The discovery of graphene, a one-atom-thick layer of carbon with a chicken-wire structure, in 2004 not only led to a Nobel Prize for its discoverers, but also to the uncovering of a whole host of other atom-thick materials, collectively known as two-dimensional (2D) materials. Many of these materials are made up of several layers of atoms – for example, transition metal dichalcogenides (TMDs) comprise a layer of a transition metal such as tungsten sandwiched between two layers of a chalcogenide such as sulfur – but they are essentially all surface, hence the term 2D.
Between them, 2D materials possess a whole host of interesting properties. Graphene is still their most famous member, with its impressive strength and electrical conductivity, but 2D materials also include semiconductors and insulators. As such, scientists are experimenting with joining different 2D materials together into stacks and combining them with thin films to produce novel nanoscale devices such as transistors and solar cells. Now, they have shown that a similar approach can also be used to produce nanoscale ultraviolet (UV) detectors.
To produce their UV detector, Liwei Lin and his colleagues at the University of California, Berkeley in the US combined graphene with a thin film of microcrystalline diamond (MCD) to create a heterojunction that can absorb UV light and then generate a detectable current between two electrodes. This was no easy task, however, because in order to absorb UV light effectively the heterojunction needs to be nice and smooth. Current MCD fabrication techniques, which involve growing the MCD film on a silicon substrate, tend to produce films with fairly rough surfaces, preventing the graphene from forming a smooth junction when deposited on top.
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