A Stanford University research team has just come up with a new way to work with the super-strong but super-finicky semiconductor material graphene. The idea is to use DNA as a platform for mass producing precisely engineered ribbons of graphene, and the goal is to open the door to a new age of super-efficient, super-small, ultra-fast electronic devices. What could possibly go wrong?
Nothing, we’re pretty sure, but it does seem like some strange and unanticipated results could come about when you combine DNA, the “blueprint of life” with graphene, an exotic form of carbon that is 200 times stronger than steel.
The Stanford University Graphene/DNA Combo
Graphene consists of a sheet of carbon only one atom thick. It was discovered less than ten years ago and it has already engendered thousands of research papers around the globe.
The uniquely powerful potential of graphene as a semiconductor leads to the possibility of accelerating Moore’s Law beyond anything Gordon L. Moore could have imagined (back in 1965, Moore, a co-founder of Intel, predicted that the size of transistors would shrink apace with advances in technology).
Aside from the obvious application to portable electronic devices, the next generation of low cost, high efficiency photovoltaic cells could be ushered in by replacing silicon with graphene.
The problem is, with a thickness of only one atom deep graphene is notoriously difficult to work with.
This is where the Stanford team comes in. They started with the goal of forming precise ribbons of graphene of 20 to 50 atoms across. When laid side by side, the ribbons could form extremely small, fast, and energy-efficient semiconductor circuits.
The idea of using DNA as a fabrication platform has two aspects. First, the ribbon-like structure of DNA is fairly similar to the ribbons of graphene desired by the team. Second, since DNA contains carbon atoms it shares a chemical link with graphene (that’s what set us thinking of Dr. Frankenstein, but whatever).
The Stanford team deployed a fabrication method using a silicon platter, which is somewhat ironic given that the ultimate goal is to replace silicon computer chips with graphene, but here goes. As described by Tom Abate at Stanford Engineering, the research team first dipped a platter of silicon into a solution of bacteria-derived DNA, and “combed” the strands into lines.
The next step was to introduce copper ions into the DNA, by exposing the platter to a copper salt solution. When the platter was exposed to heat and bathed in carbon-rich methane gas (much safer than lightning!), the result was a chemical reaction that freed carbon atoms from both the gas and the DNA.
The free carbon atoms joined to form the familiar honeycomb or “chicken wire” structure of graphene. Since the carbon atoms from the DNA tended to stay close to their point of origin, the result was a long ribbon of graphene rather than an amorphous sheet.
For the record, the Stanford team also succeeded in making working transistors on the ribbons.
Another Path To DNA-Engineered Graphene
Meanwhile, researchers at Harvard and MIT have also been developing a method for using DNA as a platform for fabricating precisely engineered graphene shapes, resulting in Lego-like graphene “blocks.”
In contrast to the Stanford method, which is based entirely on chemical reactions, the Harvard/MIT graphene project is partly based on a standard plasma lithography technique.
The Harvard/MIT method starts with DNA blocks formed by manipulating strands into 90-degree angles. After binding the DNA to a graphene surface, the block is coated with a micro-clusters of silver, which in turn binds to a top layer of gold.
The lithographic step is based on oxygen plasma, in which ionized molecules “wear away” excess graphene to leave a structure precisely identical to the DNA platform. Lastly, a bath of sodium cyanide washes the DNA away, leaving only the graphene.
As with the Standford research, the MIT/Harvard project is still far from commercialization, but the team was able to create precise shapes with the “Lego” approach, including rings, ribbons and X and Y junctions.
Graphene Manipulation Without DNA
DNA is just one of many platforms that are being explored as avenues for creating a cost-effective, reliable graphene fabrication process.
Among the new developments are a technique for “unzipping” carbon nanotubes to form long ribbons of graphene, and a method for forming a graphene nanowire within a larger sheet of graphene.
Another example comes from a team at the University of Illinois, which has found that nanoscale droplets of water can be used to herd graphene into precise shapes, while the US Air Force is the funder behind a method for engineering flakes of graphene with dry ice.
Not to be outdone by the Air Force, the US Navy has funded a graphene ribbon project based on an etching technique.
An entirely different approach comes from Northwestern Engineering, where a team is using a low-cost exfoliation method to produce a printable graphene “ink.”
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