Graphene: New electronics material closer to commercial reality

May 26, 2011 by Emil Venere
This scanning electron microscope picture shows individual crystal "grains" in an array of a material called graphene. Researchers have developed a method for creating the arrays, an advancement that opens up the possibility of a replacement for silicon in high-performance computers and electronics. (Image Care of University of Houston)

(PhysOrg.com) -- Researchers have developed a method for creating single-crystal arrays of a material called graphene, an advance that opens up the possibility of a replacement for silicon in high-performance computers and electronics.

Graphene is a one-atom-thick layer of carbon that conducts electricity with little resistance or heat generation. The arrays could make possible a new class of high-speed transistors and that consume less energy than conventional silicon electronics.

The new findings represent an advance toward perfecting a method for manufacturing large quantities of single crystals of the material, similar to the production of .

" isn't there yet, in terms of high quality like silicon, but this is a very important step in that direction," said Yong P. Chen, corresponding author for the new study and Miller Family Assistant Professor of and Physics at Purdue University.

Other researchers have grown single crystals of graphene, but no others have demonstrated how to create ordered arrays, or patterns that could be used to fabricate commercial and integrated circuits.

The hexagonal single crystals are initiated from graphite "seeds" and then grown on top of a copper foil inside a chamber containing using a process called . The seeded growth method, critical to the new findings, was invented by Qingkai Yu, co-corresponding author for the study and an 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."

Findings are detailed in a research paper appearing online this week and in the June issue of Nature Materials. The work was conducted by researchers at Purdue, the University of Houston, Texas State University, Brookhaven National Laboratory, Argonne National Laboratories and Carl Zeiss SMT Inc.

Graphene currently is 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, 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 ; 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.

Knowing the orientation is necessary to measure the precise properties of the crystals, providing information needed to create better electronic devices. To determine the orientation of the graphene lattice, the researchers used two kinds of advanced microscopy techniques known as transmission electron microscopy and scanning tunneling microscopy. The techniques provided extremely 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 paper was authored by Yu and Purdue graduate student Luis A. Jauregui, Houston graduate student Wei Wu, Purdue graduate student Robert Colby, Purdue postdoctoral researcher Jifa Tian, along with 12 other researchers including Stach and Chen.

Explore further: Graphene reinvents the future

More information: Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapour Deposition, Nature Materials (2011). www.nature.com/nmat/journal/v1… 6/full/nmat3010.html

Abstract
The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. As the large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman ‘D' peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene . Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route toward scalable fabrication of single-crystal graphene devices without grain boundaries.

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User comments : 7

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PS3
1 / 5 (3) May 26, 2011
The Goa'uld use crystal tech.
that_guy
5 / 5 (4) May 26, 2011
I'm dreaming of graphene chips that are faster than my computer in a phone that needs to be recharged once every two weeks.
Jeffhans1
5 / 5 (5) May 26, 2011
If you include a solar panel on the phone using more carbon in the form of standing pillars to gather the sunlight you might never need to charge it.
that_guy
not rated yet May 26, 2011
@jeff
I like the way you think.
spectator
not rated yet May 26, 2011
If you include a solar panel on the phone using more carbon in the form of standing pillars to gather the sunlight you might never need to charge it.


Yup.

I was thinking about that yesterday as it regards the eventual photonic computers.

This stuff is going to use so little power you should never need to charge it if you have about a centimeter worth of PV cells on it. Thinking like those old school "solar" pocket calculators that have a small PV cell on them...

The screen and speakers might be another issue, and might eventually represent 99.99% of power consumption in a mobile device, so that might be what defeats the PV idea. Still, continuous PV re-charge might further extend usage-per-charge significantly once you cut most of the energy consumption in the silicon to graphene transition.

I suspect between graphene itself and the benefits of miniaturization, the graphene computers may eventually use thousands of times less energy per logic operation on average.
SurfAlbatross
not rated yet May 27, 2011
Indeed, the cut off frequency (f_T) of graphene is really high which makes it look like a good replacement for silicon. I think IBM published a paper with it in the hundreds of gigahertz range. The issue that no one confronts is that the power gain (f_max) is really low. How are you going drive realistic loads at the necessary frequencies when you don't have a saturation like in a MOSFET?
SurfAlbatross
not rated yet May 27, 2011
A good reference:
http://www.nature...41a.html

Also, how you make complimentary logic (low power) out of a zero band gap material is beyond me.