Graphene mass production a step closer?

Author of the paper, Yong Chen, professor of nanoscience and physics at Purdue University, Indiana, believes the new findings represent an advance toward perfecting a method for manufacturing large quantities of single crystals of graphene. Similar research has resulted in single crystals of graphene being grown but, as yet, it has not been possible to create ordered arrays that could be used to fabricate commercial electronic devices and ICs. "Graphene isn't there yet, in terms of high quality mass production like silicon," said Chen, "but this is a very important step in that direction." According to Chen, the hexagonal single crystals are initiated from graphite 'seeds', then grown on top of a copper foil inside a chamber containing methane gas. This is achieved using a process called chemical vapour deposition. This method was invented by Qingkai Yu, co-corresponding author for the study and assistant professor at Texas State University's Ingram School of Engineering. "Using these seeds, we can grow an ordered array of thousands or millions of single crystals of graphene," said Yu, who pioneered the method while a researcher at the University of Houston. "We hope that industry will look at these findings and consider the ordered arrays as a possible means of fabricating electronic devices." Graphene is currently created in 'polycrystalline' sheets made up of randomly positioned and irregularly shaped 'grains' merged together. Having an ordered array means the positions of each crystal are predictable and not random as they are in polycrystalline film. The arrays enable researchers to precisely position electronic devices in each grain, which is a single crystal having a seamless lattice structure that improves electrical properties. 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. By controlling the growth of ordered arrays, the team demonstrated the electrical properties of the individual grain boundaries and found that the edges of a single hexagonal crystal grain are parallel to well defined directions in the graphene's atomic lattice. This revealed the orientation of each crystal, making it possible to measure the precise properties of the crystals and providing information needed to create better electronic devices. To determine the orientation of the graphene lattice, two kinds of advanced microscopy techniques known as transmission electron microscopy and scanning tunneling microscopy were employed. The techniques provided high resolution images of individual carbon atoms making up graphene. The electronic properties across the grain boundaries were measured using tiny electrodes connected to two adjoining grains. Findings demonstrated a higher electrical resistance at the grain boundaries and also showed that the boundaries hinder electrical conduction due to scattering of electrons. That finding was correlated using another technique called Raman spectroscopy. The findings will be published in Nature Materials.