6th December 2006

New Form of Germanium Synthesized

Workers at the University of Houston have for the first-time, synthesised a low-density synthetic form of germanium. Arnold Guloy, a UH chemistry professor, and a team of researchers from UH and the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany, where Guloy is also a guest scientist, reported their findings in the paper “A Guest-free Germanium Clathrate” in Nature.

The usual form of germanium has the same structure as a diamond but this new form has a unique ‘cage’ structure. Moreover, it is less dense and has the uncommon property of ice in that it floats in its own liquid.

“There is a high interest in clathrate or open-framework semiconductors as a general class of high-tech materials,” Guloy said. “These materials have lower densities and larger band gaps than the usual forms of semiconductors due to their rather open or ‘porous’ structures. Until our report, there was no scalable and high-yield preparative technique to produce these materials – particularly the silicon- and germanium-based clathrate semiconductors.”

“The synthesis of this new form of germanium should allow for new avenues of research in the germanium semiconductor,” said John Bear, dean of UH’s College of Natural Sciences and Mathematics. “Clathrate semiconductors have significant technological potential because they exhibit a very wide variety of materials properties.”

This new caged form of germanium will provide scientists useful information to, for example, design high-efficiency thermoelectrics “Furthermore one cannot make this empty germanium clathrate or ‘cage’ compound by any other means. Our method is done at relatively mild temperatures – 300C – and being a solution technique it can easily be scaled to prepare thin films and its other functional forms.

“We have created a low-density, metastable form of germanium that has lots of holes in it – a cage structure – and this has been predicted to have unusual thermoelectric and optoelectronic properties, such as the potential to emit light. All previously known compounds with clathrate structures have something in the cages to keep them from collapsing. It’s amazing that our new germanium structure can be constructed even though its cages are empty.”

Bear adds that this particular synthesis of germanium allows for the preparation of bulk material, and the scalability of the solution method offers excellent prospects of processing clathrate semiconductors.

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