World's first monolayer amorphous film created


Rebecca Pool

Thursday, January 9, 2020 - 21:45
Image: Researchers at the National University of Singapore have synthesised the world's first atomically thin amorphous carbon film. 
Researchers from the National University of Singapore have synthesised the world's first one-atom-thick amorphous material.
Atomic resolution imaging revealed the complete absence of long-range periodicity in the monolayer amorphous carbon (MAC), which the researchers hope will settle decades-old debate of exactly how atoms are arranged in amorphous solids.
"With MAC, we have shown for the first time that fully amorphous materials can be stable and free-standing in single atomic layers,” says Professor Barbaros Özyilmaz, Head of the NUS Department of Materials Science and Engineering. “Amorphous materials are of great technological importance, but surprisingly, they remain poorly understood from a basic science point of view.”
“This breakthrough allows for direct imaging to reveal how atoms are arranged in amorphous materials, and could be of commercial value for batteries, semiconductors, membranes and many more applications," he adds.
Using laser-assisted chemical vapour deposition, Özyilmaz and colleagues deposited a stable monolayer of amorphous carbon onto a substrate.
They then used Raman and X-ray spectroscopy, and transmission electron microscopy to characterise the film.
In past studies, researchers had suggested that these materials could either have a fully-disordered, completely random structure or display nanometre-sized order of tiny crystallites, surrounded by random disorder.
The newly synthesised MAC films show the latter arrangement with nanometre-sized patches of strained and distorted hexagonal carbon rings in a continuous random network.
As Özyilmaz highlights in Nature: “Extensive atomic-resolution TEM characterisation shows unambiguously both the complete absence of long-range periodicity and... randomly oriented and strained crystallites comprising only six-member rings embedded in a Zachariasen continuous random network environment.”
The MAC films also contained 5-, 7-, and 8-membered rings.
The amorphous structure has a widely varying atom-to-atom distance unlike a material with a crystalline structure. This is because of the random arrangement of five-, six-, seven- and eight-carbon rings in a planar carbon network, leading to a wide distribution of bond lengths (in Å) and bond angles. [NUS]
Despite its disordered atomic structure, the researchers claim MAC is capable of some truly incredible behaviour.
As Dr Toh Chee Tat from NUS says: "What is amazing about MAC is that it exhibits some properties that are totally different from traditional monolayer materials."
For example, the films can be plastically deformed; so far no other single-layer material has been known to display significant plastic deformation.
"Everything that is understood from atomically thin crystals - in terms of their properties and how they are analysed - does not apply here. It is a completely new material that we are studying," adds Toh.
The researchers reckon MAC has the potential to serve as a cost-effective alternative to two-dimensional crystals such as graphene.
"MAC is much more hardy and cheaper to make than conventional crystalline two-dimensional films,” says Özyilmaz. “The laser-assisted deposition process through which MAC is synthesised is already commonly used in industry. Hence, we can grow a large-area, defect-free, monolayer film on a wide variety of substrates with high throughput and at low temperature."
"Our monolayer amorphous films not only achieve the ultimate thickness limit, but also do not compromise on uniformity and reliability, and are generally considered viable for industry," he adds.
Research is published in Nature
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