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NEWS
Welcome to graphene: the flat carbon sheetwith revolutionary
aspirations. This thinnestpossible pencil-lead shaving has already
inter-ested theoretical physicists with its electronicproperties,
and is predicted to edge aside sili-con in the microchips of the
future. Now itsready for its first practical application.
Carbon exists in many forms: buckyballs,
diamond, nanotubes and graphite to name afew. In 2004, Andr Geim
of the Universityof Manchester, UK, together with
Russiancolleagues, created another form carbon lay-ers just one
atom thick, called graphene(K. S. Novoselovet al. Science
306,666669; 2004). Physicists havesince documented some remark-able
properties of this material.But industrial applications haveseemed
some way off, as graphenehas proved difficult to produce on a large
scale.It was made by unwieldy methods such as rub-bing flecks off a
piece of graphite, as Geim did,
or boiling up silicon carbide in a vacuum.Now, Rodney Ruoff and
his team at North-
western University, Illinois, have come up witha way to make
large amounts of grapheneembedded in a polymer matrix.
Theresearchers start with graphite oxide graphite with
oxygen-containing chemicalgroups attached. After further chemical
modi-fication and treatment with ultrasound, thematerial separates
into layers, and dispersesthrough a solvent in which a polymer such
aspolystyrene is also dissolved. Chemical reduc-tion removes most
of the oxygen groups, andremoving the solvent leaves behind
graphene
sheets crumpled within the solid polymer (seepages 282 and
254).The resulting material is strong, and electri-
cally and thermally conducting. Such proper-ties are similar to
those of carbon nanotubecomposites, which isnt surprising as a
sheet ofgraphene is basically an unrolled nanotube. Butthe
graphene-based composites produced byRuoff s chemical method are
cheaper and morereliable to manufacture, so could be perfect
forthings that need to be lightweight, strong andconducting, such
as aircraft fuselages.
Although graphenes first foray into indus-try is likely to be as
a composite, several groups
are working on unlocking the potential of theisolated sheets.
For one thing, the sheets elec-
tronic properties make graphene a candidateto replace silicon in
a fresh era of microchipelectronics. Graphene is quite different
fromconventional semiconductors such as silicon,explains Philip
Kim, a physicist from Colum-bia University in New York. Electrons
movethough silicon in a series of collisions; thesegenerate heat
and limit the speed and size
of silicon transistors. The density of compo-nents on silicon
chips has doubled every 18months or so since the 1960s, a trend
knownas Moores law after Intels co-founder Gor-don Moore predicted
it in 1965. But many
believe silicon chips will soonreach their limit.
In graphene, however, electronsshoot along with minimal
resis-tance. This, says Kim, may allowfor low-power,
faster-switching
transistors. But its difficult to turn grapheneoff, which will
make it hard to use in an electri-cal switch, he notes. Really, we
need
new types of electronic architecture tomake best use of
graphene.
Trumping siliconAlso enthusiastic about graphenespotential in
computing is Walt deHeer, of Georgia Techs School ofPhysics in
Atlanta. His team, withFrench collaborators at the NationalCentre
of Scientific Research inGrenoble, is attempting to etchelectronic
structures into layers ofgraphene wafers grown on siliconcarbide.
He points out that carbon nanotubes
would give the same electronic advantages asgraphene sheets but
that it is difficult to pro-duce them in large amounts and
organizethem on a chip, and that high electrical resis-tances occur
when nanotubes are connectedwith metal wires in an electronic
circuit.
No one sees nanotubes as a serious avenue,says de Heer. In
contrast, flat graphene wafersare easily etched using conventional
lithogra-phy techniques. De Heer also hopes that con-necting wires
wont be necessary. He envisagesfuture electronic circuits made up
of continu-ous graphene sheets, saying that cuttinggraphene into
ribbons of different widths con-
trols its conducting properties.De Heer, who along with his team
has
attracted funding from Intel, is confident in
graphenes electronic potential, although hecheerfully predicts
that the revolution wontcome just yet. Industry has no reason to
switchover from silicon until the end of Moores law in10 or 15
years, he says. Geim is more wary.Electronic applications require
reliable large-scale production of graphene, he says. At themoment
the quality is rather mediocre.
Geim is more excited about graphenes use-fulness as a research
tool. The carbon lattice inthe sheets is extremely regular, giving
the elec-trons within the lattice unusual properties.The electrons
move collectively in a mannerthat mimics particle behaviour at
close to light
speed, explains Geim. He and other teamsare using graphene to
investigate quantum
Nothing is an
insurmountable
problem. All the
lights are still go.
