"Long before it's in the papers"
January 28, 2015


Single atoms viewed thanks to super-material

July 21, 2008
World Science staff

A ma­te­ri­al that has be­come one of the hot­test sub­jects of phys­ics re­search has yielded two sur­pris­ing new find­ings, sci­en­tists say.

First, the ma­te­ri­al, graph­ene, has let ex­pe­ri­menters cre­ate the first im­ages of small, in­di­vid­ual at­oms such as hy­dro­gen. As if that weren’t enough, a sec­ond group of sci­en­tists claims graphene is the strongest ma­te­ri­al known, adding to its al­ready record-breaking sta­tus as the thinnest.

Individual atoms of hy­drogen and car­bon (cour­tesy Zettl et al./Na­ture)

Graphene is an ultra-thin—just one at­om thick—lay­er of or­di­nary graph­ite, the form of car­bon used as the writ­ing ma­te­ri­al in pen­cils. Graph­ene grabbed the sci­en­tif­ic com­mun­ity’s at­ten­tion start­ing in 2005 when re­search­ers re­ported ex­ot­ic elec­tron­ic be­hav­ior in the ma­te­ri­al. 

For in­stance, in graph­ene, elec­tron­s—the subat­omic par­t­i­cles that car­ry elec­tric charge—act as though they are weight­less. Graph­ene’s sur­pris­ing at­tributes have made re­search­ers view it as a pos­sibly ide­al ma­te­ri­al for use in mi­nus­cule elec­tron­ic de­vices.

In a pa­per in the July 17 is­sue of the re­search jour­nal Na­ture, sci­en­tists re­ported that graphene had al­lowed them the un­usu­al achieve­ment of im­ag­ing sin­gle small at­oms.

A de­vice known as the trans­mis­sion elec­tron mi­cro­scope has re­vealed a wealth of im­por­tant fea­tures at a scale nearly that small, but but catch­ing a glimpse of light­weight in­di­vid­ual at­oms such as hy­dro­gen and car­bon has been be­yond its grasp. The dif­fi­cul­ty arises be­cause their sig­nals are drowned out by back­ground sig­nals from what­ev­er is around and be­hind the at­oms. 

Diagram of a graph­ene lay­er poked by a dia­mond tip (cour­tesy Sci­ence)

Al­ex Zettl of the Uni­ver­s­ity of Cal­i­for­nia, Berke­ley and col­leagues re­ported in the Na­ture pa­per that they had solved the prob­lem by us­ing a sin­gle-lay­er sheet of graphene as a sup­port ma­te­ri­al. Graphene is all but in­vis­i­ble un­der the mi­cro­scope, they ex­plained, thanks in part to its near-perfect un­iform­ity. 

As a re­sult, in­di­vid­ual hy­dro­gen and car­bon at­oms un­der the mi­cro­scope ap­peared as though sus­pended in space, the re­search­ers said. These at­oms could al­so be watched as they in­ter­acted with oc­ca­sion­al ir­reg­u­lar­i­ties that arose in the graphene struc­ture. This means the new tech­nique could be used for deeper study of graphene it­self, Zettl and col­leagues ar­gued.

In a sec­ond pa­per pub­lished in the July 18 is­sue of the jour­nal Sci­ence, Changgu Lee of Co­lum­bia Uni­ver­s­ity in New York and col­leagues poked at stretched-out lay­ers of graphene with a sharp dia­mond tip to de­ter­mine its stiff­ness. “These ex­pe­ri­ments es­tab­lish graphene as the strongest ma­te­ri­al ev­er mea­sured,” they wrote, thanks again to the ex­tra­or­di­nary un­iform­ity of its struc­ture and to the strength of the bonds be­tween its at­oms.

Graphene is a sin­gle lay­er of car­bon at­oms ar­ranged in hexagons, like a sheet of chick­en wire with an at­om at each nex­us. As free-stand­ing ob­jects, such two-di­men­sion­al crys­tals were be­lieved impos­sible to cre­ate un­til phys­i­cists at the Uni­ver­s­ity of Man­ches­ter, U.K. ac­tu­ally made graph­ene in 2004.

The fa­mil­iar pencil-lead form of car­bon, graph­ite, con­sists of lay­ers of car­bon at­oms tightly bond­ed in flat sheets, or planes, but only loosely bond­ed be­tween those planes. Be­cause the lay­ers move easily over one an­oth­er, graph­ite is a good lub­ri­cant. In fact these graph­ite lay­ers are graph­ene. Af­ter its disco­very, re­search im­me­di­ately took off, in­spired by the ma­te­ri­al’s un­ex­pected elec­tron­ic prop­er­ties. Ex­pe­ri­ments con­tin­ue un­abat­ed.

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A material that has become one of the hottest subjects of physics research has yielded two surprising new findings, scientists say. First, the material, graphene, has allowed experimenters to create the first images of small, individual atoms such as hydrogen. As if that weren’t enough, a second group of scientists claims graphene is the strongest material known, adding to its already record-breaking status as the thinnest. Graphene is an ultra-thin—just one atom thick—layer of ordinary graphite, the form of carbon used as the writing material in pencils. Graphene grabbed the scientific community’s attention starting in 2005 when researchers reported exotic electronic behavior in the material. For instance, in graphene, electrons—the subatomic particles that carry electric charge—act as though they are weightless. Graphene’s surprising attributes have made researchers view it as a possibly ideal material for use in minuscule electronic devices. In a paper in the July 17 issue of the research journal Nature, scientists reported that graphene had allowed them the unusual achievement of imaging single small atoms. A device known as the transmission electron microscope has revealed a wealth of important features at a scale nearly that small, but but catching a glimpse of lightweight individual atoms such as hydrogen and carbon has been beyond its grasp. The difficulty arises because their signals are drowned out by background signals from whatever is around and behind the atoms. Alex Zettl of the University of California, Berkeley and colleagues reported in the Nature paper that they had solved the problem by using a single-layer sheet of graphene as a support material. Graphene is all but invisible under the microscope, they explained, thanks in part to its near-perfect uniformity. As a result, individual hydrogen and carbon atoms under the microscope appeared as though suspended in space, the researchers said. These atoms could also be watched as they interacted with occasional irregularities that arose in the graphene structure. This means the new technique could be used for deeper study of graphene itself, Zettl and colleagues said. In a second paper published in the July 18 issue of the journal Science, Changgu Lee of Columbia University in New York and colleagues poked at stretched-out layers of graphene with a sharp diamond tip to determine its stiffness. “These experiments establish graphene as the strongest material ever measured,” they wrote, thanks again to the extraordinary uniformity of its structure and to the strength of the bonds between its atoms. Graphene is a single layer of carbon atoms arranged in hexagons, like a sheet of chicken wire with an atom at each nexus. As free-standing objects, such two-dimensional crystals were believed impossible to create until physicists at the University of Manchester, U.K. actually made graphene in 2004. The familiar pencil-lead form of carbon, graphite, consists of layers of carbon atoms tightly bonded in flat sheets, or planes, but only loosely bonded between those planes. Because the layers move easily over one another, graphite is a good lubricant. In fact these graphite layers are graphene. After its discovery, research immediately took off, inspired by the material’s unexpected electronic properties. Experiments continue unabated.