A team of researchers from China and Japan has designed a new method to make minuscule ribbons of graphene that are highly sought-after building blocks for semiconductor devices thanks to their predicted electronic properties. These structures, however, have proven challenging to make.
Previous attempts at making graphene nanoribbons relied on placing sheets of graphene over a layer of silica and using atomic hydrogen to etch strips with zigzag edges, a process known as anisotropic etching. This method, however, only worked well to make ribbons that had two or more graphene layers. Irregularities in silica created by electronic peaks and valleys roughen its surface, so creating precise zigzag edges on graphene monolayers was a challenge. Efforts to solve this problem included replacing the commonly used silica with boron nitride and by using this substrate and the anisotropic etching technique, the group successfully made graphene nanoribbons that were only one-layer thick, and had well-defined zigzag edges. The zigzag-edged nanoribbons showed high electron mobility in the range of 2000 cm2/Vs even at widths of less than 10nm and created clean, narrow energy band gaps, which makes them promising materials for spintronic and nano-electronic devices.
The team explained that decreasing the width of the nanoribbons makes the mobility decrease drastically because of edge defects. Using standard lithography fabrication techniques, studies have seen mobility of 100 cm2/Vs or even lower, but this material still exceeds 2000 cm2/Vs even at the sub-10 nanometer scale, demonstrating that these nanoribbons are of very high quality.
In future studies, extending this method to other kinds of substrates could enable the quick large scale processing of monolayers of graphene to make high-quality nanoribbons with zigzag edges.