Moving towardsa graphene worldPROM
EDIA/ALAMY
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NATURE|Vol 442|20 July 2006 NEWS
229
Embryonic stem-cellresearchers in Italy havereacted strongly to
commentsmade by a Catholic cardinalearlier this month that
anyoneinvolved in destroyinghuman embryos including scientists
derivingstem cells for research should be excommunicated.
Concerned at the press
coverage that followedthe cardinals statements,which implied
that humanembryonic stem-cellresearch is illegal in
Italy,scientists from six differentgroups held a conference inRome
on 14 July to defendand explain their work.
The organizers includedCarlo Flamigni of theInstitute of
ClinicalObstetrics and Gynaecologyin Bologna, Maurizio Mori, a
bioethicist at the Universityof Turin, and Elena Cattaneo,a
stem-cell researcher at theUniversity of Milan.
They also sent an openletter to Italian primeminister Romano
Prodistating that their work islegal under Italian law, andasking
the government toactively promote stem-cellwork and guarantee
thefreedom to carry out suchresearch. Freedom of
scientific research is aprinciple enshrined in ourConstitution.
We would likereality to reflect that, theletter says.
Cardinal Alfonso LpezTrujillo ignited controversywhen he became
the first topVatican official to publiclysupport excommunicationof
those involved indestroying embryosto derive stem cells
forresearch. The comments
by Trujillo, who heads theVaticans Pontifical Council
for the Family, werepublished in Italys leadingCatholic
magazineFamigliaCristianaon 2 July.
The Catholic Churchopposes the destruction ofembryos for any
purpose, asit believes that life begins atconception. The
researchersbehind the Italian protestsay they are worried that
such comments couldaffect political supportfor embryonic
stem-cell
research in their stronglyCatholic country.
Italy already has some ofthe worlds most restrictivelaws
regarding embryoresearch, and does not allowembryos to be created
ordestroyed for researchpurposes. However,researchers are
allowed
to work on importedembryonic stem-cell lines.Cattaneo, one of
the
organizers of the Romeconference and a Catholicherself, says she
fears furtherrestrictions and fundingcuts for the already
smallnumber of Italian groupsworking on embryonic stemcells. We
will remaindependent on science doneabroad, she says. In thefuture,
Im not sure this
will entitle our country tobenefit from such research.
Luca Gianaroli, scientificdirector of the
SISMERreproductive-medicine unitin Bologna, agrees that theVatican
has a powerfulinfluence over Italianpoliticians. Italys
currentstem-cell law, approved byparliament in 2004, waswhat the
Vatican wanted, hesays. It was drafted by the
Church. But he doesntbelieve Trujillos commentswill trigger
further cuts:Its like adding water to analready full glass.
Trujillo may alsohave hoped to influencepoliticians beyond Italy
his comments have comeas politicians in both theUnited States and
theEuropean Union debatethe use of public fundsfor embryonic
stem-cell
research. A blockingminority of countriesthreatens to
overturnthe European Parliamentsdecision to include suchwork in its
latest round ofresearch funding. And asNaturewent to press, the
USSenate was preparing to voteon a bill that would
loosenrestrictions on federalfunding for embryonicstem-cell
research.
How much influence the
statement will have is likelyto depend on whether PopeBenedict
XVI, whose wordscarry far more power thanthose of a cardinal, feels
thesame way.
Since Trujillos comments,the Vatican has remainedsilent on the
issue. It has not
voiced support for Trujillosstand, but perhaps moreimportantly
nor has itsaid that Trujillo wasspeaking personally and not
for the Church leadership.
Jacopo Pasotti and Ned Stafford
Its legal: Italian researchers defend
their work with embryonic stem cells
Alfonso Lpez Trujillo wants
researchers excommunicated.
mechanical effects previously thought tooccur only in dense
plasmas around blackholes and neutron stars, or in powerful
par-ticle accelerators. One example is the Kleinparadox, in which
fast-moving particlespass straight through a seemingly
impene-trable barrier.
Meanwhile Ruoff believes his compos-ites might yet trump other
applications. By
chemically modifying the sheets within thepolymer matrix and
studying the resultingproperties, he hopes to usher in a new
classof graphene-based materials. He suggeststhat chemically tuned
composites could beused as electrically conductive plastics insolar
panels, for example, or to dissipateexcess heat within computer
parts: Thetechnology wizards will take this in
variousdirections.
One thing researchers agree on is thatwere likely to hear a lot
more aboutgraphene. Nothing is a sure deal, says deHeer. But
nothing is an insurmountable
problem. All the lights are still go.
Richard Van Noorden
Electrons pass through graphene (left) with
less resistance than through silicon, making the
carbon sheet a good candidate for future chips.
AP
NaturePublishingGroup2006
