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terials, yielding novel artificial materials that do not exist in nature,” Lee said. “This ‘epitaxy‘ technique can be used to design entirely new materials or to specifically modify the composition of thin-film crystals with sub-nanometer accuracy.”
While band gap tuning has been widely successful for more conventional semiconductors, the 30% band gap reduction demonstrated with oxides easily surpasses previous accomplishments of 6% – or 0.2 electron volt – in this area and opens pathways to new approaches to controlling band gap in com- plex-oxide materials.
With this discovery, the potential exists for oxides with band gaps to be continuously controlled over 1 electron volt by site-specific alloying developed by the ORNL team. “Therefore,” Lee said, “this work represents a major achievement using complex oxides that offer a number of advantages as they are very stable under extreme and severe environ- ments.”
Woo Seok Choi, Matthew F. Chisholm, David J. Singh, Taekjib Choi, Gerald E. Jellison Jr. & Ho Nyung Lee: Wide bandgap tunability in complex transition metal oxides by site-specific substitution, In: Nature Communi- cations, Vol. 3(2012), February 21, 2012, Article number 689, DOI:10.1038/ncomms1690: http://dx.doi.org/10.1038/ncomms1690
12-02 :: February/March 2012
In this photo, a transmission electron microscope image, taken at a magnification 330000x , shows the nano-sized apex of a silicon carbide tip. © IBM
Scientists at the University of Pennsylvania, the University of Wisconsin-Madison and IBM Re- search - Zurich (NYSE: IBM) have fabricated an ultrasharp silicon carbide tip possessing such high strength that it is thousands of times more wear- resistant at the nanoscale than previous designs. The new tip, which is 100,000 times smaller than the tip of a pencil, represents an important step towards nanomanufacturing for applications, in- cluding bio sensors for healthcare and the environ- ment. The search for hard materials to extend the working life of sharp tools is an age-old problem that started with the first chisels used in stone carving. Even- tually iron was discovered and steel tools revolu- tionized the era. Today, the challenge remains the same, but on a much smaller scale – the need for a nano-sized tip that is both ultrasharp, yet still physically robust, particularly under extreme tempe- ratures and harsh chemical environments.