September 20, 2011 — Rice University researchers devised a method to grow high-quality bilayer graphene on a functional substrate, circumventing the transfer step from catalyst to insulator substrate commonly used.
The lab of Rice chemist James Tour grew graphene on a functional substrate by first having it diffuse into a layer of nickel. Large-scale bilayer graphene can be grown directly onto a variety of insulating substrates, ready for incorporation into patterned transistors, Tour, Rice’s T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science, explained.
Figure. The process of creating bilayer graphene on an insulating substrate, skipping roll-to-roll transfer of graphene from a metal catalyst. The electron microscope image shows two layers of graphene produced via the process. SOURCE: Tour Lab, Rice University. |
A group led by graduate student Zhiwei Peng evaporated a coat of nickel onto silicon dioxide and placed a polymer film — the carbon source — on top. Heating the sandwich to 1000C in the presence of flowing argon and hydrogen gas allowed the polymer to diffuse into the metal; upon cooling, graphene formed on the nickel and on the silicon dioxide surfaces. When the nickel and incidental graphene that formed on top were etched away, bilayer graphene was left attached to the silicon dioxide substrate.
Alternatively, graduate student Zheng Yan topped a layer of silicon dioxide with a sliver of one of a variety of polymers and then put the nickel on top. Again, under high temperature and low pressure, bilayer graphene formed between the silicon dioxide and nickel. Experimentation with other substances revealed that bilayer graphene would also form on hexagonal boron nitride, silicon nitride and sapphire.
Since graphene does not have a bandgap at its single-layer form, semiconductors will use bilayer graphene in new device architectures. Bilayer graphene’s properties depend upon the offset or rotation of the layers in relation to each other, tunable using an electric field applied across the layers.
The new processes are outlined in two related ACS Nano papers: Growth of Bilayer Graphene on Insulating Substrates: http://pubs.acs.org/doi/abs/10.1021/nn202829y and Direct Growth of Bilayer Graphene on SiO2 Substrates by Carbon Diffusion Through Nickel: http://pubs.acs.org/doi/abs/10.1021/nn202923y
Authors of the first paper, "Growth of Bilayer Graphene on Insulating Substrates," are Yan, Peng, graduate student Zhengzong Sun, former graduate student Jun Yao, postdoctoral research associates Yu Zhu and Zheng Liu, Tour and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.
The Office of Naval Research MURI program, Lockheed Martin and the Air Force Office of Scientific Research supported the research.
Authors of the second paper, "Direct Growth of Bilayer Graphene on SiO2 Substrates by Carbon Diffusion Through Nickel," are Peng, Yan, Sun and Tour.
The Office of Naval Research MURI program, the Air Force Research Laboratory through United Technology Corp., the Air Force Office of Scientific Research and M-I SWACO supported the research.