal - molybdenum combined with sulphur.

This novel class of thin metal/sulphide materials, known as transition metal di-chalcogenides (TMDCs), has become an exciting complimentary material to graphene, researchers claim.

The researchers explained that graphene and MoS2 has the ability to work together well, for example, to make flexible displays. MoS2 is used as the transistor channel and graphene as contact electrodes and circuit interconnects.

These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics, the researchers said.

However, unlike graphene, TMDCs can also emit light allowing applications, such as photodetectors and light emitting devices, to be manufactured.

Dan Hewak, who assisted in the research, told LaboratoryTalk: “The key to MoS2’s photonic properties is in the structure of its energy band gap. As the material’s layer count decreases, it transitions from an indirect to direct band gap, which allows electrons to easily move between energy bands by releasing photons.

“Graphene is inefficient at light emission because it has no band gap.”

Fabrication of TMDCs, such as MoS2, has, until recently, been difficult, as most techniques produce only flakes, typically just a few hundred square microns in area.

“We have been working on the synthesis of chalcogenide materials using a chemical vapour deposition (CVD) process since 2001 and our technology has now achieved the fabrication of large area (>1000 mm2) ultra- thin films only a few atoms thick,” said Kevin Huang, from ORC who led the research.

“Being able to manufacture sheets of MoS2 and related materials, rather than just microscopic flakes, as previously was the case, greatly expands their promise for nanoelectronic and optoelectronic applications.”

Huang, who is currently working several UK companies and universities, as well as experts from MIT and Nanyang Technological University, Singapore, said that his research team’s ability to not only synthesise large uniform thin films but also to transfer these films to virtually any substrate has led to increased demand for its materials.

“We welcome enquiries from universities and industry who wish to collaborate with us,” he said.