From cameras to computers, new material could change how we work and play

That's what North­eastern physi­cists Swastik Kar and Srinivas Sridhar found during their four-year project to modify graphene, a stronger-than-steel infin­i­tes­i­mally thin lat­tice of tightly packed carbon atoms. Pri­marily funded by the Army Research Lab­o­ra­tory and Defense Advanced Research Projects Agency, or DARPA, the researchers were charged with imbuing the decade-old mate­rial with thermal sen­si­tivity for use in infrared imaging devices such as night-vision gog­gles for the military.

What they unearthed, pub­lished in the journal Science Advances, was so much more: an entirely new mate­rial spun out of boron, nitrogen, carbon, and oxygen that shows evi­dence of mag­netic, optical, and elec­trical prop­er­ties as well as DARPA's sought-after thermal ones. Its poten­tial appli­ca­tions run the gamut: from 20-megapixel arrays for cell­phone cam­eras to photo detec­tors to atom­i­cally thin tran­sis­tors that when mul­ti­plied by the bil­lions could fuel computers.

"We had to start from scratch and build every­thing," says Kar, an assis­tant pro­fessor of physics in the Col­lege of Sci­ence. "We were on a journey, cre­ating a new path, a new direc­tion of research."

The pair was familiar with "alloys," con­trolled com­bi­na­tions of ele­ments that resulted in mate­rials with prop­er­ties that sur­passed graphene's--for example, the addi­tion of boron and nitrogen to graphene's carbon to con­note the con­duc­tivity nec­es­sary to pro­duce an elec­trical insu­lator. But no one had ever thought of choosing oxygen to add to the mix.

What led the North­eastern researchers to do so?

"Well, we didn't choose oxygen," says Kar, smiling broadly. "Oxygen chose us."

Oxygen, of course, is every­where. Indeed, Kar and Sridhar spent a lot of time trying to get rid of the oxygen seeping into their brew, wor­ried that it would con­t­a­m­i­nate the "pure" mate­rial they were seeking to develop.

"That's where the Aha! moment hap­pened for us," says Kar. "We real­ized we could not ignore the role that oxygen plays in the way these ele­ments mix together."

"So instead of trying to remove oxygen, we thought: Let's con­trol its intro­duc­tion," adds Sridhar, the Arts and Sci­ences Dis­tin­guished Pro­fessor of Physics and director of Northeastern's Elec­tronic Mate­rials Research Institute.

Oxygen, it turned out, was behaving in the reac­tion chamber in a way the sci­en­tists had never antic­i­pated: It was deter­mining how the other elements--the boron, carbon, and nitrogen--combined in a solid, crystal form, while also inserting itself into the lat­tice. The trace amounts of oxygen were, metaphor­i­cally, "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 con­trol­ling the geo­metric struc­ture," says Sridhar.

They named the new mate­rial, sen­sibly, 2D-BNCO, rep­re­senting the four ele­ments in the mix and the two-dimensionality of the super-thin light­weight mate­rial, and set about char­ac­ter­izing and man­u­fac­turing it, to ensure it was both repro­ducible and scal­able. That meant inves­ti­gating the myriad per­mu­ta­tions of the four ingre­di­ents, holding three con­stant while varying the mea­sure­ment of the remaining one, and vice versa, mul­tiple times over.

After each trial, they ana­lyzed the struc­ture and the func­tional prop­er­ties of the product-- elec­trical, optical--using elec­tron micro­scopes and spec­tro­scopic tools, and col­lab­o­rated with com­pu­ta­tional physi­cists, who cre­ated models of the struc­tures to see if the con­fig­u­ra­tions would be fea­sible in the real world.

Next they will examine the new material's mechan­ical prop­er­ties and begin to exper­i­men­tally val­i­date the mag­netic ones con­ferred, sur­pris­ingly, by the inter­min­gling of these four non­mag­netic ele­ments. "You begin to see very quickly how com­pli­cated that process is," says Kar.

Helping with that com­plexity were col­lab­o­ra­tors from around the globe. In addi­tion to North­eastern asso­ciate research sci­en­tists, post­doc­toral fel­lows, and grad­uate stu­dents, con­trib­u­tors included researchers in gov­ern­ment, industry, and acad­emia from the United States, Mexico, and India.

"There is still a long way to go but there are clear indi­ca­tions that we can tune the elec­trical prop­er­ties of these mate­rials," says Sridhar. "And if we find the right com­bi­na­tion, we will very likely get to that point where we reach the thermal sen­si­tivity that DARPA was ini­tially looking for as well as many as-yet unfore­seen applications."