14 DAY TRIAL // Graphene, a carbon compound that was discovered only 6 years ago, is one of the materials that promise to innovate science, creating better radios, computers, electronics and phones, in addition to revolutionizing materials science. But the atom-thick, semi-metallic graphene suffers from a major drawback, and namely the fact that it has a zero band gap. This means it cannot function effectively as a semiconductor, in switching of amplifying electrical signals passing through it. But a collaboration of researchers from the University of California in Los Angeles (UCLA) may have just found a solution to this problem, PhysOrg reports.
Many have tried various methods of achieving the semiconducting effect in graphene, by creating, for example, structures called nanoribbons. This means that they basically cut graphene sheets in strips that exhibit a large band gap. But devices based on nanoribbons have limited driving currents, which makes them useless to practical applications. It would be necessary to produce dense arrays of ordered nanoribbons in order for the material to actually make a difference, and this process has thus far proven to be elusive. Scientists don't even have a clear concept on how they should go about doing this.
The new approach comes from researchers at the UCLA Henry Samueli School of Engineering and Applied Science, led by professor of materials science and engineering Yu Hang. This group worked closely together with UCLA chemistry professor Xiangfeng Duan and managed to crack the semiconducting problem in graphene by creating new structures called nanoscale meshes, or nanomeshes (GNM). Details of the work will be published in the upcoming March issue of the respected scientific journal Nature Nanotechnology, but a preview is already available online. The thing that makes GNM so promising is the fact that they open a very large band gap.
But the difference is that is creates gaps inside a large sheet of graphene, which means that highly-uniform, continuous semiconducting thin film can be created. These larger structures could, in turn, be processed by industrial machines using standard, planar semiconductor processing methods. “The nanomeshes are prepared by punching a high-density array of nanoscale holes into a single or a few layers of graphene using a self-assembled block copolymer thin film as the mask template. GNM can address many of the critical challenges facing graphene, as well as bypass the most challenging assembly problems,” Huang explains.
“In conjunction with recent advances in the growth of graphene over a large-area substrate, this concept has the potential to enable a uniform, continuous semiconducting nanomesh thin film that can be used to fabricate integrated devices and circuits with desired device size and driving current. The concept of the GNM therefore points to a clear pathway towards practical application of graphene as a semiconductor material for future electronics. The unique structural and electronic characteristics of the GNMs may also open up exciting opportunities in highly sensitive biosensors and a new generation of spintronics, from magnetic sensing to storage,” she concludes.