Chemical and molecular engineers at at MIT and Harvard have successfully used templates made of DNA to cheaply and easily pattern graphene into nanoscale structures that could eventually be fashioned into electronic circuits.
Graphene, as you are surely aware by now, is a material with almost magical properties. It is the strongest and most electrically conductive material known to humankind. Semiconductor masters, such as Intel and TSMC, would absolutely love to use graphene to fashion computer chips are capable of operating at hundreds of gigahertz while consuming tiny amounts of power. Unfortunately, though, graphene is much more difficult and expensive to work with than silicon — and, in its base state, it isn’t a semiconductor. The DNA patterning performed by MIT and Harvard seeks to rectify both of these issues, by making graphene easy to work with, and thus easy to turn it into a semiconductor for use in computer chips.
Late last year, Harvard’s Wyss Institute announced that it had discovered a technique for building intricately detailed DNA nanostructures out of DNA “Lego bricks.” These bricks are specially crafted strands of DNA that join together with other DNA bricks at a 90-degree angle. By joining enough of these bricks together, a three-dimensional 25-nanometer cube emerges. By altering which DNA bricks are available during this process, the Wyss Institute was capable of forming 102 distinct 3D shapes, as seen in the image and video below.
The MIT and Harvard researchers are essentially taking these shapes and binding them to a graphene surface with a molecule called aminopyrine. Once bound, the DNA is coated with a layer of silver, and then a layer of gold to stabilize it. The gold-covered DNA is then used as a mask for plasma lithography, where oxygen plasma burns away the graphene that isn’t covered. Finally, the DNA mask is washed away with sodium cyanide, leaving a piece of graphene that is an almost-perfect copy of the DNA template.
So far, the researchers have used this process — dubbed metallized DNA nanolithography — to create X and Y junctions, rings, and ribbons out of graphene. Nanoribbons, which are simply very narrow strips of graphene, are of particular interest because they have a bandgap — a feature that graphene doesn’t normally possess. A bandgap means that these nanoribbons have semiconductive properties, which means they might one day be used in computer chips. Graphene rings are also of interest, because they can be fashioned into quantum interference transistors — a new and not-well-understood transistor that connects three terminals to a ring, with the transistor’s gate being controlled by the flow of electrons around the ring.
Moving forward, the MIT and Harvard researchers need to improve the precision of the process — some detail is lost when the DNA is coated in metal — so that it can compete with e-beam lithography, which is currently the best (but very expensive) method of patterning graphene. For now, though, metallized DNA nanolithography is more than good enough for exploratory research into graphene-based electronics — and eventually, maybe as a replacement for silicon in computer chips.
Research paper: doi:10.1038/ncomms2690 – “Metallized DNA nanolithography for encoding and transferring spatial information for graphene patterning”