Experiments show metallic wires can be created using bilayer graphene sheets, but researchers said they're still a long way from applications.
In theory, coloured electrons could travel unhindered along the wires for a long distance with very little resistance. Smaller resistance means power consumption is lower in electronic devices and less heat is generated. Both power consumption and thermal management are challenges in current miniaturised devices. "Our experiments show that the metallic wires can be created," said Jing Li, Ph.D. student at Penn State. "Although we are still a long way from applications."
Jun Zhu, associate professor of physics, Penn State, who directed the research, added, "It's quite remarkable that such states can be created in the interior of an insulating bilayer graphene sheet, using just a few gates. They are not yet resistance-free, and we are doing more experiments to understand where resistance might come from. We are also trying to build valves that control the electron flow based on the colour of the electrons. That's a new concept of electronics called valleytronics."
Figure 1: This is a scanned electron micrograph of a device used in this experiment. Thin sheets of graphene and hexagonal Boron Nitride are stacked and shaped by electron beam lithography to create this device. The purple layer is the bilayer graphene sheet. The bottom pair of split gates (dark squares) are made of multi-layer graphene. The top pair of split gates (gold bars) are made of gold. The one-dimensional wires live in the gap created by the split gates. (Source: Jun Zhu/Penn State)
Li worked closely with the technical staff of Penn State's nanofabrication facility to turn the theoretical framework into a working device.
"The alignment of the top and bottom gates was crucial and not a trivial challenge," said Chad Eichfeld, nanolithography engineer. "The state-of-the-art electron beam lithography capabilities at the Penn State Nanofabrication Laboratory allowed Jing to create this novel device with nanoscale features."
Their paper, "Gate-controlled topological conducting channels in bilayer graphene," appeared in the journal Nature Nanotechnology. Additional authors include Ke Wang and Yafei Ren and their advisor Zenhua Qiao of University of Science and Technology of China, who performed numerical studies to model the behavior of the wires. The high-quality hexagonal Boron Nitride crystals used in the experiment came from Kenji Watanabe and Takashi Taniguchi of National Institute for Material Science, Japan. Two undergraduate students, Kenton McFaul and Zachary Zern, contributed to the research.
The U.S. Office of Naval Research, the National Science Foundation and funding agencies in China and Japan funded this project. Kenton McFaul, a visiting student from Grove City College, was supported by a Research Experience for Undergraduates grant from the NSF NNIN. Jun Zhu is a member of the Centre for 2-Dimensional and Layered Materials in Penn State's Materials Research Institute.