DCN Corp - Innovative thinkers with ethical societal practice... our mission

The Next Generation - Spot welding Graphene transistors on the atomic scale

DCN Corp® - Spot welding Graphene transistors on the atomic scale. Credit - Professor Peter Liljeroth, Aalto University (AU), and Dr Ingmar Swart, Utrecht University (UU)Unfortunately, researchers worldwide are still struggling to open a band gap in Graphene at Room temperature (RT) sufficient for transistor applications. The appeal in endeavouring with Graphene and ultimately force engineering a band gap into a material which typically does not have one is because of its high electron mobility and this relating to simpler chemical doping techniques, which could provide an easier path to interconnection than its cousin, namely Carbon nanotubes (CNT)

Researchers at Aalto University (AU), Finland, and Utrecht University (UU), Netherlands, have managed to demonstrate the ability to create single atom contacts between Gold (Au) and Graphene nanoribbons. The research was published in Nature Communications entitled: Suppression of electron-vibron coupling in Graphene nanoribbons contacted via a single atom, and it was reported that contacts between Graphene and Au could be established without modifying the electrical properties of Graphene's honeycomb lattice. Please Note the honeycomb lattice is what makes Graphene attractive in the first instance.

The process begins with an atomic-scale mapping of Graphene employing Atomic Force microscopy (AFM) and a Scanning Tunneling microscope (STM). The chemical bond is achieved by sending voltage pulses from the tip of a STM to create a single bond on to the Graphene nanoribbons at accurately determined locations. The pulse from the STM removes one Hydrogen (H) atom from the end of the Graphene nanoribbon which initiates the bond formation.

Professor Peter Liljeroth, head of Atomic Scale Physics at AU explained in an e-mail to the author of The Next Generation (TNG) article, , that "The edges of the chemically synthesised ribbons that we use are hydrogen terminated just as you would have in a molecule, e.g. pentacene," - and - "We can use bias voltage pulses from the STM tip to knock off the hydrogen atoms one-by-one. When you remove a single hydrogen, you form what a chemist would call a radical and a physicist would call a dangling bond: the carbon atom without the hydrogen has an unpaired electron that would like to form a bond with something. It does this with one of the atoms of the underlying Au substrate. So we remove the hydrogen, the carbon atom becomes more reactive and forms a bond spontaneously with one of the gold atoms."

As continued by Dr Ingmar Swart, lead of the team concentrating on STM and AFM measurements at UU - "Combined AFM and STM allows us to characterise the Graphene nanostructures atom by atom, which is critical in understanding how the structure, the bonds with the contacts and their electrical properties are related."

The research study demonstrated that by employing advanced computer modelling in the physical experiments, the research team could determine that bonds do not affect the electronic structure and/or the intrinsic ribbon properties of the Graphene nanoribbons. Also, in an another demonstration, Graphene could be bonded with Au on an atomic scale, and the research examined the theoretical concepts to understand the type of electronics that Graphene could enable. For example, a concept frequently mentioned in the journals, but not yet realised is a concept dubbed "valleytronics" whereby low energy electrons in Graphene can have two different momenta, and the foresight would be to use the valley degree of freedom in the same manner that spin is exploited in spintronics. When theoretically designed the Graphene device would be required which could force the electrons only to occupy one of the valleys, which is called a valley filter.

In concluding Professor Liljeroth states in his e-mail that "There are also some other ideas on how you could use Graphene to make electronic devices that do not have an analogue in existing Silicon technology," - and - "To realise these experimentally, one would need atomically well-defined Graphene structures (certain type of edges, widths etc.). This could be either made entirely out of the Graphene (and then talking of a "contact" between the leads and the active part of a device is a bit funny) or one could have a Graphene nanostructure made by other means (e.g., some kind of bottom up approach) and then connect it to external leads. In this case, the contact would have to be well defined at the atomic scale. This would be important not to alter the properties of the Graphene nanostructures (or to alter them in a controlled manner)." Original article available here

As with similar type of studies, the future potential of Graphene has been handsomely sold. As stated previously, DCN Corp strongly believes it can supersede, by providing a dip controlling process which supplements the attributes of Graphene. Going forward, if you and/or your colleagues are interested in making DCN Corp's alternative process reality - please ensure to contact the company as soon as practicably possible.