Scientists are using two nearly ubiquitous materials, carbon and DNA, to push cheap and scalable graphene electronics to the nanoscale.
|At left, metallized DNA (red) forms letters on a graphene surface. Treatment with oxygen plasma etches the shape of the letters into the graphene, right. Image Credit: Zhong Jin / MIT News|
DNA holds our genetic information in sequences of base pairs: guanine-cytosine and adenine-thymine. For a decade, scientists have been exploring DNA as a synthetic biological building block. By programming the sequences of base pairs on the computer, researchers are able to fold DNA into two- and three-dimensional shapes that some call DNA Origami.
Now, researchers at MIT and Harvard have used DNA origami to create tiny structures out of graphene. While current methods of patterning graphene rely on costly and time-consuming processes like electron-beam lithography to etch tiny shapes in the graphene, the new research, led by Peng Yin at Harvard and Michael Strano at MIT, proposed that using DNA to relay patterns and structural features may enable cheap and scalable production of graphene devices such as electronic chips. The study was published on April 9, 2013 in Nature Communications.
First, the researchers designed the DNA structures using a DNA-specific 3D modeling software which combines the strands of DNA in a simple reaction to form the desired shapes. To transfer the easily-built but delicate DNA patterns to robust graphene, the team silver- and then gold-coated the DNA to a sheet of graphene.
The team then exposed the graphene sheet to oxygen plasma, a soupy mixture of ionized oxygen molecules that removed the uncovered graphene. Those parts beneath the protective DNA layer remained unscathed. Finally, the researchers washed away the DNA coating using a solution of sodium cyanide.
Using this straightforward and scalable procedure the researchers were able to pattern graphene into ribbons and rings. They were also able to pattern x-junctions and y-junctions, which have unique electrical properties in graphene.
Graphene is lauded for its conductivity and lack of energy gap between conduction and valence electron bands. But, thin strands of graphene do exhibit a "band gap" -- and the researchers hope that DNA patterning will provide a large-scale means of making graphene ribbons for digital circuits.