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'White graphene' to the rescue

 

http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=14568&SnID=115549982

 

BY MIKE WILLIAMS

Rice News staff

 

What researchers might call "white graphene" may be the perfect sidekick for the real thing as a new era unfolds in nanoscale electronics.

 

But single-atom-thick layers of hexagonal boron nitride (h-BN), the material under intense study at Rice University's world-class Department of Mechanical Engineering and Materials Science, are likely to find some macro applications as well.

 

A transmission electron microscope image shows one-atom-thick layers of hexagonal boron nitride (h-BN) edge-on. Rice scientists have found a way to deposit large sheets of h-BN onto a copper substrate.

 

Researchers in the lab of Pulickel Ajayan, Rice's Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry, have figured out how to make sheets of h-BN, which could turn out to be the complementary apple to graphene's orange.

 

The results were reported in the online journal Nano Letters.

 

Graphene, touted as a possible successor to silicon in microelectronics applications, is the new darling of research labs that hope to take advantage of its superb electronic properties.

 

Hexagonal boron nitride, on the other hand, is an insulator. Earlier this year, Rice postdoctoral researchers in Ajayan's group found a way to implant islands of h-BN into sheets of graphene, which gave them a unique way to exert a level of control over the sheet's electronic character.

 

Now the team, led by primary author Li Song, has figured out how to deposit sheets of pure h-BN, which is naturally white in bulk form, anywhere from one to five atoms thick on a copper substrate. The material can then be transferred to other substrates.

 

They used a chemical vapor deposition process to grow the h-BN sheets on a 5-by-5 centimeter copper backing at temperatures around 1,000 degrees Celsius. The sheets could then be stripped from the copper and placed on a variety of substrates.

 

Ultimately, Song sees h-BN sheets finding wide use as a highly effective insulator in graphene-based electronics, another stride on the quick-step march toward the replacement of silicon with materials that could push beyond the boundaries of Moore's Law, which states the number of transistors that can be placed on an integrated circuit doubles about every two years.

 

Song said it should also be possible to draw microscopic patterns of graphene and h-BN, which could be useful in creating nanoscale field-effect transistors, quantum capacitors or biosensors.

 

The strength of the material was tested using the tip of an atomic force microscope to push h-BN into holes in a silicon substrate. The tests showed it to be highly elastic and nearly as strong as graphene, the single-atom form of pure carbon.

 

Song said the size of h-BN sheets is limited only by the size of the copper foil and furnace used to grow it. The process should be adaptable to the same kind of roll-to-roll technique recently used to form 30-inch sheets of graphene. "If you have a huge furnace, you can go large," he said.

 

Co-authors of the paper with Song and Ajayan are Boris Yakobson, professor in mechanical engineering and materials science and of chemistry; Jun Lou, assistant professor in mechanical engineering and materials science; postdoctoral research associates Lijie Ci and Pavel Sorokin; and graduate student Hao Lu, all of Rice; Chuanhong Jin of the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan; visiting student Jie Ni of Tsinghua University, China; and Alexander Kvashnin and Dmitry Kvashnin of Siberian Federal University of Krasnoyarsk, Russia.

 

The research was funded by Rice University, the Office of Naval Research MURI program on graphene, the Basic Energy Science division of the Department of Energy, the National Science Foundation, the Welch Foundation, the International Balzan Foundation and the Chinese State Scholarship Fund.

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Researchers at the University of Rio de Janeiro (UFRJ), Brazil, have developed a solar heating system that uses nanotechnology to heat water to five times the temperature of a conventional system, while also permitting the collector surface area to retain up to 98 percent of heat from solar radiation. The surfaces of the collectors are comprised of aluminum films coated with several thin layers of metal oxides. The water can reach temperatures of 300ºC, which, according to Luiz Carlos de Lima, a doctor of metallurgical and materials engineering, "[W]ith that level of heating, it is possible, for example, to convert water into steam, allowing you to use turbines to generate electricity more efficiently." Lima's research, in collaboration with that of Marta de Moraes Bueno, has given rise to the founding of Nano Select, the first company in Brazil to develop selective surfaces for solar collectors using nanotechnology. The company recently won the Technological Innovation prize awarded by the FINEP, the Brazilian Innovation Agency that funds scientific and technological studies. The new technology is expected to be launched onto the market at an industrial scale during the first six months of 2011. The article can be viewed online at the link below.

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