Serendipity has as much a place in sciÂence as in love.
That’s what NorthÂeastern physiÂcists Swastik Kar and Srinivas Sridhar found during their four-year project to modify graphene, a stronger-than-steel infinÂiÂtesÂiÂmally thin latÂtice of tightly packed carbon atoms. PriÂmarily funded by the Army Research LabÂoÂraÂtory and Defense Advanced Research Projects Agency, or DARPA, the researchers were charged with imbuing the decade-old mateÂrial with thermal senÂsiÂtivity for use in infrared imaging devices such as night-vision gogÂgles for the military.
What they unearthed, pubÂlished Friday in the journal Science Advances, was so much more: an entirely new mateÂrial spun out of boron, nitrogen, carbon, and oxygen that shows eviÂdence of magÂnetic, optical, and elecÂtrical propÂerÂties as well as DARPA’s sought-after thermal ones. Its potenÂtial appliÂcaÂtions run the gamut: from 20-megapixel arrays for cellÂphone camÂeras to photo detecÂtors to atomÂiÂcally thin tranÂsisÂtors that when mulÂtiÂplied by the bilÂlions could fuel computers.
“We had to start from scratch and build everyÂthing,†says Kar, an assisÂtant proÂfessor of physics in the ColÂlege of SciÂence. “We were on a journey, creÂating a new path, a new direcÂtion of research.â€
The pair was familiar with “alloys,†conÂtrolled comÂbiÂnaÂtions of eleÂments that resulted in mateÂrials with propÂerÂties that surÂpassed graphene’s–for example, the addiÂtion of boron and nitrogen to graphene’s carbon to conÂnote the conÂducÂtivity necÂesÂsary to proÂduce an elecÂtrical insuÂlator. But no one had ever thought of choosing oxygen to add to the mix.
What led the NorthÂeastern researchers to do so?
“Well, we didn’t choose oxygen,†says Kar, smiling broadly. “Oxygen chose us.â€
Oxygen, of course, is everyÂwhere. Indeed, Kar and Sridhar spent a lot of time trying to get rid of the oxygen seeping into their brew, worÂried that it would conÂtÂaÂmÂiÂnate the “pure†mateÂrial they were seeking to develop.
“That’s where the Aha! moment hapÂpened for us,†says Kar. “We realÂized we could not ignore the role that oxygen plays in the way these eleÂments mix together.â€
“So instead of trying to remove oxygen, we thought: Let’s conÂtrol its introÂducÂtion,†adds Sridhar, the Arts and SciÂences DisÂtinÂguished ProÂfessor of Physics and director of Northeastern’s ElecÂtronic MateÂrials Research Institute.
Oxygen, it turned out, was behaving in the reacÂtion chamber in a way the sciÂenÂtists had never anticÂiÂpated: It was deterÂmining how the other elements–the boron, carbon, and nitrogen–combined in a solid, crystal form, while also inserting itself into the latÂtice. The trace amounts of oxygen were, metaphorÂiÂcally, “etching away†some of the patches of carbon, explains Kar, making room for the boron and nitrogen to fill the gaps.
“It was as if the oxygen was conÂtrolÂling the geoÂmetric strucÂture,†says Sridhar.
They named the new mateÂrial, senÂsibly, 2D-BNCO, repÂreÂsenting the four eleÂments in the mix and the two-dimensionality of the super-thin lightÂweight mateÂrial, and set about charÂacÂterÂizing and manÂuÂfacÂturing it, to ensure it was both reproÂducible and scalÂable. That meant invesÂtiÂgating the myriad perÂmuÂtaÂtions of the four ingreÂdiÂents, holding three conÂstant while varying the meaÂsureÂment of the remaining one, and vice versa, mulÂtiple times over.
After each trial, they anaÂlyzed the strucÂture and the funcÂtional propÂerÂties of the product– elecÂtrical, optical–using elecÂtron microÂscopes and specÂtroÂscopic tools, and colÂlabÂoÂrated with comÂpuÂtaÂtional physiÂcists, who creÂated models of the strucÂtures to see if the conÂfigÂuÂraÂtions would be feaÂsible in the real world.
Next they will examine the new material’s mechanÂical propÂerÂties and begin to experÂiÂmenÂtally valÂiÂdate the magÂnetic ones conÂferred, surÂprisÂingly, by the interÂminÂgling of these four nonÂmagÂnetic eleÂments. “You begin to see very quickly how comÂpliÂcated that process is,†says Kar.
Helping with that comÂplexity were colÂlabÂoÂraÂtors from around the globe. In addiÂtion to NorthÂeastern assoÂciate research sciÂenÂtists, postÂdocÂtoral felÂlows, and gradÂuate stuÂdents, conÂtribÂuÂtors included researchers in govÂernÂment, industry, and acadÂemia from the United States, Mexico, and India.
“There is still a long way to go but there are clear indiÂcaÂtions that we can tune the elecÂtrical propÂerÂties of these mateÂrials,†says Sridhar. “And if we find the right comÂbiÂnaÂtion, we will very likely get to that point where we reach the thermal senÂsiÂtivity that DARPA was iniÂtially looking for as well as many as-yet unforeÂseen applications.â€
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