The research was led by UH Associate Professor of Chemistry Arnold Guloy. Their findings, titled “A guest-free germanium clathrate,” are published in the September 21 issue of Nature magazine.
Analogous to the 1985 discovery of the buckyball, which added a new form of carbon to the family of graphite and diamond, this breakthrough has resulted in a form of germanium with a low-density, open-caged structure and the potential to emit light.
“The synthesis of this new form of germanium should allow for new avenues of research in the germanium semiconductor,” says John Bear, dean of the College of Natural Sciences and Mathematics.
As an important semiconductor material, germanium has thousands of applications that range from use in fiber optics communications networks to infrared night vision systems. Anything that is computerized or uses radio waves uses semiconductors.
“There is only one known form of germanium at ambient conditions, and it is called a-germanium,” explains Guloy. “While there are other forms made at high pressure, they are normally dense and only stable at high pressure. We have created a low-density metastable form of germanium that has lots of holes in it—it has a cage structure—and this has been predicted to have unusual thermoelectric and electronic properties, such as the potential to emit light, which a-germanium cannot do.”
This new form will allow scientists to design high efficiency thermoelectrics, gain a better understanding of superconductivity in this class of materials, and create more new materials based on Guloy’s synthetic technique, in addition to other yet unforeseen applications.
The scientists used a novel technique to create low-density germanium.
“We dissolved simple elemental molecular clusters in solutions and oxidized them under mild conditions until they began to condense, but we had to optimize the temperature to get this to happen. Scientists have tried this before with other solvents, but we used an ionic liquid, which is very polar and dissolves the anion clusters, and then also acts as a mild oxidizing agent,” says Guloy.
“One of the difficulties we had was proving that this new caged form of germanium is empty, because all known compounds with this clathrate structure have something inside, otherwise the structure should collapse. What is amazing about this structure is that it forms even though it is empty,” says Guloy.
”The synthesis allows for the preparation of the bulk material, and the scalability of the solution method offers excellent prospects of processing clathrate semiconductors for a wide range of applications.”
Seed money for this research was funded in part by the Welch Foundation and the Petroleum Research fund. Current supporters include the NSF, the Texas Center for Superconductivity at the University of Houston (TcSUH), and the Max Planck Institute for Chemical Physics of Solids.
Guloy received a BS in chemistry from the University of the Philippines and a PhD in inorganic solid state chemistry from Iowa State University. He joined the UH faculty in 1994 as an assistant professor of inorganic chemistry. He was granted tenure and promoted to associate professor of chemistry in fall 2000.
Guloy has published over 50 papers and has one patent. Over the years, he has mentored numerous PhD, MS, postdoctoral, undergraduate, and high school students.
In recognition of his accomplishments, Guloy received an NSF CAREER Development Award in 1998 and the UH Award for Excellence in Research and Scholarship in 1997. He has received other recognitions and awards, including the Philippine Department of Science and Technology DOST-ESEP Visiting Scientist Award in 1997.
For more information, please visit http://www.uh.edu/~chembi/.