MANHASSET, NY -- Purdue University researchers have advanced a manufacturing method for creating single-crystal arrays of graphene which is similar to the production of silicon wafers.
"Graphene isn't there yet, in terms of high quality mass production like silicon, but this is a very important step in that direction," said Yong P. Chen, Assistant Professor of Nanoscience and Physics at Purdue University.
This is believed to be the first demonstration how to create ordered patterns that could be used to fabricate commercial electronic devices and integrated circuits.
The researchers used chemical vapor deposition to grow the hexagonal single crystals from graphite "seeds" on top of a copper foil inside a chamber containing methane gas.
"Using these seeds, we can grow an ordered array of thousands or millions of single crystals of graphene," said Qingkai Yu u, who pioneered the method while a researcher at the University of Houston. Yu, is co-corresponding author for the study and an assistant professor at Texas State University's Ingram School of Engineering.
"We hope that industry will look at these findings and consider the ordered arrays as a possible means of fabricating electronic devices."
Graphene currently is created in polycrystalline sheets made up of randomly positioned and irregularly shaped "grains" merged together. By contrast ordered arrays enable positions of each crystal to be predictable.
The arrays enable researchers to precisely position electronic devices in each grain, said Eric Stach, a researcher at Brookhaven and former Purdue professor of materials engineering.
The new research findings confirmed a theory that the flow of electrons is hindered at the point where one grain meets another. The arrays of single-crystal grains could eliminate that problem.
The researchers demonstrated that they could control the growth of the ordered arrays; were the first to demonstrate the electronic properties of individual grain boundaries; and they found that the edges of a single hexagonal crystal grain are parallel to well-defined directions in graphene's atomic lattice, revealing the orientation of each crystal.
The researchers used transmission electron microscopy and scanning tunneling microscopy to determine the orientation of the graphene lattice and the electronic properties across the grain boundaries were measured using tiny electrodes connected to two adjoining grains.
Findings correlated also using Raman spectroscopy which demonstrated a higher electrical resistance at the grain boundaries and also showed that the boundaries hinder electrical conduction due to scattering of electrons.
The findings are detailed in a research paper appearing online this week and in the June issue of Nature Materials. The research was supported through a variety of funding sources, including the National Science Foundation, the U.S. Department of Energy, the Department of Homeland Security, Defense Threat Reduction Agency, IBM Inc., the Welch Foundation, the Miller Family Endowment and Midwest Institute for Nanoelectronics Discovery.