Nanotechnology's hot pick-up artist

(Nanowerk Spotlight) First there was graphene, an atomically thin film of carbon atoms with record-crushing properties. Then thousands of other atomically thin materials entered the scene which can be layered to create new hybrid supermaterials – so called van der Waals heterostructures.

Until now, only a few leading groups have been able assemble these materials with sufficiently high quality. With the "hot pickup" stacking method, researchers at DTU Nanotech aim to make atomic scale nano-assembly faster and easier than ever before.

The team reported their findings in the June 16, 2016 online edition of Nature Communications ("The hot pick-up technique for batch assembly of van der Waals heterostructures").

Since graphene was isolated for the first time in 2004, more than 200,000 articles and 40,000 patents have been published, a testament to the enormous interest from both scientific and commercial communities.

Thanks to the long list of extraordinary properties of these atomically thin films of carbon atoms, applications in diverse areas such as digital electronics, solar cells, high speed communications, water filtering, corrosion protection, flexible electronics, quantum computing, polymer reinforcements, catalysis, energy storage, gas sensing and energy harvesting are being developed – to mention just a few.

In the past few years, it has become clear that graphene is not at all the only two-dimensional supermaterial. More than 2,500 other layered, atomically thin, materials have signed up, ready to be studied and exploited.

While these materials cover an amazing range of electrical, chemical, optical and mechanical properties, perhaps the most astounding discovery is that these materials can be combined freely to create altogether new materials, so called van der Waals heterostructures.

Since all atoms and molecules attract each other by the ubiquitous van der Waals forces, there are virtually no limitations to how all these new superthin materials can be assembled into stacks – just like LEGO blocks.

The difficulty lies in doing this without damaging the thin films, and without incorporating dirt and wrinkles as one may imagine.

In collaboration with James Hone's group at Columbia University, researchers at DTU Nanotech, led by Professor Peter Bøggild and Associate Professor Timothy J. Booth, have developed what they call the 'hot pickup' technique for creating stacks of atomically thin films.

Hot pick up technique for assembly of van der Waals heterostructures. (Image: DTU Nanotech) (click on image to enlarge)

The trick is to control the temperature of the stack as well as the manipulator – the 'nanohand'. The nanohand is a a thin plastic coating on a glass slide can be used to both pick up and drop down the thin films, and the temperature is used to tune the adhesion for either picking up or releasing the films.

At the same time, the assembly -– where the films are 'laminated' – is done at high temperatures since this turns out to lead to super-clean interfaces - contamination is simply squeezed out during the nano-lamination process.

Perhaps the most wide ranging feature is the ability to assemble already nanopatterned films. Stacking of multiple structured layers allows interconnects and much more complex circuitry, much in the same way that modern computer chips use multiple active layers to achieve higher speed and more functionality – just much, much smaller.

The researchers used the method to batch fabricate high quality devices, which is crucial for accelerating research and development of the many emerging layered materials.

The research was funded by the Centre for Nanostructured Graphene and the Graphene Flagship.