The UK National Physical Laboratory is part of a european collaborative research project. They have brought the world a step closer to producing a new material on which future nanotechnology could be based. Researchers across Europe, including NPL, have demonstrated how an incredible material, graphene, could hold the key to the future of high-speed electronics, such as micro-chips and touchscreen technology.
A paper published in Nature Nanotechnology explains how researchers have, for the first time, produced graphene to a size and quality where it can be practically developed and successfully measured its electrical characteristics. These significant breakthroughs overcome two of the biggest barriers to scaling up the technology.
This project saw researchers, for the first time, produce and successfully operate a large number of electronic devices from a sizable area of graphene layers (approximately 50 mm^2). [ two inch square. There have been other researchers who have created 4 inch wafers of graphene.]
The graphene sample, was produced epitaxially – a process of growing one crystal layer on another – on silicon carbide. Having such a significant sample not only proves that it can be done in a practical, scalable way, but also allows the scientists to better understand important properties.
The second key breakthrough of the project was measuring graphene’s electrical characteristics with unprecedented precision, paving the way for convenient and accurate standards to be established. For products such as transistors in computers to work effectively and be commercially viable, manufacturers must be able to make such measurements with incredible accuracy against an agreed international standard.
The international standard for electrical resistance is provided by the Quantum Hall Effect, a phenomenon whereby electrical properties in 2D materials can be determined based only on fundamental constants of nature. The effect has, until now, only been demonstrated with sufficient precision in a small number of conventional semiconductors. Furthermore, such measurements need temperatures close to absolute zero, combined with very strong magnetic fields, and only a few specialised laboratories in the world can achieve these conditions.
Graphene was long tipped to provide an even better standard, but samples were inadequate to prove this. By producing samples of sufficient size and quality, and accurately demonstrate Hall resistance, the team proved that graphene has the potential to supersede conventional semiconductors on a mass scale.
Furthermore, graphene shows the Quantum Hall Effect at much higher temperatures. This means the graphene resistance standard could be used much more widely as more labs can achieve the conditions required for its use. In addition to its advantages of operating speed and durability, this would also speed the production and reduce costs of future electronics technology based on graphene.
The quantum Hall effect1 allows the international standard for resistance to be defined in terms of the electron charge and Planck’s constant alone. The effect comprises the quantization of the Hall resistance in two-dimensional electron systems in rational fractions of RK = h/e2 = 25 812.807 557(18) Ω, the resistance quantum. Despite 30 years of research into the quantum Hall effect, the level of precision necessary for metrology—a few parts per billion—has been achieved only in silicon and iii–v heterostructure devices. Graphene should, in principle, be an ideal material for a quantum resistance standard, because it is inherently two-dimensional and its discrete electron energy levels in a magnetic field (the Landau levels) are widely spaced. However, the precisions demonstrated so far have been lower than one part per million. Here, we report a quantum Hall resistance quantization accuracy of three parts per billion in monolayer epitaxial graphene at 300 mK, four orders of magnitude better than previously reported. Moreover, by demonstrating the structural integrity and uniformity of graphene over hundreds of micrometres, as well as reproducible mobility and carrier concentrations across a half-centimetre wafer, these results boost the prospects of using epitaxial graphene in applications beyond quantum metrology